WDIFF

draft-ietf-ipngwg-addrconf-privacy-01.txt --> draft-ietf-ipngwg-addrconf-privacy-03.txt

INTERNET-DRAFT Thomas Narten
<draft-ietf-ipngwg-addrconf-privacy-01.txt>
<draft-ietf-ipngwg-addrconf-privacy-03.txt> IBM
R.
Richard Draves
Microsoft Research
October 1999
September 19, 2000

Privacy Extensions for Stateless Address Autoconfiguration in IPv6

<draft-ietf-ipngwg-addrconf-privacy-01.txt>

<draft-ietf-ipngwg-addrconf-privacy-03.txt>

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

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.

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."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

Abstract

Nodes use IPv6 stateless address autoconfiguration to generate
addresses without the necessity of a DHCP server. Addresses are
formed by combining network prefixes with an interface identifier. On
interfaces that contain embedded IEEE Identifiers, the interface
identifier is typically derived from it. On other interface types,
the interface identifier is generated through other means, for
example, via random number generation. This document describes an
optional
extension to IPv6 stateless address autoconfiguration for interfaces
whose interface identifier is derived from an IEEE identifier. Use of
the extension causes nodes to generate global-
scope global-scope addresses from
interface identifiers that change over time, even in cases where the
interface contains an embedded IEEE identifier. Changing the
interface identifier (and the global-scope addresses generated from
it) over time makes it more difficult for

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information collectors to identify when different addresses used in

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different transactions actually correspond to the same node.

Contents

Status of this Memo.......................................... 1

1. Introduction............................................. 2

2. Background............................................... 3
2.1. Extended Use of the Same Identifier................. 3
2.2. Not a New Issue..................................... 4
2.3. Possible Approaches................................. 6

3. Protocol Description..................................... 7
3.1. Assumptions......................................... 8
3.2. Generation Of Randomized Interface Identifiers...... 9
3.3. Generating Anonymous Addresses...................... 10
3.4. Expiration of Anonymous Addresses................... 11
3.5. Regeneration of Randomized Interface Identifiers.... 12

4. Implications of Changing Interface Identifiers........... 10 13

5. Defined Constants........................................ 14

6. Open Issues and Future Work.............................. 11

6. 14

7. Security Considerations.................................. 12

7. References............................................... 12 14

8. Acknowledgments.......................................... 14

9. Appendix................................................. 13 References............................................... 15

1. Introduction

Stateless address autoconfiguration [ADDRCONF] defines how an IPv6
node generates addresses without the need for a DHCP server. Some
types of network interfaces come with an embedded IEEE Identifier
(i.e., a link-layer MAC address), and in those cases stateless
address autoconfiguration uses the IEEE identifier to generate a
64-bit interface identifier [ADDRARCH]. By design, the interface
identifier is globally unique when generated in this fashion. The
interface identifier is in turn appended to a prefix to form a
128-bit IPv6 address.

All nodes combine interface identifiers (whether derived from an IEEE
identifier or generated through some other technique) with the
reserved link-local prefix to generate link-local addresses for their

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attached interfaces. Additional addresses, including site-local and
global-scope addresses, are then created by combining prefixes
advertised in Router Advertisements via Neighbor Discovery
[DISCOVERY] with the interface identifier.

Not all nodes and interfaces contain IEEE identifiers. In such cases,
an interface identifier is generated through some other means (e.g.,
at random), and the resultant interface identifier is not globally

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unique and may also change over time. The focus of this document is
on addresses derived from IEEE identifiers, as the concern being
addressed exists only in those cases where the interface identifier
is globally unique and non-changing. The rest of this document
assumes that IEEE identifiers are being used, but the techniques
described may also apply to interfaces with other types of globally
unique and persistent identifiers.

This document discusses concerns associated with the embedding of
non-changing interface identifiers within IPv6 addresses and
describes optional extensions to stateless address autoconfiguration that can
help mitigate those concerns in environments where such concerns are
significant. Section 2 provides background information on the issue.
Section 3 describes a procedure for generating alternate interface
identifiers and global-scope addresses. Section 4 discusses
implications of changing interface identifiers.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].

2. Background

This section discusses the problem in more detail, provides context
for evaluating the significance of the concerns in specific
environments and makes comparisons with existing practices.

2.1. Extended Use of the Same Identifier

The use of a non-changing interface identifier to form addresses is a
specific instance of the more general case where a constant
identifier is reused over an extended period of time and in multiple
independent activities. Anytime the same identifier is used in
multiple contexts, it becomes possible for that identifier to be used
to correlate seemingly unrelated activity. For example, a network
sniffer placed strategically on a link across which all traffic
to/from a particular host crosses could keep track of which
destinations a node communicated with and at what times. Such

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information can in some cases be used to infer things, such as what
hours an employee was active, when someone is at home, etc.

