Network Working Group J. Carlson
INTERNET-DRAFT Sun Microsystems
Expires December 2001 June 2001
PPP EAP SRP-SHA1 Authentication Protocol
<draft-ietf-pppext-eap-srp-02.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
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This document is the product of the Point-to-Point Protocol
Extensions Working Group of the Internet Engineering Task Force
(IETF). Comments should be submitted to the ietf-ppp@merit.edu
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Abstract
The Point-to-Point Protocol (PPP) [1] provides a standard method for
transporting multi-protocol datagrams over point-to-point links. PPP
also defines an Extensible Authentication Protocol (EAP) [2]
framework to allow the use of multiple authentication mechanisms
without fixing the mechanism to be used during initial link
negotiation. This document defines an authentication mechanism for
EAP called SRP-SHA1, and allows the use of the Secure Remote Password
(SRP) [3] protocol as a PPP link authentication method.
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Table of Contents
1. Introduction ........................................... 2
2. Detailed Description of EAP SRP-SHA1 Authentication .... 3
2.1. EAP SRP-SHA1 Packet Formats ............................ 4
2.2. EAP SRP-SHA1 Challenge Subtype-Data .................... 5
2.3. EAP SRP-SHA1 Client Key Subtype-Data ................... 7
2.4. EAP SRP-SHA1 Server Key Subtype-Data ................... 7
2.5. EAP SRP-SHA1 Client Validator Subtype-Data ............. 8
2.6. EAP SRP-SHA1 Server Validator Subtype-Data ............. 9
2.7. EAP SRP-SHA1 Subtype 3 Response Packet ................. 10
3. Use with EAP ........................................... 10
3.1. One-Way Versus Bidirectional Encryption ................ 10
3.2. One-Way Versus Mutual Authentication ................... 11
3.3. DESEbis Versus 3DES .................................... 11
4. Use with AAA ........................................... 11
5. Security Considerations ................................ 12
6. Intellectual Property Rights Notices ................... 12
6.1. Patent Issues .......................................... 12
6.2. Full Copyright Statement ............................... 13
7. References ............................................. 13
8. Acknowledgements ....................................... 14
9. Author's Address ....................................... 15
10. Appendix A - Well-Known Prime Modulus .................. 15
1. Introduction
PPP-EAP allows the use of multiple authentication mechanisms within a
single negotiation framework. This design overcomes the chief design
limitation of the original PPP authentication mechanisms, PAP [4] and
CHAP [5], which require that the protocol to be used for authentica-
tion be chosen before the user's identity is known. EAP also simpli-
fies the process of adding authentication mechanisms to PPP.
SRP is an open source protocol that provides strong, password-based
authentication based on cryptographic hashing. Unlike PAP, the pass-
word never appears on the wire. Unlike CHAP (and variants MS-CHAPv1
[6] and MS-CHAPv2 [7]), access to the cleartext password is not
required for the authenticator. Unlike all of these authentication
protocols, SRP is resistant to dictionary attacks against the over-
the-wire information. SRP is also resistant to eavesdropping and
active attacks. As a side-effect, SRP also creates a session key
that is resistant to man-in-the-middle attacks and can be used for
data encryption.
SHA-1 [8] is a message digest algorithm that can be used as a hashing
mechanism for SRP, producing an SRP variant known as SRP-SHA1. For
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calculation of the shared key in SRP, SHA-1 is used in an interleaved
form to produce 40 octet hashes. See [3] for details.
This document describes the message exchanges REQUIRED for one PPP
peer to authenticate the other using EAP and SRP-SHA1. As with all
PPP authentication mechanisms, the peers are independent and equal,
and either or both may demand authentication from the other, and dif-
ferent protocols may be used independently in each direction.
When the PPP Encryption Control Protocol (ECP) [9] is used along with
EAP SRP-SHA1, this document describes methods that SHOULD be used to
generate the necessary shared keys from the SRP-SHA1 session key.
Because authentication necessarily requires prior arrangement between
the peers, pre-configured keys MAY be used in place of the SRP-SHA1
session key, and any such selection is outside the scope of this
document.
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 BCP 14 [10].
2. Detailed Description of EAP SRP-SHA1 Authentication
Unlike CHAP, SRP-SHA1 requires more than one exchange to authenticate
the peer. For this reason, three message subtypes are defined.
