📄 rfc2759.txt
字号:
Network Working Group G. Zorn
Request for Comments: 2759 Microsoft Corporation
Category: Informational January 2000
Microsoft PPP CHAP Extensions, Version 2
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
The Point-to-Point Protocol (PPP) [1] provides a standard method for
transporting multi-protocol datagrams over point-to-point links. PPP
defines an extensible Link Control Protocol and a family of Network
Control Protocols (NCPs) for establishing and configuring different
network-layer protocols.
This document describes version two of Microsoft's PPP CHAP dialect
(MS-CHAP-V2). MS-CHAP-V2 is similar to, but incompatible with, MS-
CHAP version one (MS-CHAP-V1, described in [9]). In particular,
certain protocol fields have been deleted or reused but with
different semantics. In addition, MS-CHAP-V2 features mutual
authentication.
The algorithms used in the generation of various MS-CHAP-V2 protocol
fields are described in section 8. Negotiation and hash generation
examples are provided in section 9.
Specification of Requirements
In this document, the key words "MAY", "MUST, "MUST NOT", "optional",
"recommended", "SHOULD", and "SHOULD NOT" are to be interpreted as
described in [3].
Zorn Informational [Page 1]
RFC 2759 Microsoft MS-CHAP-V2 January 2000
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. LCP Configuration . . . . . . . . . . . . . . . . . . . . . . . 3
3. Challenge Packet . . . . . . . . . . . . . . . . . . . . . . . 3
4. Response Packet . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Success Packet . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Failure Packet . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Change-Password Packet . . . . . . . . . . . . . . . . . . . . 6
8. Pseudocode . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. GenerateNTResponse() . . . . . . . . . . . . . . . . . . . . 7
8.2. ChallengeHash() . . . . . . . . . . . . . . . . . . . . . . . 8
8.3. NtPasswordHash() . . . . . . . . . . . . . . . . . . . . . . 9
8.4. HashNtPasswordHash() . . . . . . . . . . . . . . . . . . . . 9
8.5. ChallengeResponse() . . . . . . . . . . . . . . . . . . . . . 9
8.6. DesEncrypt() . . . . . . . . . . . . . . . . . . . . . . . . 10
8.7. GenerateAuthenticatorResponse() . . . . . . . . . . . . . . . 10
8.8. CheckAuthenticatorResponse() . . . . . . . . . . . . . . . . 12
8.9. NewPasswordEncryptedWithOldNtPasswordHash() . . . . . . . . . 12
8.10. EncryptPwBlockWithPasswordHash() . . . . . . . . . . . . . . 13
8.11. Rc4Encrypt() . . . . . . . . . . . . . . . . . . . . . . . . 13
8.12. OldNtPasswordHashEncryptedWithNewNtPasswordHash() . . . . . 14
8.13. NtPasswordHashEncryptedWithBlock() . . . . . . . . . . . . . 14
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Negotiation Examples . . . . . . . . . . . . . . . . . . . . 14
9.1.1. Successful authentication . . . . . . . . . . . . . . . . . 15
9.1.2. Authenticator authentication failure . . . . . . . . . . . 15
9.1.3. Failed authentication with no retry allowed . . . . . . . . 15
9.1.4. Successful authentication after retry . . . . . . . . . . . 15
9.1.5. Failed hack attack with 3 attempts allowed . . . . . . . . 15
9.1.6. Successful authentication with password change . . . . . . 16
9.1.7. Successful authentication with retry and password change. . 16
9.2. Hash Example . . . . . . . . . . . . . . . . . . . . . . . . 16
9.3. Example of DES Key Generation . . . . . . . . . . . . . . . . 17
10. Security Considerations . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
13. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 19
14. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 20
Zorn Informational [Page 2]
RFC 2759 Microsoft MS-CHAP-V2 January 2000
1. Introduction
Where possible, MS-CHAP-V2 is consistent with both MS-CHAP-V1 and
standard CHAP. Briefly, the differences between MS-CHAP-V2 and MS-
CHAP-V1 are:
* MS-CHAP-V2 is enabled by negotiating CHAP Algorithm 0x81 in LCP
option 3, Authentication Protocol.
