Securing Neighbor Discovery T. Aura
Internet-Draft Microsoft Research
Expires: May 28, 2004 November 28, 2003
Cryptographically Generated Addresses (CGA)
draft-ietf-send-cga-03
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes a method for binding a public signature key
to an IPv6 address in the Secure Neighbor Discovery (SEND) protocol.
Cryptographically Generated Addresses (CGA) are IPv6 addresses where
the interface identifier is generated by computing a cryptographic
one-way hash function from a public key and auxiliary parameters. The
binding between the public key and the address can be verified by
re-computing the hash value and by comparing the hash with the
interface identifier. Messages sent from an IPv6 address can be
protected by attaching the public key and auxiliary parameters and by
signing the message with the corresponding private key. The
protection works without a certification authority or other security
infrastructure.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. CGA Address Format . . . . . . . . . . . . . . . . . . . . . . 4
3. CGA Parameters and Hash Values . . . . . . . . . . . . . . . . 6
4. CGA Generation . . . . . . . . . . . . . . . . . . . . . . . . 7
5. CGA Verification . . . . . . . . . . . . . . . . . . . . . . . 9
6. CGA Signatures . . . . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7.1 Security Goals and Limitations . . . . . . . . . . . . . . . . 13
7.2 Hash extension . . . . . . . . . . . . . . . . . . . . . . . . 13
7.3 Privacy Considerations . . . . . . . . . . . . . . . . . . . . 15
7.4 Related protocols . . . . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
Normative References . . . . . . . . . . . . . . . . . . . . . 18
Informative References . . . . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 19
A. Example of CGA Generation . . . . . . . . . . . . . . . . . . 21
B. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . . 24
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1. Introduction
This document specifies a method for securely associating a
cryptographic public key with an IPv6 address in the Secure Neighbor
Discovery (SEND) protocol [I-D.ietf-send-ndopt]. The basic idea is to
generate the interface identifier (i.e., the rightmost 64 bits) of
the IPv6 address by computing a cryptographic hash of the public key.
The resulting IPv6 addresses are called cryptographically generated
addresses (CGA). The corresponding private key can then be used to
sign messages sent from the address.
This document specifies:
o how to create CGA addresses from the cryptographic hash of a
public key and auxiliary parameters,
o how to verify the association between the public key and the CGA
address, and
o how to generate and verify a CGA signature.
In order to verify the association between the address and the public
key, the verifier needs to know the address itself, the public key,
and the values of the auxiliary parameters. No additional security
infrastructure, such as a public key infrastructure (PKI),
certification authorities, or other trusted servers, is needed.
The address format and the CGA parameter format are defined in
Sections 2 and 3. Detailed algorithms for generating addresses and
for verifying them are given in Sections 4 and 5, respectively.
Section 6 defines the procedures for generating and verifying CGA
signatures. The security considerations in Section 7 include
limitations of CGA-based authentication, the reasoning behind the
hash extension technique that enables effective hash lengths above
the 64-bit limit of the interface identifier, the implications of CGA
addresses on privacy, and protection against related-protocol
attacks.
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 [RFC2119].
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2. CGA Address Format
When talking about addresses, this document refers to IPv6 addresses
where the leftmost 64 bits of a 128-bit address form the subnet
prefix and the rightmost 64 bits of the address form the interface
identifier. [RFC3513] We number the bits of the interface identifier
starting from bit 0 on the left.
A cryptographically generated address (CGA) has a security parameter
(Sec), which determines its strength against brute-force attacks. The
security parameter is a 3-bit unsigned integer and it is encoded in
the three leftmost bits (i.e., bits 0-2) of the interface identifier.
This can be written as:
Sec = (interface identifier & 0xe000000000000000) >> 61
The CGA address is associated with a set of parameters, which consist
of a public key and auxiliary parameters. Two hash values Hash1 (64
bits) and Hash2 (112 bits) are computed from the parameters. The
formats of the public key and auxiliary parameters and the way to
compute the hash values are defined in Section 3.
A cryptographically generated address (CGA) is defined as an IPv6
address that satisfies the following two conditions:
o The 16*Sec leftmost bits of the second hash value Hash2 are zero.
o The rightmost 64 bits of the first hash value Hash1 equal the
interface identifier of the address. Bits 0, 1, 2, 6 and 7 (i.e.,
the bits that encode the security parameter Sec and the "u" and
"g" bits) are ignored in the comparison.
