Microsoft PPP CHAP Extensions
draft-ietf-pppext-mschap-00
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 2433.
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|---|---|---|---|
| Authors | Glen Zorn , Steve Cobb | ||
| Last updated | 2013-03-02 (Latest revision 1998-03-11) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 2433 (Informational) | |
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draft-ietf-pppext-mschap-00
Network Working Group G. Zorn
Internet-Draft S. Cobb
Category: Informational Microsoft Corporation
<draft-ietf-pppext-mschap-00.txt> March 1998
Microsoft PPP CHAP Extensions
1. Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working docu-
ments of the Internet Engineering Task Force (IETF), its areas, and its
working groups. Note that other groups may also distribute working doc-
uments as 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''.
To learn the current status of any Internet-Draft, please check the
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Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe),
ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. The distribution of
this memo is unlimited. It is filed as <draft-ietf-pppext-
mschap-00.txt> and expires September 13, 1998. Please send comments to
the PPP Extensions Working Group mailing list (ietf-ppp@merit.edu) or to
the authors (stevec@microsoft.com and glennz@microsoft.com).
2. 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 Con-
trol Protocols (NCPs) for establishing and configuring different net-
work-layer protocols.
This document describes Microsoft's PPP CHAP dialect (MS-CHAP), which
extends the user authentication functionality provided on Windows net-
works to remote workstations. MS-CHAP is closely derived from the PPP
Challenge Handshake Authentication Protocol described in RFC 1994 [2],
which the reader should have at hand.
The algorithms used in the generation of various MS-CHAP protocol fields
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are described in an appendix.
3. Introduction
Microsoft created MS-CHAP to authenticate remote Windows workstations,
providing the functionality to which LAN-based users are accustomed
while integrating the encryption and hashing algorithms used on Windows
networks.
Where possible, MS-CHAP is consistent with standard CHAP. Briefly, the
differences between MS-CHAP and standard CHAP are:
* MS-CHAP is enabled by negotiating CHAP Algorithm 0x80 in LCP
option 3, Authentication Protocol.
* The MS-CHAP Response packet is in a format designed for
compatibility with Microsoft's Windows NT 3.5, 3.51 and 4.0, and
Windows95 networking products. The MS-CHAP format does not require
the authenticator to store a clear- text or reversibly encrypted
password.
* MS-CHAP provides authenticator-controlled authentication retry and
password changing mechanisms.
* MS-CHAP defines a set of reason-for-failure codes returned in the
Failure packet Message field.
4. 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 [2].
5. LCP Configuration
The LCP configuration for MS-CHAP is identical to that for standard
CHAP, except that the Algorithm field has value 0x80, rather than the
MD5 value 0x05. PPP implementations which do not support MS-CHAP, but
correctly implement LCP Config-Rej, should have no problem dealing with
this non-standard option.
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6. Challenge Packet
The MS-CHAP Challenge packet is identical in format to the standard CHAP
Challenge packet.
MS-CHAP authenticators send an 8-octet challenge Value field. Peers
need not duplicate Microsoft's algorithm for selecting the 8-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.
7. Response Packet
The MS-CHAP Response packet is identical in format to the standard CHAP
Response packet. However, the Value field is sub-formatted differently
as follows:
24 octets: LAN Manager compatible challenge response
24 octets: Windows NT compatible challenge response
1 octet : "Use Windows NT compatible challenge response" flag
The LAN Manager compatible challenge response is an encoded function of
the password and the received challenge as output by the routine LmChal-
lengeResponse() (see section A.1, below). LAN Manager passwords are
limited to 14 case-insensitive OEM characters. Note that use of the LAN
Manager compatible challenge response has been deprecated; peers SHOULD
NOT generate it, and the sub-field SHOULD be zero-filled. The algorithm
used in the generation of the LAN Manager compatible challenge response
is described here for informational purposes only.
The Windows NT compatible challenge response is an encoded function of
the password and the received challenge as output by the routine NTChal-
lengeResponse() (see section A.5, below). The Windows NT password is a
string of 0 to (theoretically) 256 case-sensitive Unicode [8] charac-
ters. Current versions of Windows NT limit passwords to 14 characters,
mainly for compatibility reasons; this may change in the future.
