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Lightweight Directory Access Protocol (v3):
UTF-8 String Representation of Distinguished Names
<draft-ietf-asid-ldapv3-dn-01.txt>
<draft-ietf-asid-ldapv3-dn-02.txt>
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
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Abstract
The X.500 Directory uses distinguished names as the primary keys to
entries in the directory. Distinguished Names are encoded in ASN.1
in the X.500 Directory protocols. In the Lightweight Directory
Access Protocol, a string representation of distinguished names is
transferred. This specification defines the string format for representing
names, which is designed to give a clean representation of commonly used
distinguished names, while being able to represent any distinguished name.
1. Background
This specification assumes familiarity with X.500 [1], and the concept of
Distinguished Name. It is important to have a common format to be
able to unambiguously represent a distinguished name. The primary goal
of this specification is ease of encoding and decoding. A secondary
goal is to have names that are human readable. It is not expected that
LDAP clients with a human user interface would display these strings
directly to the user, but would most likely be performing translations
(such as expressing attribute type names in the local national language).
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2. A Notation for Distinguished Name Converting DistinguishedName from ASN.1 to a String
In X.501 [2] the ASN.1 structure of Distinguished Name distinguished name is defined as:
DistinguishedName ::= RDNSequence
RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
RelativeDistinguishedName ::= SET SIZE (1..MAX) OF
AttributeTypeAndValue
AttributeTypeAndValue ::= SEQUENCE {
type AttributeType,
value AttributeValue }
The following sections 2.1 and 2.2 define defines the algorithm for converting
between from an
ASN.1 structured representation and to a UTF-8 string representation.
2.1
2.1. Converting DistinguishedName from ASN.1 to a String the RDNSequence
If the RDNSequence is an empty sequence, the result is the empty
or zero length string.
Otherwise, the output consists of the string encodings of each
RelativeDistinguishedName in the RDNSequence (according to 2.2),
starting with the last element of the sequence and moving backwards
toward the first.
The encodings of adjoining RelativeDistinguishedNames are separated by
either a comma or
a semicolon character. There may be space
characters present on either side of the comma or semicolon.
Either the comma or the semicolon character is to be used to separate
all the RelativeDistinguishedNames in a particular string.
2.1.2. (',' ASCII 44).
2.2. Converting RelativeDistinguishedName from ASN.1 to a String
When converting from an ASN.1 RelativeDistinguishedName to a
string, the output consists of the string encodings of each
AttributeTypeAndValue (according to 2.1.3), 2.3), in any order.
Where there is a multi-valued RDN, the outputs from adjoining
AttributeTypeAndValues are separated by a plus ('+' ASCII 43) character.
2.1.3.
2.3. Converting AttributeTypeAndValue from ASN.1 to a String
The AttributeTypeAndValue is encoded as the string representation
of the AttributeType, followed by an equals character, character ('=' ASCII 61),
followed by the string representation of the AttributeValue. The
encoding of the AttributeValue is given in section 2.4.
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If the AttributeType is one defined in Table 1, in a published table of LDAP attribute types, or in the IANA-maintained register of valid attribute types, types
associated with LDAP [4], then the type name string from that table is
used, otherwise it is encoded as the dotted-decimal encoding of the
AttributeType's OBJECT IDENTIFIER. The dotted-decimal notation is
described in [3].
Table 1: Standardized Attribute Types used As an example, strings for a few of the attribute
types frequently seen in RDNs include:
String X.500 AttributeType
------------------------------
CN commonName
L localityName
ST stateOrProvinceName
O organizationName
OU organizationalUnitName
C countryName
STREET streetAddress
DC domainComponent
2.1.4.
UID userid
2.4. Converting an AttributeValue from ASN.1 to a String
If the AttributeValue is of a type which does not have a string
representation defined in [4], for it, then it is simply encoded as an octothorpe
character ("#") ('#' ASCII 35) followed by the hexidecimal hexadecimal representation of the
each of the bytes of the BER encoding of the X.500 AttributeValue. This
form SHOULD be used if the AttributeType is of the dotted-decimal form.