The above definition can be stated in terms of the following two bit
masks:
Mask1 (112 bits) = 0x0000000000000000000000000000 if Sec=0,
0xffff000000000000000000000000 if Sec=1,
0xffffffff00000000000000000000 if Sec=2,
0xffffffffffff0000000000000000 if Sec=3,
0xffffffffffffffff000000000000 if Sec=4,
0xffffffffffffffffffff00000000 if Sec=5,
0xffffffffffffffffffffffff0000 if Sec=6, and
0xffffffffffffffffffffffffffff if Sec=7
Mask2 (64 bits) = 0x1cffffffffffffff
A cryptographically generated address is an IPv6 address for which
the following two equations hold:
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Hash1 & Mask2 == interface identifier & Mask2
Hash2 & Mask1 == 0x0000000000000000000000000000
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3. CGA Parameters and Hash Values
Each CGA address is associated with a public key and auxiliary
parameters. The public key is formatted as a DER-encoded
[ITU.X690.2002] ASN.1 structure of the type SubjectPublicKeyInfo
defined in the Internet X.509 certificate profile [RFC3280]. The
public key SHOULD be an RSA encryption key with the object identifier
rsaEncryption (i.e., "1.2.840.113549.1.1.1") and the subject public
key field SHOULD be formatted as an ASN.1 data structure of the type
RSAEncryptionKey defined in [PKCS.1.2002]. The RSA key length SHOULD
be at least 384 bits. Using any other public key type or format is
strongly discouraged as it will result in incompatible CGA
implementations.
The auxiliary parameters are the following three unsigned integers:
o a 128-bit modifier, which can get any value,
o a 64-bit subnet prefix, which is equal to the subnet prefix of the
CGA address, and
o an 8-bit collision count, which can get values 0, 1 and 2.
We use the name CGA Parameters for the data structure that is the
concatenation of the 16-octet modifier, the 8-octet subnet prefix,
the 1-octet collision count, and the variable-length encoded public
key (i.e., the SubjectPublicKeyInfo structure).
The two hash values are computed with the SHA-1 hash algorithm
[FIPS.180-1.1995] from the public key and auxiliary parameters. When
computing Hash1, the input to the SHA-1 algorithm is the CGA
Parameters data structure. The 64-bit Hash1 is obtained by taking the
leftmost 64 bits of the 160-bit SHA-1 hash value.
When computing Hash2, the input is the same CGA Parameters data
structure except that the subnet prefix and collision count are set
to zero. The 112-bit Hash2 is obtained by taking the leftmost 112
bits of the 160-bit SHA-1 hash value.
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4. CGA Generation
The process of generating a new CGA address takes three input values:
a 64-bit subnet prefix, the public key of the address owner as a
DER-encoded ASN.1 structure of the type SubjectPublicKeyInfo, and the
security parameter Sec, which is an unsigned 3-bit integer. The cost
of generating a new CGA address depends on the security parameter
Sec, which gets values from 0 to 7.
A CGA address and associated parameters SHOULD be generated as
follows:
1. Set the modifier to a random or pseudorandom 128-bit value.
2. Concatenate the modifier, 9 zero octets, and the encoded public
key. Execute the SHA-1 algorithm on the concatenation. Take the
112 leftmost bits of the SHA-1 hash value. The result is Hash2.
3. Compare the 16*Sec leftmost bits of Hash2 with zero. If they are
all zero (or if Sec=0), continue with step (4). Otherwise,
increment the modifier and go back to step (2).
4. Set the 8-bit collision count to zero.
5. Concatenate the final modifier value, the subnet prefix, the
collision count and the encoded public key. Execute the SHA-1
algorithm on the concatenation. Take the 64 leftmost bits of the
SHA-1 hash value. The result is Hash1.
6. Form an interface identifier from Hash1 by writing the value of
Sec into the three leftmost bits and by setting bits 6 and 7
(i.e., the "u" and "g" bits) both to zero.
7. Concatenate the 64-bit subnet prefix and the 64-bit interface
identifier to form a 128-bit IPv6 address.
8. If an address collision is detected, increment the collision
count and go back to step (5). However, after three collisions,
stop and report the error.