The "use Windows NT compatible challenge response" flag, if 1, indicates
that the Windows NT response is provided and should be used in prefer-
ence to the LAN Manager response. The LAN Manager response will still
be used if the account does not have a Windows NT password hash, e.g.
if the password has not been changed since the account was uploaded from
a LAN Manager 2.x account database. If the flag is 0, the Windows NT
response is ignored and the LAN Manager response is used. Since the use
of LAN Manager authentication has been deprecated, this flag SHOULD
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always be set (1) and the LAN Manager compatible challenge response
field SHOULD be zero-filled.
The Name field 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 "john-
doe"). If a domain is not provided, the backslash should also be omit-
ted, (e.g. "johndoe").
8. Success Packet
The Success packet is identical in format to the standard CHAP Success
packet.
9. 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, affects the protocol. The
Message field format is:
"E=eeeeeeeeee R=r C=cccccccccccccccc V=vvvvvvvvvv"
where
The "eeeeeeeeee" is the 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 a 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 cre-
dentials and resubmit the response.
The "cccccccccccccccc" is 16 hexadecimal digits representing an
ASCII representation of a new challenge value. This field is
optional. If it is not sent, the authenticator expects the resub-
mitted response to be calculated based on the previous challenge
value plus decimal 23 in the first octet, i.e. the one immediately
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following the Value Size field. Windows 95 authenticators may
send this field. Windows NT authenticators do not, but may in the
future. Both systems implement peer support of this field.
The "vvvvvvvvvv" is the decimal version code (need not be 10 dig-
its) indicating the MS-CHAP protocol version supported on the
server. Currently, this is interesting only in selecting a Change
Password packet type. If the field is not present the version
should be assumed to be 1; since use of the version 1 Change Pass-
word packet has been deprecated, this field SHOULD always contain
a value greater than or equal to 2.
Implementations should accept but ignore additional text they do not
recognize.
10. Change Password Packet (version 1)
The version 1 Change Password packet does not appear in standard CHAP.
It allows the peer to change the password on the account specified in
the previous Response packet. The version 1 Change Password packet
should be sent only if the authenticator reports ERROR_PASSWD_EXPIRED
(E=648) and V is either missing or equal to one in the Message field of
the Failure packet.
The use of the Change Password Packet (version 1) has been deprecated;
the format of the packet is described here for informational purposes,
but peers SHOULD NOT transmit it.
The format of this packet is as follows:
1 octet : Code (=5)
1 octet : Identifier
2 octets: Length (=72)
16 octets: Encrypted LAN Manager Old password Hash
16 octets: Encrypted LAN Manager New Password Hash
16 octets: Encrypted Windows NT Old Password Hash
16 octets: Encrypted Windows NT New Password Hash
2 octets: Password Length
2 octets: Flags
Code
5
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.
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Length
72
Encrypted LAN Manager New Password Hash
Encrypted LAN Manager Old Password Hash
These fields contain the LAN Manager password hash of the new and
old passwords encrypted with the last received challenge value, as
output by the routine LmEncryptedPasswordHash() (see section A.8,
below).
Encrypted Windows NT New Password Hash
Encrypted Windows NT Old Password Hash
These fields contain the Windows NT password hash of the new and
old passwords encrypted with the last received challenge value, as
output by the pseudo-code routine NtEncryptedPasswordHash() (see
section A.10, below).
Password Length
The length in octets of the LAN Manager compatible form of the new
password. If this value is greater than or equal to zero and less
than or equal to 14 it is assumed that the encrypted LAN Manager
password hash fields are valid. Otherwise, it is assumed these
fields are not valid, in which case the Windows NT compatible
passwords MUST be provided.
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:
Bit 0
If this bit is set (1), it indicates that the encrypted Windows NT
hashed passwords are valid and should be used.
If this bit is cleared (0), the Windows NT fields are not used and
the LAN Manager fields must be provided.
Bits 1-15
Reserved, always clear (0).
11. Change Password Packet (version 2)
The version 2 Change Password packet does not appear in standard CHAP.
It allows the peer to change the password on the account specified in
the preceding Response packet. The version 2 Change Password packet
should be sent only if the authenticator reports ERROR_PASSWD_EXPIRED
(E=648) and a version of 2 or greater in the Message field of the Fail-
ure packet.
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This packet type is supported by Windows NT 3.51, 4.0 and recent ver-
sions of Windows 95. It is not supported by Windows NT 3.5 or early
versions of Windows 95.
The format of this packet is as follows:
1 octet : Code
1 octet : Identifier
2 octets : Length
516 octets : Password Encrypted with Old NT Hash
16 octets : Old NT Hash Encrypted with New NT Hash
516 octets : Password Encrypted with Old LM Hash
16 octets : Old LM Hash Encrypted With New NT Hash
24 octets : LAN Manager compatible challenge response
24 octets : Windows NT compatible challenge response
2-octet : Flags
Code
6
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
1118
Password Encrypted with Old NT Hash
This field contains the PWBLOCK form of the new Windows NT pass-
word encrypted with the old Windows NT password hash, as output by
the NewPasswordEncryptedWithOldNtPasswordHash() routine (see sec-
tion A.11, below).
Old NT Hash Encrypted with New NT Hash
This field contains the old Windows NT password hash encrypted
with the new Windows NT password hash, as output by the OldNtPass-
wordHashEncryptedWithNewNtPasswordHash() routine (see section
A.14, below).
Password Encrypted with Old LM Hash
This field contains the PWBLOCK form of the new Windows NT pass-
word encrypted with the old LAN Manager password hash, as output
by the NewPasswordEncryptedWithOldLmPasswordHash() routine
described in section A.15, below. Note, however, that the use of
this field has been deprecated: peers SHOULD NOT generate it, and
this field SHOULD be zero-filled.
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Old LM Hash Encrypted With New NT Hash
This field contains the old LAN Manager password hash encrypted
with the new Windows NT password hash, as output by the OldLmPass-
wordHashEncryptedWithNewNtPasswordHash() routine (see section
A.16, below). Note, however, that the use of this field has been
deprecated: peers SHOULD NOT generate it, and this field SHOULD be
zero-filled.
LAN Manager compatible challenge response
Windows NT compatible challenge response
The challenge response field (as described in the Response packet
description), but calculated on the new password and the same
challenge used in the last response. Note that use of the LAN
Manager compatible challenge response has been deprecated; peers
SHOULD NOT generate it, and the field SHOULD be zero-filled.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Bit 0
The "use Windows NT compatible challenge response" flag as
described in the Response packet.
Bit 1
Set (1) indicates that the "Password Encrypted with Old LM
Hash" and "Old LM Hash Encrypted With New NT Hash" fields
are valid and should be used. Clear (0) indicates these
fields are not valid. This bit SHOULD always be clear (0).
Bits 2-15
Reserved, always clear (0).
12. Security Considerations
As an implementation detail, the authenticator SHOULD limit the number
of password retries allowed to make brute-force password guessing
attacks more difficult.
Because the challenge value is encrypted using the password hash to form
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the response and the challenge is transmitted in clear-text form, both
passive known-plaintext and active chosen-plaintext attacks against the
password hash are possible. Suitable precautions (i.e., frequent pass-
word changes) SHOULD be taken in environments where eavesdropping is
likely.
The Change Password (version 1) packet is vulnerable to a passive eaves-
dropping attack which can easily reveal the new password hash. For this
reason, it MUST NOT be sent if eavesdropping is possible.
13. References
[1] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661,
July 1994
[2] Simpson, W., "PPP Challenge Handshake Authentication Protocol
(CHAP)", RFC 1994, August 1996
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
[4] "Data Encryption Standard (DES)", Federal Information Processing
Standard Publication 46-2, National Institute of Standards and
Technology, December 1993
[5] Rivest, R., "MD4 Message Digest Algorithm", RFC 1320, April 1992.
[6] RC4 is a proprietary encryption algorithm available under license
from RSA Data Security Inc. For licensing information, contact:
RSA Data Security, Inc.
100 Marine Parkway
Redwood City, CA 94065-1031
[7] Eastlake, D., et. al., "Randomness Recomnendations for Security",
RFC 1750, December 1994
[8] "The Unicode Standard, Version 2.0", The Unicode Consortium, Addi-
son-Wesley, 1996. ISBN 0-201-48345-9.