One of the requirements for correlating seemingly unrelated
activities is the use (and reuse) of an identifier that is
recognizable over time within different contexts. IP addresses
provide one obvious example, but there are more. Many nodes also have
DNS names associated with their addresses, in which case the DNS name
serves as a similar identifier. Although the DNS name associated with
an address is more work to obtain (it may require a DNS query) the
information is often readily available. In such cases, changing the
address on a machine over time would do little to address the concern

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raised in this document, as the DNS name would become the correlating
identifier.

The use of a constant identifier within an address is of special
concern because addresses are a fundamental requirement of
communication and cannot easily be hidden from eavesdroppers and
other parties. Even when higher layers encrypt their payloads,
addresses in packet headers appear in the clear. Consequently, if a
mobile host (e.g., laptop) accessed the network from several
different locations, an eavesdropper might be able to track the
movement of that mobile host from place to place, even if the upper
layer payloads were encrypted [SERIALNUM].

2.2. Not a New Issue

Although the topic of this document may at first appear to be an
issue new to IPv6, similar issues exist in today's Internet already.
That is, addresses used in today's Internet are often non-changing in
practice for extended periods of time. In many sites, addresses are
assigned statically; such addresses typically change infrequently.
However, many sites are moving away from static allocation to dynamic
allocation via DHCP [DHCP]. In theory, the address a client gets via
DHCP can change over time, but in practice servers return the same
address to the same client (unless addresses are in such short supply
that they are reused immediately by a different node when they become
free). Thus, although many sites use DHCP, clients end up using the
same address for months at a time.

Nodes that need a (non-changing) DNS name generally have static
addresses assigned to them to simplify the configuration of DNS
servers. Although Dynamic DNS [DDNS] can be used to update the DNS
dynamically, it is not widely deployed today. In addition, changing
an address but keeping the same DNS name does not really address the
underlying concern, since the DNS name becomes a non-changing
identifier. Servers generally require a DNS name (so clients can

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connect to them), and clients often do as well (e.g., some servers
refuse to speak to a client whose address cannot be mapped into a DNS
name that also maps back into the same address).

Many network services require that the client authenticate itself to
the server before gaining access to a resource. The authentication
step binds the activity (e.g., TCP connection) to a specific entity
(e.g., an end user). In such cases, a server already has the ability
to track usage by an individual, independent of the address they
happen to use. Indeed, such tracking is an important part of
accounting.

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Web browsers and servers typically exchange "cookies" with each other
[COOKIES]. Cookies allow web servers to correlate a current activity
with a previous activity. One common usage is to send back targeted
advertising to a user by using the cookie supplied by the browser to
identify what earlier queries had been made (e.g., for what type of
information). Based on the earlier queries, advertisements can be
targeted to match the (assumed) interests of the end-user.

The use of non-changing interface identifiers in IPv6 has
implications in two quite different contexts: stationary devices
(i.e., those that generally do not move physically such as desktop
PCs), and mobile devices (i.e., those that move frequently, including
laptops, cell phones, etc.).

In today's internet, many home users do not have permanent
connections and indeed are assigned temporary addresses each time
they connect to their ISP. Consequently, the addresses they use
change frequently over time and are shared among a number of
different users. If addresses are generated from an interface
identifier, however, a home user's address could contain an interface
identifier that remains the same from one dialup session to the next.
The way PPP is used today, however, PPP servers typically
unilaterally inform the client what address they are to use (i.e.,
the client doesn't generate one on its own). This practice, if
continued in IPv6, would avoid the concerns that are the focus of
this document.

A more interesting case concerns always-on connections (e.g., cable
modems, ISDN, DSL, etc.) that result in a home site using the same
address for extended periods of time. This is a scenario that is just
starting to become common in IPv4 and promises to become more of a
concern as always-on internet connectivity becomes widely available.
The technique described later in the document attempt attempts to address
this concern by changing the interface identifier portion of an
address. However, it should be noted that in the case of always-on
connections, the network prefix portion of an address is in effect a

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constant identifier. All nodes at (say) a home, would have the same
network prefix. This has implications for privacy, though not at the
same granularity (i.e., all nodes within a home would be lumped
together for the purposes of collecting information). This issue is
also non-trivial to address, because the routing prefix part of an
address contains topology information and cannot contain arbitrary
values.

Another case concerns mobile devices (e.g., laptops, PDAs, etc.) that
move topologically within the Internet. Whenever they move (in the
absence of technology such as mobile IP [MOBILEIP]), they form new
addresses for their current topological point of attachment. This is

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typified today by the "road warrior" who has Internet connectivity
both at home and at the office. While the node's address changes as
it moves, however, the interface identifier contained within the
address remains the same (when derived from an IEEE Identifier). In
such cases, the interface identifier could (in theory) be used to
track the movement and usage of a particular machine [SERIALNUM]. For
example, a server that logs usage information together with a source
addresses, is also recording the interface identifier since it is
embedded within an address. Consequently, any data-mining technique
that correlates activity based on addresses could trivially easily be extended
to do the same using the interface identifier. This is of particular
concern with the expected proliferation of next-generation network-connected network-
connected devices (e.g, (e.g., PDAs, cell phones, etc.) in which large
numbers of devices are in practice associated with individual users
(i.e., not shared). Thus, the interface identifier embedded within an
address could be used to track activities of an individual, even as
they move topologically within the internet.

2.3. Possible Approaches

One way to avoid some of the problems discussed above is to use DHCP
for obtaining addresses. With DHCP, the DHCP server could arrange to
hand out addresses that change over time.

Another approach, compatible with the stateless address
autoconfiguration architecture, would be to change the interface id
portion of an address over time and generate new addresses from the
interface identifier for some address scopes. Changing the interface
identifier can make it more difficult to look at the IP addresses in
independent transactions and identify which ones actually correspond
to the same node, both in the case where the routing prefix portion
of an address changes and when it does not.

Many machines function as both clients and servers. In such cases,
the machine would need a DNS name for its use as a server. Whether

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the address stays fixed or changes has no little privacy implications implication
since the DNS name remains constant and serves as a constant
identifier. When acting as a client (e.g., initiating communication),
however, such a machine may want to vary the addresses it uses. In
such environments, one may need multiple addresses: a "public" (i.e., non-
secret)
non-secret) server address, registered in the DNS, that is used to
accept incoming connection requests from other machines, and
(possibly) a an "anonymous" address used to shield the identity of the
client when it initiates communication. These two cases are roughly
analogous to telephone numbers and caller ID, where a user may list
their telephone number in the public phone book, but disable the
display of its number via caller ID when initiating calls.

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To make it difficult to make educated guesses as to whether two
different interface identifiers belong to the same node, the
algorithm for generating alternate identifiers must include input
that has an unpredictable component from the perspective of the
outside entities that are collecting information. Picking identifiers
from a pseudo-random sequence suffices, so long as the specific
sequence cannot be determined by an outsider examining just the
identifiers that appear in addresses or are otherwise readily
available.
available (e.g., a node's link-layer address). This document proposes
the generation of a pseudo-random sequence of interface identifiers
via an MD5 hash. Periodically, the next interface identifier in the
sequence is generated, a new set of anonymous addresses is created,
and the previous anonymous addresses are deprecated to discourage
their further use. The precise pseudo-
random pseudo-random sequence depends on both
a random component and the globally unique interface identifier (when
available), to increase the likelihood that all node different nodes generate a
different sequence. sequences.

3. Protocol Description

The goal of this section is to define procedures that:

1) Result Do not result in any changes to the creation basic behavior of addresses from the same (constant)
interface identifier just as is the case with
generated via stateless address autoconfiguration [ADDRCONF]. Link-local and site-local addresses
would be used just as in [ADDRCONF], but global-scope addresses
would be used only for the acceptance of incoming connections
(i.e., they are server addresses), and not used when initiating
outgoing communication.

2) Create Define new procedures that create additional global-scope
addresses based on a random interface identifier for use with
global scope addresses. Such addresses would be used to initiate
outgoing sessions. These "random" or anonymous addresses would be
used for a short period of times time (hours to days) and would then be deprecated (where they could
deprecated. Deprecated address can continue to be used for
already established connections, but are not for used to initiate new
connections).
connections. New anonymous addresses are generated periodically, periodically to
replace anonymous addresses that expire, with the exact time
between address generation a matter of local policy.

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3) Produce a sequence of anonymous global-scope addresses from a
sequence of interface identifiers that appear to be random in the
sense that it is difficult for an outside observer to predict a
future address (or identifier) based on a current one and it is
difficult to determine previous addresses (or identifiers) knowing
only the present one.

We describe two approaches. The first assumes the presence of stable
storage that can be used to record state history for use as input
into the next iteration

4) Generate a set of the algorithm. A second approach addresses

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the case where stable storage is unavailable and from the same (randomized) interface
identifier must be
identifier, one address for each prefix for which a global address
has been generated at random. via stateless address autoconfiguration. Using
the same interface identifier to generate a set of anonymous
addresses reduces the number of IP multicast groups a host must
join. Nodes join the solicited-node multicast address for each
unicast address they support, and solicited-node addresses are
dependent only on the low-order bits of the corresponding address.
This decision was made to address the concern that a node that
joins a large number of multicast groups may be required to put
its interface into promiscuous mode, resulting in possible reduced
performance.

3.1. When Stable Storage is Present Assumptions

The following algorithm assumes the presence of a 64-bit "history
value" that is used as input in generating each interface maintains an
associated randomized interface identifier.
The very first time When anonymous addresses
are generated, the system boots (i.e., out-of-the-box), a random current value should be generated using techniques that help ensure of the
initial value is hard to guess [RANDOM]. Whenever a new associated randomized
interface identifier is generated, a value generated by the computation is
saved in the history used. The actual value for the next iteration of the algorithm.