9. Form the CGA Parameters data structure by concatenating the final
modifier value, the subnet prefix, the final collision count
value, and the encoded public key.
The output of the address generation algorithm is a new CGA address
and a CGA Parameters data structure.
The initial value of the modifier in step (1) is chosen randomly in
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order to make addresses generated from the same public key unlinkable
to enhance privacy (see Section 7.3). The quality of the random
number generator does not affect the strength of the binding between
the address and the public key.
For Sec=0, the above algorithm is deterministic and relatively fast.
Nodes that implement CGA generation MAY always use the security
parameter value Sec=0. If Sec=0, steps (2)-(3) of the generation
algorithm can be skipped.
For Sec values greater than 0, the above algorithm is not guaranteed
to terminate after a certain number of iterations. The brute-force
search in steps (2)-(3) takes O(2^(16*Sec)) iterations to complete.
It is intentional that generating CGA addresses with high Sec values
is infeasible with current technology.
If the subnet prefix of the address changes but the address owner's
public key does not, the old modifier value MAY be reused. If it is
reused, the algorithm SHOULD be started from step (4). This avoids
repeating the expensive search for an acceptable modifier value.
Note that this document does not specify whether duplicate address
detection should be performed and how the detection is done. Step (8)
only defines what to do if some form of duplicate address detection
is performed and an address collision is detected.
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5. CGA Verification
CGA verification takes as input an IPv6 address and a CGA Parameters
data structure. The CGA Parameters consist of the concatenated
modifier, subnet prefix, collision count and public key. The
verification either succeeds or fails.
The CGA address MUST be verified with the following steps:
1. Check that the collision count in the CGA Parameters data
structure is 0, 1 or 2. The CGA verification fails if the
collision count is out of the valid range.
2. Check that the subnet prefix in the CGA Parameters data structure
is equal to the subnet prefix (i.e., the leftmost 64 bits) of the
address. The CGA verification fails if the prefix values differ.
3. Execute the SHA-1 algorithm on the CGA Parameters data structure.
Take the 64 leftmost bits of the SHA-1 hash value. The result is
Hash1.
4. Compare Hash1 with the interface identifier (i.e., the rightmost
64 bits) of the address. Differences in the three leftmost bits
and in bits 6 and 7 (i.e., the "u" and "g" bits) are ignored. If
the 64-bit values differ (other than in the five ignored bits),
the CGA verification fails.
5. Read the security parameter Sec from the three leftmost bits of
the 64-bit interface identifier of the address. (Sec is an
unsigned 3-bit integer.)
6. Concatenate the modifier, 9 zero octets, and the public key.
Execute the SHA-1 algorithm on the concatenation. Take the 112
leftmost bits of the SHA-1 hash value. The result is Hash2.
7. Compare the 16*Sec leftmost bits of Hash2 with zero. If any one
of them is non-zero, the CGA verification fails. Otherwise, the
verification succeeds. (If Sec=0, the CGA verification never
fails at this step.)
If the verification succeeds, the verifier knows that the public key
in the CGA Parameters is the authentic public key of the address
owner. The verifier can extract the public key by removing 25 bytes
from the beginning of the CGA Parameters and by decoding the
following SubjectPublicKeyInfo data structure. Future versions of
this specification may add new fields to the end of the CGA
Parameters and the verifier SHOULD ignore any unrecognized data that
follows the encoded public key.
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Note that the values of bits 6 and 7 (the "u" and "g" bits) of the
interface identifier are ignored during CGA verification. After the
verification succeeds, the verifier SHOULD process all CGA addresses
the in the same way regardless of the Sec, modifier and collision
count values. In particular, the verifier SHOULD NOT have any
security policy that differentiates between addresses based on the
value of Sec. That way, the address generator is free choose any
value of Sec.
All nodes that implement CGA verification MUST be able to process all
security parameter values Sec = 0, 1, 2, 3, 4, 5, 6, 7. The
verification procedure is relatively fast and always requires a
constant amount of computation. If Sec=0, the verification never
fails in steps (6)-(7) and these steps can be skipped.
Nodes that implement CGA verification SHOULD be able to process RSA
public keys that have the OID rsaEncryption and key length between
384 and 2048 bits. Implementations MAY support longer keys. Future
versions of this specification may recommend support for longer keys.