[9] "DES Modes of Operation", Federal Information Processing Standards
Publication 81, National Institute of Standards and Technology,
December 1980
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14. Acknowledgements
Thanks (in no particular order) to Jeff Haag (Jeff_Haag@3com.com), Bill
Palter (palter@network-alchemy.com), Bruce Johnson (bjohn-
son@microsoft.com), Tony Bell (tonybe@microsoft.com), Benoit Martin
(ehlija@vircom.com), and Joe Davies (josephd@microsoft.com) for useful
suggestions and feedback.
15. Chair's Address
The PPP Extensions Working Group can be contacted via the current chair:
Karl Fox
Ascend Communications
3518 Riverside Drive
Suite 101
Columbus, OH 43221
Phone: +1 614 326 6841
Email: karl@ascend.com
16. Authors' Addresses
Questions about this memo can also be directed to:
Glen Zorn
Microsoft Corporation
One Microsoft Way
Redmond, Washington 98052
Phone: +1 425 703 1559
FAX: +1 425 936 7329
EMail: glennz@microsoft.com
Steve Cobb
Microsoft Corporation
One Microsoft Way
Redmond, Washington 98052
EMail: stevec@microsoft.com
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17. Expiration Date
This memo is filed as <draft-ietf-pppext-mschap-00.txt> and expires on
September 13, 1998.
Appendix A - Pseudocode
The routines mentioned in the text are described in pseudocode below.
A.1 LmChallengeResponse()
LmChallengeResponse(
IN 8-octet Challenge,
IN 0-to-14-oem-char Password,
OUT 24-octet Response )
{
LmPasswordHash( Password, giving PasswordHash )
ChallengeResponse( Challenge, PasswordHash, giving Response )
}
A.2 LmPasswordHash()
LmPasswordHash(
IN 0-to-14-oem-char Password,
OUT 16-octet PasswordHash )
{
Set UcasePassword to the uppercased Password
Zero pad UcasePassword to 14 characters
DesHash( 1st 7-octets of UcasePassword,
giving 1st 8-octets of PasswordHash )
DesHash( 2nd 7-octets of UcasePassword,
giving 2nd 8-octets of PasswordHash )
}
A.3 DesHash()
DesHash(
IN 7-octet Clear,
OUT 8-octet Cypher )
{
/*
* Make Cypher an irreversibly encrypted form of Clear by
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* encrypting known text using Clear as the secret key.
* The known text consists of the string
*
* KGS!@#$%
*/
Set StdText to "KGS!@#$%"
DesEncrypt( StdText, Clear, giving Cypher )
}
A.4 DesEncrypt()
DesEncrypt(
IN 8-octet Clear,
IN 7-octet Key,
OUT 8-octet Cypher )
{
/*
* Use the DES encryption algorithm [4] in ECB mode [9]
* to encrypt Clear into Cypher such that Cypher can
* only be decrypted back to Clear by providing Key.
* Note that the DES algorithm takes as input a 64-bit
* stream where the 8th, 16th, 24th, etc. bits are
* parity bits ignored by the encrypting algorithm.
* Unless you write your own DES to accept 56-bit input
* without parity, you will need to insert the parity bits
* yourself.
*/
}
A.5 NtChallengeResponse()
NtChallengeResponse(
IN 8-octet Challenge,
IN 0-to-256-unicode-char Password,
OUT 24-octet Response )
{
NtPasswordHash( Password, giving PasswordHash )
ChallengeResponse( Challenge, PasswordHash, giving Response )
}
A.6 NtPasswordHash()
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NtPasswordHash(
IN 0-to-256-unicode-char Password,
OUT 16-octet PasswordHash )
{
/*
* Use the MD4 algorithm [5] to irreversibly hash Password
* into PasswordHash. Only the password is hashed without
* including any terminating 0.