[ADDRCONF] describes identifier
changes over time as described below, but the steps same identifier can be
used to generate more than one anonymous address.

The algorithm also assumes that for generating a link-local address
when an interface becomes enabled, and for generating addresses for
other scopes. This document extends [ADDRCONF] in given anonymous address, one
can determine the following way:

1) corresponding public address. When processing a Router Advertisement with a Prefix Information
option carrying an anonymous
address is deprecated, a global-scope prefix new anonymous address is generated. The
specific valid and preferred lifetimes for the purposes of new address
autoconfiguration (i.e., are
dependent on the A bit is set), effectively ignore corresponding lifetime values in the
Preferred Timer value. A value public address.

Finally, this document assumes that when a node initiates outgoing
communication, anonymous addresses can be given preference over other
public addresses. This can mean that all outgoing connections use
anonymous addresses by default, or that applications individually
indicate whether they prefer to use anonymous or public addresses.
Giving preference to anonymous address is consistent with on-going
work that addresses the topic of 0 should source address-selection in the more
general case [ADDR_SELECT].

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3.2. Generation Of Randomized Interface Identifiers.

We describe two approaches for the maintenance of the randomized
interface identifier. The first assumes the presence of stable
storage that can be used instead. This
deprecates to record state history for use as input
into the address, allowing it next iteration of the algorithm across system restarts. A
second approach addresses the case where stable storage is
unavailable and a randomized interface identifier may need to be
generated at random.

3.2.1. When Stable Storage Is Present

The following algorithm assumes the presence of a 64-bit "history
value" that is used as input in generating a randomized interface
identifier. The very first time the system boots (i.e., out-of-the-
box), a random value should be generated using techniques that help
ensure the initial value is hard to guess [RANDOM]. Whenever a new
interface identifier is generated, a value generated by the
computation is saved in the history value for accepting
incoming connections, but not (in general) for outgoing
connections. In addition, for such Prefix Information options,
perform the following steps.
2) next iteration of
the algorithm.

A randomized interface identifier is created as follows:

1) Take the history value from the previous iteration of this
algorithm (or a random value if there is no previous value) and
append to it the interface identifier generated as described in
[ADDRARCH].
3)
2) Compute the MD5 message digest [MD5] over the quantity created in
the previous step.
4)
3) Take the left-most 64-bits of the MD5 digest and set bit 6 (the
left-most bit is numbered 0) to zero. This creates an interface
identifier with the universal/local bit indicating local
significance only. Use Save the resultant generated identifier to generate an
address as outlined in [ADDRCONF]. That is, use the associated
randomized interface
identifier to generate a global-scope address.
5) Perform duplicate address detection (DAD) on the generated
address. If DAD indicates the address is already in use, repeat
steps 2-5 as appropriate up to 5 times. If after 5 consecutive
attempts no non-unique address was generated, log a system error
and give up attempting to generate a random address for that
prefix.
6) Take identifier.
4) Take the rightmost 64-bits of the MD5 digest computed in step 3) 2)
and save them in stable storage as the history value to be used in
the next iteration of the algorithm.

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MD5 was chosen for convenience, not and because its particular properties
were adequate to produce the desired level of strict requirements. randomization. IPv6
nodes are already required to implement MD5 as part of IPsec [IPSEC],
thus the code will already be present on IPv6 machines.

In theory, generating successive randomized interface identifiers
using a history scheme as above has no advantages over generating
them at random. In practice, however, generating truly random numbers
can be tricky. Use of a history value is intended to avoid the

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particular scenario where two nodes generate the same randomized
interface identifier, both detect the situation via DAD, but then
proceed to generate identical randomized interface identifiers via
the same (flawed) random number generation algorithm. The above
algorithm avoids this problem by having the interface identifier
(which will often be globally unique) used in the calculation that
generates subsequent randomized interface identifiers. Thus, if two
nodes happen to generate the same randomized interface identifier,
they should generate different ones on the followup attempt.

3.2.

3.2.2. In The Absence of Stable Storage

In the absence of stable storage, no history information value will be available
across system restarts to generate a pseudo-random sequence of
interface identifiers. Consequently, identifiers the initial history value used
above will need to be generated at random. A number of techniques
might be appropriate. Consult [RANDOM] for suggestions on good
sources for obtaining random numbers. Note that even though machines
may not have stable storage for storing the
previously using interface identifier, a history value, they will in
many cases have configuration information that differs from one
machine to another (e.g., user identity, security keys, serial
numbers, etc.). One approach to generating a random interface identifiers initial history
value in such cases is to use the configuration information to
generate some data bits (which may remain constant for the life of
the machine, but will vary from one machine to another), append some
random data and compute the MD5 digest as before. The remaining details

3.3. Generating Anonymous Addresses

[ADDRCONF] describes the steps for generating addresses
would be analogous to those of the previous section.