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6. CGA Signatures
This section defines the procedures for generating and verifying CGA
signatures. In order to sign a message, a node needs the CGA address,
the associated CGA Parameters data structure, the message, and the
private cryptographic key that corresponds to the public key in the
CGA Parameters. The node also needs to have a 128-bit type tag for
the message from CGA Message Type name space.
To sign a message, a node SHOULD do the following:
o Concatenate the 128-bit type tag and the message. The
concatenation is the message to be signed in the next step.
o Generate the RSA signature using the RSASSA-PKCS1-v1_5
[PKCS.1.2002] signature algorithm with the SHA-1 hash algorithm.
The inputs to the generation operation are the private key and the
concatenation created above.
The SEND protocol specification [I-D.ietf-send-ndopt] defines several
messages that contain a signature in the Signature Option. The SEND
protocol specification also defines a type tag from the CGA Message
Type name space. The same type tag is used for all the SEND messages
that have the Signature Option. This type tag is an IANA-allocated
128 bit integer that has been chosen in random to prevent accidental
type collision with messages of other protocols that use the same
public key but may or may not use IANA-allocated type tags.
The CGA address, the CGA Parameters data structure, the message, and
the signature are sent to the verifier. The SEND protocol
specification defines how this data is sent in SEND protocol
messages. Note that the 128-bit type tag is not included in the SEND
protocol messages because the verifier knows its value implicitly
from the ICMP message type field in the SEND message.
In order to verify a signature, the verifier needs the CGA address,
the associated CGA Parameters data structure, the message, and the
signature. The verifier also needs to have the 128-bit type tag for
the message.
To verify the signature, a node SHOULD do the following:
o Verify the CGA address as defined in Section 5. The inputs to the
CGA verification are the CGA address and the CGA Parameters data
structure.
o Concatenate the 128-bit type tag and the message. The
concatenation is the message whose signature is to be verified in
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the next step.
o Verify the RSA signature using the RSASSA-PKCS1-v1_5 [PKCS.1.2002]
algorithm with the SHA-1 hash algorithm. The inputs to the
verification operation are the public key (i.e., the
RSAEncryptionKey structure from the SubjectPublicKeyInfo structure
that is a part of the CGA Parameters data structure), the
concatenation created above, and the signature.
The verifier accepts the signature as authentic only if both the CGA
verification and the signature verification succeed.
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7. Security Considerations
7.1 Security Goals and Limitations
The purpose of CGA addresses is to prevent stealing and spoofing of
existing IPv6 addresses. The public key of the address owner is bound
cryptographically to the address. The address owner can use the
corresponding private key to assert its ownership of the address and
to sign SEND messages sent from the address.
It is important to understand that an attacker can create a new
address from an arbitrary subnet prefix and its own public key. What
the attacker cannot do is to impersonate somebody else's address.
This is because the attacker would have to find a collision of the
cryptographic hash value Hash1. (The property of the hash function
needed here is called second pre-image resistance or weak collision
resistance.)
For each valid CGA Parameters data structure, there are 4*(Sec+1)
different CGA addresses that match the value. This is because
decrementing the Sec value in the three leftmost bits of the
interface identifier does not invalidate the address, and the "u" and
"g" bits can be chosen freely. In SEND, this fact does not have any
security or implementation implications.
Another limitation of CGA addresses is that there is no mechanism for
proving that an address is not a CGA address. Thus, an attacker could
take someone else's CGA address and present it as a non-CGA address
(e.g., as an RFC-3041 address). An attacker does not benefit from
this because although SEND nodes accept both signed and unsigned
messages from every address, they give priority to the information in
the signed messages.
7.2 Hash extension
As computers become faster, the 64 bits of the interface identifier
will not be sufficient to prevent attackers from searching for hash
collisions. It helps somewhat that we include the subnet prefix of
the address in the hash input. This prevents the attacker from using
a single pre-computed database to attack addresses with different
subnet prefixes. The attacker needs to create a separate database for
each subnet prefix. Link-local addresses are, however, left
vulnerable because the same prefix is used by all IPv6 nodes.
In the long term, some kind of hash extension technique must be used
to counter the effect of faster computers. Otherwise, the CGA
technology could become outdated after 5-20 years. The idea in this
document is to increase the cost of both address generation and
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brute-force attacks by the same parameterized factor while keeping
the cost of address use and verification constant. This provides
protection also for link-local addresses. Introduction of the hash
extension is the main difference between this document and earlier
CGA proposals [OR01][Nik01][MC02].