* MS-CHAP-V2 provides mutual authentication between peers by
piggybacking a peer challenge on the Response packet and an
authenticator response on the Success packet.
* The calculation of the "Windows NT compatible challenge response"
sub-field in the Response packet has been changed to include the
peer challenge and the user name.
* In MS-CHAP-V1, the "LAN Manager compatible challenge response"
sub-field was always sent in the Response packet. This field has
been replaced in MS-CHAP-V2 by the Peer-Challenge field.
* The format of the Message field in the Failure packet has been
changed.
* The Change Password (version 1) and Change Password (version 2)
packets are no longer supported. They have been replaced with a
single Change-Password packet.
2. LCP Configuration
The LCP configuration for MS-CHAP-V2 is identical to that for
standard CHAP, except that the Algorithm field has value 0x81, rather
than the MD5 value 0x05. PPP implementations which do not support
MS-CHAP-V2, but correctly implement LCP Config-Rej, should have no
problem dealing with this non-standard option.
3. Challenge Packet
The MS-CHAP-V2 Challenge packet is identical in format to the
standard CHAP Challenge packet.
MS-CHAP-V2 authenticators send an 16-octet challenge Value field.
Peers need not duplicate Microsoft's algorithm for selecting the 16-
octet value, but the standard guidelines on randomness [1,2,7] SHOULD
be observed.
Microsoft authenticators do not currently provide information in the
Name field. This may change in the future.
Zorn Informational [Page 3]
RFC 2759 Microsoft MS-CHAP-V2 January 2000
4. Response Packet
The MS-CHAP-V2 Response packet is identical in format to the standard
CHAP Response packet. However, the Value field is sub-formatted
differently as follows:
16 octets: Peer-Challenge
8 octets: Reserved, must be zero
24 octets: NT-Response
1 octet : Flags
The Peer-Challenge field is a 16-octet random number. As the name
implies, it is generated by the peer and is used in the calculation
of the NT-Response field, below. Peers need not duplicate
Microsoft's algorithm for selecting the 16-octet value, but the
standard guidelines on randomness [1,2,7] SHOULD be observed.
The NT-Response field is an encoded function of the password, the
user name, the contents of the Peer-Challenge field and the received
challenge as output by the routine GenerateNTResponse() (see section
8.1, below). The Windows NT password is a string of 0 to
(theoretically) 256 case-sensitive Unicode [8] characters. Current
versions of Windows NT limit passwords to 14 characters, mainly for
compatibility reasons; this may change in the future. When computing
the NT-Response field contents, only the user name is used, without
any associated Windows NT domain name. This is true regardless of
whether a Windows NT domain name is present in the Name field (see
below).
The Flag field is reserved for future use and MUST be zero.
The Name field is a string of 0 to (theoretically) 256 case-sensitive
ASCII characters which identifies the peer's user account name. The
Windows NT domain name may prefix the user's account name (e.g.
"BIGCO\johndoe" where "BIGCO" is a Windows NT domain containing the
user account "johndoe"). If a domain is not provided, the backslash
should also be omitted, (e.g. "johndoe").
5. Success Packet
The Success packet is identical in format to the standard CHAP
Success packet. However, the Message field contains a 42-octet
authenticator response string and a printable message. The format of
the message field is illustrated below.
"S=<auth_string> M=<message>"
Zorn Informational [Page 4]
RFC 2759 Microsoft MS-CHAP-V2 January 2000
The <auth_string> quantity is a 20 octet number encoded in ASCII as
40 hexadecimal digits. The hexadecimal digits A-F (if present) MUST
be uppercase. This number is derived from the challenge from the
Challenge packet, the Peer-Challenge and NT-Response fields from the
Response packet, and the peer password as output by the routine
GenerateAuthenticatorResponse() (see section 8.7, below). The
authenticating peer MUST verify the authenticator response when a
Success packet is received. The method for verifying the
authenticator is described in section 8.8, below. If the
authenticator response is either missing or incorrect, the peer MUST
end the session.