*/
}
A.7 ChallengeResponse()
ChallengeResponse(
IN 8-octet Challenge,
IN 16-octet PasswordHash,
OUT 24-octet Response )
{
Set ZPasswordHash to PasswordHash zero-padded to 21 octets
DesEncrypt( Challenge,
1st 7-octets of ZPasswordHash,
giving 1st 8-octets of Response )
DesEncrypt( Challenge,
2nd 7-octets of ZPasswordHash,
giving 2nd 8-octets of Response )
DesEncrypt( Challenge,
3rd 7-octets of ZPasswordHash,
giving 3rd 8-octets of Response )
}
A.8 LmEncryptedPasswordHash()
LmEncryptedPasswordHash(
IN 0-to-14-oem-char Password,
IN 8-octet KeyValue,
OUT 16-octet Cypher )
{
LmPasswordHash( Password, giving PasswordHash )
PasswordHashEncryptedWithBlock( PasswordHash,
KeyValue,
giving Cypher )
}
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A.9 PasswordHashEncryptedWithBlock()
PasswordHashEncryptedWithBlock(
IN 16-octet PasswordHash,
IN 8-octet Block,
OUT 16-octet Cypher )
{
DesEncrypt( 1st 8-octets PasswordHash,
1st 7-octets Block,
giving 1st 8-octets Cypher )
DesEncrypt( 2nd 8-octets PasswordHash,
1st 7-octets Block,
giving 2nd 8-octets Cypher )
}
A.10 NtEncryptedPasswordHash()
NtEncryptedPasswordHash( IN 0-to-14-oem-char Password IN 8-octet
Challenge OUT 16-octet Cypher ) {
NtPasswordHash( Password, giving PasswordHash )
PasswordHashEncryptedWithBlock( PasswordHash,
Challenge,
giving Cypher )
}
A.11 NewPasswordEncryptedWithOldNtPasswordHash()
datatype-PWBLOCK
{
256-unicode-char Password
4-octets PasswordLength
}
NewPasswordEncryptedWithOldNtPasswordHash(
IN 0-to-256-unicode-char NewPassword,
IN 0-to-256-unicode-char OldPassword,
OUT datatype-PWBLOCK EncryptedPwBlock )
{
NtPasswordHash( OldPassword, giving PasswordHash )
EncryptPwBlockWithPasswordHash( NewPassword,
PasswordHash,
giving EncryptedPwBlock )
}
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A.12 EncryptPwBlockWithPasswordHash()
EncryptPwBlockWithPasswordHash(
IN 0-to-256-unicode-char Password,
IN 16-octet PasswordHash,
OUT datatype-PWBLOCK PwBlock )
{
Fill ClearPwBlock with random octet values
PwSize = lstrlenW( Password ) * sizeof( unicode-char )
PwOffset = sizeof( ClearPwBlock.Password ) - PwSize
Move PwSize octets to (ClearPwBlock.Password + PwOffset ) from Password
ClearPwBlock.PasswordLength = PwSize
Rc4Encrypt( ClearPwBlock,
sizeof( ClearPwBlock ),
PasswordHash,
sizeof( PasswordHash ),
giving PwBlock )
}
A.13 Rc4Encrypt()
Rc4Encrypt(
IN x-octet Clear,
IN integer ClearLength,
IN y-octet Key,
IN integer KeyLength,
OUT x-octet Cypher )
{
/*
* Use the RC4 encryption algorithm [6] to encrypt Clear of
* length ClearLength octets into a Cypher of the same length
* such that the Cypher can only be decrypted back to Clear
* by providing a Key of length KeyLength octets.
*/
}
A.14 OldNtPasswordHashEncryptedWithNewNtPasswordHash()
OldNtPasswordHashEncryptedWithNewNtPasswordHash(
IN 0-to-256-unicode-char NewPassword,
IN 0-to-256-unicode-char OldPassword,
OUT 16-octet EncryptedPasswordHash )
{
NtPasswordHash( OldPassword, giving OldPasswordHash )
NtPasswordHash( NewPassword, giving NewPasswordHash )
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NtPasswordHashEncryptedWithBlock( OldPasswordHash,
NewPasswordHash,
giving EncryptedPasswordHash )
}
A.15 NewPasswordEncryptedWithOldLmPasswordHash()
NewPasswordEncryptedWithOldLmPasswordHash(
IN 0-to-256-unicode-char NewPassword,
IN 0-to-256-unicode-char OldPassword,
OUT datatype-PWBLOCK EncryptedPwBlock )
{
LmPasswordHash( OldPassword, giving PasswordHash )
EncryptPwBlockWithPasswordHash( NewPassword, PasswordHash,
giving EncryptedPwBlock )
}
A.16 OldLmPasswordHashEncryptedWithNewNtPasswordHash()
OldLmPasswordHashEncryptedWithNewNtPasswordHash(
IN 0-to-256-unicode-char NewPassword,
IN 0-to-256-unicode-char OldPassword,
OUT 16-octet EncryptedPasswordHash )
{
LmPasswordHash( OldPassword, giving OldPasswordHash )
NtPasswordHash( NewPassword, giving NewPasswordHash )
NtPasswordHashEncryptedWithBlock( OldPasswordHash, NewPasswordHash,
giving EncrytptedPasswordHash )
}
A.17 NtPasswordHashEncryptedWithBlock()
NtPasswordHashEncryptedWithBlock(
IN 16-octet PasswordHash,
IN 16-octet Block,
OUT 16-octet Cypher )
{
DesEncrypt( 1st 8-octets PasswordHash,
1st 7-octets Block,
giving 1st 8-octets Cypher )
DesEncrypt( 2nd 8-octets PasswordHash,
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2nd 7-octets Block,
giving 2nd 8-octets Cypher )
}
Appendix B - Examples
B.1 Negotiation Examples
Here are some examples of typical negotiations. The peer is on the left
and the authenticator is on the right.