To achieve the effective extension of the hash length, the input to
the second hash function Hash2 is modified (by changing the modifier
value) until the leftmost 16*Sec bits of the hash value are zero.
This increases the cost of address generation approximately by a
factor of 2^(16*Sec). It also increases the cost of brute-force
attacks by the same factor. That is, the cost of creating a CGA
Parameters data structure that binds the attacker's public key with
somebody else's address is increased from O(2^59) to
O(2^(59+16*Sec)). The address generator may choose the security
parameter Sec depending on its own computational capacity, perceived
risk of attacks, and the expected lifetime of the address. Currently,
Sec values between 0 and 2 are sufficient for most IPv6 nodes. As
computers become faster, higher Sec values will slowly become useful.
Theoretically, if no hash extension is used (i.e., Sec=0) and a
typical attacker is able to tap into N local networks at the same
time, an attack against link-local addresses is N times as efficient
as an attack against addresses of a specific network. The effect
could be countered by using a slightly higher Sec value for
link-local addresses. When higher Sec values (such that 2^(16*Sec) >
N) are used for all addresses, the relative advantage of attacking
link-local addresses becomes insignificant.
The effectiveness of the hash extension depends on the assumption
that the computational capacities of the attacker and the address
generator will grow at the same (potentially exponential) rate. This
is not necessarily true if the addresses are generated on low-end
mobile devices where the main design goals are lower cost and smaller
size rather than increased computing power. But there is no reason
for doing so. The expensive part of the address generation (steps
(1)-(3) of the generation algorithm) may be delegated to a more
powerful computer. Moreover, this work can be done in advance or
offline, rather than in real time when a new address is needed.
In order to make it possible for mobile nodes whose subnet prefix
changes frequently to use Sec values greater than 0, we have decided
not to include the subnet prefix in the input of Hash2. The result is
weaker than if the subnet prefix were included in the input of both
hashes. On the other hand, our scheme is at least as strong as using
the hash extension technique without including the subnet prefix in
either hash. It is also at least as strong as not using the hash
extension but including the subnet prefix. This trade-off was made
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because mobile nodes frequently move to insecure networks where they
are at the risk of denial-of-service (DoS) attacks, for example,
during the duplicate address detection procedure.
In most networks, the goal of Secure Neighbor Discovery and CGA-based
authentication is to prevent denial-of-service attacks. Therefore, it
is usually sensible to start by using a low Sec value and to replace
addresses with stronger ones only when denial-of-service attacks
based on brute-force search become a significant problem. (If CGA
addresses were used as a part of a strong authentication or secrecy
mechanisms, it would be necessary to start with higher Sec values.)
The collision count value is used to modify the input to Hash1 if
there is an address collision. It is important not to allow collision
count values higher than 2. First, it is extremely unlikely that
three collisions would occur and the reason is certain to be either a
configuration or implementation error or a denial-of-service attack.
(When the SEND protocol is used, the deliberate collisions caused by
a DoS attacker are detected and ignored.) Second, an attacker who is
doing a brute-force search to match a given CGA address can try all
different values of collision count without repeating the brute-force
search for the modifier value. Thus, the more different values are
allowed for the collision count, the less effective the
hash-extension technique is in preventing brute-force attacks.
7.3 Privacy Considerations
CGA addresses can give the same level pseudonymity as the IPv6
address privacy extensions defined in RFC 3041 [RFC3041]. An IP host
can generate multiple pseudorandom CGA addresses by executing the CGA
generation algorithm of Section 4 multiple times and by using every
time a different random or pseudorandom initial value for the
modifier. The host should change its address periodically as in
[RFC3041]. When privacy protection is needed, the (pseudo)random
number generator used in address generation SHOULD be strong enough
to produce unpredictable and unlinkable values.
There are two apparent limitations to this privacy protection.
However, as we will explain below, neither limitation is very
serious.
