WDIFF

draft-ietf-pkix-ipki-part1-02.txt --> draft-ietf-pkix-ipki-part1-03.txt

PKIX Working Group R. Housley (SPYRUS)
Internet Draft W. Ford (Nortel) (Verisign)
W. Polk (NIST)
D. Solo (BBN)
expires in six months June December 1996

Internet Public Key Infrastructure

Part I: X.509 Certificate and CRL Profile

<draft-ietf-pkix-ipki-part1-02.txt>

<draft-ietf-pkix-ipki-part1-03.txt>

Status of this Memo

This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."

To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet- Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).

Abstract

This is the second draft of the Internet Public Key Infrastructure
X.509 Certificate and CRL Profile. Since the first version was
distributed, ISO has completed work on X.509 Version 3 Certificates
and X.509 Version 2 Certificate Revocation Lists (CRLs). Many of the
Internet community requirements that were in the previous version of
this document have been included in the final ISO document. As a
result, this document has gotten simpler. Please send comments on
this document to the ietf-pkix@tandem.com mail list.

1 Executive Summary

<< Write this last. >>

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1 Executive Summary

This specification is Part 1 of a four part standard for development
of a Public Key Infrastructure for the Internet. This specification
is a standalone document; implementations of this standard may
proceed before completion of parts two through four.

This specification profiles the format and semantics of certificates
and certificate revocation lists for the Internet PKI. Procedures
are described for processing of certification paths in the Internet
environment. Encoding rules are provided for popular cryptographic
algorithms. Finally, a comprehensive ASN.1 module is provided in the
appendices for all data structure defined or referenced.

The specification presents profiles of the X.509 version 3
certificate and version 2 certificate revocation lists. The profiles
include the identification of ISO and ANSI extensions which may be
useful in the Internet PKI and definition of new extensions to meet
the Internet's requirements. The profiles are presented in the 1988
Abstract Syntax Notation One (ASN.1) rather than the 1993 syntax used
in the ISO standards.

This specification also includes path validation procedures. These
procedures are based upon the ISO definition, but incorporate the
Internet defined extensions. Implementations are required to derive
the same results but are not required to use the specified
procedures.

Finally, the specification describes procedures for identification
and encoding of public key materials and digital signatures.
Implementations are not required to use any particular cryptographic
algorithms. However, conforming implementations which use the
identified algorithms are required to identify and encode the public
key materials and digital signatures as described.

An Appendix is provided containing all ASN.1 structures defined or
referenced within this specification. As above, the material is
presented in the 1988 Abstract Syntax Notation One (ASN.1) rather
than the 1993 syntax.

2 Requirements and Assumptions

Goal is to develop a profile and associated management structure to
facilitate the adoption/use of X.509 certificates within Internet
applications for those communities wishing to make use of X.509
technology. Such applications may include WWW, electronic mail, user
authentication, electronic payment systems, and IPSEC, as well as others. In order to relieve
some of the obstacles to using X.509 certificates, this document

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defines a profile to promote the development of certificate
management systems; development of application tools; and
interoperability determined by policy, as opposed to syntax.

Some communities will need to supplement, or possibly replace, this
profile in order to meet the requirements of specialized application
domains or environments with additional authorization, assurance, or
operational requirements. However, for basic applications, common
representations of frequently used attributes are defined so that
application developers can obtain necessary information without
regard to the issuer of a particular certificate or certificate
revocation list (CRL).

As supplemental authorization and attribute management tools emerge,
such as attribute certificates, it may be appropriate to limit the
authenticated attributes that are included in a certificate. These
other management tools may be more appropriate method of conveying
many authenticated attributes.

2.1 Communication and Topology

The users of certificates will operate in a wide range of
environments with respect to their communication topology, especially
users of secure electronic mail. This profile supports users without
high bandwidth, real-time IP connectivity, or high connection
availablity. In addition, the profile allows for the presence of
firewall or other filtered communication.

This profile does not assume the deployment of an X.500 Directory
system. The profile does not prohibit the use of an X.500 Directory,
but other means of distributing certificates and certificate
revocation lists (CRLs) are supported.

2.2 Acceptability Criteria

The goal of the Internet Public Key Infrstructure Infrastructure (PKI) is to meet
the needs of deterministic, automated identification, authentication,
access control, and authorization functions. Support for these
services determines the attributes contained in the certificate as
well as the ancillary control information in the certificate such as
policy data and certification path constraints.

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2.3 User Expectations

Users of the Internet PKI are people and processes who use client
software and are the subjects named in certificates. These uses
include readers and writers of electronic mail, the clients for WWW
browsers, WWW servers, and the key manager for IPSEC within a router.

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This profile recognizes the limitations of the platforms these users
employ and the sophistication/attentiveness of the users themselves.
This manifests itself in minimal user configuration responsibility
(e.g., root keys, rules), explicit platform usage constraints within
the certificate, certification path constraints which shield the user
from many malicious actions, and applications which sensibly automate
validation functions.

2.4 Administrator Expectations

As with users, the Internet PKI profile is structured to support the
individuals who generally operate Certification Authorities (CAs).
Providing administrators with unbounded choices increases the chances
that a subtle CA administrator mistake will result in broad
compromise. Also, unbounded choices greatly complicates the software
that must process and validate the certificates created by the CA.

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3 Overview of Approach

Following is a simplified view of the architectural model assumed by
the PKIX specifications.

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+---+
| C | +------------+
| e | <-------------------->| End entity |
| r | Operational +------------+
| t | transactions ^
| | and management | Management
| / | transactions | transactions
| | |
| C | PKI users v
| R | -------+-------+--------+------
| L | PKI management ^ ^
| | entities | |
| | v |
| R | +------+ |
| e | <-------------- | RA | <-----+ |
| p | certificate | | | |
| o | publish +------+ | |
| s | | |
| i I | v v
| t | +------------+
| o | <--------------------------| CA |
| r | certificate publish +------------+
| y | CRL publish ^
| | |
+---+ | Management
| transactions
v
+------+
| CA |
+------+

Figure 1 - PKI Entities

The components in this model are:

end entity: user of PKI certificates and/or end user system that
the PKI certifies;
CA: certification authority;
RA: registration authority, i.e., an optional system to
which a CA delegates certain manaagement management functions;
repository: a system or collection of distributed systems that
store certificates and CRLs and serves as a means of
distributing these certificates and CRLs to end
entities.

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entities.

3.1 X.509 Version 3 Certificate

Application of public key technology requires the user of a public
key to be confident that the public key belongs to the correct remote
subject (person or system) with which an encryption or digital
signature mechanism will be used. This confidence is obtained
through the use of public key certificates, which are data structures
that bind public key values to subject identities. The binding is
achieved by having a trusted certification authority (CA) digitally
sign each certificate. A certificate has a limited valid lifetime
which is indicated in its signed contents. Because a certificate's
signature and timeliness can be independently checked by a
certificate-using client, certificates can be distributed via
untrusted communications and server systems, and can be cached in
unsecured storage in certificate-using systems.

The standard known as ITU-T X.509 (formerly CCITT X.509) or ISO/IEC
9594-8, which was first published in 1988 as part of the X.500
Directory recommendations, defines a standard certificate format. The
certificate format in the 1988 standard is called the version 1 (v1)
format. When X.500 was revised in 1993, two more fields were added,
resulting in the version 2 (v2) format. These two fields are used to
support directory access control.

The Internet Privacy Enhanced Mail (PEM) proposals, published in
1993, include specifications for a public key infrastructure based on
X.509 v1 certificates [RFC 1422]. The experience gained in attempts
to deploy RFC 1422 made it clear that the v1 and v2 certificate
formats are deficient in several respects. Most importantly, more
fields were needed to carry information which PEM design and
implementation experience has proven necessary. In response to these
new requirements, ISO/IEC and ANSI X9 developed the X.509 version 3
(v3) certificate format. The v3 format extends the v2 format by
adding provision for additional extension fields. Particular
extension field types may be specified in standards or may be defined
and registered by any organization or community. In June 1996,
standardization of the basic v3 format was completed [X.509-AM].

ISO/IEC and ANSI X9 have also developed a set of standard extensions
for use in the v3 extensions field [X.509-AM][X9.55]. These
extensions can convey such data as additional subject identification
information, key attribute information, policy information, and
certification path constraints.

However, the ISO/IEC and ANSI standard extensions are very broad in
their applicability. In order to develop interoperable

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implementations of X.509 v3 systems for Internet use, it is necessary
to specify a profile for use of the X.509 v3 extensions tailored for

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the Internet. It is one goal of this document to specify a profile
for Internet WWW, electronic mail, and IPSEC applications.
Environments with additional requirements may build on this profile
or may replace it.

3.2 Certification Paths and Trust

A user of a security service requiring knowledge of a public key
generally needs to obtain and validate a certificate containing the
required public key. If the public-key user does not already hold an
assured copy of the public key of the CA that signed the certificate,
then it might need an additional certificate to obtain that public
key. In general, a chain of multiple certificates may be needed,
comprising a certificate of the public key owner (the end entity)
signed by one CA, and zero or more additional certificates of CAs
signed by other CAs. Such chains, called certification paths, are
required because a public key user is only initialized with a limited
number (often one) of assured CA public keys.

There are different ways in which CAs might be configured in order
for public key users to be able to find certification paths. For
PEM, RFC 1422 defined a rigid hierarchical structure of CAs. There
are three types of PEM certification authority:

(a) Internet Policy Registration Authority (IPRA): This authority,
operated under the auspices of the Internet Society, acts as the root
of the PEM certification hierarchy at level 1. It issues
certificates only for the next level of authorities, PCAs. All
certification paths start with the IPRA.

(b) Policy Certification Authorities (PCAs): PCAs are at level 2 of
the hierarchy, each PCA being certified by the IPRA. A PCA must
establish and publish a statement of its policy with respect to
certifying users or subordinate certification authorities. Distinct
PCAs aim to satisfy different user needs. For example, one PCA (an
organizational PCA) might support the general electronic mail needs
of commercial organizations, and another PCA (a high-assurance PCA)
might have a more stringent policy designed for satisfying legally
binding signature requirements.

(c) Certification Authorities (CAs): CAs are at level 3 of the
hierarchy and can also be at lower levels. Those at level 3 are
certified by PCAs. CAs represent, for example, particular
organizations, particular organizational units (e.g., departments,
groups, sections), or particular geographical areas.

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RFC 1422 furthermore has a name subordination rule which requires
that a CA can only issue certificates for entities whose names are

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subordinate (in the X.500 naming tree) to the name of the CA itself.
The trust associated with a PEM certification path is implied by the
PCA name. The name subordination rule ensures that CAs below the PCA
are sensibly constrained as to the set of subordinate entities they
can certify (e.g., a CA for an organization can only certify entities
in that organization's name tree). Certificate user systems are able
to mechanically check that the name subordination rule has been
followed.

The RFC 1422 CA hierarchical model has been found to have several
deficiencies, including:

(a) The pure top-down hierarchy, with all ertification certification paths
starting from the root, is too restrictive for many purposes. For
some applications, verification of certification paths should start
with a public key of a CA in a user's own domain, rather than
mandating that verification commence at the top of a hierarchy. In
many environments, the local domain is often the most trusted. Also,
initialization and key-pair-update operations can be more effectively
conducted between an end entity and a local management system.

(b) The name subordination rule introduces undesirable constraints
upon the X.500 naming system an organization may use.

(c) Use of the PCA concept requires knowledge of individual PCAs to
be built into certificate chain verification logic. In the
particular case of Internet mail, this is not a major problem -- the
PCA name can always be displayed to the human user who can make a
decision as to what trust to imply from a particular chain. However,
in many commercial applications, such as electronic commerce or EDI,
operator intervention to make policy decisions is impractical. The
process needs to be automated to a much higher degree. In fact, the
full process of certificate chain processing needs to be
implementable in trusted software.

Because of the above shortcomings, it is proposed that more flexible
CA structures than the RFC 1422 hierarchy be supported by the PKIX
specifications. In fact, the main reason for the structural
restrictions imposed by RFC 1422 was the restricted certificate
format provided with X.509 v1. With X.509 v3, most of the
requirements addressed by RFC 1422 can be addressed using certificate
extensions, without a need to restrict the CA structures used. In
particular, the certificate extensions relating to certificate
policies obviate the need for PCAs and the constraint extensions
obviate the need for the name subordination rule.

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3.3 Revocation

When a certificate is issued, it is expected to be in use for its
entire validity period. However, various circumstances may cause a
certificate to become invalid prior to the expiration of the validity
period. Such circumstances might include change of name, change of
association between subject and CA (e.g., an employee terminates
employment with an organization), and compromise or suspected
compromise of the corresponding private key. Under such
circumstances, the CA needs to revoke the certificate.

X.509 defines one method of certificate revocation. This method
involves each CA periodically issuing a signed data structure called
a certificate revocation list (CRL). A CRL is a time stamped list
identifying revoked certificates which is signed by a CA and made
freely available in a public repository. Each revoked certificate is
identified in a CRL by its certificate serial number. When a
certificate-using system uses a certificate (e.g., for verifying a
remote user's digital signature), that system not only checks the
certificate signature and validity but also acquires a suitably-
recent CRL and checks that the certificate serial number is not on
that CRL. The meaning of "suitably-recent" may vary with local
policy, but it usually means the most recently-issued CRL. A CA
issues a new CRL on a regular periodic basis (e.g., hourly, daily, or
weekly). Entries are added to CRLs as revocations occur, and an
entry may be removed when the certificate expiration date is reached.

An advantage of this revocation method is that CRLs may be
distributed by exactly the same means as certificates themselves,
namely, via untrusted communications and server systems.

One limitation of the CRL revocation method, using untrusted
communications and servers, is that the time granularity of
revocation is limited to the CRL issue period. For example, if a
revocation is reported now, that revocation will not be reliably
notified to certificate-using systems until the next periodic CRL is
issued -- this may be up to one hour, one day, or one week depending
on the frequency that the CA issues CRLs.

Another potential problem with CRLs is the risk of a CRL growing to
an entirely unacceptable size. In the 1988 and 1993 versions of
X.509, the CRL for the end-user certificates needed to cover the
entire population of end-users for one CA. It is desirable to allow
such populations to be in the range of thousands, tens of thousands,
or possibly even hundreds of thousands of users. The end-user CRL is
therefore at risk of growing to such sizes, which present major
communication and storage overhead problems. With the version 2 CRL
format, introduced along with the v3 certificate format, it becomes

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possible to arbitrarily divide the population of certificates for one
CA into a number of partitions, each partition being associated with
one CRL distribution point (e.g., directory entry or URL) from which
CRLs are distributed. Therefore, the maximum CRL size can be
controlled by a CA. Separate CRL distribution points can also exist
for different revocation reasons. For example, routine revocations
(e.g., name change) may be placed on a different CRL to revocations
resulting from suspected key compromises, and policy may specify that
the latter CRL be updated and issued more frequently than the former.

As with the X.509 v3 certificate format, in order to facilitate
interoperable implementations from multiple vendors, the X.509 v2 CRL
format needs to be profiled for Internet use. It is one goal of this
document to specify such profiles.

Furthermore, it is recognized that on-line methods of revocation
notification may be applicable in some environments as an alternative
to the X.509 CRL. On-line revocation checking eliminates the latency
between a revocation report and CRL the next issue. Once the
revocation is reported, any query to the on- line on-line service will
correctly reflect the certificate validation impacts of the
revocation. Therefore, this document profile will also consider standard
approaches to on-line revocation notification.

3.4 Operational Protocols

Operational protocols are required to deliver certificates and CRLs
to certificate using client systems. Provision is needed for a
variety of different means of certificate and CRL delivery, including
request/delivery procedures based on E-mail, http, X.500, and
WHOIS++. These specifications include definitions of, and/or
references to, message formats and procedures for supporting all of
the above operational environments, including definitions of or
references to appropriate MIME content types.

3.5 Management Protocols

Management protocols are required to support on-line interactions
between Public Key Infrastructure (PKI) components. For example,
management protocol might be used between a CA and a client system
with which a key pair is associated, or between two CAs which cross-
certify each other. The set of functions which potentially need to
be supported by management protocols include:

(a) registration: This is the process whereby a user first makes
itself known to a CA, prior to that CA issuing a certificate or
certificates for that user.

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(b) initialization: Before a client system can operate securely it
is necessary to install in it necessary key materials which have the
appropriate relationship with keys stored elsewhere in the
infrastructure. For example, the client needs to be securely
initialized with the public key of a CA, to be used in validating
certificate paths. Furthermore, a client typically needs to be
initialized with its own key pair(s).

(c) certification: This is the process in which a CA issues a
certificate for a user's public key, and returns that certificate to
the user's client system and/or posts that certificate in a public
repository.

(d) key pair recovery: As an option, user client key materials
(e.g., a user's private key used for encryption purposes) may be
backed up by a CA or a key backup system associated with a CA. If a
user needs to recover these backed up key materials (e.g., as a
result of a forgotten password or a lost key chain file), an on-line
protocol exchange may be needed to support such recovery.

(e) key pair update: All key pairs need to be updated regularly,
i.e., replaced with a new key pair, and new certificates issued.

(f) revocation request: An authorized person advises a CA of an
abnormal situation requiring certificate revocation.

(g) cross-certification: Two CAs exchange the information necessary
to establish cross-certificates between those CAs.

Note that on-line protocols are not the only way of implementing the
above functions. For all functions there are off-line methods of
achieving the same result, and this specification does not mandate
use of on- line protocols. For example, when hardware tokens are
used, many of the functions may be achieved through as part of the
physical token delivery. Furthermore, some of the above functions
may be combined into one protocol exchange. In particular, two or
more of the registration, initialization, and certification functions
can be combined into one protocol exchange.

Part 3 of the PKIX series of specifications defines a set of standard
message formats supporting the above functions. The protocols for
conveying these messages in different environments (on-line, e-mail,
and WWW) are also specified.

4 Certificate and Certificate Extensions Profile

The goal of this document is to create

This section presents a profile for X.509 v3 public key certificates that will
foster interoperability and a reusable public key infrastructure.

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key infrastructure. Since the publication of earlier versions of
this draft, substantial changes have been made to

This section is based upon the Amendment
[X.509-AM] to X.509 defining version 3 V3 certificate format and the
standard certificate extensions.
Those changes have brought extensions defined in the base document into close alignment
with Amendment [X.509-AM].
The ISO definitions use the recommendations of earlier versions 1993 version of this draft. As a
result, ASN.1; while this
document provides a concise profile rather than
attempting to recreate uses the Amendment as older ASN.1 syntax, the encoded certificate and
standard extensions are equivalent. This section also defines
private extensions required to support a standalone document. public key infrastructure
for the Internet community.

Certificates may be used in a wide range of applications and
environments covering a broad spectrum of interoperability goals and
a broader spectrum of operational and assurance requirements. The
goal of this document is to establish a common baseline for generic
applications requiring broad interoperability and limited special
purpose requirements. In particular, the emphasis will be on
supporting the use of X.509 v3 certificates for informal internet
electronic mail, IPSEC, and WWW applications. Other efforts are
looking at certificate profiles for payment systems.

4.1 Basic Certificate Fields

The X.509 v3 certificate basic syntax is as follows. For signature
calculation, the certificate is encoded using the ASN.1 distinguished
encoding rules (DER) [X.208]. ASN.1 DER encoding is a tag, length,
value encoding system for each element.

Certificate ::= SEQUENCE {
tbsCertificate TBSCertificate,
signatureAlgorithm AlgorithmIdentifier,
signature BIT STRING }

TBSCertificate ::= SEQUENCE {
version [0] Version DEFAULT v1,
serialNumber CertificateSerialNumber,
signature AlgorithmIdentifier,
issuer Name,
validity Validity,
subject Name,
subjectPublicKeyInfo SubjectPublicKeyInfo,
issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL,
-- If present, version must be v2 or v3
subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL,
-- If present, version must be v2 or v3
extensions [3] Extensions OPTIONAL
-- If present, version must be v3
}

Version ::= INTEGER { v1(0), v2(1), v3(2) }

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CertificateSerialNumber ::= INTEGER

Validity ::= SEQUENCE {
notBefore UTCTime, CertificateValidityDate,
notAfter UTCTime CertificateValidityDate }

CertificateValidityDate ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime }

UniqueIdentifier ::= BIT STRING

SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING }

Extensions ::= SEQUENCE OF Extension

Extension ::= SEQUENCE {
extnID OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING }

The following items describe a proposed use of the X.509 v3
certificate for the Internet.

4.1.1 Version

This field describes the version of the encoded certificate. When
extensions are used, as expected in this profile, use X.509 version 3
(value Certificate Fields

The Certificate is 2). If no extensions are present, but a UniqueIdentifier
is present, use version 2 (value is 1). If only basic SEQUENCE of three required fields. The fields
are
present, use version 1 (the value is omitted from are described in detail in the certificate as following subsections

4.1.1.1 tbsCertificate

The first field in the default value).

Implementations should be prepared to accept any version certificate.
In particular, at sequence is the tbsCertificate. This is a minimum, implementations should recognize version
3 certificates; determine whether any critical extensions are
present;
itself a sequence, and accept certificates without critical extensions even if
they don't recognize any extensions. A certificate with an
unrecognized critical extension must always be rejected.

Generation contains the names of version 2 certificates is not expected by
implementations based on this profile.

4.1.2 Serial number

The serial number is an integer assigned by the certification
authority to each certificate. It must be unique for each
certificate issued by subject and issuer,
a given CA (i.e., public key associated with the issuer name subject an expiration date, and serial
number identify a unique certificate).

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4.1.3 Signature

This
other associated information. The fields of the basic tbsCertificate
are described in detail in section 4.1.2; the tbscertificate may also
include extensions which are described in section 4.2.

4.1.1.2 signatureAlgorithm

The signatureAlgorithm field contains the algorithm identifier for
the algorithm used by the CA to sign the certificate. Section 7.2
lists the supported signature algorithms.

4.1.4 Issuer Name

The issuer name identifies

This field should contain the entity who has signed (and issued the
certificate). The issuer identity may be carried in same algorithm identifier as the issuer name field and/or the issuerAltName extension. If identity information is
present only
signature in the issuerAltName extension, then the issuer name may
be an empty sequence and the issuerAltName extension must be
critical.

<< Should we say anything about name constraints here? >>

4.1.5 Validity

This tbsCertificate (see section 4.1.2.3)

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4.1.1.3 signature

The signature field indicates contains a digital signature computed upon the dates on which
ASN.1 DER encoded TBSCertificate. The ASN.1 DER encoded
TBSCertificate is used as the certificate becomes valid
(notBefore) input to a one-way hash function. The
one-way hash function output value is ASN.1 encoded as an OCTET
STRING and on which the certificate ceases result is encrypted (e.g., using RSA Encryption) to be valid
(notAfter). It
form the signed quantity. This signature value is strongly recommended that UTCTime values be
expressed Greenwich Mean Time (Zulu) then ASN.1 encoded
as a BIT STRING and not use seconds (i.e., times
are YYMMDDHHMMZ). If seconds are used, included in the Certificate's signature field.

By generating this signature, a value of 00 seconds should
never be encoded.

4.1.6 Subject Name

The subject name identifies CA certifies the entity associated with validity of the public key
stored
information in tbscertificate. In particular, the CA certifies the
binding between the subject public key field. The subject identity may be
carried in material and the subject field and/or of the subjectAltName extension. If
identity information
certificate.

4.1.2 TBSCertificate

The sequence TBSCertificate is present only in the subjectAltName extension
(e.g., a key bound only to an email address or URI), then sequence which contains information
associated with the subject
name may be an empty sequence of the certificate and the subjectAltName extension must
be critical.

<< Should we say anything about name constraints here? >>

4.1.7 Subject Public Key Info

This field is used to carry CA who issued
it. Every TBSCertificate contains the names of the subject and
issuer, a public key and identify the algorithm associated with which the key is used.

4.1.8 Unique Identifiers

The subject subject, an expiration date,
a version number and issuer a serial number; some will contain optional
unique identifier fields. The remainder of this section describes
the syntax and semantics of these fields. A TBSCertificate may also
include extensions. Extensions for the Internet PKI are present described in
Section 4.2.

4.1.2.1 Version

This field describes the version of the encoded certificate. When
extensions are used, as expected in this profile, use X.509 version 3
(value is 2). If no extensions are present, but a UniqueIdentifier
is present, use version 2 (value is 1). If only basic fields are
present, use version 1 (the value is omitted from the certificate to handle as
the possibility of reuse default value).

Implementations should be prepared to accept any version certificate.
In particular, at a minimum, implementations must recognize version 3
certificates; determine whether any critical extensions are present;
and accept certificates without critical extensions even if they
don't recognize any extensions. A certificate with an unrecognized
critical extension must always be rejected.

Generation of subject and/or
issuer names over time. This profile recommends that names version 2 certificates is not be expected by
implementations based on this profile.

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reused and that Internet certificates not make use of unique
identifiers. CA's conforming

4.1.2.2 Serial number

The serial number is an integer assigned by the certification
authority to this profile should not generate
certificates with unique identifiers. Applications conforming to
this profile should each certificate. It must be capable of parsing unique identifiers and
making comparisons.

4.2 Certificate Extensions

The extensions defined for X.509 v3 certificates provide methods for
associating additional attributes with users or public keys, for
managing each
certificate issued by a given CA (i.e., the certification hierarchy, issuer name and serial
number identify a unique certificate).

4.1.2.3 Signature

This field contains the algorithm identifier for managing CRL
distribution. The X.509 v3 certificate format also allows
communities to define private extensions the algorithm used
by the CA to carry sign the certificate. Section 7.2 lists the supported
signature algorithms.

4.1.2.4 Issuer Name

The issuer name identifies the entity who has signed (and issued the
certificate). The issuer identity may be carried in the issuer name
field and/or the issuerAltName extension. If identity information unique
to those communities. Each extension is
present only in a certificate the issuerAltName extension, then the issuer name may
be
designated as critical or non-critical. A certificate using system
(an application validating a certificate) an empty sequence and the issuerAltName extension must reject be
critical.

4.1.2.5 Validity

This field indicates the dates on which the certificate
if it encounters a critical extension it does not recognize. A non-
critical extension becomes valid
(notBefore) and on which the certificate ceases to be valid
(notAfter). Both notBefore and notAfter may be ignored if it is encoded as UTCTime or
GeneralizedTime.

CAs conforming to this profile shall not recognized. The
following presents recommended extensions used within Internet issue certificates and standard locations for information. Communities may
elect where
notAfter or notBefore is encoded as GeneralizedTime before the year
2005. CAs conforming to use additional extensions; however, caution should be
exercised in adopting any critical extensions in this profile shall not issue certificates which
might be used in a general context.
where notAfter or notBefore is encoded as UTCTime after the year
2015.

4.1.2.5.1 UTCTime

The extensions referenced below are defined in detail in universal time type, UTCTime, is a standard ASN.1 type intended
for international applications where local time alone is not
adequate. UTCTime specifies the X.509
Amendment along with year through the specification of syntax two low order digits
and object
identifiers. Because the intent time is specified to align exactly with those
definitions, the material is not reproduced here. The following
sections describe Internet profiling decisions and Internet private
extensions.

<< Once finalized, the certificate ASN.1 definition will be included
in an appendix to this document. >>

4.2.1 Standard Extensions

4.2.1.1 Authority Key Identifier

The authority key identifier extension provides a means precision of
identifying the particular public key used to sign a certificate.
The identification can be based on one minute or one second.
UTCTime includes either the key identifier (the
subject key identifier in the issuer's certificate) Z (for Zulu, or on Greenwich Mean Time) or a
time differential.

For the issuer
name and serial number. The key identifier method is recommended in purposes of this profile. This extension would profile, UTCTime values shall be used expressed
Greenwich Mean Time (Zulu) and shall include< seconds (i.e., times
are YYMMDDHHMMSSZ), even where an issuer has
multiple signing keys (either due to multiple concurrent key pairs or
due to changeover). In general, this extension should be included in
certificates. the number of seconds is zero.
Conforming systems shall interpret the year field (YY) as follows:

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4.2.1.2 Subject Key Identifier

The subject key identifier extension provides a means of identifying

Where YY is greater than 50, the particular public key used in an application. year shall be interpreted as
19YY; and

Where a reference
to a public key identifier YY is needed (as with an Authority Key
Identifier) and one less than or equal to 50, the year shall be
interpreted as 20YY.

4.1.2.6 GeneralizedTime

The generalized time type, GeneralizedTime, is not included in a standard ASN.1 type
for variable precision representation of time. Optionally, the associated certificate,
GeneralizedTime field can include a
SHA-1 hash representation of the subject public key time
differential between local and Greenwich Mean Time.

For the purposes of this profile, GeneralizedTime values shall be used. The hash
expressed Greenwich Mean Time (Zulu) and shall
be calculated over include seconds (i.e.,
times are YYYYMMDDHHMMSSZ), even where the value (excluding tag and length) number of the seconds is zero.
GeneralizedTime values shall not include fractional seconds.

4.1.2.6 Subject Name

The subject name identifies the entity associated with the public key field
stored in the certificate. This extension should
be marked non-critical.

4.2.1.3 Key Usage

The subject public key usage extension defines field. The subject identity may be
carried in the purpose (e.g., encipherment,
signature, certificate signing) of subject field and/or the key contained subjectAltName extension. If
identity information is present only in the
certificate. The usage restriction might be employed when subjectAltName extension
(e.g., a
multipurpose key is bound only to an email address or URI), then the subject
name may be restricted (e.g., when an RSA key should empty sequence and the subjectAltName extension must
be critical.

4.1.2.7 Subject Public Key Info

This field is used only for signing or only for to carry the public key encipherment). and identify the algorithm
with which the key is used.

4.1.2.8 Unique Identifiers

The subject and issuer unique identifier are present in the
certificate to handle the possibility of reuse of subject and/or
issuer names over time. This profile recommends that when used, this names not be marked as a critical extension.

4.2.1.4 Private Key Usage Period

This profile recommends against the
reused and that Internet certificates not make use of this extension. CA's unique
identifiers. CAs conforming to this profile should not generate
certificates with
private key usage period extensions.

4.2.1.5 Certificate Policies

The certificate policies extension contains a sequence of policy
information terms, each of which consists unique identifiers. Applications conforming to
this profile should be capable of an object identifier
(OID) parsing unique identifiers and optional qualifiers. These policy information terms
indicate the policy under which
making comparisons.

4.2 Certificate Extensions

The extensions defined for X.509 v3 certificates provide methods for
associating additional attributes with users or public keys, for

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managing the certificate has been issued certification hierarchy, and
the purposes for which the managing CRL
distribution. The X.509 v3 certificate may be used. This profile
strongly recommends that a simple OID be present in this field.
Optional qualifiers which may be present are expected format also allows
communities to provide define private extensions to carry information about obtaining CA rules, not change the definition of
the policy. Applications are expected unique
to have a list of those
policies which they will accept and to compare the policy OIDs communities. Each extension in a certificate may be
designated as critical or non-critical. A certificate using system
(an application validating a certificate) must reject the certificate to that list.

<< Do we want to say anything about criticality? >>

4.2.1.6 Policy Mappings

This
if it encounters a critical extension it does not recognize. A non-
critical extension may be supported by CAs and/or applications, and ignored if it is
always non-critical.

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4.2.1.7 Subject Alternative Name not recognized. The subject alternative names extension allows additional identities
following presents recommended extensions used within Internet
certificates and standard locations for information. Communities may
elect to use additional extensions; however, caution should be bound to the subject of the certificate. Defined options
include an rfc822 name (electronic mail address),
exercised in adopting any critical extensions in certificates which
might be used in a DNS name, general context.

Each extension includes an IP
address, object identifier and an ASN.1 structure.
When an extension appears in a URI. Other options exist, including completely local
definitions. Multiple instances certificate, the object identifier
appears as the field extnID and the corresponding ASN.1 encoded
structure is the value of the bit string extnValue. Only one
instance of a name and multiple name forms particular extension may be included. Whenever such identities are to be bound into appear in a
certificate, the subject alternative name (or issuer alternative
name) extension shall be used. (Note: particular
certificate. For example, a form of such an certificate may contain only one
authority key identifier extension (4.2.1.1). An extension may also be present in the subject distinguished name; however,
include the
alternative name extension optional boolean critical; critical's default value is
FALSE. The text for each extension specifies the preferred location acceptable values
for finding such
information.) Further, if the only subject identity included in critical field.

Conforming CAs are required to support the
certificate is an alternative name form (e.g., an electronic mail
address), then Basic Constraints
extension (Section 4.2.1.10). If the subject distinguished name should be empty (an CA issues certificates with an
empty sequence), sequence for the subjectAltName extension should be used, and subject field, the
subjectAltName extension CA must be marked critical.

<< In support the previous version we said: The use of otherName should not
be used in conjunction
altSubjectName extension. If the CA issues certificates with an
empty sequence for the issuer field, the CA must support the
altIssuerName extension. Support for the remaining extensions is
optional. Conforming CAs may support extensions that are not
identified within this profile. Should we put specification; certificate issuers are
cautioned that marking such extensions as critical may inhibit
interoperability.

At a minimum, applications conforming to this
restriction back? >>

Alternative names profile shall recognize
extensions which shall or may be constrained in critical. These extensions are: key
usage (4.2.1.3), certificate policies (4.2.1.5), the same manner as alternative
subject
distinguished names using the name (4.2.1.7), issuer alternative name (4.2.1.8), basic
constraints extension as described
in section 4.2.1.11.

4.2.1.8 Issuer Alternative Name

As with 4.2.1.7, (4.2.1.10), name constraints (4.2.1.11), policy
constraints (4.2.1.12), authority information access (4.2.2.2), and
CA information access (4.2.2.3).

In addition, this extension is used to associate Internet style
identities with the profile recommends support for key identifiers
(4.2.1.2 and 4.2.1.3) and CRL distribution points (4.2.1.13).

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4.2.1 Standard Extensions

This section identifies standard certificate issuer. If the only issuer identity
included extensions defined in
[X.509-AM] for use in the certificate Internet Public Key Infrastructure. Each
extension is associated with an alternative name form (e.g., an
electronic mail address), then object identifier defined in [X.509-
AM]. These object identifiers are members of the issuer distinguished name should
be empty (an empty sequence),
certificateExtension arc, which is defined by the issuerAltName following:

certificateExtension OBJECT IDENTIFIER ::= {joint-iso-ccitt(2) ds(5) 29}
id-ce OBJECT IDENTIFIER ::= certificateExtension

4.2.1.1 Authority Key Identifier

The authority key identifier extension should be
used, and provides a means of
identifying the issuerAltName particular public key used to sign a certificate.
This extension must would be marked critical.

4.2.1.9 Subject Directory Attributes used where an issuer has multiple signing
keys (either due to multiple concurrent key pairs or due to
changeover). In general, this extension should be included in
certificates.

The identification can be based on either the key identifier (the
subject directory attributes extension key identifier in the issuer's certificate) or on the issuer
name and serial number. The key identifier method is not recommended as an
essential part of in
this profile, but it may profile. Conforming CAs that generate this extension shall
include or omit both authorityCertIssuer and
authorityCertSerialNumber. If authorityCertIssuer and
authorityCertSerialNumber are omitted, the keyIdentifier field shall
be used in local
environments. present.

This extension is always non-critical.

4.2.1.10 Basic Constraints shall not be marked critical.

id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 35 }

AuthorityKeyIdentifier ::= SEQUENCE {
keyIdentifier [0] KeyIdentifier OPTIONAL,
authorityCertIssuer [1] GeneralNames OPTIONAL,
authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL
}

KeyIdentifier ::= OCTET STRING

4.2.1.2 Subject Key Identifier

The basic constraints extension identifies whether the subject key identifier extension provides a means of identifying
the
certificate is particular public key used in an application. Where a CA and how deep reference
to a certification path may exist
through that CA. This profile requires public key identifier is needed (as with an Authority Key
Identifier) and one is not included in the use associated certificate, a
SHA-1 hash of this extension,
and it the subject public key shall be used. The hash shall critical for all certificates issued to CAs.

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4.2.1.11 Name Constraints

The name constraints extension provides permitted and excluded
subtrees that place restrictions on names that may

be included within
a certificate issued by a given CA. Restrictions may apply to calculated over the
subject distringuished name or subject alternative names. Any name
matching a restriction in value (excluding tag and length) of the excluded subtrees
subject public key field is invalid
regardless of information appearing in the permitted subtrees.
Restrictions for certificate. This extension should
be marked non-critical.

id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 14 }

SubjectKeyIdentifier ::= KeyIdentifier

4.2.1.3 Key Usage

The key usage extension defines the rfc822, dNSName, and uri name forms are all
expressed in terms purpose (e.g., encipherment,
signature, certificate signing) of strings with wild card matching. An "*" is the
wildcard character. The minimum and maximum fields key contained in general
subtree are not used for these name forms. For uris and rfc822 names, the
certificate. The usage restriction applies to the host part of the name. Examples would might be foo.bar.com; www*.bar.com; *.xyz.com.

<< X.208 (1988) defines employed when a
multipurpose key is IA5String as PrintableString plus
NumericString plus SPACE and DELETE. Thus, it does not allow the for
the * character. What to be restricted (e.g., when an RSA key should we use instead? >>

4.2.1.12 Policy Constraints

The policy constraints extension may be
used by CAs.

4.2.1.13 CRL Distribution Points

The CRL distribution points extension identifies how CRL information
is obtained. only for signing or only for key encipherment). The profile
recommends support for that when used, this extension by
CAs and applications. Further discussion of CRL management is
contained in section 5.

4.2.2 be marked as a critical extension.

id-ce-keyUsage OBJECT IDENTIFIER ::= { id-ce 15 }

KeyUsage ::= BIT STRING {
digitalSignature (0),
nonRepudiation (1),
keyEncipherment (2),
dataEncipherment (3),
keyAgreement (4),
keyCertSign (5),
cRLSign (6) }

4.2.1.4 Private Internet Extensions

4.2.2.1 Subject Information Access Key Usage Period

The name information in private key usage period extension allows the certificate identifies the entity issuer
to
which specify a different validty period for the public private key than the
certificate. This extension is bound. In some instances, it may also intended for use with digital
signature keys. This extension consists of two optional components
notBefore and notAfter. The private key associated with the
certificate should not be
necessary to know where used to find additional information about sign objects before or after the
named entity. In
times specified by the case of X.500 names, two components, respectively. CAs conforming
to this relationship is
automatic. The subject information access extension provides a means profile shall not generate certificates with private key
usage period extensions unless at least one of identifying where and how to find information about the subject.
The extension specifies a method of obtaining information and a
general name form indicating where. two components is
present.

This extension should always be
non-critical.

subjectInfoAccess EXTENSION profile recommends against the use of this extension. CAs
conforming to this profile shall not generate certificates with
critical private key usage period extensions.

id-ce-privateKeyUsagePeriod OBJECT IDENTIFIER ::= {
SYNTAX SubjectInfoAccessSyntax
IDENTIFIED BY { TBD-OID-1 } id-ce 16 }

PrivateKeyUsagePeriod ::= SEQUENCE {

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SubjectInfoAccessSyntax ::= SEQUENCE SIZE (1..MAX) OF AccessDescription

AccessDescription ::= SEQUENCE {
accessMethod OBJECT IDENTIFIER,
accessLocation GeneralName

notBefore [0] GeneralizedTime OPTIONAL,
notAfter [1] GeneralizedTime OPTIONAL }

<< What upper bound should be assigned for MAX? >>

<< Where is the list of access method OIDs going to be specified? >>

4.2.2.2 Authority Information Access

4.2.1.5 Certificate Policies

The authority information access certificate policies extension indicates how to access CA contains a sequence of policy
information terms, each of which consists of an object identifier
(OID) and services for optional qualifiers. These policy information terms
indicate the issuer of policy under which the certificate in has been issued and
the purposes for which the extension appears. Information and services include certificate
status or on-line validation services, certificate retrieval, CA
policy data, and CA certificates (certificates certifying the target
CA to aid in certification path navigation). This extension may be
included used. This profile
strongly recommends that a simple OID be present in subject or CA certificates and this field.
Optional qualifiers which may be critical or non-
critical.

<< What does it mean present are expected to mark this extension critical? >>

authorityInfoAccess EXTENSION ::= {
SYNTAX AuthorityInfoAccessSyntax
IDENTIFIED BY { TBD-OID-2 } }

AuthorityInfoAccessSyntax ::= SEQUENCE {
certStatus [0] SEQUENCE OF AccessDescription,
certRetrieval [1] SEQUENCE OF AccessDescription,
caPolicy [2] SEQUENCE OF AccessDescription,
caCerts [3] SEQUENCE OF AccessDescription }

4.2.2.3 CA Information Access

The CA provide
information access extension indicates how to access about obtaining CA
information and services for rules, not change the subject definition of
the certificate in policy.

Applications with specific policy requirements are expected to have a
list of those policies which
the extension appears. Information they will accept and services include certificate
status or on-line validation services, certificate retrieval, CA to compare the
policy data, and CA certificates (certificates certifying OIDs in the target
CA certificate to aid in cert path navigation). This that list. If this extension may be included
only in CA certificates and may is
critical, the path validation software must be critical able to interpret this
extension, or non-critical. CA
certificates may include both an authority and a caInfoAccess
extension must reject the certificate. (Applications are free to describe access methods
ignore the policy field, even if the extension is marked critical.)

This specification defines two policy qualifiers types for both use by
certificate policy writers and certificate issuers at their own
discretion. The quailfier types are the CA CPS Pointer qualifier, and its issuer.

caInfoAccess EXTENSION ::= {
SYNTAX CAInfoAccessSyntax
IDENTIFIED BY { TBD-OID-2 }
the User Notice qualifier.

The CPS Pointer qualifier contains a pointer to a Certification
Practice Statement (CPS) published by the CA. The pointer is in the
form of a URI.

The User Notice qualifier contains a text string that is to be
displayed to a certificate user (including subscribers and relying
parties) prior to the use of the certificate. The text string may be
an IA5String or a BMPString - a subset of the ISO 100646-1 multiple
octet coded character set. A CA may invoke a procedure that requires
that the certficate user acknowledge that the applicable terms and
conditions have been disclosed or accepted.

id-ce-certificatePolicies OBJECT IDENTIFIER ::= { id-ce 32 }

certificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

PolicyInformation ::= SEQUENCE {
policyIdentifier CertPolicyId,
policyQualifiers SEQUENCE SIZE (1..MAX) OF
PolicyQualifierInfo OPTIONAL }

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CAInfoAccessSyntax

CertPolicyId ::= OBJECT IDENTIFIER

PolicyQualifierInfo ::= SEQUENCE {
certStatus [0] SEQUENCE OF AccessDescription,
certRetrieval [1] SEQUENCE OF AccessDescription,
caPolicy [2] SEQUENCE OF AccessDescription,
caCerts [3] SEQUENCE OF AccessDescription
policyQualifierId PolicyQualifierId,
qualifier ANY DEFINED BY policyQualifierId }

4.3 Examples

<< Certificate samples including descriptive text and ASN.1 encoded
blobs will be inserted. >>

-- policyQualifierIds for Internet policy qualifiers

id-pkix-cps OBJECT IDENTIFIER ::= { pkix 4 }
id-pkix-unotice OBJECT IDENTIFIER ::= { pkix 5 CRL and CRL Extensions Profile

As described above, one goal of this X.509 v2 CRL profile }

PolicyQualifierId ::= ENUMERATED { id-pkix-cps, id-pkix-unotice }

Qualifier ::= CHOICE {
cPSuri CPSuri,
userNotice UserNotice }

CPSuri ::= IA5String

UserNotice ::= CHOICE {
ia5String IA5String,
bmpString ANY }

4.2.1.6 Policy Mappings

This extension is to
foster the creation used in CA certificates. It lists pairs of
obbjectidentifiers; each pair includes an interoperable issuerDomainPolicy and reusable Internet PKI.
To achieve this goal, guidelines a
subjectDomainPolicy. The pairing indicates the issuing CA considers
its issuerDomainPolicy equivalent to the subject CA's
subjectDomainPolicy.

The issuing CA's users may accept an issuerDomainPolicy for certain
applications. The policy mapping tells the use of extensions are
specified, and some assumptions are made about issuing CA's users which
policies associated with the nature of
information included in subject CA are comparable to the CRL.

CRLs may be used in a wide range of applications and environments
covering a broad spectrum of interoperability goals and an even
broader spectrum of operational and assurance requirements. This
profile establishes a common baseline for generic applications
requiring broad interoperability. Emphasis is placed on support for
X.509 v2 CRLs. The profile defines a baseline set of information
that can be expected in every CRL. Also, the profile defines common
locations within the CRL for frequently used attributes, and common
representations for these attributes. policy
they accept.

This profile does not define any private Internet CRL extensions or
CRL entry extensions.

Environments with additional or special purpose requirements may
build on this profile or extension may replace it.

5.1 CRL Fields

The X.509 v2 CRL syntax is as follows. For signature calculation,
the data that is to be signed is ASN.1 DER encoded. ASN.1 DER
encoding supported by CAs and/or applications, and it is a tag, length, value encoding system for each element.

CertificateList
always non-critical.

id-ce-policyMappings OBJECT IDENTIFIER ::= SEQUENCE {
tbsCertList TBSCertList,
signatureAlgorithm AlgorithmIdentifier,
signature BIT STRING id-ce 33 }

TBSCertList

PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
version Version OPTIONAL,
issuerDomainPolicy CertPolicyId,
subjectDomainPolicy CertPolicyId }

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-- if present, must

4.2.1.7 Subject Alternative Name

The subject alternative names extension allows additional identities
to be v2
signature AlgorithmIdentifier,
issuer Name,
thisUpdate UTCTime,
nextUpdate UTCTime,
revokedCertificates SEQUENCE OF SEQUENCE {
userCertificate CertificateSerialNumber,
revocationDate UTCTime,
crlEntryExtensions Extensions OPTIONAL } OPTIONAL,
crlExtensions [0] Extensions OPTIONAL }

Version ::= INTEGER { v1(0), v2(1), v3(2) }

AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL }
-- contains a value of bound to the type
-- registered for use with subject of the
-- algorithm object identifier value

CertificateSerialNumber ::= INTEGER

Extensions ::= SEQUENCE OF Extension

Extension ::= SEQUENCE {
extnId OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING }
-- contains certificate. Defined options
include an rfc822 name (electronic mail address), a DER encoding of DNS name, an IP
address, and a value
-- of the type registered for use with
-- the extnId object identifier value

The following items describe the proposed use of the X.509 v2 CRL for
in Internet PKI.

5.1.1 Version

This field describes the version URI. Other options exist, including completely local
definitions. Multiple instances of the encoded CRL. When extensions
are used, as expected in this profile, use version 2 (the integer
value is 1). If neither CRL extensions nor CRL entry extensions a name and multiple name forms
may be included. Whenever such identities are
present, use version 1 (the integer value must to be omitted).

5.1.2 Signature

This field contains bound into a
certificate, the algorithm subject alternative name (or issuer alternative
name) extension shall be used. (Note: a form of such an identifier for the algorithm used
to sign the CRL. Section 7.2 lists the signature algorithms used
may also be present in the Internet PKI.

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5.1.3 Issuer Name

The issuer subject distinguished name; however, the
alternative name identifies extension is the entity who has signed (and issued preferred location for finding such
information.)

Further, if the
CRL). The issuer only subject identity may be carried included in the issuer certificate is
an alternative name field
and/or the issuerAltName extension. If identity information is
present only in the issuerAltName extension, form (e.g., an electronic mail address), then the issuer
subject distinguished name may should be empty (an empty sequence), the
subjectAltName extension should be used. If the subject field
contains an empty sequence and squence, the issuerAltName subjectAltName extension must shall be
marked critical.

5.1.4 This Update

This field indicates

Alternative names may be constrained in the issue date of same manner as subject
distinguished names using the name constraints extension as described
in section 4.2.1.11.

id-ce-subjectAltName OBJECT IDENTIFIER ::= { id-ce 17 }

SubjectAltName ::= GeneralNames

GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

GeneralName ::= CHOICE {
otherName [0] ANY,
rfc822Name [1] IA5String,
dNSName [2] IA5String,
x400Address [3] ORAddress,
directoryName [4] Name,
ediPartyName [5] EDIPartyName,
uniformResourceIdentifier [6] IA5String,
iPAddress [7] OCTET STRING,
registeredID [8] OBJECT IDENTIFIER }

EDIPartyName ::= SEQUENCE {
nameAssigner [0] DirectoryString OPTIONAL,
partyName [1] DirectoryString }

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4.2.1.8 Issuer Alternative Name

As with 4.2.1.7, this CRL.. It extension is strongly
recommended that UTCTime values be expressed Greenwich Mean Time
(Zulu) and not use seconds (i.e., times are YYMMDDHHMMZ). used to associate Internet style
identities with the certificate issuer. If seconds
are used, a value of 00 seconds should never be encoded.

5.1.5 Next Update

This field indicates the date by which only issuer identity
included in the next CRL will be issued.
The next CRL could certificate is an alternative name form (e.g., an
electronic mail address), then the issuer distinguished name should
be issued before empty (an empty sequence), the indicated date, but it will
not issuerAltName extension should be issued any later than
used. If the indicated date.

As described issuer field is empty and more than one issuerAltName
extension is included in the previous section, certificate, the UTCTime for Next Update
should issuerAltName extension
shall be expressed Greenwich Mean Time (Zulu) and marked critical.

id-ce-issuerAltName OBJECT IDENTIFIER ::= { id-ce 18 }

IssuerAltName ::= GeneralNames

4.2.1.9 Subject Directory Attributes

The subject directory attributes extension is not use seconds.

5.1.6 Revoked Certificates

Revoked certificates are listed. recommended as an
essential part of this profile, but it may
be used in local environments. This extension is always non-critical.

id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::= { id-ce 9 }

SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

4.2.1.10 Basic Constraints

The revoked certificates are named
by their serial numbers. Certificates are uniquely identified by basic constraints extension identifies whether the
combination subject of the issuer name or issuer alternative name along with
the user
certificate serial number. The date on which the revocation
occured is specified. As described in section 5.1.4, the UTCTime for
revocationDate should be expressed Greenwich Mean Time (Zulu) and not
use seconds.. CRL entry extensions are discussed in section 5.3.

When a CA wishes to revoke and how deep a certificate certification path may exist
through that CA. This profile requires the use of this extension,
and it shall be critical for all certificates issued to another
CA, the revocation shall appear on the CRL. CAs.

id-ce-basicConstraints OBJECT IDENTIFIER ::= { id-ce 19 }

BasicConstraints ::= SEQUENCE {
cA BOOLEAN DEFAULT FALSE,
pathLenConstraint INTEGER (0..MAX) OPTIONAL }

4.2.1.11 Name Constraints

The revocation should
also appear name constraints extension provides permitted and excluded
subtrees that place restrictions on the authority revocation list (ARL). The CA is
revoking names that may be included within
a certificate that it issued.

5.2 CRL Extensions

The extensions defined issued by ANSI X9 and ISO for X.509 v2 CRLs [X.509-
AM] [X9.55] provide methods for associating additional attributes
with CRLs. The X.509 v2 CRL format also allows communities a given CA. Restrictions may apply to define
private extensions to carry the
subject distringuished name or subject alternative names. Any name
matching a restriction in the excluded subtrees field is invalid
regardless of information unique to those communities.
Each extension appearing in a CRL the permitted subtrees. This
extension may be designated as critical or non-
critical. A CRL validation must fail if it encounters an critical non-critical.

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extension which it does not know how to process. However, an
unrecognized non-critical extension may be ignored.

Restrictions for the rfc822, dNSName, and uri name forms are all
expressed in terms of strings with wild card matching. An "*" is the
wildcard character. The following
presents those extensions minimum and maximum fields in general
subtree are not used within Internet CRLs. Communities may
elect for these name forms. For uris and rfc822
names, the restriction applies to use additional extensions; however, caution should be
exercised in adopting any critical extensions in CRLs which might the host part of the name.
Examples would be
used in a general context.

5.2.1 Authority Key Identifier

The authority key identifier extension provides a means foo.bar.com; www*.bar.com; *.xyz.com.

Restrictions of
identifying the particular public key used to sign a CRL. The
identification can form directoryName shall be based on either applied to the key identifier (the
subject
key identifier field in the CRL signer's certificate) or on certificate and to the issuer subjectAltName extensions
of type directoryName. Restrictions of the form x400Address shall be
applied to subjectAltName extensions of type x400Address.

The syntax and semantics for name constraints for otherName,
ediPartyName, and serial number. The key identifier method is recommended in registeredID are not defined by this
profile. This extension would be used where an issuer has multiple
signing keys, either due to multiple concurrent key pairs or due to
changeover. In general, this non-critical specification.

id-ce-nameConstraints OBJECT IDENTIFIER ::= { id-ce 30 }

NameConstraints ::= SEQUENCE {
permittedSubtrees [0] GeneralSubtrees OPTIONAL,
excludedSubtrees [1] GeneralSubtrees OPTIONAL }

GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree

GeneralSubtree ::= SEQUENCE {
base GeneralName,
minimum [0] BaseDistance DEFAULT 0,
maximum [1] BaseDistance OPTIONAL }

BaseDistance ::= INTEGER (0..MAX)

4.2.1.12 Policy Constraints

The policy constraints extension should can be
included used in certificates.

5.2.2 Issuer Alternative Name certificates issued
to CAs. The issuer alternative names policy constraints extension allows additional identities
to constrains path validation
in two ways. It can be associated with the issuer of used to prohibit policy mapping or limit the CRL. Defined options include
an rfc822 name (electronic mail address), a DNS name, an IP address,
and a URI. Multiple instances
set of a name and multiple name forms poicies that can in subsequent certificates. This extension
may be included. Whenever such identities are used, the issuere
alternative name critical or non-critical.

id-ce-policyConstraints OBJECT IDENTIFIER ::= { id-ce 34 }

PolicyConstraints ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
policySet [0] CertPolicySet OPTIONAL,
requireExplicitPolicy [1] SkipCerts OPTIONAL,
inhibitPolicyMapping [2] SkipCerts OPTIONAL }

SkipCerts ::= INTEGER (0..MAX)

CertPolicySet ::= SEQUENCE SIZE (1..MAX) OF CertPolicyId

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4.2.1.13 CRL Distribution Points

The CRL distribution points extension shall be used. Further, if the only
issuer identity included in the identifies how CRL information
is an alternative name form
(e.g., an electronic mail address), then the issuer distinguished
name should be empty (an empty sequence), the issuerAltName obtained. The extension
should shall be used, and the issuerAltName non-critical, but this profile
recommends support for this extension must be marked
critical.

5.2.3 CRL Number

The by CAs and applications.
Further discussion of CRL number management is a non-critical CRL extension which conveys a
monotonically increacing sequence number contained in section 5.

id-ce-cRLDistributionPoints OBJECT IDENTIFIER ::= { id-ce 31 }

cRLDistributionPoints ::= {
CRLDistPointsSyntax }

CRLDistPointsSyntax ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint

DistributionPoint ::= SEQUENCE {
distributionPoint [0] DistributionPointName OPTIONAL,
reasons [1] ReasonFlags OPTIONAL,
cRLIssuer [2] GeneralNames OPTIONAL }

DistributionPointName ::= CHOICE {
fullName [0] GeneralNames,
nameRelativeToCRLIssuer [1] RelativeDistinguishedName }

ReasonFlags ::= BIT STRING {
unused (0),
keyCompromise (1),
cACompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6) }

4.2.2 Private Internet Extensions

This section defines new extensions for each CRL issued by a
given CA through a specific CA X.500 Directory entry use in the Internet Public
Key Infrastructure. These extensions may be used to direct
applications to additional information about the certificate's
subject or CRL
distribution point. issuer. This extension allows users to easily determine
when a particular CRL superceeds another CRL. CAs conforming to this
profile shall include this CRL.
5.2.4 Issuing Distribution Point

The issuing distribution point includes the type of information,
where it is located, and a critical CRL extension that
identifies the CRL distribution point method for a particular CRL, and it
indicates whether obtaining the CRL covers revocation for end entity
certificates only, information. The
types of information include certificate status, CA certificates only, policy
information, and related certificates.

The object identifiers associated with the private extensions are
defined under the iso (1), org (3), dod (6), internet (1),
security(5) or a limitied set 1.3.6.1.5, branch of reason
codes. Since this extension is critical, all certificate users must the name space. These extensions
make use of OIDs of the form {applTCPProtoID port}, which identify
TCP-based protocols that don't have OIDs assigned by other means, to
identify common methods for retrieving information.

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be prepared to receive CRLs with this extension.

The CRL is signed using following ASN.1 defines object identifiers which may be used by
applications that implement the CA's private key. CRL Distribution
Points do not have their own key pairs. If extensions; additional access
methods may be used, but the CRL is stored in semantics are undefined by this
document.

pkix OBJECT IDENTIFIER ::= { iso(1) org(3) dod (6) internet (1)
security(5) pkix(?) }

-- Object identifiers for ftp, http, smtp and ldap protocols

applTCPProto OBJECT IDENTIFIER ::= { 1 3 6 1 2 1 27 4 }

ftpID OBJECT-IDENTIFIER ::= {applTCPProtoID 21}
httpID OBJECT-IDENTIFIER ::= {applTCPProtoID 80}
smtpID OBJECT-IDENTIFIER ::= {applTCPProtoID 25}
ldapID OBJECT-IDENTIFIER ::= {applTCPProtoID 389}

-- Object identifier for the X.500 Directory, it is stored directory access protocol

dap OBJECT-IDENTIFIER ::= { 2 5 3 1 }

4.2.2.1 Subject Information Access

The name information in the Directory entry corresponding to certificate identifies the CRL distribution point, entity to
which the public key is bound. In some instances, it may also be different that
necessary to know where to find additional information about the Directory
entry of
named entity. In the CA.

CRL distribution points, if used by case of X.500 names, this relationship is
automatic. The subject information access extension provides a CA, should be partition the CRL
on the basis means
of compromise and routine revocation. That is, the
revocations with reason code keyCompromise (1) shall appear in one
distribution point, identifying where and how to find information about the revocations with other reason codes shall
appear in another distribution point.

5.2.5 Delta CRL Indicator subject.
The delta CRL indicator is a critical CRL extension that identifies specifies a
delta-CRL. The use method of delta-CRLs can significantly improve
processing time for applications which store revocation obtaining information
in and a format other than the CRL structure.
general name form indicating where. This allows changes to be
added to the local database while ignoring unchanged information that
is already in the local databse.

When a delta-CRL is issued, the CAs extension shall also issue a complete CRL.

The value of BaseCRLNumber identifies the CRL number of the base CRL
that was used as the starting point in always be
non-critical.

id-pkix-subjectInfoAccess OBJECT-IDENTIFIER ::= { pkix 1}

-- subjectInfoAccess ::= { SubjectInfoAccessSyntax }

SubjectInfoAccessSyntax ::= SEQUENCE SIZE (1..MAX) OF AccessDescription

AccessDescription ::= SEQUENCE {
accessMethod OBJECT IDENTIFIER,
accessLocation GeneralName }

This specification defines the generation of this delta-
CRL. following values for accessMethod:
ftpID, httpID, smtpID, ldapID, and dap. The delta-CRL contains the changes between accessMethod value
indicates the base CRL and protocol required to obtain the
current CRL issued along with information. If
accessMethod is ftpID, then the delta-CRL. It information must available through
anonymous ftp. If accessMethod is ftpID, httpID, smtpID, or ldapID,

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then the decision of a
CA as to whether to provide delta-CRLs. Again, a delta-CRL accessLocation shall not be issued without a corresponding CRL. uniformResourceIndicator (i.e., a
URI). The value of CRLNumber for
both URI shall specify all information required to retrieve the delta-CRL and
information. If accessMethod is dap, then the corresponding CRL accessLocation shall
be identical.

A CRL user constructing a locally held CRL from delta-CRLs shall
consider the constructed CRL incomplete directoryName.

4.2.2.2 Authority Information Access

The authority information access extension indicates how to access CA
information and unusable if services for the CRLNumber issuer of the received delta-CRL is more that one greater that certificate in which
the CRLnumber
of extension appears. Information and services include certificate
status or on-line validation services, certificate retrieval, CA
policy data, and CA certificates (certificates certifying the delta-CRL last processed.
5.3 CRL Entry Extensions

The CRL entry extensions already defined by ANSI X9 target
CA to aid in certification path navigation). This extension may be
included in subject or CA certificates and ISO for X.509
v2 CRLs [X.509-AM] [X9.55] provide methods for associating additional
attributes with CRL entries. The X.509 v2 CRL format also allows
communities to define private CRL entry extensions to carry
information unique to those communities. Each extension in a CRL
entry may be designated as critical or non-critical. A non-
critical.

id-pkix-authorityInfoAccess OBJECT-IDENTIFIER ::= { pkix 2}

-- authorityInfoAccess ::= { AuthorityInfoAccessSyntax }

AuthorityInfoAccessSyntax ::= SEQUENCE {
certStatus [0] SEQUENCE OF AccessDescription OPTIONAL,
certRetrieval [1] SEQUENCE OF AccessDescription OPTIONAL,
caPolicy [2] SEQUENCE OF AccessDescription OPTIONAL,
caCerts [3] SEQUENCE OF AccessDescription OPTIONAL }

If certStatus is present, each entry in that sequence describes a
mechanism and location for

on-line verification of the status of this certificate, or

the CRL
validation must fail on which this certificate would appear if it encounters an critical CRL revoked.

If certRetrieval is present, each entry extension in the sequence describes how
to retrieve all current certificates whose subject is the issuer of
the certificate in which it does not know this extension appears.

If caPolicy is present, each entry in the sequence describes how to process. However, an unrecognized
non-critical CRL
retrieve the policy that was in effect when this certificate was
issued.

If caCerts is present, each entry extension may be ignored. The following in the sequence describes a
mechanism and location for retrieval of certificates the issuer has
issued to other CAs.

If the certStatus, certRetrieval, caPolicy, or caCerts sequence has
more than one value, conforming applications are not required to
process all the values. Successful processing of any one

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presents recommended extensions used within Internet CRL entries and
standard locations for information. Communities may elect to use
additional CRL entry extensions; however, caution should be exercised
in adopting any critical extensions in CRL entries which might

AccessDescritpion shall be
used in a general context.

5.3.1 Reason Code

The reasonCode sufficient. It is a non-critical CRL entry extension that identifies the reason for responsibility of
the certificate revocation. As are strongly encouraged issuer to include reason codes in CRL entries; however, the reason code CRL
entry extension should be absent instead of using ensure all mechanisms provide the unspecified (0)
reasonCode value.

5.3.2 Hold Instruction Code same
information.

The hold instruction code is a non-critical CRL entry extension that
provides a registered instruction identifier which indicates expected values for AccessDescription are the
action to be taken after encountering a certificate that has been
placed on hold.

<< The Directory Specification does values defined in
4.2.2.1. Processing rules for other values for accessMethod are not define any standard hold
instruction codes. Where will they be defined? Are any specific to
the Internet environment? >>

5.3.3 Invalidity Date

The invalidity date is a non-critical CRL entry
defined.

If this extension that
provides the date on which it is known or suspected that the private
key was compromised or that the certificate otherwise became invalid.
This date may be earlier than critical, applications are required to use the revocation date
information in the CRL entry,
but it must be later than the issue date of the previously issued
CRL. Remember that certStatus field (if present) to check the
revocation date in status of this certificate, the CRL entry specifies certRetrieval field (if
present) to obtain the date that issuer's current certificates, and the CA revoked caCerts
field (if present) to obtain certificates issued by the certificate. Whenever this
information is available, CAs are strongly encouraged subject to share it
with CRL users.

The GeneralizedTime values included in this field shall be expressed
in Greenwich Mean Time (Zulu) and omit trailing zeros in fractional
seconds. Normally, GeneralizedTime will be expressed as
YYYYMMDDHHMMSSZ.
5.4 Examples

<< CRL samples including descriptive text and ASN.1 encoded blobs
will be inserted. >>

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6 Certificate Path Validation

<<
other CAs.

There used to be long section here that contained the
certification path validation procedures. The major deviations from
the procedures outlined in [X.509-AM] were due to certificate hold
processing. These procedures are no longer onerous, so there additional processing requirements for cAPolicy if the
extension is no
reason to prohibit marked as critical.

4.2.2.3 CA Information Access

Where the use subject of the hold facility. Does anyone see a
reason to reatin this section? >>

7 Algorithm Support

7.1 One-way Hash Functions

One-way hash functions are also called message digest algorithms.
SHA-1 certificate is a CA, the subjectInfoAccess
extension may be insufficient. The CA information access extension
indicates how to access CA information and services for the most popular one-way hash function used subject
of the certificate in which the
Internet PKI. However, PEM uses MD2 for extension appears. Information and
services include certificate status or on-line validation services,
certificate retrieval, CA policy data, and CA certificates [RFC 1422] [RFC
1423]. For this reason, MD2 is included in this profile.

7.1.1 MD2 One-way Hash Function

MD2 was also developed by Ron Rivest, but RSA Data Security has not
placed
(certificates certifying the MD2 algorithm target CA to aid in the public domain. Rather, RSA Data
Security has granted license cert path
navigation). This extension is syntactically identical to use MD2 for non-commerical Internet
Privacy-Enhanced Mail. For this reason, MD2 may continue to be used
with PEM certificates,
authorityInfoAccess, but SHA-1 is preferred. MD2 is fully
described in RFC 1319 [RFC 1319].

At the Selected Areas in Cryptography '95 conference identified by a different OID. This
extension may be included only in May 1995,
Rogier CA certificates and Chauvaud presented may be critical
or non-critical. CA certificates may include both an attack on MD2 that can nearly find
collisions [RC95]. Collisions occur when two different messages
generate authority and a
caInfoAccess extension to describe access methods for both the same message digest. A checksum operation CA and
its issuer.

id-pkix-caInfoAccess OBJECT-IDENTIFIER ::= { pkix 3 }

-- caInfoAccess ::= { AuthorityInfoAccessSyntax }

If certStatus is present, each entry in MD2 that sequence describes a
mechanism and location for

on-line verification of the status of this certificate, or

CRL issued by the subject of this certificate.

If certRetrieval is present, each entry in the
only remaining obstacle sequence describes how
to retrieve all current certificates whose subject is the success subject of
the attack. For certificate in which this
reason, extension appears.

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If caPolicy is present, each entry in the use sequence describes how to
retrieve the current policy tssociated with the subject of MD2 this
certificate.

If caCerts is present, each entry in the sequence describes a
mechanism and location for new retrieval of certificates the subject has
issued to other CAs.

If the certStatus, certRetrieval, caPolicy, or caCerts sequence has
more than one value, conforming applications is discouraged. are not required to
process all the values. Successful processing of any one
AccessDescritpion shall be sufficient. It is
still reasonable the responsibility of
the certificate issuer to use MD2 to verify existing signatures, as ensure all mechanisms provide the
ability to find collisions same
information.

The legal values for AccessDescription shall be as defined in MD2 does not enable an attacker
4.2.2.1.

If this extension is critical, applications are required to find
new messages having a previously computed hash value.

<< More use the
information on in the attack certStatus field (if present) to check the
revocation status of this certificate, the certRetrieval field (if
present) to obtain the subject's other current certificates, and its implications can be
obtained from a RSA Laboratories security bulletin. These bulletins
are available from <http://www.rsa.com/>. >>

7.1.2 SHA-1 One-way Hash Function

SHA-1 was developed by the U.S. Government. SHA-1 is fully described
in FIPS 180-1 [FIPS 180-1].

SHA-1 is
caCerts field (if present) to obtain certificates issued by the one-way hash function of choice
subject to other CAs.

There are no additional processing requirements for use with both RSA cAPolicy if the DSA signature algorithms.
extension is marked as critical.

4.3 Examples

<< Certificate samples including descriptive text and ASN.1 encoded
blobs will be inserted. >>

4.3.1 Simple certificate, no extensions

<<TBD>>

4.3.2 Certificate with Private extensions

<<TBD>>

4.3.3 certificate with no subject DN

<<TBD>>

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7.2 Signature Algorithms

RSA

5 CRL and DSA are the most popular signature algorithms used in the
Internet.

There is some ambiguity in 1988 CRL Extensions Profile

As described above, one goal of this X.509 document with respect v2 CRL profile is to
foster the
definition creation of an interoperable and reusable Internet PKI.
To achieve this goal, guidelines for the SIGNED macro use of extensions are
specified, and some assumptions are made about the representation nature of a signature
information included in a certificate or a CRL. The interpretation selected for the
Internet requires that the data to CRL.

CRLs may be signed (e.g., the one-way hash
function output value) is first ASN.1 encoded as used in a wide range of applications and environments
covering a broad spectrum of interoperability goals and an OCTET STRING even
broader spectrum of operational and
the result assurance requirements. This
profile establishes a common baseline for generic applications
requiring broad interoperability. Emphasis is encrypted (e.g., using RSA Encryption) to form the
signed quantity. Asd part placed on support for
X.509 v2 CRLs. The profile defines a baseline set of information
that can be expected in every CRL. Also, the profile defines common
locations within the SIGNED macro, CRL for frequently used attributes, and common
representations for these attributes.

This profile does not define any private Internet CRL extensions or
CRL entry extensions.

Environments with additional or special purpose requirements may
build on this signature value profile or may replace it.

Conforming CAs are not required to issue CRLs if other revocation or
status mechanisms are provided. Conforming CAs that issue CRLs are
required to issue version 2 CRLs. Conforming applications are
required to process version 1 and 2 certificates.

5.1 CRL Fields

The X.509 v2 CRL syntax is then ASN.1 encoded as a BIT STRING.

7.2.1 RSA Signature Algorithm

A patent statement regarding follows. For signature calculation,
the RSA algorithm can data that is to be found at the
end of this profile.

The RSA algorithm signed is named ASN.1 DER encoded. ASN.1 DER
encoding is a tag, length, value encoding system for it's inventors: Rivest, Shamir, and
Adleman. The RSA each element.

CertificateList ::= SEQUENCE {
tbsCertList TBSCertList,
signatureAlgorithm AlgorithmIdentifier,
signature algorithm is defined in PKCS #1 [PKCS#1].
It combines either BIT STRING }

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userCertificate CertificateSerialNumber,
revocationDate ChoiceOfTime,
crlEntryExtensions Extensions OPTIONAL
-- if present, must be v2
} OPTIONAL,
crlExtensions [0] Extensions OPTIONAL
-- if present, must be v2
}

ChoiceOfTime ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime }

Version ::= INTEGER { v1(0), v2(1), v3(2) }

AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL }
-- contains a value of the MD2 or type
-- registered for use with the SHA-1 one-way hash function
-- algorithm object identifier value

CertificateSerialNumber ::= INTEGER

Extensions ::= SEQUENCE OF Extension

Extension ::= SEQUENCE {
extnId OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING }
-- contains a DER encoding of a value
-- of the type registered for use with
-- the RSA asymmetric encryption algorithm. As defined extnId object identifier value

The following items describe the proposed use of the X.509 v2 CRL in PKCS #1,
the
ASN.1 object identifiers used to identify these signature algorithms
are: Internet PKI.

5.1.1 CertificateList Fields

The CertificateList is a SEQUENCE of three required fields. The
fields are are described in detail in the following subsections

5.1.1.1 tbsCertList

The first field in the sequence is the tbsCertList. This is a itself
a sequence, and is generally thought of as the X.509 CRL. It contains
the names of the subject and issuer, a public key associated with the
subject an expiration date, and other associated information. The

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fields of the basic tbsCertificate are described in detail in section
4.1.2; the tbscertificate may also include extensions which are
described in section 4.2.

5.1.1.2 signatureAlgorithm

The signatureAlgorithm field contains the algorithm identifier for
the algorithm used by the CA to sign the CertificateList. Section
7.2 lists the supported signature algorithms.

5.1.1.3 signature

The signature field contains a digital signature computed upon the
ASN.1 DER encoded TBSCertList. The ASN.1 DER encoded TBSCertificate
is used as the input to a one-way hash function. The one-way hash
function output value is ASN.1 encoded as an OCTET STRING and the
result is encrypted (e.g., using RSA Encryption) to form the signed
quantity. This signature value is then ASN.1 encoded as a BIT STRING
and included in the Certificate's signature field.

5.1.2 Certificate List "To Be Signed"

The certificate list to be signed, or tBSCertList, is a SEQUENCE of
required and optional fields. The required fields identify the CRL
issuer, the algorithm used to sign the CRL, the date and time the CRL
was issued, and the date and time by which the CA will issue the next
CRL.

Optional fields include lists of revoked certificates and CRL
extensions. The revoked certificate list is optional to support the
special case where a CA has not revoked any unexpired certificates it
has issued. It is expected that nearly all CRLs issued in the
Internet PKI will contain one or more lists of revoked certificates.
Similarly, the profile requires conforming CAs to use of one CRL
extension (CRL number) in all CRLs issued.

5.1.2.1 Version

This field describes the version of the encoded CRL. When extensions
are used, as expected in this profile, use version 2 (the integer
value is 1). If neither CRL extensions nor CRL entry extensions are
present, version 1 CRLs are recommended (e.g., the integer value
should be omitted).

5.1.2.2 Signature

This field contains the algorithm identifier for the algorithm used
to sign the CRL. Section 7.2 lists the signature algorithms used in

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the Internet PKI.

5.1.2.3 Issuer Name

The issuer name identifies the entity who has signed (and issued the
CRL). The issuer identity may be carried in the issuer name field
and/or the issuerAltName extension. If identity information is
present only in the issuerAltName extension, then the issuer name may
be an empty sequence and the issuerAltName extension must be
critical.

5.1.2.4 This Update

This field indicates the issue date of this CRL. ThisUpdate may be
encoded as UTCTime or GeneralizedTime.

CAs conforming to this profile shall not issue CRLs where thisUpdate
is encoded as GeneralizedTime before the year 2005. CAs conforming to
this profile shall not issue CRLs where thisUpdate is encoded as
UTCTime after the year 2015.

Where encoded as UTCTime, thisUpdate shall be specified and
interpreted as defined in Section 4.1.2.5.1. Where encoded as
GeneralizedTime, thisUpdate shall be specified and interpreted as
defined in Section 4.1.2.5.2.

5.1.2.5 Next Update

This field indicates the date by which the next CRL will be issued.
The next CRL could be issued before the indicated date, but it will
not be issued any later than the indicated date. nextUpdate may be
encoded as UTCTime or GeneralizedTime.

CAs conforming to this profile shall not issue CRLs where nextUpdate
is encoded as GeneralizedTime before the year 2005. CAs conforming to
this profile shall not issue CRLs where nextUpdate is encoded as
UTCTime after the year 2015.

Where encoded as UTCTime, nextUpdate shall be specified and
interpreted as defined in Section 4.1.2.5.1. Where encoded as
GeneralizedTime, nextUpdate shall be specified and interpreted as
defined in Section 4.1.2.5.2.

5.1.2.6 Revoked Certificates

Revoked certificates are listed. The revoked certificates are named
by their serial numbers. Certificates are uniquely identified by the
combination of the issuer name or issuer alternative name along with

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the user certificate serial number. The date on which the revocation
occured is specified. The time for revocationDate shall be expressed
as described in section 5.1.2.4. Additional information may be
supplied in CRL entry extensions; CRL entry extensions are discussed
in section 5.3.

5.2 CRL Extensions

The extensions defined by ANSI X9 and ISO for X.509 v2 CRLs [X.509-
AM] [X9.55] provide methods for associating additional attributes
with CRLs. The X.509 v2 CRL format also allows communities to define
private extensions to carry information unique to those communities.
Each extension in a CRL may be designated as critical or non-
critical. A CRL validation must fail if it encounters an critical
extension which it does not know how to process. However, an
unrecognized non-critical extension may be ignored. The following
presents those extensions used within Internet CRLs. Communities may
elect to include extensions in CRLs which are not defined in this
specification. However, caution should be exercised in adopting any
critical extensions in CRLs which might be used in a general context.

Conforming CAs that issue CRLs are required to support the CRL number
extension (5.2.3), and include it in all CRLs issued. Conforming
applications are required to support the critical and optionally
critical CRL extensions issuer alternative name (5.2.2), issuing
distribution point (5.2.4) and delta CRL indicator (5.2.5).

5.2.1 Authority Key Identifier

The authority key identifier extension provides a means of
identifying the particular public key used to sign a CRL. The
identification can be based on either the key identifier (the subject
key identifier in the CRL signer's certificate) or on the issuer name
and serial number. The key identifier method is recommended in this
profile. This extension would be used where an issuer has multiple
signing keys, either due to multiple concurrent key pairs or due to
changeover. In general, this non-critical extension should be
included in certificates.

The syntax for this CRL extension is defined in Section 4.2.1.1.

5.2.2 Issuer Alternative Name

The issuer alternative names extension allows additional identities
to be associated with the issuer of the CRL. Defined options include
an rfc822 name (electronic mail address), a DNS name, an IP address,
and a URI. Multiple instances of a name and multiple name forms may
be included. Whenever such identities are used, the issuer

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alternative name extension shall be used.

Further, if the only issuer identity included in the CRL is an
alternative name form (e.g., an electronic mail address), then the
issuer distinguished name should be empty (an empty sequence), the
issuerAltName extension should be used, and the issuerAltName
extension must be marked critical. If more than one issuerAltName
extension appears in the CRL and the issuer distinguished name is
empty, exactly one issuerAltName extension must be marked critical.

The object identifier and syntax for this CRL extension are defined
in Section 4.2.1.8.

5.2.3 CRL Number

The CRL number is a non-critical CRL extension which conveys a
monotonically increacing sequence number for each CRL issued by a
given CA through a specific CA X.500 Directory entry or CRL
distribution point. This extension allows users to easily determine
when a particular CRL supercedes another CRL. CAs conforming to this
profile shall include this extension in all CRLs.

id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

cRLNumber ::= INTEGER (0..MAX)

5.2.4 Issuing Distribution Point

The issuing distribution point is a critical CRL extension that
identifies the CRL distribution point for a particular CRL, and it
indicates whether the CRL covers revocation for end entity
certificates only, CA certificates only, or a limitied set of reason
codes. Since this extension is critical, all certificate users must
be prepared to receive CRLs with this extension.

The CRL is signed using the CA's private key. CRL Distribution
Points do not have their own key pairs. If the CRL is stored in the
X.500 Directory, it is stored in the Directory entry corresponding to
the CRL distribution point, which may be different that the Directory
entry of the CA.

CRL distribution points, if used by a CA, should be partition the CRL
on the basis of compromise and routine revocation. That is, the
revocations with reason code keyCompromise (1) shall appear in one
distribution point, and the revocations with other reason codes shall
appear in another distribution point.

id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }

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issuingDistributionPoint ::= SEQUENCE {
distributionPoint [0] DistributionPointName OPTIONAL,
onlyContainsUserCerts [1] BOOLEAN DEFAULT FALSE,
onlyContainsCACerts [2] BOOLEAN DEFAULT FALSE,
onlySomeReasons [3] ReasonFlags OPTIONAL,
indirectCRL [4] BOOLEAN DEFAULT FALSE }

5.2.5 Delta CRL Indicator

The delta CRL indicator is a critical CRL extension that identifies a
delta-CRL. The use of delta-CRLs can significantly improve
processing time for applications which store revocation information
in a format other than the CRL structure. This allows changes to be
added to the local database while ignoring unchanged information that
is already in the local databse.

When a delta-CRL is issued, the CAs shall also issue a complete CRL.

The value of BaseCRLNumber identifies the CRL number of the base CRL
that was used as the starting point in the generation of this delta-
CRL. The delta-CRL contains the changes between the base CRL and the
current CRL issued along with the delta-CRL. It is the decision of a
CA as to whether to provide delta-CRLs. Again, a delta-CRL shall not
be issued without a corresponding CRL. The value of CRLNumber for
both the delta-CRL and the corresponding CRL shall be identical.

A CRL user constructing a locally held CRL from delta-CRLs shall
consider the constructed CRL incomplete and unusable if the CRLNumber
of the received delta-CRL is more that one greater that the CRLnumber
of the delta-CRL last processed.

id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }

deltaCRLIndicator ::= BaseCRLNumber

BaseCRLNumber ::= CRLNumber

5.3 CRL Entry Extensions

The CRL entry extensions already defined by ANSI X9 and ISO for X.509
v2 CRLs [X.509-AM] [X9.55] provide methods for associating additional
attributes with CRL entries. The X.509 v2 CRL format also allows
communities to define private CRL entry extensions to carry
information unique to those communities. Each extension in a CRL
entry may be designated as critical or non-critical. A CRL
validation must fail if it encounters a critical CRL entry extension
which it does not know how to process. However, an unrecognized
non-critical CRL entry extension may be ignored. The following

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All CRL entry extensions are non-critical; support for these
extensions is optional for conforming CAs and applications. However,
CAs that issue CRLs are strongly encouraged to include reason codes
(5.3.1) whenever this information is available.

5.3.1 Reason Code

The reasonCode is a non-critical CRL entry extension that identifies
the reason for the certificate revocation. CAs are strongly
encouraged to include reason codes in CRL entries; however, the
reason code CRL entry extension should be absent instead of using the
unspecified (0) reasonCode value.

id-ce-cRLReason OBJECT IDENTIFIER ::= { id-ce 21 }

-- reasonCode ::= { CRLReason }

CRLReason ::= ENUMERATED {
unspecified (0),
keyCompromise (1),
cACompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6),
removeFromCRL (8) }

5.3.2 Hold Instruction Code

The hold instruction code is a non-critical CRL entry extension that
provides a registered instruction identifier which indicates the
action to be taken after encountering a certificate that has been
placed on hold.

id-ce-holdInstructionCode OBJECT IDENTIFIER ::= { id-ce 23 }

holdInstructionCode ::= OBJECT IDENTIFIER

The following instruction codes have been defined. Conforming applications
that process this extension shall recognize the following instruction codes.

holdInstruction OBJECT IDENTIFIER ::=

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{ iso(1) member-body(2) us(840) x9-57(10040) 2 }

id-holdinstruction-none OBJECT IDENTIFIER ::= {holdInstruction 1}
id-holdinstruction-callissuer OBJECT IDENTIFIER ::= {holdInstruction 2}
id-holdinstruction-reject OBJECT IDENTIFIER ::= {holdInstruction 3}

Conforming applications which encounter a id-holdinstruction-
callissuer must call the certificate issuer or reject the
certificate. Conforming applications which encounter a id-
holdinstruction-reject ID shall reject the transaction. id-
holdinstruction-none is semantically equivalent to the absence of a
holdInstructionCode. Its use is strongly deprecated for the Internet
PKI.

<<Note: I didn't think id-holdinstruction-pickupToken was appropriate
for the Internet PKI>>

5.3.3 Invalidity Date

The invalidity date is a non-critical CRL entry extension that
provides the date on which it is known or suspected that the private
key was compromised or that the certificate otherwise became invalid.
This date may be earlier than the revocation date in the CRL entry,
but it must be later than the issue date of the previously issued
CRL. Remember that the revocation date in the CRL entry specifies
the date that the CA revoked the certificate. Whenever this
information is available, CAs are strongly encouraged to share it
with CRL users.

The GeneralizedTime values included in this field shall be expressed
in Greenwich Mean Time (Zulu) and omit trailing zeros in fractional
seconds. GeneralizedTime shall be expressed as YYYYMMDDHHMMSSZ.

id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }

invalidityDate ::= GeneralizedTime

5.4 Examples

5.4.1 Empty CRL

<<TBD>>

5.4.2 CRL with entries, no extensions

<<TBD>>

5.4.3 CRL with extensions

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<<TBD>>

6 Certificate Path Validation

Certification path validation procedures for the Internet PKI are
based on Section 12.4.3 of [X.509-AM].

Certification path processing verifies the binding between the
subject distinguished name and subject public key. The basic
constraints and policy constraints extensions facilitate automated,
self-contained implementation of certification path processing logic.

The following is an outline of a procedure for validating
certification paths. An implementation shall be functionally
equivalent to the external behaviour resulting from this procedure.
Any algorithm may be used by a particular implementation so long as
it derives the correct result.

The inputs to the certification path processing procedure are:

(a) a set of certificates comprising a certification path;

(b) a CA name and trusted public key value (or an identifier of
such a key if the key is stored internally to the certification
path processing module) for use in verifying the first certificate
in the certification path;

(c) a set of initial-policy identifiers (each comprising a
sequence of policy element identifiers), which identifies one or
more certificate policies, any one of which would be acceptable
for the purposes of certification path processing; and

(d) the current date/time (if not available internally to the
certification path processing module).

The outputs of the procedure are:

(a) an indication of success or failure of certification path
validation;

(b) if validation failed, a reason for failure; and

The procedure makes use of the following set of state variables:

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(a) acceptable policy set: A set of certificate policy
identifiers comprising the policy or policies recognized by the
public key user together with policies deemed equivalent through
policy mapping;

(b) constrained subtrees: A set of root names defining a set of
subtrees within which all subject names in subsequent certificates
in the certification path shall fall; if no restriction is in
force this state variable takes the special value unbounded; and

(c) excluded subtrees: A set of root names defining a set of
subtrees within which no subject name in subsequent certificates
in the certification path may fall; if no restriction is in force
this state variable takes the special value empty.

The procedure involves an initialization step, followed by a
series of certificate-processing steps. The initialization step
comprises:

(a) Initialize the constrained subtress to unbounded;

(b) Initialize the excluded subtrees indicator to empty; and

Each certificate is then processed in turn, starting with the
certificate signed using the trusted CA public key which was input to
this procedure. The last certificate is processed as an end-entity
certificate; all other certificates (if any) are processed as CA-
certificates.

The following checks are applied to all certificates:

(a) Check that the signature verifies, that dates are valid, that
the subject and issuer names chain correctly, and that the
certificate has not been revoked;

If the certificate has an empty sequence in the name field, name
chaining will use the critical altSubjectNames and altIssuerNames
fields. If the certificate has a critical authorityInfoAccess or
caInfoAccess extension, the information in that extension must be
used to determine the status of the certificates.

(b) If a key usage restriction extension is present in the
certificate and contains a certPolicySet component, check that at
least one member of the acceptable policy set appears in the
field;

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(c) Check that the subject name or critical AltSubjectName
extension is consistent with the constrained subtrees state
variables; and

(d) Check that the subject name or critical AltSubjectName
extension is consistent with the excluded subtrees state
variables.

If any one of the above checks fails, the procedure terminates,
returning a failure indication and an appropriate reason. If none of
the above checks fail on the end-entity certificate, the procedure
terminates, returning a success indication together with the set of
all policy qualifier values encountered in the set of certificates.

For a CA-certificate, the following constraint recording actions are
then performed, in order to correctly set up the state variables for
the processing of the next certificate:

(a) If permittedSubtrees is present in the certificate, set the
constrained subtrees state variable to the intersection of its
previous value and the value indicated in the extension field.

(b) If excludedSubtrees is present in the certificate, set the
excluded subtrees state variable to the union of its previous
value and the value indicated in the extension field.

Note: It is possible to specify an extended version of the above
certification path processing procedure which results in default
behaviour identical to the rules of Privacy Enhanced Mail [RFC
1422]. In this extended version, additional inputs to the
procedure are a list of one or more Policy Certification Authority
(PCA) names and an indicator of the position in the certification
path where the PCA is expected. At the nominated PCA position,
the CA name is compared against this list. If a recognized PCA
name is found, then a constraint of SubordinateToCA is implicitly
assumed for the remainder of the certification path and processing
continues. If no valid PCA name is found, and if the
certification path cannot be validated on the basis of identified
policies, then the certification path is considered invalid.

7 Algorithm Support

This section describes cryptographic alogrithms which may be used
with this standard. The section describes one-way hash functions and
digital signature algorithms which may be used to sign certificates
and CRLs, and identifies object identifiers for public keys contained
in a certificate.

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Conforming CAs and applications are not required to support the
algorithms or algorithm identifiers described in this section.
However, this profile requires conforming CAs and applications to
conform when they use the algorithms identified here.

7.1 One-way Hash Functions

This section identifies one-way hash functions for use in the
Internet PKI. One-way hash functions are also called message digest
algorithms. SHA-1 is the preferred one-way hash function for the
Internet PKI. However, PEM uses MD2 for certificates [RFC 1422] [RFC
1423]. For this reason, MD2 is included in this profile.

7.1.1 MD2 One-way Hash Function

MD2 was developed by Ron Rivest, but RSA Data Security has not placed
the MD2 algorithm in the public domain. Rather, RSA Data Security
has granted license to use MD2 for non-commerical Internet Privacy-
Enhanced Mail. For this reason, MD2 may continue to be used with PEM
certificates, but SHA-1 is preferred. MD2 is fully described in RFC
1319 [RFC 1319].

At the Selected Areas in Cryptography '95 conference in May 1995,
Rogier and Chauvaud presented an attack on MD2 that can nearly find
collisions [RC95]. Collisions occur when two different messages
generate the same message digest. A checksum operation in MD2 is the
only remaining obstacle to the success of the attack. For this
reason, the use of MD2 for new applications is discouraged. It is
still reasonable to use MD2 to verify existing signatures, as the
ability to find collisions in MD2 does not enable an attacker to find
new messages having a previously computed hash value.

<< More information on the attack and its implications can be
obtained from a RSA Laboratories security bulletin. These bulletins
are available from <http://www.rsa.com/>. >>

7.1.2 SHA-1 One-way Hash Function

SHA-1 was developed by the U.S. Government. SHA-1 is fully described
in FIPS 180-1 [FIPS 180-1].

SHA-1 is the one-way hash function of choice for use with both the
RSA and DSA signature algorithms.

7.2 Signature Algorithms

Certificates and CRLs described by this standard may be signed with
any public key signature algorithm. The certificate or CRL indicates

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the algorithm through an algorithmidentifier which appears in the
signatureAlgorithm field in a Certificate or CertificateList. This
algorithmidentfier is an OID and has optionally associated
parameters. This section identifies algorithm identifiers and
parameters that shall be used in the signatureAlgorithm field in a
Certificate or CertificateList.

RSA and DSA are the most popular signature algorithms used in the
Internet. Signature algorithms are always used in conjunction with a
one-way hash function identified in Section 7.1.

The signature algorithm (and one-way hash function) used to sign a
certificate or CRL is indicated by use of an algorithm identifier.
An algorithm identifier is an object identifier, and may include
associated parameters. This section identifies OIDS for RSA and DSA
and the corresponding parameters.

The data to be signed (e.g., the one-way hash function output value)
is first ASN.1 encoded as an OCTET STRING and the result is encrypted
(e.g., using RSA Encryption) to form the signed quantity. This
signature value is then ASN.1 encoded as a BIT STRING and included in
the Certificate or CertificateList (in the signature field).

7.2.1 RSA Signature Algorithm

A patent statement regarding the RSA algorithm can be found at the
end of this profile.

The RSA algorithm is named for it's inventors: Rivest, Shamir, and
Adleman. The RSA signature algorithm combines either the MD2 or the
SHA-1 one-way hash function with the RSA asymmetric encryption
algorithm. The RSA signature algorithm with MD2 and the RSA
encryption algorithm is defined in PKCS #1 [PKCS#1]. As defined in
PKCS #1, the ASN.1 object identifier used to identify this signature
algorithm is:

md2WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1)
pkcs-1(1) 2 }

The RSA signature algorithm with SHA-1 and the RSA encryption
algorithm is defined in by the OSI Ineroperability Workshop in []. As
defined in [OIW], the ASN.1 object identifier used to identify this
signature algorithm is:

sha-1WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) oiw(14)
secsig(3) algorithm(2) 29 }

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When either of these object identifiers is used within the ASN.1 type
AlgorithmIdentifier, the parameters component of that type shall be
the ASN.1 type NULL.

When signing, the RSA algorithm generates an integer y. This value
is converted to a bit string such that the most significant bit in y
is the first bit in the bit string and the least significant bit in y
is the last bit in the bit string.

(In general this occurs in two steps. The integer y is converted to
an octect string such that the first octect has the most significance
and the last octect has the least significance. The octet string is
converted into a bit string such that the most significant bit of the
first octect shall become the first bit in the bit string, and the
least significant bit of the last octect is the last bit in the BIT
STRING.

7.2.2 DSA Signature Algorithm

A patent statement regarding the DSA can be found at the end of this
profile.

The Digital Signature Algorithm (DSA) is also called the Digital
Signature Standard (DSS). DSA was developed by the U.S. Government,
and DSA is used in conjunction with the the SHA-1 one-way hash
function. DSA is fully described in FIPS 186 [FIPS 186]. The ASN.1
object identifiers used to identify this signature algorithm are:

id-dsa-with-sha1 ID ::= {
iso(1) member-body(2) us(840) x9-57 (10040) secsig(2)
x9algorithm(4) 3 }

The id-dsa-with-sha1 algorithm syntax has NULL parameters. The DSA
parameters in the subjectPublicKeyInfo field of the certificate of
the issuer shall apply to the verification of the signature.

If the subjectPublicKeyInfo AlgorithmIdentifier field has NULL
parameters and the CA signed the subject certificate using DSA, then
the certificate issuer's parameters apply to the subject's DSA key.
If the subjectPublicKeyInfo AlgorithmIdentifier field has NULL
parameters and the CA signed the subject with a signature algorithm
other than DSA, then clients shall not validate the certificate.

When signing, the DSA algorithm generates two values. These values
are commonly referred to as r and s. To easily transfer these two
values as one signature, they shall be ASN.1 encoded using the
following ASN.1 structure:

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Dss-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER }

7.3 Subject Public Key Algorithms

Certificates described by this standard may convey a public key for
any public key algorithm. The certificate indicates the algorithm
through an algorithmidentifier. This algorithmidentfieier is an OID
and optionally associated parameters.

This section identifies preferred OIDs and parameters for the RSA,
DSA, KEA, and Diffie-Hellman algorithms. Conforming CAs shall use
the identified OIDs when issuing certificates containing public keys
for these algorithms. Conforming applications supporting any of these
algorithms shall, at a minimum, recognize the OID identified in this
section.

7.3.1 RSA Keys

The object identifier rsaEncryption identifies RSA public keys.

pkcs-1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) US(840)
rsadsi(113549) pkcs(1) 1 }

rsaEncryption OBJECT IDENTIFIER ::= { pkcs-1 1}

The rsaEncryption object identifier is intended to be used in the
algorithm field of a value of type AlgorithmIdentifier. The
parameters field shall have ASN.1 type NULL for this algorithm
identifier.

The rsa public key shall be encoded using the ASN.1 type
RSAPublicKey:

RSAPublicKey ::= SEQUENCE {
modulus INTEGER, -- n
publicExponent INTEGER -- e
}

where modulus is the modulus n, and publicExponent is the public
exponent e. The DER encoded RSAPublicKey is the value of the BIT
STRING subjectPubliKey.

This object identifier is used in public key certificates for both
RSA signature keys and RSA encryption keys. The intended application
for the key may be indicated in the key usage field (see Section
4.2.1.3). The use of a single key for both signature and encryption

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purposes is not recommended, but is not forbidden.

7.3.2 Diffie-Hellman Key Exchange Key

This diffie-hellman object identifier supported by this standard is
defined by ANSI X9.42.

dhpublicnumber OBJECT IDENTIFIER ::= { iso(1) member-body(2)
US(840) ansi-x942(10046) number-type(2) 1 }

DHParameter ::= SEQUENCE {
prime INTEGER, -- p
base INTEGER, -- g }

The dhpublicnumber object identifier is intended to be used in the
algorithm field of a value of type AlgorithmIdentifier. The
parameters field of that type, which has the algorithm-specific
syntax ANY DEFINED BY algorithm, would have ASN.1 type DHParameter
for this algorithm.

DHParameter ::= SEQUENCE {
prime INTEGER, -- p
base INTEGER, -- g }

The fields of type DHParameter have the following meanings:

prime is the prime p.

base is the base g.

The Diffie-Hellman public key (an INTEGER) is mapped to a
subjectPublicKey (a BIT STRING) as follows: the most significant bit
(MSB) of the INTEGER becomes the MSB of the BIT STRING; the least
significant bit (LSB) of the INTEGER becomes the LSB of the BIT
STRING.

7.3.3 DSA Signature Keys

The object identifier supported by this standard is

id-dsa ID ::= { iso(1) member-body(2) us(840) x9-57(10040)
secsig(2) x9algorithm(4) 1 }

The id-dsa algorithm syntax includes optional parameters. These
parameters are commonly referred to as p, q, and g. If the DSA
algorithm parameters are absent from the subjectPublicKeyInfo
AlgorithmIdentifier and the CA signed the subject certificate using
DSA, then the certificate issuer's DSA parameters apply to the

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subject's DSA key. If the DSA algorithm parameters are absent from
the subjectPublicKeyInfo AlgorithmIdentifier and the CA signed the
subject certificate using a signature algorithm other than DSA, then
the subject's DSA parameters are distributed by other means. The
parameters are included using the following ASN.1 structure:

Dss-Parms ::= SEQUENCE {
p INTEGER,
q INTEGER,
g INTEGER }

When signing, DSA algorithm generates two values. These values are
commonly referred to as r and s. To easily transfer these two values
as one signature, they are ASN.1 encoded using the following ASN.1
structure:

Dss-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER }

The encoded signature is conveyed as the value of the BIT STRING
signature in a Certificate or CertificateList.

The DSA public key shall be ASN.1 encoded as an INTEGER; this
encoding shall be used as the contents (i.e., the value) of the
subjectPublicKey component (a BIT STRING) of the SubjectPublicKeyInfo
data element.

DSAPublicKey ::= INTEGER -- public key Y

7.3.4 Key Exchange Algorithm (KEA)

The Key Exchange Algorithm (KEA) is a classified algorithm for
exchanging keys. A KEA "pairwise key" may be generated between two
users if their KEA public keys were generated with the same KEA
parameters. The KEA parameters are not included in a certificate;
instead a "domain identifier" is supplied in the parameters field.

When the subjectPublicKeyInfo field contains a KEA key, the algorithm
identifier and parameters shall be as defined in [sdn.701r]:

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id-keyEncryptionAlgorithm OBJECT IDENTIFIER ::=
{ 2 16 840 1 101 2 1 1 22 }

KEA-Parms-Id ::= OCTET STRING

The Kea-Parms-Id shall always appear when the subjectPublicKeyInfo
field algorithm identifier is id-keyEncryptionAlgorithm. Kea-Parms-Id
is the "domain identifier" and is ten octets in length. If the Kea-
Parms-Id of two KEA keys are equivalent, the subjects possess the
same KEA parameter values and may exchange keys.

<<Need encoding of KEA key>>

8. ASN.1 Structures and OIDs

PKIX1 DEFINITIONS ::=

BEGIN

-- need ASN.1 for:
-- AlgorithmIdentifier
-- ORAddress

-- attribute data types --

Attribute ::= SEQUENCE {
type AttributeValue,
values SET OF AttributeValue
-- at least one value is required -- }

AttributeType ::= OBJECT IDENTIFIER

AttributeValue ::= ANY

AttributeTypeAndValue ::= SEQUENCE {
type AttributeValue,
value AttributeValue }

AttributeValueAssertion ::= SEQUENCE {AttributeType, AttributeValue}

-- naming data types --

Name ::= CHOICE { -- only one possibility for now --

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rdnSequence RDNSequence }

RDNSequence ::= SEQUENCE OF RelativeDistinguishedName

DistinguishedName ::= RDNSequence

RelativeDistinguishedName ::= SET SIZE (1 .. MAX) OF AttributeTypeAndValue

-- Directory string type --

DirectoryString ::= CHOICE {
teletexString TeletexString (SIZE (1..maxSize)),
printableString PrintableString (SIZE (1..maxSize)),
universalString ANY -- the '93 ASN.1 type UniversalString
}

-- basic stuff starts here

Certificate ::= SEQUENCE {
tbsCertificate TBSCertificate,
signatureAlgorithm AlgorithmIdentifier,
signature BIT STRING }

Version ::= INTEGER { v1(0), v2(1), v3(2) }

CertificateSerialNumber ::= INTEGER

Validity ::= SEQUENCE {
notBefore CertificateValidityDate,
notAfter CertificateValidityDate }

CertificateValidityDate ::= CHOICE {

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utcTime UTCTime,
generalTime GeneralizedTime }

UniqueIdentifier ::= BIT STRING

SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING }

Extensions ::= SEQUENCE OF Extension

Extension ::= SEQUENCE {
extnID OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING }

-- Extension ::= { {id-ce 15}, ... , keyUsage }

ID ::= OBJECT IDENTIFIER
joint-iso-ccitt ID ::= { 2 }
ds ID ::= {joint-iso-ccitt 5}
certificateExtension ID ::= {ds 29}
-- id-ce ID ::= certificateExtension
id-ce ID ::= {ds 29}

AuthorityKeyIdentifier ::= SEQUENCE {
keyIdentifier [0] KeyIdentifier OPTIONAL,
authorityCertIssuer [1] GeneralNames OPTIONAL,
authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL
}
( WITH COMPONENTS {..., authorityCertIssuer PRESENT,
authorityCertSerialNumber PRESENT} |
WITH COMPONENTS {..., authorityCertIssuer ABSENT,
authorityCertSerialNumber ABSENT} )

-- authorityKeyIdentifier ::= AuthorityKeyIdentifier

KeyIdentifier ::= OCTET STRING

-- subjectKeyIdentifier ::= KeyIdentifier

KeyUsage ::= BIT STRING {
digitalSignature (0),
nonRepudiation (1),
keyEncipherment (2),
dataEncipherment (3),
keyAgreement (4),
keyCertSign (5),

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cRLSign (6) }

id-ce-privateKeyUsagePeriod OBJECT IDENTIFIER ::= { id-ce 16 }

PrivateKeyUsagePeriod ::= SEQUENCE {
notBefore [0] GeneralizedTime OPTIONAL,
notAfter [1] GeneralizedTime OPTIONAL }
( WITH COMPONENTS {..., notBefore PRESENT} |
WITH COMPONENTS {..., notAfter PRESENT} )

id-ce-certificatePolicies OBJECT IDENTIFIER ::= { id-ce 32 }

CertificatePolicies ::= SEQUENCE SIZE (1..MAX) OF PolicyInformation

PolicyInformation ::= SEQUENCE {
policyIdentifier CertPolicyId,
policyQualifiers SEQUENCE SIZE (1..MAX) OF
PolicyQualifierInfo OPTIONAL }

CertPolicyId ::= OBJECT IDENTIFIER

-- PolicyQualifierInfo ::= SEQUENCE {
-- policyQualifierId CERT-POLICY-QUALIFIER.&id
-- ({SupportedPolicyQualifiers}),
-- qualifier CERT-POLICY-QUALIFIER.&Qualifier
--
-- ({SupportedPolicyQualifiers}{@policyQualifierId})
-- OPTIONAL }

-- SupportedPolicyQualifiers CERT-POLICY-QUALIFIER ::= { ... }

PolicyQualifierInfo ::= SEQUENCE {
policyQualifierId PolicyQualifierId,
qualifier ANY DEFINED BY policyQualifierId }

PolicyQualifierId ::= ENUMERATED {
qualId1 (1), qualId2 (2), qualId3 (3), qualId4 (4), qualId5 ( 5 ) }

id-ce-policyMappings OBJECT IDENTIFIER ::= { id-ce 33 }

PolicyMappings ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
issuerDomainPolicy CertPolicyId,
subjectDomainPolicy CertPolicyId }

id-ce-subjectAltName OBJECT IDENTIFIER ::= { id-ce 17 }

SubjectAltName ::= GeneralNames

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GeneralNames ::= SEQUENCE SIZE (1..MAX) OF GeneralName

-- OTHER-NAME ::= TYPE-IDENTIFIER note: not supported in '88 ASN.1
-- substituted ANY where used [GeneralName otherName]

EDIPartyName ::= SEQUENCE {
nameAssigner [0] DirectoryString OPTIONAL,
partyName [1] DirectoryString }

id-ce-issuerAltName OBJECT IDENTIFIER ::= { id-ce 18 }

IssuerAltName ::= GeneralNames

id-ce-subjectDirectoryAttributes OBJECT IDENTIFIER ::= { id-ce 9 }

SubjectDirectoryAttributes ::= SEQUENCE SIZE (1..MAX) OF Attribute

id-ce-basicConstraints OBJECT IDENTIFIER ::= { id-ce 19 }

BasicConstraints ::= SEQUENCE {
cA BOOLEAN DEFAULT FALSE,
pathLenConstraint INTEGER (0..MAX) OPTIONAL }

id-ce-nameConstraints OBJECT IDENTIFIER ::= { id-ce 30 }

NameConstraints ::= SEQUENCE {
permittedSubtrees [0] GeneralSubtrees OPTIONAL,
excludedSubtrees [1] GeneralSubtrees OPTIONAL }

GeneralSubtrees ::= SEQUENCE SIZE (1..MAX) OF GeneralSubtree

GeneralSubtree ::= SEQUENCE {
base GeneralName,
minimum [0] BaseDistance DEFAULT 0,
maximum [1] BaseDistance OPTIONAL }

BaseDistance ::= INTEGER (0..MAX)

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id-ce-policyConstraints OBJECT IDENTIFIER ::= { id-ce 34 }

PolicyConstraints ::= SEQUENCE SIZE (1..MAX) OF SEQUENCE {
policySet [0] CertPolicySet OPTIONAL,
requireExplicitPolicy [1] SkipCerts OPTIONAL,
inhibitPolicyMapping [2] SkipCerts OPTIONAL }

SkipCerts ::= INTEGER (0..MAX)

CertPolicySet ::= SEQUENCE SIZE (1..MAX) OF CertPolicyId

-- cRLDistributionPoints CRLDistPointsSyntax ::=
-- SEQUENCE SIZE (1..MAX) OF DistributionPoint

CRLDistPointsSyntax ::= SEQUENCE SIZE (1..MAX) OF DistributionPoint

DistributionPoint ::= SEQUENCE {
distributionPoint [0] DistributionPointName OPTIONAL,
reasons [1] ReasonFlags OPTIONAL,
cRLIssuer [2] GeneralNames OPTIONAL }

DistributionPointName ::= CHOICE {
fullName [0] GeneralNames,
nameRelativeToCRLIssuer [1] RelativeDistinguishedName }

ReasonFlags ::= BIT STRING {
unused (0),
keyCompromise (1),
cACompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6) }

pkix OBJECT IDENTIFIER ::= { 1 3 6 1 5 3 }

-- Object identifiers for ftp, http, smtp and ldap protocols

applTCPProto OBJECT IDENTIFIER ::= { 1 3 6 1 2 1 27 4 }

ftpID OBJECT-IDENTIFIER ::= {applTCPProtoID 21}
httpID OBJECT-IDENTIFIER ::= {applTCPProtoID 80}
smtpID OBJECT-IDENTIFIER ::= {applTCPProtoID 25}
ldapID OBJECT-IDENTIFIER ::= {applTCPProtoID 389}

-- Object identifier for the X.500 directory access protocol

dap OBJECT-IDENTIFIER ::= { 2 5 3 1 }

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id-pkix-subjectInfoAccess OBJECT IDENTIFIER ::= { pkix 1 }

AccessDescription ::= SEQUENCE {
accessMethod OBJECT IDENTIFIER,
accessLocation GeneralName }

--subjectInfoAccess SubjectInfoAccessSyntax ::=
-- SEQUENCE SIZE (1..MAX) OF AccessDescription
SubjectInfoAccessSyntax ::=
SEQUENCE OF AccessDescription

id-pkix-authorityInfoAccess OBJECT IDENTIFIER ::= { pkix 2 }

id-pkix-caInfoAccess OBJECT-IDENTIFIER ::= { pkix 3 }

-- caInfoAccess ::= {
-- AuthorityInfoAccessSyntax }

-- CRL structures

CertificateList ::= SEQUENCE {
tbsCertList TBSCertList,
signatureAlgorithm AlgorithmIdentifier,
signature BIT STRING }

TBSCertList ::= SEQUENCE {
version Version OPTIONAL,
-- if present, must be v2
signature AlgorithmIdentifier,
issuer Name,
thisUpdate ChoiceOfTime,
nextUpdate ChoiceOfTime,
revokedCertificates SEQUENCE OF SEQUENCE {
userCertificate CertificateSerialNumber,
revocationDate ChoiceOfTime,
crlEntryExtensions Extensions OPTIONAL
-- if present, must be v2
} OPTIONAL,
crlExtensions [0] Extensions OPTIONAL
-- if present, must be v2
}

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Version ::= INTEGER { v1(0), v2(1), v3(2) }

AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL }
-- contains a value of the type
-- registered for use with the
-- algorithm object identifier value

ChoiceOfTime ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime }

CertificateSerialNumber ::= INTEGER

Extensions ::= SEQUENCE OF Extension

id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

CRLNumber ::= INTEGER (0..MAX)

id-ce-issuingDistributionPoint OBJECT IDENTIFIER ::= { id-ce 28 }

IssuingDistributionPoint ::= SEQUENCE {
distributionPoint [0] DistributionPointName OPTIONAL,
onlyContainsUserCerts [1] BOOLEAN DEFAULT FALSE,
onlyContainsCACerts [2] BOOLEAN DEFAULT FALSE,
onlySomeReasons [3] ReasonFlags OPTIONAL,
indirectCRL [4] BOOLEAN DEFAULT FALSE }

id-ce-deltaCRLIndicator OBJECT IDENTIFIER ::= { id-ce 27 }

-- deltaCRLIndicator ::= BaseCRLNumber

BaseCRLNumber ::= CRLNumber

id-ce-cRLNumber OBJECT IDENTIFIER ::= { id-ce 20 }

-- reasonCode EXTENSION ::= {

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-- SYNTAX CRLReason
-- IDENTIFIED BY { id-ce 21 } }

CRLReason ::= ENUMERATED {
unspecified (0),
keyCompromise (1),
cACompromise (2),
affiliationChanged (3),
superseded (4),
cessationOfOperation (5),
certificateHold (6),
removeFromCRL (8) }

id-ce-holdInstructionCode OBJECT IDENTIFIER ::= { id-ce 23 }

HoldInstructionCode ::= OBJECT IDENTIFIER

member-body ID ::= { iso 2 }
us ID ::= { member-body 840 }
x9cm ID ::= { us 10040 }
holdInstruction ID ::= {x9cm 2}

id-holdinstruction-none ID ::= {holdInstruction 1}
id-holdinstruction-callissuer ID ::= {holdInstruction 2}
id-holdinstruction-reject ID ::= {holdInstruction 3}

id-ce-invalidityDate OBJECT IDENTIFIER ::= { id-ce 24 }

InvalidityDate ::= GeneralizedTime

-- Algorithm strustures

md2WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1)
pkcs-1(1) 2 }

sha-1WithRSAEncryption OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) oiw(14) secsig(3)
algorithm(2) 29 }

When either of these object identifiers is used within the ASN.1 type
AlgorithmIdentifier, the parameters component of that type shall the
ASN.1 type NULL.

7.2.2 DSA Signature Algorithm

A patent statement regarding the DSA can be found at the end of this
profile.

id-dsa-with-sha1 ID ::= {
iso(1) member-body(2) us(840) x9-57 (10040) secsig(2)
x9algorithm(4) 3 }

Dss-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER }

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dsaWithSHA-1

pkcs-1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) oiw(14) secsig(3)
algorithm(2) 27 }

The DSA algorithm syntax includes optional parameters. These
parameters are commonly referred to as p, q, and g. The
AlgorithmIdentifier within subjectPublicKeyInfo is the only place
within a certificate where these parameters shall be present. If the
DSA algorithm parameters are absent from the subjectPublicKeyInfo
AlgorithmIdentifier and the CA signed the subject certificate using
DSA, then the certificate issuer's DSA parameters apply to the
subject's DSA key. If the DSA algorithm parameters are absent from
the subjectPublicKeyInfo AlgorithmIdentifier and the CA signed the
subject certificate using a signature algorithm other than DSA, then
the subject's DSA parameters are distributed by other means. The
parameters are included using the following ASN.1 structure: member-body(2) US(840)
rsadsi(113549) pkcs(1) 1 }

rsaEncryption OBJECT IDENTIFIER ::= { pkcs-1 1}

dhpublicnumber OBJECT IDENTIFIER ::= { iso(1) member-body(2)
US(840) ansi-x942(10046) 1 }

DHParameter ::= SEQUENCE {
prime INTEGER, -- p
base INTEGER -- g
}

id-dsa ID ::= { iso(1) member-body(2) us(840) x9-57(10040)
secsig(2) x9algorithm(4) 1 }

Dss-Parms ::= SEQUENCE {
p INTEGER,
q INTEGER,
g INTEGER }

When signing, DSA algorithm generates two values. These values are
commonly referred to as r and s. To easily transfer these two values
as one siganture, they are ASN.1 encoded using the following ASN.1
structure:

Dss-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER }

7.3 Subject Public Key Algorithms

<< Add a section that lists the public key algorithms that are
supported by this profile. Obviously, RSA, DSA, Diffie-Hellman, and
KEA will be included. Are there others? >>

<< Should a different algorithm identifier be assigned to RSA
signature keys and RSA key management keys? If so, there will be one
subsection for each within this section.>>

id-keyEncryptionAlgorithm OBJECT IDENTIFIER ::=
{ 2 16 840 1 101 2 1 1 22 }

KEA-Parms-Id ::= OCTET STRING

id-ce-authorityKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 35 }
id-ce-subjectKeyIdentifier OBJECT IDENTIFIER ::= { id-ce 14 }
id-ce-keyUsage OBJECT IDENTIFIER ::= { id-ce 15 }
id-pkix-policy-CPS OBJECT IDENTIFIER ::= { pkix 4 }

CPSuri ::= IA5String

id-pkix-policy-userNotice OBJECT IDENTIFIER ::= { pkix 5 }

UserNotice ::= CHOICE {
ia5String IA5String,
bnpString ANY -- defined as BMPString in '93 ASN.1
}

END

References

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[X9.57] ANSI X9.57

[FIPS 180-1] Federal Information Processing Standards Publication
(FIPS PUB) 180-1, Secure Hash Standard, 17 April 1995.
[Supersedes FIPS PUB 180 dated 11 May 1993.]

[FIPS 186] Federal Information Processing Standards Publication
(FIPS PUB) 186, Digital Signature Standard, 18 May 1994.

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[PKCS#1] PKCS #1: RSA Encryption Standard, Version 1.4, RSA Data
Security, Inc., 3 June 1991.

[RC95] Rogier, N. and Chauvaud, P., "The compression function of
MD2 is not collision free," Presented at Selected Areas in
Cryptography '95, Carleton University, Ottawa, Canada,
18-19 May 1995.

[RFC 1319] Kaliski, B., "The MD2 Message-Digest Algorithm," RFC 1319,
RSA Laboratories, April 1992.

[RFC 1422] Kent, S., "Privacy Enhancement for Internet Electronic
Mail: Part II: Certificate-Based Key Management," RFC
1422, BBN Communications, February 1993.

[RFC 1423] Balenson, D., "Privacy Enhancement for Internet Electronic
Mail: Part III: Algorithms, Modes, and Identifiers,"
RFC 1423, Trusted Information Systems, February 1993.

[RFC 1959] T. Howes, M. Smith, "An LDAP URL Format", RFC 1959,
June 1996.

[SDN.701R] SDN.701, "Message Security Protocol", Revision 4.0
1996-06-07 with "Corrections to Message Security Protocol,
SDN.701, Rev 4.0, 96-06-07." August 30, 1996.

[X.208] << Do we want to reference the 1988 or 1993 version? >>

[X.509-AM] << Need final reference >>

[X9.55] << Need final reference >>

Patent Statements

The Internet PKI relies on the use of patented public key technology.
The Internet Standards Process as defined in RFC 1310 requires a
written statement from the Patent holder that a license will be made
available to applicants under reasonable terms and conditions prior
to approving a specification as a Proposed, Draft or Internet

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Standard.

Patent statements for DSA, RSA, and Diffie-Hellman follow. These
statements have been supplied by the patent holders, not the authors
of this profile.

Digital Signature Algorithm (DSA)

The U.S. Government holds patent 5,231,668 on the Digital
Signature Algorithm (DSA), which has been incorporated into
Federal Information Processing Standard (FIPS) 186. The patent
was issued on July 27, 1993.

The National Institute of Standards and Technology (NIST) has a
long tradition of supplying U.S. Government-developed techniques

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to committees and working groups for inclusion into standards on a
royalty-free basis. NIST has made the DSA patent available
royalty-free to users worldwide.

Regarding patent infringement, FIPS 186 summarizes our position;
the Department of Commerce is not aware of any patents that would
be infringed by the DSA. Questions regarding this matter may be
directed to the Deputy Chief Counsel for NIST.

RSA Signature and Encryption

<< Now that PKP has dissolved, a revised patent statement for RSA
from RSADSI is needed. >>

Diffie-Hellman Key Agreement

<< Now that PKP has dissolved, a revised patent statement for
Diffie-Hellman from Cylink is needed. >>

Obsolete PKP Patent Statement

<< This statement is included here until a replacement from RSADSI
and Cylink can be obtained. >>

The Massachusetts Institute of Technology and the Board of
Trustees of the Leland Stanford Junior University have granted
Public Key Partners (PKP) exclusive sub-licensing rights to the
following patents issued in the United States, and all of their
corresponding foreign patents:

Cryptographic Apparatus and Method
("Diffie-Hellman")......................... No. 4,200,770

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Public Key Cryptographic Apparatus
and Method ("Hellman-Merkle").............. No. 4,218,582

Cryptographic Communications System and
Method ("RSA")............................. No. 4,405,829

Exponential Cryptographic Apparatus
and Method ("Hellman-Pohlig").............. No. 4,424,414

These patents are stated by PKP to cover all known methods of
practicing the art of Public Key encryption, including the
variations collectively known as El Gamal.

Public Key Partners has provided written assurance to the Internet
Society that parties will be able to obtain, under reasonable,

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nondiscriminatory terms, the right to use the technology covered
by these patents. This assurance is documented in RFC 1170 titled
"Public Key Standards and Licenses". A copy of the written
assurance dated April 20, 1990, may be obtained from the Internet
Assigned Number Authority (IANA).

The Internet Society, Internet Architecture Board, Internet
Engineering Steering Group and the Corporation for National
Research Initiatives take no position on the validity or scope of
the patents and patent applications, nor on the appropriateness of
the terms of the assurance. The Internet Society and other groups
mentioned above have not made any determination as to any other
intellectual property rights which may apply to the practice of
this standard. Any further consideration of these matters is the
user's own responsibility.

Security Considerations

This entire memo is about security mechanisms.
Author Addresses:

Russell Housley
SPYRUS
PO Box 1198
Herndon, VA 22070 20172
USA
housley@spyrus.com

Warwick Ford
Nortel Secure Networks
PO Box 3511, Station C
Ottawa, Ontario
Canada KY 4H7
wford@bnr.ca
VeriSign, Inc.
One Alewife Center
Cambridge, MA 02140
wford@verisign.com

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Tim Polk
NIST
Building 820, Room 426
Gaithersburg, MD 20899
wpolk@nist.gov

David Solo
BBN
150 CambridgePark Drive
Cambridge, MA 02140
USA
solo@bbn.com

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