The packet sequence ID is incremented on each authentication retry
Response and on the change password response. All cases where the
packet sequence ID is updated are noted below.
Response retry is never allowed after Change Password. Change Password
may occur after Response retry. The implied challenge form is shown in
the examples, though all cases of "first challenge+23" should be
replaced by the "C=cccccccccccccccc" challenge if authenticator supplies
it in the Failure packet.
B.1.1 Successful authentication
<- Challenge
Response ->
<- Success
B.1.2 Failed authentication with no retry allowed
<- Challenge
Response ->
<- Failure (E=691 R=0)
B.1.3 Successful authentication after retry
<- Challenge
Response ->
<- Failure (E=691 R=1), disable short timeout
Response (++ID) to first challenge+23 ->
<- Success
B.1.4 Failed hack attack with 3 attempts allowed
<- Challenge
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Response ->
<- Failure (E=691 R=1), disable short timeout
Response (++ID) to first challenge+23 ->
<- Failure (E=691 R=1), disable short timeout
Response (++ID) to first challenge+23+23 ->
<- Failure (E=691 R=0)
B.1.5 Successful authentication with password change
<- Challenge
Response ->
<- Failure (E=648 R=0 V=2), disable short timeout
ChangePassword (++ID) to first challenge ->
<- Success
B.1.6 Successful authentication with retry and password change
<- Challenge
Response ->
<- Failure (E=691 R=1), disable short timeout
Response (++ID) to first challenge+23 ->
<- Failure (E=648 R=0 V=2), disable short timeout
ChangePassword (++ID) to first challenge+23 ->
<- Success
B.2 Hash Example
Intermediate values for password "MyPw".
8-octet Challenge:
10 2D B5 DF 08 5D 30 41
0-to-256-unicode-char NtPassword:
4D 00 79 00 50 00 77 00
16-octet NtPasswordHash:
FC 15 6A F7 ED CD 6C 0E DD E3 33 7D 42 7F 4E AC
24-octet NtChallengeResponse:
4E 9D 3C 8F 9C FD 38 5D 5B F4 D3 24 67 91 95 6C
A4 C3 51 AB 40 9A 3D 61
B.3 Example of DES Key Generation
DES uses 56-bit keys, expanded to 64 bits by the insertion of parity
bits. After the parity of the key has been fixed, every eighth bit is a
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parity bit and the number of bits that are set (1) in each octet is odd;
i.e., odd parity. Note that many DES engines do not check parity, how-
ever, simply stripping the parity bits. The following example illus-
trates the values resulting from the use of the 16-octet NTPasswordHash
shown in Appendix B.2 to generate a pair of DES keys (e.g., for use in
the NtPasswordHashEncryptedWithBlock() described in Appendix A.17).
16-octet NtPasswordHash:
FC 15 6A F7 ED CD 6C 0E DD E3 33 7D 42 7F 4E AC
First "raw" DES key (initial 7 octets of password hash):
FC 15 6A F7 ED CD 6C
First parity-corrected DES key (eight octets):
FD 0B 5B 5E 7F 6E 34 D9
Second "raw" DES key (second 7 octets of password hash)
0E DD E3 33 7D 42 7F
Second parity-corrected DES key (eight octets):
0E 6E 79 67 37 EA 08 FE
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