First, the high cost of address generation may prevent hosts that use
a high Sec value from changing their address frequently. This problem
is mitigated by the fact that the expensive part of the address
generation may be done in advance or offline, as explained in the
previous section. It should also be noted that the nodes that benefit
most from high Sec values (e.g., DNS servers, routers, and data
servers) usually do not require pseudonymity, while the nodes that
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have high privacy requirements (e.g., client PCs and mobile hosts)
are unlikely targets for expensive brute-force attacks and can do
with lower Sec values.
Second, the public key of the address owner is revealed in the
authenticated SEND messages. This means that if the address owner
wants to be pseudonymous towards the nodes in the local links that it
accesses, it should not only generate a new address but also a new
public key. With typical local-link technologies, however, a node's
link-layer address is a unique identifier for the node. As long as
the node keeps using the same link-layer address, it makes little
sense to ever change the public key for privacy reasons.
7.4 Related protocols
While this document defines CGA addresses only for the purposes of
Secure Neighbor Discovery, other protocols could be defined elsewhere
that use the same addresses and public keys. This raises the
possibility of related-key attacks where a signed message from one
protocol is replayed in another protocol. This means that other
protocols (perhaps designed without an intimate knowledge of SEND)
could endanger the security of SEND.
To prevent the related-protocol attacks, a type tag is prepended to
every message before signing it. The type-tags are 128-bit randomly
chosen values, which prevents accidental type collisions with even
poorly designed protocols that do not use any type tags.
Finally, some cautionary notes should be made about using CGA-based
authentication for other purposes than SEND. First, the other
protocols should use type tags in all signed messages in the same way
as SEND does. Because of the possibility of related-protocol attacks,
it is advisable to use the public key only for signing and not for
encryption. Second, CGA-based authentication is particularly suitable
for securing neighbor discovery [RFC2461] and duplicate address
detection [RFC2462] because these are network-layer signaling
protocols where IPv6 addresses are natural endpoint identifiers. In
any protocol that aims to protect higher-layer data, CGA-based
authentication alone is not sufficient and there must also be a
secure mechanism for mapping higher-layer identifiers, such as DNS
names, to IP addresses.
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8. IANA Considerations
This document defines a new CGA Message Type name space for use as
type tags in messages may be signed using CGA signatures. The values
in this name space are 128-bit integers. Values in this name space
are allocated as First Come First Served [RFC2434]. IANA assigns new
128-bit values directly without a review.
The new values SHOULD be generated with a strong random-number
generator by the requester. Continuous ranges of at most 256 values
can be allocated provided that the 120 most significant bits of the
values have been generated with a strong random-number generator. It
is not necessary for IANA to verify the randomness of the requested
values. The name space is essentially unlimited and any number of
individual values or ranges of at most 256 values can be allocated.
CGA Message Type values for private use MAY be generated with a
strong random-number generator without IANA allocation.
This document does not define any new values in any name space.
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Normative References
[I-D.ietf-send-ndopt]
Arkko, J., Kempf, J., Sommerfeld, B., Zill, B. and P.
Nikander, "SEcure Neighbor Discovery (SEND)",
draft-ietf-send-ndopt-00 (work in progress), October 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
[RFC3280] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[ITU.X690.2002]
International Telecommunications Union, "Information
Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, July 2002.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[PKCS.1.2002]
RSA Laboratories, "RSA Encryption Standard, Version 2.1",
Public-Key Cryptography Standard PKCS 1, June 2002.
[FIPS.180-1.1995]
National Institute of Standards and Technology, "Secure
Hash Standard", Federal Information Processing Standards
Publication FIPS PUB 180-1, April 1995, <http://
www.itl.nist.gov/fipspubs/fip180-1.htm>.
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Internet-Draft Cryptographically Generated Addresses (CGA) November 2003
Informative References
[AAKMNR02]
Arkko, J., Aura, T., Kempf, J., Mantyla, V., Nikander, P.
and M. Roe, "Securing IPv6 neighbor discovery and router
discovery", ACM Workshop on Wireless Security (WiSe 2002),
Atlanta, GA USA , September 2002.
[Aura03] Aura, T., "Cryptographically Generated Addresses (CGA)",
6th Information Security Conference (ISC'03), Bristol, UK
, October 2003.
[MC02] Montenegro, G. and C. Castelluccia, "Statistically unique
and cryptographically verifiable identifiers and
addresses", ISOC Symposium on Network and Distributed
System Security (NDSS 2002), San Diego, CA USA , February
2002.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
[RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[Nik01] Nikander, P., "A scaleable architecture for IPv6 address
ownership", draft-nikander-addr-ownership-00 (work in
progress), March 2001.