With SRP, the authenticator must communicate at least three values to
the authenticatee, referred to as 's' (the password salt), 'B' (an
ephemeral public key), and 'M2' (a hash value). The authenticatee
must communicate at least three values to the authenticator, referred
to as 'C' (the client name), 'A' (an ephemeral public key), and 'M1'
(a hash value).
(The value 'u' passed from authenticator to authenticatee in the gen-
eral SRP algorithm is derived from the first 32 bits of a SHA-1 hash
of the 'B' value itself in the SRP-SHA1 algorithm. Thus, it does not
need to be sent explicitly.)
In order to send its last value (M1), the authenticatee needs A, B,
and u. However, in order to guarantee that the authenticatee's value
chosen for A isn't a rogue value (see section 3.2.4 of the SRP
description [11]), the value of u must not be sent until the authen-
ticatee reveals A. This implies that there are at least three steps
-- authenticatee sends A, authenticator sends B, authenticatee sends
M1.
The adaptation described in this document recommends the use of the
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EAP Identity Request/Response mechanism to obtain C from the peer.
It then uses a new message type, called EAP SRP-SHA1, with three sub-
types to handle the SRP authentication. The Subtype 1 Request
("Challenge") message contains s, g, and N. The Subtype 1 Response
("Client Key") contains A. The Subtype 2 Request ("Server Key") con-
tinues with B and the Subtype 2 Response ("Client Validator") con-
tains M1. Finally, the Subtype 3 Request ("Server Validator") con-
tains the M2 value and the Subtype 3 response is an acknowledgement
containing only the Subtype number and no data.
2.1. EAP SRP-SHA1 Packet Formats
All SRP authentication is driven by the authenticator (server). The
authenticatee (client) MUST NOT retransmit Response messages, but
SHOULD terminate the link if a Request is not received within a rea-
sonable time period. The authenticator SHOULD silently ignore unex-
pected Response messages. The authenticatee MUST respond using EAP
Nak if any unknown Subtype or otherwise unacceptable message is
received.
A summary of the PPP EAP SRP-SHA1 Request/Response packet format is
shown below. The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Subtype | Subtype-Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+-
Code
1 - Request
2 - Response
Identifier
The Identifier field is one octet and aids in matching responses
with requests. The Identifier SHOULD be changed for each Request
message sent. The Identifier in the Response message MUST match
the corresponding Request. The authenticator MUST discard
non-matching Response messages.
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Length
The Length field is two octets and indicates the length of the
EAP packet including the Code, Identifier, Length, Type, Subtype,
and Subtype-Data fields. Octets outside the range of the Length
field should be treated as Data Link Layer padding and should be
ignored on reception. Truncated packets (with Length greater
than the link layer reported length) MUST be silently discarded.
Type
19 - EAP SRP-SHA1
Subtype
1 - Challenge / Client Key
2 - Server Key / Client Validator
3 - Server Validator
The Subtype field is one octet and must contain the value 1, 2,
or 3. If any other subtype value is encountered in an EAP
SRP-SHA1 Request message, then the authenticatee SHOULD return an
EAP Response with the Type field set to Nak. In EAP SRP-SHA1
Response messages, the Subtype value must be copied from the
corresponding Request message. The authenticator should treat
unknown Subtype values in Response messages as malformed packets
and silently discard.
Subtype-Data
The format of the Subtype-Data field is determined by the Code
and Subtype fields as described in the sections below.
2.2. EAP SRP-SHA1 Challenge Subtype-Data
The PPP EAP SRP-SHA1 Challenge (Subtype 1 Request) packet MUST be
sent after the peer's identity has been obtained; use of the EAP
Identity Request/Response packet as described in [2] is RECOMMENDED.
Using the peer's unauthenticated identity, the authenticator MUST
look up the password salt, verifier ('v'), prime modulus, and genera-
tor values in an implementation-dependent manner. Use of EAP Iden-
tity is not required by this specification, and determination of
salt, verifier, prime modulus, and generator may be done in any con-
venient manner.
A summary of the PPP EAP SRP-SHA1 Challenge Subtype-Data format is
shown below. Code (1), Identifier, Length, Type (19), and Subtype
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(1) fields are as described above. The fields are transmitted from
left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Hash Type | Salt Length | Salt ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Prime Modulus Length | Prime Modulus ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
| Generator ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Hash Type
A single octet specifying the type of hash algorithm to be used
with SRP. For SHA-1 based SRP as described in this document,
this value MUST be set to 1. An authenticatee that does not
support the hash algorithm specified by the authenticator MUST
reply with EAP Nak to disable EAP SRP authentication.