3.3. Regenerating Interface Identifiers

How often to change addresses depends on how a device is being used
(e.g., how frequently it initiates new communication) and the
concerns of link-local address
when an interface becomes enabled as well as the end user. The most egregious privacy concerns appear
to involve steps for generating
addresses used for long periods other scopes. This document extends [ADDRCONF] as
follows. When processing a Router Advertisement with a Prefix
Information option carrying a global-scope prefix for the purposes of time (weeks to months
to years). The more frequently an
address changes, autoconfiguration (i.e., the less feasible
collecting A bit is set), perform the
following steps:

1) Process the Prefix Information Option as defined in [ADDRCONF],
either creating a public address or coordinating information keyed on interface identifiers
becomes. Moreover, adjusting the cost lifetimes of collecting information
existing addresses, both public and attempting
to correlate it based on interface identifiers will only be justified
if enough addresses contain such identifiers to make it worthwhile.
Thus, having large numbers anonymous. When adjusting the
lifetimes of clients change their an existing anonymous address, only lower the
lifetimes. Implementations MUST NOT increase the lifetimes of an
existing anonymous address on when processing a daily

draft-ietf-ipngwg-addrconf-privacy-01.txt Prefix Information
Option.
2) When a new public address is created as described in [ADDRCONF]
(because the prefix advertised does not match the prefix of any

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or weekly basis is likely to be sufficient September 19, 2000

address already assigned to alleviate most privacy
concerns.

There are the interface, and the Valid Lifetime
in the option is not zero), also client costs associated with having a large number of
addresses associated with create a node (e.g., in doing address lookups).
Thus, changing addresses frequently (e.g., every few minutes) may
have performance implications.

This document recommends that implementations generate new addresses
on a periodic basis of once per day. At that time, previously
generated random addresses should be placed in a deprecated state.
The valid lifetime for anonymous address.
3) When creating an anonymous address, the lifetime values are
derived from the corresponding public address should be a minimum as follows:

- Its Valid Lifetime is the lower of a) the valid lifetime Valid Lifetime of the corresponding
public address, and b) (a
default value of) two weeks. The preferred lifetime for an anonymous address then or ANON_VALID_LIFETIME.
- Its Preferred Lifetime is in effect the minimum lower of a) its valid lifetime, and
b) (a default of) one day. As an optional optimization, the Preferred Lifetime
of the public address or ANON_PREFERRED_LIFETIME.

An anonymous address is created only if this calculated Preferred
Lifetime is greater than REGEN_ADVANCE time units. In particular,
an implementation can remove a deprecated MUST NOT create an anonymous address that is not
in use with a zero
Preferred Lifetime.
4) New anonymous addresses are created by applications or upper-layers. For TCP connections, such
information is available in control blocks. For UDP-based
applications, it may be appending the case interface's
current randomized interface identifier to the prefix that only was
used to generate the applications have
knowledge about what addresses are actually in use. Consequently, it
may need to use heuristics in deciding when an corresponding public address. If by chance
the new anonymous address is no longer
in use (e.g., the two week default suggested above).

Because same as an address already
assigned to the precise frequency at which it interface, generate a new randomized interface
identifier and repeat this step.
5) Perform duplicate address detection (DAD) on the generated
anonymous address. If DAD indicates the address is already in use,
generate a new randomized interface identifier as described in
Section 3.2 above, and repeat the previous steps as appropriate up
to 5 times. If after 5 consecutive attempts no non-unique address
was generated, log a system error and give up attempting to
generate
new anonymous addresses varies for that interface.

Note: because multiple anonymous addresses are generated from one environment to another, implementations
should provide end users with the ability to change
same associated randomized interface identifier, there is little
benefit in running DAD on every anonymous address. This document
recommends that DAD be run on the frequency at
which addresses are regenerated. The default value should first address generated from a
given randomized identifier, but that DAD be one day.
In addition, skipped on all
subsequent addresses generated from the exact time at which to invalidate same randomized interface
identifier.

3.4. Expiration of Anonymous Addresses

When an anonymous address depends on how applications are used becomes deprecated, a new one should be
generated. This is done by end users. Thus repeating the
default value of two weeks may not be appropriate actions described in all
environments. Implementations should provide end users with Section
3.3, starting at step 3). Note that, except for the
ability transient period
when an anonymous address is being regenerated, in normal operation
at most one anonymous address corresponding to override the default value.

4. Implications of Changing Interface Identifiers

The IPv6 addressing architecture goes to great lengths to ensure that
interface identifiers are globally unique. During the IPng
discussions of the GSE proposal [GSE], it was felt that keeping
interface identifiers globally unique in practice might prove useful
to future transport protocols. Usage of the algorithms a public address
should be in this
document would eliminate a non-deprecated state at any given time. Note that future flexibility.