Otherwise, if the AttributeValue is of a type which has a string
representation, the value is converted first to a UTF-8 string according to
that
its syntax specification.
If the UTF-8 string does not have any of the following characters which need
escaping, then that string can be used as the string representation of the
value.
o a space or "#" character occurring at the beginning of the string
o a space character occurring at the end of the string
o a space character adjoining another space character
o non-printing characters other than the single space, such as
control characters 0-31 or 127
o one of the characters ",", "+", "=", """, "\", "<", ">", "#" ">" or ";"
There are two possible escaping mechanisms.
Implementations MAY escape other characters.
If a character to be escaped is a one of the string does not contain
the double quote character, list shown above, then it is
prefixed by a backslash ('\' ASCII 92).
Otherwise the entire string can character to be surrounded escaped is replaced by
double quote characters, a backslash and that used as two
hex digits, which form a single byte in the encoding. The alternative
is to prefix each code of the characters which need escaping by a backslash character.
Examples of these mechanisms the escaping mechanism are shown in section 3. 5.
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2.2.
3. Parsing a String back to a Distinguished Name
The structure of the string is specified in a BNF grammar, based on the
grammar defined in RFC 822, with the terminals enclosed in <> [5].
Server implementations parsing a DN string generated by an LDAPv2
client MUST also accept (and ignore) the variants given in section 4 of
this document.
<distinguishedName> ::= <name> | "" -- empty string
<name> ::= <name-component> ( <spaced-separator> ) | <name-component> <spaced-separator> <name>
<spaced-separator> ::= <optional-space>
<separator>
<optional-space>
<separator> ::= "," | ";"
<optional-space> ::= *( " " ) <name>
<name-component> ::= <attributeTypeAndValue>
| <attributeTypeAndValue> <optional-space> "+"
<optional-space> <name-component>
<attributeTypeAndValue> ::=
<attributeType> <optional-space> "=" <optional-space> <attributeValue>
<attributeType> ::= 1*( <keychar> ) | <oid> | "OID." <oid> | "oid." <oid>
<keychar> ::= letters, numbers, digits and space '-'
<oid> ::= <digitstring> | <digitstring> "." <oid>
<digitstring> ::= 1*<digit>
<digit> 1* ( <oidchar> )
<oidchar> ::= digits 0-9 and '.'
<attributeValue> ::= <string>
<string> ::= *( <stringchar> | <pair> )
| "#" <hexstring>
| '"' *( <stringchar> | <special> | <pair> ) '"'
| "#" <hex> -- only from v2
<special> ::= "," | "=" | <control> | "+" | "<" | ">" | "#" | ";"
<control> :: characters 0-31 and 127
<pair> ::= "\" ( <special> | "\" | '"') '"' | <hexpair> )
<stringchar> ::= any character except <special> or "\" or '"'
<hex>
<hexstring> 1* ( <hexpair> )
<hexpair> ::= 2*<hexchar> <hexchar><hexchar>
<hexchar> ::= 0-9, a-f, A-F
4. Relationship with RFC 1779 and LDAPv2
The syntax given in this document is more restrictive than the
syntax in RFC 1779. Implementations parsing a string must also allow generated by an oid in
LDAPv2 client MUST accept the attribute
type syntax of RFC 1779. Implementations
MUST NOT, however, generate any of the RFC 1779 encodings which are not
described above in section 2.
Implementations MUST allow a semicolon character to be prefixed by the used instead of a
comma to separate RDNs in a distinguished name, and MUST also allow
whitespace characters "oid." to be present on either side of the comma or "OID.".
semicolon. The whitespace characters are ignored, and the semicolon
replaced with a comma.
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3. Differences from RFC 1779
The following changes have been made
Implementations MUST allow an oid in this version of the specification:
o The use of angle brackets attribute type to surround the strings is not described, as
this is not used in LDAP. Also be prefixed by
the grammar characters "oid." or "OID.".
Implementations MUST allow for UFNs has been removed.