[OR01] O'Shea, G. and M. Roe, "Child-proof authentication for
MIPv6 (CAM)", ACM Computer Communications Review 31(2),
April 2001.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
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Author's Address
Tuomas Aura
Microsoft Research
Roger Needham Building
7 JJ Thomson Avenue
Cambridge CB3 0FB
United Kingdom
Phone: +44 1223 479708
EMail: tuomaura@microsoft.com
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Appendix A. Example of CGA Generation
We generate a CGA address with Sec=1 from the subnet prefix fe80::
and the following public key:
305c 300d 0609 2a86 4886 f70d 0101 0105 0003 4b00 3048 0241
00c2 c2f1 3730 5454 f10b d9ce a368 44b5 30e9 211a 4b26 2b16
467c b7df ba1f 595c 0194 f275 be5a 4d38 6f2c 3c23 8250 8773
c786 7f9b 3b9e 63a0 9c7b c48f 7a54 ebef af02 0301 0001
The modifier is initialized to a random value 89a8 a8b2 e858 d8b8
f263 3f44 d2d4 ce9a. The input to Hash2 is:
89a8 a8b2 e858 d8b8 f263 3f44 d2d4 ce9a 0000 0000 0000 0000 00
305c 300d 0609 2a86 4886 f70d 0101 0105 0003 4b00 3048 0241
00c2 c2f1 3730 5454 f10b d9ce a368 44b5 30e9 211a 4b26 2b16
467c b7df ba1f 595c 0194 f275 be5a 4d38 6f2c 3c23 8250 8773
c786 7f9b 3b9e 63a0 9c7b c48f 7a54 ebef af02 0301 0001
The 112 first bits of the SHA-1 hash value computed from the above
input is Hash2=436b 9a70 dbfd dbf1 926e 6e66 29c0. This does not
begin with 16*Sec=16 zero bits. Thus, we must increment the modifier
and recompute the hash. The new input to Hash2 is:
89a8 a8b2 e858 d8b8 f263 3f44 d2d4 ce9b 0000 0000 0000 0000 00
305c 300d 0609 2a86 4886 f70d 0101 0105 0003 4b00 3048 0241
00c2 c2f1 3730 5454 f10b d9ce a368 44b5 30e9 211a 4b26 2b16
467c b7df ba1f 595c 0194 f275 be5a 4d38 6f2c 3c23 8250 8773
c786 7f9b 3b9e 63a0 9c7b c48f 7a54 ebef af02 0301 0001
The new hash value is Hash2=0000 01ca 680b 8388 8d09 12df fcce. The
16 leftmost bits of Hash2 are all zero. Thus, we found a suitable
modifier. (We were very lucky to find it so soon.)
The input to Hash1 is:
89a8 a8b2 e858 d8b8 f263 3f44 d2d4 ce9b fe80 0000 0000 0000 00
305c 300d 0609 2a86 4886 f70d 0101 0105 0003 4b00 3048 0241
00c2 c2f1 3730 5454 f10b d9ce a368 44b5 30e9 211a 4b26 2b16
467c b7df ba1f 595c 0194 f275 be5a 4d38 6f2c 3c23 8250 8773
c786 7f9b 3b9e 63a0 9c7b c48f 7a54 ebef af02 0301 0001
The 64 first bits of the SHA-1 hash value of the above input are
Hash1=fd4a 5bf6 ffb4 ca6c. We form an interface identifier from this
by writing Sec=1 into the three leftmost bits and by setting bits 6
and 7 (the "u" and "g" bits) to zero. The new interface identifier is
3c4a:5bf6:ffb4:ca6c.
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Finally, we form the IPv6 address fe80::3c4a:5bf6:ffb4:ca6c. This is
the new CGA address. No address collisions were detected this time.
(Collisions are very rare.) The CGA Parameters data structure
associated with the address is the same as the input to Hash1 above.
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Appendix B. Acknowledgments
The author gratefully acknowledges the contributions of Jari Arkko,
Francis DuPont, Pasi Eronen, Christian Huitema, Pekka Nikander,
Michael Roe, Dave Thaler, and several other participants of the IETF
working group.
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