Salt Length
A single octet giving the length of the Salt field in octets.
This MUST be at least 4 octets and MAY be any length up to 255
octets.
Salt
Password salt string; may contain any values and be of any
length, subject to link MTU restrictions. This field is not
padded.
Prime Modulus Length
Length of the Prime Modulus field in octets. This value MAY be
zero to select the 2048 bit value for N listed in Appendix A and
select g=2. In this case, the Prime Modulus and the Generator
field MUST NOT be present in the message.
If the Prime Modulus Length field is non-zero, then it SHOULD be
at least 64 octets (512 bits). Longer values are RECOMMENDED.
Prime Modulus
Prime Modulus value. This value (called 'N' in the SRP
documentation) is in network byte order and has a length equal to
the Prime Modulus Length field.
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Generator
The Generator value. This value (called 'g' in the SRP
documentation) is in network byte order and fills the rest of the
message without padding. If the Generator field is omitted, then
g is set to 2.
2.3. EAP SRP-SHA1 Client Key Subtype-Data
The PPP EAP SRP-SHA1 Client Key (Subtype 1) Response message MUST be
sent in reply to an EAP SRP-SHA1 Subtype 1 Request message.
A summary of the PPP EAP SRP-SHA1 Client Key Subtype-Data format is
shown below. Code (2), Identifier, Length, Type (19), and Subtype
(1) fields are as described above. The fields are transmitted from
left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value A ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value A
The result of (g^a) mod N, where 'a' is a randomly chosen number
in the range 1 .. N (exclusive). The randomly chosen number is
the authenticatee's private key, and the Value A field is the
corresponding public key. This field is in network byte order
and is not padded.
The A value MUST NOT be zero. If the authenticator receives zero
for this field, it SHOULD take action to disconnect the link.
2.4. EAP SRP-SHA1 Server Key Subtype-Data
The PPP EAP SRP-SHA1 Server Key (Subtype 2 Request) message MUST NOT
be sent until a valid Client Key Response message has be received.
The Subtype 2 Request message SHOULD be retransmitted on time-out.
A summary of the PPP EAP SRP-SHA1 Server Key Subtype-Data format is
shown below. Code (1), Identifier, Length, Type (19), and Subtype
(2) fields are as described above. The fields are transmitted from
left to right.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value B ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Value B
The result of (v + g^b) mod N, where 'b' is a randomly chosen
number in the range 1 .. N (exclusive), and v is the stored
verifier from the authentication database. The randomly chosen
number is the authenticator's private key, and the Value B field
is the corresponding public key. This field is in network byte
order and is not padded.
The B value MUST NOT be zero. If the authenticatee receives zero
for this field, it SHOULD take action to disconnect the link.
2.5. EAP SRP-SHA1 Client Validator Subtype-Data
The PPP EAP SRP-SHA1 Client Validator (Subtype 2 Response) message
MUST be sent by the authenticatee in response to a valid EAP SRP-SHA1
Subtype 2 Request. The authenticator validates this Response message
by calculating the M1 value from its own copies of A, B, and K, and
compares the result. If the values match, then the authentication is
successful, and EAP SRP-SHA1 Server Validator Request SHOULD be sent.
If the values do not match, then EAP Failure SHOULD be returned and
the link terminated.
A summary of the PPP EAP SRP-SHA1 Client Validator Subtype-Data for-
mat is shown below. Code (2), Identifier, Length, Type (19), and
Subtype (2) fields are as described above. The fields are transmit-
ted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value M1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M1 (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M1 (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M1 (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M1 (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Value M1
The 20 octet result of SHA1(SHA1(N) xor SHA1(g), SHA1(peername),
s, A, B, K).
As described in SRP [3], the authenticatee computes x = SHA1(s,
SHA1(peername, ":", password)), and then computes K =
SHA_Interleave((B - g^x)^(a + u*x) mod N). The authenticator com-
putes K = SHA1_Interleave((A * v^u)^b mod N). The calculated K
values MAY be used with ECP (see section 3). Finally, M1 is then
computed as SHA1(SHA1(N) xor SHA1(g), SHA1(peername), s, A, B, K).
(Note that reference [11] gives different definitions of these
values; the [3] document should be treated as the normative refer-
ence.)
The above described SHA1 hash to produce the long-term private key x,
as described in [3], SHOULD be used by default in EAP SRP-SHA1. As
an implementation open, however, the x value used above MAY instead
be derived from any mutually-chosen hashing algorithm, provided that
the security of that algorithm is acceptable to both authentication
parties.