However it is suggested that angle brackets may be used in preference space (' ' ASCII 32) characters to
quotes or other be
present between <name-component> and ',', between <attributeTypeAndValue>
and '+', between <attributeType> and '=', and between '=' and
<attributeValue>. These space characters as delimiters are ignored when including distinguished
names in paragraphs.
o Only space parsing.
Implementations MUST allow a value to be surrounded by quote ('"' ASCII
34) characters, not newlines, which are shown between RDNs.
o The AttributeType name "DC" has been added.
o The "oid" prefix in attribute types is removed.
4. not part of the value. Inside the quoted value,
the following characters can occur without any escaping:
",", "=", "+", "<", ">", "#" and ";"
5. Examples
This notation is designed to be convenient for common forms of name.
This section gives a few examples of distinguished names written
using this notation: notation. First is a name containing three relative
distinguished names (RDNs):
CN=Steve Kille, O=Isode Limited, C=GB
CN=Christian Huitema, O=INRIA, C=FR Kille,O=Isode Limited,C=GB
Here is an example of a multi-valued Relative Distinguished Name,
where name containing three RDNs, in which the namespace is flat within an organization, and department first RDN is
used to disambiguate certain names:
OU=Sales + CN=J. Smith, O=Widget Inc., C=US
These examples show both methods
multi-valued:
OU=Sales+CN=J. Smith,O=Widget Inc.,C=US
This example shows the method of quoting of a comma in an
Organization organization name:
CN=L. Eagle, O="Sue, Eagle,O=Sue\, Grabbit and Runn", C=GB
CN=L. Eagle, O=Sue\, Grabbit and Runn, C=GB Runn,C=GB
An example name in which a value contains a newline carriage return character:
CN="Before
After", O=Test, C=GB
5.
CN=Before\0DAfter,O=Test,C=GB
An example name in which an RDN was of an unrecognized type. The value
is the BER encoding of an OCTET STRING containing two bytes 0x48 and
0x69.
1.3.6.1.4.1.1466.0=#04024869,O=Test,C=GB
Finally, an example of an RDN surname value consisting of five letters:
Unicode Letter Description 10646 code UTF-8 Quoted
=============================== ========== ====== =======
LATIN CAPITAL LETTER L U0000004C 0x4C L
LATIN SMALL LETTER U U00000075 0x75 u
LATIN SMALL LETTER C WITH CARON U0000010D 0xC48D \C4\8D
LATIN SMALL LETTER I U00000069 0x69 i
LATIN SMALL LETTER C WITH ACUTE U00000107 0xC487 \C4\87
Could be written in printable ASCII (useful for debugging purposes):
SN=Lu\C4\8Di\C4\C7
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6. References
[1] The Directory -- overview of concepts, models and services.
ITU-T Rec. X.500(1993).
[2] The Directory -- Models. ITU-T Rec. X.501(1993).
[3] M. Wahl, S. Kille, T. Howes, "Lightweight Directory Access Protocol
(v3)", INTERNET DRAFT, draft-ietf-asid-ldapv3-protocol-04.txt.
February
March 1997.
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[4] M. Wahl, S. Kille, T. Howes, A. Coulbeck, "Lightweight Directory Access
Protocol (v3): Standard and Pilot Attribute Definitions", INTERNET
DRAFT, draft-ietf-asid-ldapv3-attributes-04.txt.
February
March 1997.
[5] D. Crocker, "Standard of the Format of ARPA-Internet Text
Messages", STD 11, RFC 822, August 1982.
6. Security Considerations
Security issues are not discussed in this memo.
7. Author's Address
Mark Wahl
Critical Angle Inc.
4815 W. Braker Lane #502-385
Austin, TX 78759
USA
EMail: M.Wahl@critical-angle.com
Steve Kille
Isode Ltd.
The Dome
The Square
Richmond, Surrey
TW9 1DT
England
Phone: +44-181-332-9091
EMail: S.Kille@ISODE.COM
Tim Howes
Netscape Communications Corp.
501 E. Middlefield Rd
Mountain View, CA 94043
USA
Phone: +1 415 254-1900
EMail: howes@netscape.com
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