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RFC2433 - Microsoft PPP CHAP Extensions

王朝other·作者佚名  2008-05-31
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Network Working Group G. Zorn

Request for Comments: 2433 S. Cobb

Category: Informational Microsoft Corporation

October 1998

Microsoft PPP CHAP Extensions

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 (1998). All Rights Reserved.

IESG Note

The protocol described here has significant vulnerabilities. People

planning on implementing or using this protocol should read section

12, "Security Considerations".

1. 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 Microsoft's PPP CHAP dialect (MS-CHAP), which

extends the user authentication functionality provided on Windows

networks to remote workstations. MS-CHAP is closely derived from the

PPP Challenge Handshake Authentication Protocol described in RFC1994

[2], which the reader should have at hand.

The algorithms used in the generation of various MS-CHAP protocol

fields are described in an appendix.

2. 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.

3. 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].

4. 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.

5. 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.

6. 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

LmChallengeResponse() (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

NTChallengeResponse() (see section A.5, 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.

The "use Windows NT compatible challenge response" flag, if 1,

indicates that the Windows NT response is provided and should be used

in preference 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 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 omitted, (e.g. "johndoe").

7. Success Packet

The Success packet is identical in format to the standard CHAP

Success packet.

8. 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

credentials 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

resubmitted response to be calculated based on the previous

challenge value plus decimal 23 in the first octet, i.e. the

one immediately 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

digits) 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 Password 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.

9. 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.

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).

10. 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 Failure packet.

This packet type is supported by Windows NT 3.51, 4.0 and recent

versions 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

password encrypted with the old Windows NT password hash, as

output by the NewPasswordEncryptedWithOldNtPasswordHash()

routine (see section 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

OldNtPasswordHashEncryptedWithNewNtPasswordHash() routine (see

section A.14, below).

Password Encrypted with Old LM Hash

This field contains the PWBLOCK form of the new Windows NT

password 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.

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

OldLmPasswordHashEncryptedWithNewNtPasswordHash() 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).

11. 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 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 password changes) SHOULD be taken in environments

where eavesdropping is likely.

The Change Password (version 1) packet is vulnerable to a passive

eavesdropping attack which can easily reveal the new password hash.

For this reason, it MUST NOT be sent if eavesdropping is possible.

12. 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)", RFC1994, August 1996.

[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement

Levels", BCP 14, RFC2119, 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", RFC1320, 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., Crocker, S., and J. Schiller, "Randomness

Recomnendations for Security", RFC1750, December 1994.

[8] "The Unicode Standard, Version 2.0", The Unicode Consortium,

Addison-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

13. Acknowledgements

Thanks (in no particular order) to Jeff Haag (Jeff_Haag@3com.com),

Bill Palter (palter@network-alchemy.com), Bruce Johnson

(bjohnson@microsoft.com), Tony Bell (tonybe@microsoft.com), Benoit

Martin (ehlija@vircom.com), and Joe Davies (josephd@microsoft.com)

for useful suggestions and feedback.

14. 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

15. 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

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

* 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()

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 )

}

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 )

}

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 )

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,

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

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

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,

however, simply stripping the parity bits. The following example

illustrates 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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