2.6. EAP SRP-SHA1 Server Validator Subtype-Data
The PPP EAP SRP-SHA1 Server Validator (Subtype 3 Request) message
MUST be sent by the authenticator after reception of a valid EAP
SRP-SHA1 Subtype 2 Response. If the authenticatee receives a Server
Validator message with invalid contents, it MUST terminate the link.
A summary of the PPP EAP SRP-SHA1 Server Validator Subtype-Data for-
mat is shown below. Code (1), Identifier, Length, Type (19), and
Subtype (3) fields are as described above. The fields are transmit-
ted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value M2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M2 (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M2 (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M2 (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| M2 (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Value M2
The 20 octet result of SHA1(A, M1, K).
2.7. EAP SRP-SHA1 Subtype 3 Response
The authenticatee MUST transmit a PPP EAP SRP-SHA1 Subtype 3 Response
message in reply to a valid Server Validator message from the peer.
This Response message has no Subtype-Data field. The Code (2), Iden-
tifier, Length (6), Type (19), and Subtype (3) fields are as
described above.
3. Use with ECP
The 40 octet value K calculated by the SRP-SHA1 authentication pro-
cedure SHOULD be used to form encryption keys if PPP encryption is in
use and K is available (see section 4). For the DESEbis [12] algo-
rithm, a shared 56 bit key is necessary, and for the 3DES [13] algo-
rithm, a shared 168 bit key is required. Complicating this, ECP may
be negotiated in only one direction or both. In addition, PPP
authentication may be performed one-way (the most common case) or
mutually, and when mutual authentication is chosen, different authen-
tication schemes may be used to authenticate each peer. The effects
of these details are described below.
The "decryptor" is the peer that sends ECP Configure-Request suggest-
ing an algorithm and receives a corresponding ECP Configure-Ack. The
"encryptor" is the sender of the ECP Configure-Ack, and will transmit
the encrypted data.
Rekeying can be accomplished by restarting EAP authentication.
3.1. One-Way Versus Bidirectional Encryption
When encryption is employed in only one direction, then the K value
that is chosen for the shared key is the value associated with the
EAP SRP-SHA1 authentication in which the decryptor is the authentica-
tor. If the decryptor did not authenticate its peer with EAP SRP-
SHA1, then the K value associated with the other authentication ses-
sion is used instead.
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3.2. One-Way Versus Mutual Authentication
If only one peer authenticates the other using SRP-SHA1, and the
other either does not authenticate its peer at all or uses a method
that does not result in encryption keys, then the one K value associ-
ated with this authentication SHOULD be used for both encryption ses-
sions. The first 20 octets of K are used for the encryption of data
sent by the authenticatee to the authenticator, and the second 20
octets of K are used for encryption of data in the opposite direc-
tion.
If mutual authentication with algorithms that produce encryption keys
is done, such as SRP-SHA1, then two K values are produced. The K
values are used so that the encryptor is the authenticatee for the
corresponding authentication session, and the decryptor is the
authenticator.
3.3. DESEbis Versus 3DES
For DESEbis, the first 8 octets of the key value are used. DES keys
are constructed such that the most significant bit (MSB) of each
octet is reserved for parity.
For 3DES, 24 octets of key value are used by most implementations.
As for DESEbis, the MSBs are discarded. If the 40 octet K value has
been split into two 20 octet values because one-way authentication is
in use, then an extra 4 octets are needed for each key. The SHA-1
algorithm is run again over the 40 octet K value to produce a 20
octet hash. This hash is split into two 10 octet values that are
then appended to the two 20 octet values from the split K value. The
first 24 octets of each 30 octet value is used as the 3DES key.
4. Use with AAA
The SRP exchange uses the PPP peername as part of the calculation,
and thus depends on leaving this string unmodified between the
authenticatee and authenticator. If a mechanism, such as a AAA pro-
tocol, is used to perform the SRP authentication on behalf of the PPP
"server," then the peername MUST be identical on both ends. In par-
ticular, if a Network Access Identifier [14] is used with a proxy
authentication server, then the implementor MUST take steps to
preserve the peername string end-to-end.
Use of a AAA protocol also makes the use of the session key (K) for
ECP keying problematic, because the contents of this key are avail-
able only at the authentication endpoints (where SRP is run), and not
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the link layer endpoints (where ECP is run). Use of a directory
access protocol for the hash values, rather than a AAA protocol,
would solve this problem.
5. Security Considerations
The security of SRP on the wire relies on having a prime modulus that
is large enough to make brute force attack of the key exchange
infeasible. A length of at least 1024 bits is recommended. In addi-
tion, the SRP document [3] describes tests that MUST be performed on
the chosen modulus and generator values and random numbers. SRP is a
significant improvement over the situation with PAP, which has no
on-the-wire security, and with CHAP, which is vulnerable to diction-
ary attacks against a captured Challenge/Response pair.
The security of the credentials stored in the authenticator's data-
base relies on the entropy in the chosen password, the difficulty of
hash inversion of a salted string, and the security of the system
containing the database. For this reason, the chosen password SHOULD
be restricted to limit the effectiveness of dictionary attacks
against a disclosed database. However, since typical passwords have
only a few bits of entropy, the database itself MUST be protected
against disclosure.
6. Intellectual Property Rights Notices
6.1. Patent Issues
The SRP key-exchange protocol described in this document is available
worldwide on a royalty-free basis for commercial and non-commercial
uses.
"The IETF takes no position regarding the validity or scope of
any intellectual property or other rights that might be claimed
to pertain to the implementation or use of the technology
described in this document or the extent to which any license
under such rights might or might not be available; neither does
it represent that it has made any effort to identify any such
rights. Information on the IETF's procedures with respect to
rights in standards-track and standards-related documentation
can be found in BCP-11. Copies of claims of rights made
available for publication and any assurances of licenses to
be made available, or the result of an attempt made
to obtain a general license or permission for the use of such
proprietary rights by implementors or users of this
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specification can be obtained from the IETF Secretariat."
"The IETF invites any interested party to bring to its
attention any copyrights, patents or patent applications, or
other proprietary rights which may cover technology that may be
required to practice this standard. Please address the
information to the IETF Executive Director."
6.2. Full Copyright Statement
"Copyright (C) The Internet Society 2001. All Rights
Reserved.
This document and translations of it may be copied and
furnished to others, and derivative works that comment on or
otherwise explain it or assist in its implementation may be
prepared, copied, published and distributed, in whole or in
part, without restriction of any kind, provided that the above
copyright notice and this paragraph are included on all such
copies and derivative works. However, this document itself may
not be modified in any way, such as by removing the copyright
notice or references to the Internet Society or other Internet
organizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copyrights
defined in the Internet Standards process must be followed, or
as required to translate it into languages other than English.
The limited permissions granted above are perpetual and will
not be revoked by the Internet Society or its successors or
assigns.
This document and the information contained herein is provided
on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE
OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE."
7. References
[1] W. Simpson, "The Point-to-Point Protocol (PPP)," RFC 1661,
07/1994
[2] L. Blunk, J. Vollbrecht, "PPP Extensible Authentication
Protocol (EAP)," RFC 2284, 03/1998
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[3] T. Wu, "The SRP Authentication and Key Exchange System,"
RFC 2945, 09/2000
[4] B. Lloyd, W. Simpson, "PPP Authentication Protocols," RFC
1334, 10/1992
[5] W. Simpson, "PPP Challenge Handshake Authentication Protocol
(CHAP)," RFC 1994, 08/1996
[6] G. Zorn, S. Cobb, "Microsoft PPP CHAP Extensions," RFC 2433,
10/1998
[7] G. Zorn, "Microsoft PPP CHAP Extensions, Version 2," RFC 2759,
01/2000
[8] National Institute of Standards and Technology (NIST),
"Announcing the Secure Hash Standard," FIPS 180-1, U.S.
Department of Commerce, 04/1995
[9] G. Meyer, "The PPP Encryption Control Protocol (ECP)," RFC 1968,
06/1996
[10] S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels," BCP 14 and RFC 2119, 03/1997
[11] T. Wu, "The Secure Remote Password Protocol", in
Proceedings of the 1998 Internet Society Symposium on
Network and Distributed Systems Security, San Diego, CA,
pp. 97-111
[12] K. Sklower, G. Meyer, "The PPP DES Encryption Protocol, Version
2 (DESE-bis)," RFC 2419, September 1998.
[13] H. Kummert, "The PPP Triple-DES Encryption Protocol (3DESE),"
RFC 2420, September 1998.
[14] B. Aboba, M. Beadles, "The Network Access Identifier," RFC 2486,
January 1998.
8. Acknowledgements
The author is grateful for the many critiques and ideas offered on
the IETF PPP Extensions mailing list and by private mail. In partic-
ular, I thank Bernard Aboba, Jacques Caron, and Vernon Schryver.
Carlson expires December 2001 [Page 14]
INTERNET-DRAFT PPP EAP SRP-SHA1 Authentication Protocol June 2001
9. Author's Address
James Carlson
Sun Microsystems
1 Network Drive MS UBUR02-212
Burlington MA 01803-2757
Phone: +1 781 442 2084 Email: james.d.carlson@sun.com
Fax: +1 781 442 1677
10. Appendix A - Well-Known Prime Modulus
This 2048 bit prime modulus (and corresponding generator value 2) are
borrowed from the SRP GSS-API mechanism, an IETF work in progress.
0xAC, 0x6B, 0xDB, 0x41, 0x32, 0x4A, 0x9A, 0x9B,
0xF1, 0x66, 0xDE, 0x5E, 0x13, 0x89, 0x58, 0x2F,
0xAF, 0x72, 0xB6, 0x65, 0x19, 0x87, 0xEE, 0x07,
0xFC, 0x31, 0x92, 0x94, 0x3D, 0xB5, 0x60, 0x50,
0xA3, 0x73, 0x29, 0xCB, 0xB4, 0xA0, 0x99, 0xED,
0x81, 0x93, 0xE0, 0x75, 0x77, 0x67, 0xA1, 0x3D,
0xD5, 0x23, 0x12, 0xAB, 0x4B, 0x03, 0x31, 0x0D,
0xCD, 0x7F, 0x48, 0xA9, 0xDA, 0x04, 0xFD, 0x50,
0xE8, 0x08, 0x39, 0x69, 0xED, 0xB7, 0x67, 0xB0,
0xCF, 0x60, 0x95, 0x17, 0x9A, 0x16, 0x3A, 0xB3,
0x66, 0x1A, 0x05, 0xFB, 0xD5, 0xFA, 0xAA, 0xE8,
0x29, 0x18, 0xA9, 0x96, 0x2F, 0x0B, 0x93, 0xB8,
0x55, 0xF9, 0x79, 0x93, 0xEC, 0x97, 0x5E, 0xEA,
0xA8, 0x0D, 0x74, 0x0A, 0xDB, 0xF4, 0xFF, 0x74,
0x73, 0x59, 0xD0, 0x41, 0xD5, 0xC3, 0x3E, 0xA7,
0x1D, 0x28, 0x1E, 0x44, 0x6B, 0x14, 0x77, 0x3B,
0xCA, 0x97, 0xB4, 0x3A, 0x23, 0xFB, 0x80, 0x16,
0x76, 0xBD, 0x20, 0x7A, 0x43, 0x6C, 0x64, 0x81,
0xF1, 0xD2, 0xB9, 0x07, 0x87, 0x17, 0x46, 0x1A,
0x5B, 0x9D, 0x32, 0xE6, 0x88, 0xF8, 0x77, 0x48,
0x54, 0x45, 0x23, 0xB5, 0x24, 0xB0, 0xD5, 0x7D,
0x5E, 0xA7, 0x7A, 0x27, 0x75, 0xD2, 0xEC, 0xFA,
0x03, 0x2C, 0xFB, 0xDB, 0xF5, 0x2F, 0xB3, 0x78,
0x61, 0x60, 0x27, 0x90, 0x04, 0xE5, 0x7A, 0xE6,
0xAF, 0x87, 0x4E, 0x73, 0x03, 0xCE, 0x53, 0x29,
0x9C, 0xCC, 0x04, 0x1C, 0x7B, 0xC3, 0x08, 0xD8,
0x2A, 0x56, 0x98, 0xF3, 0xA8, 0xD0, 0xC3, 0x82,
0x71, 0xAE, 0x35, 0xF8, 0xE9, 0xDB, 0xFB, 0xB6,
0x94, 0xB5, 0xC8, 0x03, 0xD8, 0x9F, 0x7A, 0xE4,
0x35, 0xDE, 0x23, 0x6D, 0x52, 0x5F, 0x54, 0x75,
0x9B, 0x65, 0xE3, 0x72, 0xFC, 0xD6, 0x8E, 0xF2,
0x0F, 0xA7, 0x11, 0x1F, 0x9E, 0x4A, 0xFF, 0x73
Carlson expires December 2001 [Page 15]