The <message> quantity is human-readable text in the appropriate
charset and language [12].
6. Failure Packet
The Failure packet is identical in format to the standard CHAP
Failure packet. There is, however, formatted text stored in the
Message field which, contrary to the standard CHAP rules, does affect
the operation of the protocol. The Message field format is:
"E=eeeeeeeeee R=r C=cccccccccccccccccccccccccccccccc V=vvvvvvvvvv
M=<msg>"
where
The "eeeeeeeeee" is the ASCII representation of a decimal error
code (need not be 10 digits) corresponding to one of those listed
below, though implementations should deal with codes not on this
list gracefully.
646 ERROR_RESTRICTED_LOGON_HOURS
647 ERROR_ACCT_DISABLED
648 ERROR_PASSWD_EXPIRED
649 ERROR_NO_DIALIN_PERMISSION
691 ERROR_AUTHENTICATION_FAILURE
709 ERROR_CHANGING_PASSWORD
The "r" is an ASCII flag set to '1' if a retry is allowed, and '0'
if not. When the authenticator sets this flag to '1' it disables
short timeouts, expecting the peer to prompt the user for new
credentials and resubmit the response.
The "cccccccccccccccccccccccccccccccc" is the ASCII representation
of a hexadecimal challenge value. This field MUST be exactly 32
octets long and MUST be present.
Zorn Informational [Page 5]
RFC 2759 Microsoft MS-CHAP-V2 January 2000
The "vvvvvvvvvv" is the ASCII representation of a decimal version
code (need not be 10 digits) indicating the password changing
protocol version supported on the server. For MS-CHAP-V2, this
value SHOULD always be 3.
<msg> is human-readable text in the appropriate charset and
language [12].
7. Change-Password Packet
The Change-Password packet does not appear in either standard CHAP or
MS-CHAP-V1. It allows the peer to change the password on the account
specified in the preceding Response packet. The Change-Password
packet should be sent only if the authenticator reports
ERROR_PASSWD_EXPIRED (E=648) in the Message field of the Failure
packet.
This packet type is supported by recent versions of Windows NT 4.0,
Windows 95 and Windows 98. It is not supported by Windows NT 3.5,
Windows NT 3.51, or early versions of Windows NT 4.0, Windows 95 and
Windows 98.
The format of this packet is as follows:
1 octet : Code
1 octet : Identifier
2 octets : Length
516 octets : Encrypted-Password
16 octets : Encrypted-Hash
16 octets : Peer-Challenge
8 octets : Reserved
24 octets : NT-Response
2-octet : Flags
Code
7
Identifier
The Identifier field is one octet and aids in matching requests
and replies. The value is the Identifier of the received Failure
packet to which this packet responds plus 1.
Length
586
Zorn Informational [Page 6]
RFC 2759 Microsoft MS-CHAP-V2 January 2000
Encrypted-Password
This field contains the PWBLOCK form of the new Windows NT
password encrypted with the old Windows NT password hash, as
output by the NewPasswordEncryptedWithOldNtPasswordHash() routine
(see section 8.9, below).
Encrypted-Hash
This field contains the old Windows NT password hash encrypted
with the new Windows NT password hash, as output by the
OldNtPasswordHashEncryptedWithNewNtPasswordHash() routine (see
section 8.12, below).
Peer-Challenge
A 16-octet random quantity, as described in the Response packet
description.
Reserved
8 octets, must be zero.
NT-Response
The NT-Response field (as described in the Response packet
description), but calculated on the new password and the challenge
received in the Failure packet.
Flags
This field is two octets in length. It is a bit field of option
flags where 0 is the least significant bit of the 16-bit quantity.
The format of this field is illustrated in the following diagram:
1
5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -