Network Working Group G. Zorn Internet-Draft Microsoft Corporation Category: Informational November 1997 <draft-ietf-radius-mschap-attr-01.txt> RADIUS Attributes for MS-CHAP Support 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 ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow 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-radius-mschap- attr-01.txt> and expires May 21, 1998. Please send comments to the RADIUS Working Group mailing list (ietf-radius@livingston.com) or to the author (glennz@microsoft.com). 2. Abstract This document describes a set of vendor-specific RADIUS attributes designed to support the use of Microsoft's proprietary dialect of PPP CHAP (MS-CHAP) in dial-up networks. MS-CHAP is derived from and (where possible) consistent with PPP CHAP [1]; the differences between PPP CHAP and MS-CHAP are significant enough to warrant the definition of new RADIUS attributes, however. 3. Introduction Microsoft created Microsoft Challenge-Handshake Authentication Protocol (MS-CHAP) to authenticate remote Windows workstations, providing the functionality to which LAN-based users are accustomed. Where possible, Zorn [Page 1]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 MS-CHAP is consistent with standard CHAP, and the differences are easily modularized. 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 Windows NT 3.5, 3.51 and 4.0, Microsoft Windows95, and Microsoft LAN Manager 2.x networking products. The MS-CHAP format does not require the authenticator to store a clear-text or reversibly encrypted password. * MS-CHAP provides an authenticator-controlled authentication retry mechanism. * MS-CHAP provides an authenticator-controlled password changing mechanism. * MS-CHAP defines an extended set of reason-for-failure codes, returned in the Failure packet Message field. The attributes defined in this document reflect these differences. 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. Attributes The following sections describe sub-attributes which may be transmitted in one or more RADIUS attributes of type Vendor-Specific [3]. More than one sub-attribute MAY be transmitted in a single Vendor-Specific Attribute; if this is done, the sub-attributes SHOULD be packed as a sequence of Vendor-Type/Vendor-Length/Value triples following the inital Type, Length and Vendor-ID fields. The Length field of the Vendor-Spe- cific Attribute MUST be set equal to the sum of the Vendor-Length fields of the sub-attributes contained in the Vendor-Specific Attribute, plus six. The Vendor-ID field of the Vendor-Specific Attribute(s) MUST be set to decimal 311 (Microsoft). Zorn [Page 2]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 5.1. MS-CHAP-Challenge Description This Attribute contains the challenge sent by a NAS to a Microsoft Challenge-Handshake Authentication Protocol (MS-CHAP) user. It MAY be used in both Access-Request and Access-Challenge packets. A summary of the MS-CHAP-Challenge Attribute 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Type | Vendor-Length | String... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor-Type 11 for MS-CHAP-Challenge. Vendor-Length > 2 String The String field contains the MS-CHAP challenge. 5.2. MS-CHAP-Response Description This Attribute contains the response value provided by a PPP Microsoft Challenge-Handshake Authentication Protocol (MS-CHAP) user in response to the challenge. It is only used in Access- Request packets. A summary of the MS-CHAP-Response Attribute 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Type | Vendor-Length | Ident | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LM-Response +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Zorn [Page 3]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 LM-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Response(cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NT-Response +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor-Type 1 for MS-CHAP-Response. Vendor-Length 52 Ident Identical to the PPP CHAP Identifier. Flags The Flags field is one octet in length. If the Flags field is one (0x01), the NT-Response field is to be used in preference to the LM-Response field for authentication. The LM-Response field MAY still be used (if non-empty), but the NT-Response SHOULD be tried first. If it is zero, the NT-Response field MUST be ignored and the LM-Response field used. LM-Response The LM-Response field is 24 octets in length and holds an encoded function of the password and the received challenge. If this field is empty, it SHOULD be zero-filled. NT-Response The NT-Response field is 24 octets in length and holds an encoded function of the password and the received challenge. If this field is empty, it SHOULD be zero-filled. Zorn [Page 4]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 5.3. MS-CHAP-Domain Description The MS-CHAP-Domain Attribute indicates the Windows NT domain in which the user was authenticated. It MAY be included in both Access-Accept and Accounting-Request packets. A summary of the MS-CHAP-Domain Attribute format is given below. The fields are transmitted 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Type | Vendor-Length | Ident | String... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor-Type 10 for MS-CHAP-Domain. Vendor-Length > 3 Ident The Ident field is one octet and aids in matching requests and replies. String This field contains the name in ASCII of the Windows NT domain in which the user was authenticated. 5.4. MS-CHAP-Error Description The MS-CHAP-Error Attribute contains error data related to the preceding MS-CHAP exchange. It is only used in Access-Reject packets. A summary of the MS-CHAP-Error Attribute format is given below. The fields are transmitted 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Type | Vendor-Length | Ident | String... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Zorn [Page 5]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 Vendor-Type 2 for MS-CHAP-Error. Vendor-Length > 3 Ident The Ident field is one octet and aids in matching requests and replies. String This field contains up to 48 octets of specially formatted ASCII text, which is interpreted by the authenticating peer. The format of this field is as follows: "E=eeeeeeeeee R=r C=cccccccccccccccc V=vvvvvvvvvv" where the "eeeeeeeeee" represents an ASCII representation of a decimal error code of up to 10 digits corresponding to one of the following: 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 Implementations should deal with codes not on this list grace- fully, however. Please note that (unlike PPP CHAP), the receipt of some of these error codes (in particular, the ERROR_PASSWD_EXPIRED code) will modify the subsequent operation of the MS-CHAP protocol. The 'r' is a retry flag (set to '1' if a retry is allowed and '0' otherwise), the "cccccccccccccccc" repre- sents 16 hexadecimal digits ('0'-'F') specifying a new challenge value, and the "vvvvvvvvvv" is a decimal version code signifying the version of MS-CHAP supported by the server. 5.5. MS-CHAP-CPW-1 Description This Attribute allows the user to change their password if it has expired. This Attribute is only used in Access-Request packets, and should only be included if an MS-CHAP-Error attribute was included in the immediately preceding Access-Reject packet, the String field of the MS-CHAP-Error attribute indicated that the Zorn [Page 6]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 user password had expired, and the MS-CHAP version is less than 2. A summary of the MS-CHAP-CPW-1 Attribute 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Type | Vendor-Length | Code | Ident | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LM-Old-Password +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Old-Password (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Old-Password (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Old-Password (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LM-New-Password +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-New-Password (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-New-Password (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-New-Password (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NT-Old-Password +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Old-Password (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Old-Password (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Old-Password (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NT-New-Password +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-New-Password (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-New-Password (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-New-Password (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | New-LM-Password-Length | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor-Type 3 for MS-CHAP-PW-1 Zorn [Page 7]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 Vendor-Length 72 Code The Code field is one octet in length. Its value is always 5. Ident The Ident field is one octet and aids in matching requests and replies. LM-Old-Password The LM-Old-Password field is 16 octets in length. It contains the encrypted Lan Manager hash of the old password. LM-New-Password The LM-New-Password field is 16 octets in length. It contains the encrypted Lan Manager hash of the new password. NT-Old-Password The NT-Old-Password field is 16 octets in length. It contains the encrypted Lan Manager hash of the old password. NT-New-Password The NT-New-Password field is 16 octets in length. It contains the encrypted Lan Manager hash of the new password. New-LM-Password-Length The New-LM-Password-Length field is two octets in length and con- tains the length in octets of the new LAN Manager-compatible pass- word. Flags The Flags field is two octets in length. If the least significant bit of the Flags field is one, this indicates that the NT-New- Password and NT-Old-Password fields are valid and SHOULD be used. Otherwise, the LM-New-Password and LM-Old-Password fields MUST be used. 5.6. MS-CHAP-CPW-2 Description This Attribute allows the user to change their password if it has expired. This Attribute is only used in Access-Request packets, and should only be included if an MS-CHAP-Error attribute was included in the immediately preceding Access-Reject packet, the String field of the MS-CHAP-Error attribute indicated that the Zorn [Page 8]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 user password had expired, and the MS-CHAP version is 2 or greater. A summary of the MS-CHAP-CPW-2 Attribute 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Type | Vendor-Length | Code | Ident | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Old-NT-Hash +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Old-NT-Hash (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Old-NT-Hash (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Old-NT-Hash (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Old-LM-Hash +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Old-LM-Hash(cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Old-LM-Hash(cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Old-LM-Hash(cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LM-Response +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Response (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NT-Response +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) Zorn [Page 9]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Response (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor-Type 4 for MS-CHAP-PW-2 Vendor-Length 86 Code 6 Ident The Ident field is one octet and aids in matching requests and replies. The value of this field MUST be identical to that in the Ident field in all instances of the MS-CHAP-LM-Enc-PW, MS-CHAP-NT- Enc-PW and MS-CHAP-PW-2 attributes contained in a single Access- Request packet. Old-NT-Hash The Old-NT-Hash field is 16 octets in length. It contains the old Windows NT password hash encrypted with the new Windows NT pass- word hash. Old-LM-Hash The Old-LM-Hash field is 16 octets in length. It contains the old Lan Manager password hash encrypted with the new Windows NT pass- word hash. LM-Response The LM-Response field is 24 octets in length and holds an encoded function of the password and the received challenge. If this field is empty, it SHOULD be zero-filled. NT-Response The NT-Response field is 24 octets in length and holds an encoded function of the password and the received challenge. If this field is empty, it SHOULD be zero-filled. Flags The Flags field is two octets in length. If the least significant bit (bit 0) of this field is one, the NT-Response field is to be used in preference to the LM-Response field for authentication. The LM-Response field MAY still be used (if present), but the NT- Response SHOULD be tried first. If least significant bit of the Zorn [Page 10]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 field is zero, the NT-Response field MUST be ignored and the LM- Response field used instead. If bit 1 of the Flags field is one, the Old-LM-Hash field is valid and SHOULD be used. If this bit is set, at least one instance of the MS-CHAP-LM-Enc-PW attribute MUST be included in the packet. 5.7. MS-CHAP-LM-Enc-PW Description This Attribute contains the new Windows NT password encrypted with the old LAN Manager password hash. The encrypted Windows NT pass- word is 516 octets in length; since this is longer than the maxi- mum lengtth of a RADIUS attribute, the password must be split into several attibutes for transmission. A 2 octet sequence number is included in the attribute to help preserve ordering of the pass- word fragments. This Attribute is only used in Access-Request packets, in conjunc- tion with the MS-CHAP-CPW-2 attribute. It should only be included if an MS-CHAP-Error attribute was included in the immediately pre- ceding Access-Reject packet, the String field of the MS-CHAP-Error attribute indicated that the user password had expired, and the MS-CHAP version is 2 or greater. A summary of the MS-CHAP-LM-Enc-PW Attribute 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Type | Vendor-Length | Code | Ident | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence-Number | String ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor-Type 5 for MS-CHAP-LM-Enc-PW Vendor-Length > 6 Code 6. Code is the same as for the MS-CHAP-PW-2 attribute. Ident The Ident field is one octet and aids in matching requests and Zorn [Page 11]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 replies. The value of this field MUST be identical in all instances of the MS-CHAP-LM-Enc-PW, MS-CHAP-NT-Enc-PW and MS-CHAP- PW-2 attributes which are present in the same Access-Request packet. Sequence-Number The Sequence-Number field is two octets in length and indicates which "chunk" of the encrypted password is contained in the fol- lowing String field. String The String field contains a portion of the encrypted password. 5.8. MS-CHAP-NT-Enc-PW Description This Attribute contains the new Windows NT password encrypted with the old Windows NT password hash. The encrypted Windows NT pass- word is 516 octets in length; since this is longer than the maxi- mum lengtth of a RADIUS attribute, the password must be split into several attibutes for transmission. A 2 octet sequence number is included in the attribute to help preserve ordering of the pass- word fragments. This Attribute is only used in Access-Request packets, in conjunc- tion with the MS-CHAP-CPW-2 attribute. It should only be included if an MS-CHAP-Error attribute was included in the immediately pre- ceding Access-Reject packet, the String field of the MS-CHAP-Error attribute indicated that the user password had expired, and the MS-CHAP version is 2 or greater. A summary of the MS-CHAP-NT-Enc-PW Attribute 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Type | Vendor-Length | Code | Ident | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence-Number | String ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor-Type 6 for MS-CHAP-NT-Enc-PW Vendor-Length Zorn [Page 12]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 > 6 Code 6. Code is the same as for the MS-CHAP-PW-2 attribute. Ident The Ident field is one octet and aids in matching requests and replies. The value of this field MUST be identical in all instances of the MS-CHAP-LM-Enc-PW, MS-CHAP-NT-Enc-PW and MS-CHAP- PW-2 attributes which are present in the same Access-Request packet. Sequence-Number The Sequence-Number field is two octets in length and indicates which "chunk" of the encrypted password is contained in the fol- lowing String field. String The String field contains a portion of the encrypted password. 5.9. MS-CHAP-MPPE-Keys Description The MS-CHAP-MPPE-Keys Attribute contains two session keys for use by the Microsoft Point-to-Point Encryption Protocol (MPPE). This Attribute is only included in Access-Accept packets. Note that the keys are generative session keys; no processing need be done by the RADIUS client before using the keys in the MPPE protocol. A summary of the MS-CHAP-MPPE-Keys Attribute format is given below. The fields are transmitted 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vendor-Type | Vendor-Length | Keys +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Keys (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Keys (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Keys (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Keys (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Keys (cont) Zorn [Page 13]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Keys (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Keys (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Keys (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Vendor-Type 12 for MS-CHAP-MPPE-Keys. Vendor-Length 34 Keys The Keys field consists of two logical sub-fields: the LM-Key and the NT-Key. The LM-Key is eight octets in length and is derived from the first eight bytes of the hashed LAN Manager password. The NT-Key sub-field is sixteen octets in length and is derived from the first sixteen octets of the hashed Windows NT password. The format of the plaintext Keys field is illustrated in the fol- lowing diagram: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LM-Key +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ LM-Key (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | NT-Key +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Key (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Key (cont) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ NT-Key (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Padding +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Padding (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Keys field MUST be encrypted by the RADIUS server using the same method defined for the User-Password Attribute [3]. Note that the padding is required because the method referenced above requires the field to be encrypted to be a multiple of sixteen octets in length. Zorn [Page 14]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 6. Table of Attributes The following table provides a guide to which of the above attributes may be found in which kinds of packets, and in what quantity. Request Accept Reject Challenge Acct-Request # Attribute 0+ 0 0 0+ 0 11 MS-CHAP-Challenge 0+ 0 0 0 0 1 MS-CHAP-Response 0 0+ 0 0 0+ 10 MS-CHAP-Domain 0 0 0+ 0 0 2 MS-CHAP-Error 0+ 0 0 0 0 3 MS-CHAP-CPW-1 0+ 0 0 0 0 4 MS-CHAP-CPW-2 0+ 0 0 0 0 5 MS-CHAP-LM-Enc-PW 0+ 0 0 0 0 6 MS-CHAP-NT-Enc-PW 0 0+ 0 0 0 12 MS-CHAP-MPPE-Keys The following table defines the meaning of the above table entries. 0 This attribute MUST NOT be present in packet. 0+ Zero or more instances of this attribute MAY be present in packet. 0-1 Zero or one instance of this attribute MAY be present in packet. 7. Security Considerations MS-CHAP, like PPP CHAP, is susceptible to dictionary attacks. User passwords should be chosen with care, and be of sufficient length to deter easy guessing. Although the scheme used to protect the Keys field of the MS-CHAP-MPPE-Keys Attribute is believed to be relatively secure on the wire, RADIUS proxies will decrypt and re-encrypt the field for forwarding. Therefore, the MS-CHAP-MPPE-Keys attribute SHOULD NOT be used on networks where untrusted RADIUS proxies reside. 8. Acknowledgements Thanks to Carl Rigney (cdr@livingston.com), Narendra Gidwani (nareng@microsoft.com), Steve Cobb (stevec@microsoft.com), Pat Calhoun (pcalhoun@usr.com), Dave Mitton (dmitton@baynetworks.com), Paul Funk (paul@funk.com), Gurdeep Singh Pall (gurdeep@microsoft.com) and Don Rule (donaldr@microsoft.com) for useful suggestions and editorial feedback. 9. Expiration Date This document expires May 21, 1998. Zorn [Page 15]
INTERNET-DRAFT MS-CHAP RADIUS Attributes October 1997 10. Chair's Address The RADIUS Working Group can be contacted via the current chair: Carl Rigney Livingston Enterprises 4464 Willow Road Pleasanton, California 94588 Phone: +1 510 426 0770 E-Mail: cdr@livingston.com 11. Author's Address 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 12. References [1] Simpson, W., "PPP Challenge Handshake Authentication Protocol (CHAP)", RFC 1994, August 1996 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997 [3] Rigney, C., et. al., "Remote Access Dial In User Service", RFC 2138, April 1997 Zorn [Page 16]