The desires if
an anonymous address becomes deprecated as result of protecting individual privacy vs. the desire to
effectively maintain and debug processing a network can conflict
Prefix Information Option with each
other. Having clients use addresses that change over time will make
it more difficult to track down and isolate operational problems. For
example, when looking at packet traces, it could become more

draft-ietf-ipngwg-addrconf-privacy-01.txt a zero Preferred Lifetime, then a new
anonymous address MUST NOT be generated. The Prefix Information

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difficult to determine whether one is seeing behavior caused by a
single errant machine, or by September 19, 2000

Option will also deprecate the corresponding public address.

To insure that a number of them.

Some servers refuse to grant access to clients for which no DNS name
exists. That is, they perform preferred anonymous address is always available, a DNS PTR query
new anonymous address should be regenerated slightly before its
predecessor is deprecated. This is to determine the DNS
name, and may then also perform an A query on the returned name allow sufficient time to
verify that the returned DNS name maps back into avoid
race conditions in the case where generating a new anonymous address being
used. Consequently, clients
is not properly registered in the DNS may instantaneous, such as when duplicate address detection must
be unable to access some services. As noted earlier, however, a
node's DNS name (if non-changing) serves as a constant identifier. If
the extension described in this document becomes widely deployed,
servers will likely need to change their behavior to not require
every address be in the DNS. One alternative run. It is recommended that DNS servers (for
client machines) may need to fabricate "dummy" answers so that all
addresses, whether used or not, appear to have DNS names associated
with them. Another alternative is to register anonymous addresses in
DNS using random names (for example a string version of an implementation start the address
itself).

5. Open Issues and Future Work

An implementation probably needs to keep track of which addresses are
being used by upper layers so as to
regeneration process REGEN_ADVANCE time units before an anonymous
address would actually be able deprecated.

As an optional optimization, an implementation may wish to remove an a
deprecated anonymous address from
internal data structures once no upper layer protocols are using it
(but not before). This that is not in contrast to current approaches where
addresses are removed from an interface when they become invalid
[ADDRCONF], independent of whether use by applications or not upper layer protocols are
still using them.
upper-layers. For TCP connections, such information is available in
control blocks. For UDP-based applications, it may be the case that
only the applications have knowledge about what addresses are
actually in use. Consequently, it one may need to use heuristics in
deciding when an address is no longer in use (e.g., as is the default
ANON_VALID_LIFETIME suggested
in Section 3.3).

A node's permanent global above).

3.5. Regeneration of Randomized Interface Identifiers

The frequency at which anonymous addresses (i.e., those derived from a
constant interface identifier) are placed in should change depends on
how a deprecated state. This
effectively prevents the address from device is being used to initiate future
communication. In some cases, however, (e.g., how frequently it may be desirable initiates new
communication) and even
preferable to allow the permanent address to be used for new
communication on an application-by-application basis. This may
require API extensions.

Use concerns of the extensions defined in this document is likely end user. The most egregious
privacy concerns appear to make
debugging and other operational troubleshooting activities involve addresses used for long periods of
time (weeks to months to years). The more
difficult. Consequently, frequently an address
changes, the less feasible collecting or coordinating information
keyed on interface identifiers becomes. Moreover, the cost of
collecting information and attempting to correlate it may based on
interface identifiers will only be site policy that anonymous justified if enough addresses should not be used. Should a system administrator (i.e.,
and not just the end user) have control
contain non-changing identifiers to make it worthwhile. Thus, having
large numbers of whether these algorithms

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are clients change their address on a daily or weekly
basis is likely to be used? If so, it might make sense (for example) sufficient to define alleviate most privacy concerns.

There are also client costs associated with having a
bit in Router Advertisements or large number of
addresses associated with a node (e.g., in doing address lookups, the Prefix Information Option
need to
indicate whether anonymity should be enabled or disabled.

6. Security Considerations

The motivation for this document stems from privacy concerns for
individuals. join many multicast groups, etc.). Thus, changing addresses
frequently (e.g., every few minutes) may have performance
implications.

This document does not appear to add any security issues
beyond those already associated with stateless recommends that implementations generate new anonymous
addresses on a periodic basis. This can be achieved automatically by
generating a new randomized interface identifier at least once every
(ANON_PREFERRED_LIFETIME - REGEN_ADVANCE) time units. As described
above, generating a new anonymous address
autoconfiguration [ADDRCONF].

7. References

[ADDRARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.

[ADDRCONF] Thomson, S. and T. Narten, "IPv6 Address
Autoconfiguration", RFC 2462, December 1998.

[COOKIES] Kristol, D., Montulli, L., "HTTP State Management
Mechanism", draft-ietf-http-state-man-mec-12.txt.

[DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.

[DDNS] Vixie et. al., "Dynamic Updates in the Domain Name System (DNS
UPDATE)", RFC 2136, April 1997.

[DISCOVERY] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.

[GSE-ANALYSIS] Crawford et. al., "Separating Identifiers and Locators
in Addresses: An Analysis of the GSE Proposal for IPv6 ",
draft-ietf-ipngwg-esd-analysis-04.txt.

[IPSEC] Kent, S., Atkinson, R., "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.

[MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April
1992.

[MOBILEIP] Perkins, C., "IP Mobility Support", RFC 2002, October
1996.

[RANDOM] "Randomness Recommendations for Security", Eastlake 3rd, D.,
Crocker S., Schiller, J., RFC 1750, December 1994.

draft-ietf-ipngwg-addrconf-privacy-01.txt REGEN_ADVANCE time units
before an anonymous address becomes deprecated produces addresses

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[SERIALNUM] Moore, K., "Privacy Considerations for September 19, 2000

with a preferred lifetime no larger than ANON_PREFERRED_LIFETIME.
When the Use of
Hardware Serial Numbers in End-to-End Network Protocols",
draft-iesg-serno-privacy-00.txt.

8.
Authors' Addresses

Thomas Narten
IBM Corporation
P.O. Box 12195
Research Triangle Park, NC 27709-2195
USA

Phone: +1 919 254 7798
EMail: narten@raleigh.ibm.com

Richard Draves
Microsoft Research
One Microsoft Way
Redmond, WA 98052

Email: richdr@microsoft.com

9. Appendix

This section describes preferred lifetime expires, a simple alternate algorithm for changing
interface identifiers. It's main weakness new anonymous address is that it uses
generated using the same new randomized interface ID for all addresses, and does not distinguish between identifier.

Because the precise frequency at which it is appropriate to generate
new addresses used for initiating communication varies from one environment to another, implementations
should provide end users with the ability to change the frequency at
which addresses are regenerated. The default value is given in
ANON_PREFERRED_LIFETIME and those is one day. In addition, the exact time
at which to invalidate an anonymous address depends on how
applications are used by servers
for accepting incoming connections.

The goal end users. Thus the default value given of this section is to define procedures that:

1) Result
one week (ANON_PREFERRED_LIFETIME) may not be appropriate in a different interface identifier being generated at each
system restart or attachment all
environments. Implementations should provide end users with the
ability to a network.

2) Produce a sequence override both of these default values.

4. Implications of Changing Interface Identifiers

The IPv6 addressing architecture goes to great lengths to ensure that
interface identifiers are globally unique. During the IPng
discussions of the GSE proposal [GSE], it was felt that appear keeping
interface identifiers globally unique in practice might prove useful
to be
random future transport protocols. Usage of the algorithms in this
document would eliminate that future flexibility.

The desires of protecting individual privacy vs. the sense desire to
effectively maintain and debug a network can conflict with each
other. Having clients use addresses that change over time will make
it is more difficult for an outside observer to predict a future identifier based on a current one track down and isolate operational problems. For
example, when looking at packet traces, it is could become more
difficult to determine previous identifiers knowing only the
present one.

We describe two approaches. The first assumes the presence whether one is seeing behavior caused by a
single errant machine, or by a number of stable
storage that can be used them.

Some servers refuse to record state history grant access to clients for use as input
into the next iteration of the algorithm, i.e., after which no DNS name
exists. That is, they perform a system
restart. A second approach addresses DNS PTR query to determine the case where stable storage is
unavailable DNS
name, and the interface identifier must be generated at random.

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9.1. When Stable Storage is Present

The following algorithm assumes the presence of a 64-bit "history
value" that is used as input in generating may then also perform an interface identifier.
The very first time the system boots (i.e., out-of-the-box), any
value can be used including all zeros. Whenever a new interface
identifier is generated, its value is saved in the history value for A query on the next iteration of returned name to
verify that the process.

Section 5.3 of [ADDRCONF] describes returned DNS name maps back into the steps for generating a link-
local address when an interface becomes enabled. This document
modifies that step being
used. Consequently, clients not properly registered in the following way. Rather than use interface
identifiers generated DNS may be
unable to access some services. As noted earlier, however, a node's
DNS name (if non-changing) serves as a constant identifier. If the
extension described in [ADDRARCH], the identifier is
generated as follows:

1) Take the history value from the previous iteration (or 0 if there
is no previous value) and append this document becomes widely deployed, servers
will likely need to it the interface identifier
generated as described change their behavior to not require every
address be in [ADDRARCH].
2) Compute the MD5 message digest [MD5] over the quantity created DNS. Another alternative is to register anonymous
addresses in
step 1).
3) Take the left-most 64-bits DNS using random names (for example a string version of
the MD5 digest and set bit 6 (the
left-most bit is numbered 0) address itself).

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5. Defined Constants

Constants defined in this document include:

ANON_VALID_LIFETIME -- Default value: 1 week. Users should be able to zero. This creates an interface
identifier with
override the universal/local bit indicating local
significance only. Use default value.
ANON_PREFERRED_LIFETIME -- Default value: 1 day. Users should be able
to override the resultant identifier for generating default value.
REGEN_ADVANCE -- 5 seconds

6. Open Issues and Future Work

An implementation might want to keep track of which addresses are
being used by upper layers so as outlined in [ADDRCONF]. That is, use the interface
identifier to generate be able to remove a link-local and other appropriate
addresses.
4) Perform duplicate address detection (DAD) on the generated
address. If DAD indicates the deprecated
anonymous address from internal data structures once no upper layer
protocols are using it (but not before). This is already in use, repeat
steps 1-4 as appropriate up contrast to 5 times. If after 5 consecutive
attempts no non-unique address was generated, log a system error
and give up attempting
current approaches where addresses are removed from an interface when
they become invalid [ADDRCONF], independent of whether or not upper
layer protocols are still using them. For TCP connections, such
information is available in control blocks. For UDP-based
applications, it may be the case that only the applications have
knowledge about what addresses are actually in use. Consequently, it
may need to generate use heuristics in deciding when an address from the current
prefix.
5) Take the rightmost 64-bits of the MD5 digest computed in step 2)
and save them is no longer
in stable storage use (e.g., as is suggested in Section 3.4).

Use of the history value extensions defined in this document is likely to make
debugging and other operational troubleshooting activities more
difficult. Consequently, it may be used in site policy that anonymous
addresses should not be used. Implementations MAY provide a method
for a trusted administrator to override the next iteration use of the algorithm.

MD5 was chosen anonymous
addresses.

7. Security Considerations

The motivation for convenience, this document stems from privacy concerns for
individuals. This document does not because of strict requirements.
IPv6 nodes are appear to add any security issues
beyond those already required associated with stateless address
autoconfiguration [ADDRCONF].

8. Acknowledgments

The authors would like to implement MD5 as part acknowledge the contributions of IPsec
[IPSEC], thus the code will already be present on IPv6 machines.

9.2. In The Absence IPNGWG
working group and, in particular, Matt Crawford and Steve Deering for
their detailed comments.

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9. References

[ADDRARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.

[ADDRCONF] Thomson, S. and T. Narten, "IPv6 Address
Autoconfiguration", RFC 2462, December 1998.

[ADDR_SELECT] Draves, R. "Default Address Selection for IPv6", draft-
ietf-ipngwg-default-addr-select-00.txt.

[COOKIES] Kristol, D., Montulli, L., "HTTP State Management
Mechanism", draft-ietf-http-state-man-mec-12.txt.

[DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.

[DDNS] Vixie et. al., "Dynamic Updates in the Domain Name System (DNS
UPDATE)", RFC 2136, April 1997.

[DISCOVERY] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.

[GSE] Crawford et. al., "Separating Identifiers and Locators in
Addresses: An Analysis of Stable Storage

In the absence of stable storage, no history information will be
available to generate a pseudo-random sequence of interface
identifiers. Consequently, identifiers will need to be generated at
random. A number of techniques might be appropriate. Consult [RANDOM]

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INTERNET-DRAFT October, 1999

for suggestions on good sources GSE Proposal for obtaining random numbers. Note
that even though a machine may not have stable storage IPv6 ", draft-
ietf-ipngwg-esd-analysis-04.txt.

[IPSEC] Kent, S., Atkinson, R., "Security Architecture for storing
the previously using interface identifier, they will in many cases
have configuration information that differs from one machine to
another (e.g., user identity, security keys, etc.). One approach to
generating random interface identifiers in such cases is to use the
configuration information to generate some data bits (which may be
remain constant
Internet Protocol", RFC 2401, November 1998.

[KEYWORDS] Bradner,S. "Key words for the life of the machine, but will vary from one
machine use in RFCs to another), append some random data and compute the Indicate
Requirement Levels" RFC 2119, March 1997.

[MD5] Rivest, R., "The MD5
digest as before. The remaining details Message-Digest Algorithm", RFC 1321, April
1992.

[MOBILEIP] Perkins, C., "IP Mobility Support", RFC 2002, October
1996.

[RANDOM] "Randomness Recommendations for Security", Eastlake 3rd, D.,
Crocker S., Schiller, J., RFC 1750, December 1994.

[SERIALNUM] Moore, K., "Privacy Considerations for generating addresses
would be analogous to those of the previous section.

draft-ietf-ipngwg-addrconf-privacy-01.txt Use of
Hardware Serial Numbers in End-to-End Network Protocols",
draft-iesg-serno-privacy-00.txt.

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10.
Authors' Addresses

Thomas Narten
IBM Corporation
P.O. Box 12195
Research Triangle Park, NC 27709-2195
USA

Phone: +1 919 254 7798
EMail: narten@raleigh.ibm.com

Richard Draves
Microsoft Research
One Microsoft Way
Redmond, WA 98052

Phone: +1 425 936 2268
Email: richdr@microsoft.com

draft-ietf-ipngwg-addrconf-privacy-03.txt [Page 16]

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