PPPEXT Working Group Vivek Kamath INTERNET-DRAFT Ashwin Palekar Category: Informational Microsoft <draft-kamath-pppext-eap-mschapv2-00.txt> 2 September 2002 Microsoft EAP CHAP Extensions This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document defines the Microsoft EAP CHAP Extensions Protocol, Version 2, which encapsulates the MS-CHAP-v2 protocol, defined in [RFC2759], within EAP. Kamath & Palekar Informational [Page 1]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 Table of Contents 1. Introduction .......................................... 3 1.1 Requirements language ........................... 3 1.2 Terminology ..................................... 3 2. EAP MS-CHAP-v2 Packet Format .......................... 4 2.1. Challenge packet ................................ 5 2.2. Response packet ................................. 7 2.3. Success Request packet .......................... 9 2.4. Success Response packet ......................... 11 2.5. Failure Request packet .......................... 12 2.6. Failure Response packet ......................... 14 2.7. Change-Password packet .......................... 15 2.8. Alternative failure behavior .................... 17 2.9. Known bugs ...................................... 17 3. Normative references ..................................... 18 4. Informative references ................................... 19 Appendix A - Examples ........................................ 20 Acknowledgments .............................................. 23 Author Addresses ............................................. 23 Full copyright statement ..................................... 23 Kamath & Palekar Informational [Page 2]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 1. Introduction The Extensible Authentication Protocol (EAP), described in [RFC2284], provides a standard mechanism for support of multiple authentication methods. Through the use of EAP, support for a number of authentication schemes may be added, including smart cards, Kerberos, Public Key, One Time Passwords, and others. This document defines the Microsoft EAP CHAP Extensions Protocol, Version 2, which encapsulates the MS-CHAP-v2 protocol, defined in [RFC2759], within EAP. As with MS-CHAP-v2, EAP-MSCHAPv2 supports mutual authentication and key derivation. The way EAP-MSCHAPv2 derived keys are used with the Microsoft Point to Point Encryption (MPPE) cipher is described in [RFC3079]. EAP 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. 1.1. Requirements language In this document, several words are used to signify the requirements of the specification. These words are often capitalized. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 1.2. Terminology This document frequently uses the following terms: Authenticator The end of the link requiring the authentication. Peer The other end of the point-to-point link; the end which is being authenticated by the authenticator. silently discard This means the implementation discards the packet without further processing. The implementation SHOULD provide the capability of logging the error, including the contents of the silently discarded packet, and SHOULD record the event in a statistics counter. Kamath & Palekar Informational [Page 3]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 2. EAP MS-CHAP-v2 Packet Format A summary of the EAP MS-CHAP-V2 packet format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | OpCode | MS-CHAPv2-ID | MS-Length... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MS-Length | Data... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 1 - Request 2 - Response Identifier The Identifier field is one octet and aids in matching responses with requests. Length The Length field is two octets and indicates the length of the EAP packet including the Code, Identifier, Length, Type, OpCode, MS- CHAPv2-ID, MS-Length and Data fields. Octets outside the range of the Length field should be treated as Data Link Layer padding and should be ignored on reception. Type 26 - EAP MS-CHAP-V2 OpCode The OpCode field is one octet and identifies the type of EAP MS-CHAP- v2 packet. OpCodes are assigned as follows: 1 Challenge 2 Response 3 Success 4 Failure 7 Change-Password Kamath & Palekar Informational [Page 4]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 MS-CHAPv2-ID The MS-CHAPv2-ID field is one octet and aids in matching MSCHAP-v2 responses with requests. Typically, the MS-CHAPv2-ID field is the same as the Identifier field. MS-Length The MS-Length field is two octets and MUST be set to the value of the Length field minus 5. Data The format of the Data field is determined by the OpCode field. 2.1. Challenge packet The Challenge packet is used to begin the EAP MS-CHAP-V2 protocol. The authenticator MUST transmit an EAP Request packet with Type=26, and the OpCode field set to 1 (Challenge). The format of the EAP MS-CHAP-v2 Challenge packet is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | OpCode | MS-CHAPv2-ID | MS-Length... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MS-Length | Value-Size | Challenge... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Challenge... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Name... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 1 - Request Identifier The Identifier field is one octet. The Identifier field MUST be the same if a Request packet is retransmitted due to a timeout while waiting for a Response. Any new (non-retransmission) Requests MUST modify the Identifier field. If a peer receives a duplicate Request for which it has already sent a Response, it MUST resend it's Kamath & Palekar Informational [Page 5]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 Response. If a peer receives a duplicate Request before it has sent a Response to the initial Request (i.e. it's waiting for user input), it MUST silently discard the duplicate Request. Length The Length field is two octets and indicates the length of the EAP packet including the Code, Identifier, Length, Type, OpCode, MS- CHAPv2-ID, MS-Length, Value-Size, Challenge, and Name fields. Octets outside the range of the Length field should be treated as Data Link Layer padding and should be ignored on reception. Type 26 - EAP MS-CHAP-V2 OpCode 1 - Challenge MS-CHAPv2-ID The MS-CHAPv2-ID field is one octet and aids in matching MSCHAP-v2 responses with requests. Typically, the MS-CHAPv2-ID field is the same as the Identifier field. MS-Length The MS-Length field is two octets and MUST be set to the value of the Length field minus 5. Value-Size This field is one octet and indicates the length of the Challenge field. Since EAP MS-CHAPv2 utilizes a 16 octet Challenge field, it is set to 0x10 (16 decimal). Challenge The Challenge field is 16 octets. The most significant octet is transmitted first. The Challenge MUST be changed each time a Challenge is sent. Name The Name field is one or more octets representing the identification of the system transmitting the packet. There are no limitations on the content of this field. The Name should not be NUL or CR/LF Kamath & Palekar Informational [Page 6]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 terminated. The size of the Name field is equal to Length - Value- Size - 10. 2.2. Response packet The format of the EAP MS-CHAP-v2 Response packet is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | OpCode | MS-CHAPv2-ID | MS-Length... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MS-Length | Value-Size | Response... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Response... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Name... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 2 - Response Identifier The Identifier field is one octet and contains the value included in the EAP Request to which it responds. Length The Length field is two octets and indicates the length of the EAP packet including the Code, Identifier, Length, Type, OpCode, MS- CHAPv2-ID, MS-Length, Value-Size, Response, and Name fields. Octets outside the range of the Length field should be treated as Data Link Layer padding and should be ignored on reception. Type 26 - EAP MS-CHAP-V2 OpCode 2 - Response Kamath & Palekar Informational [Page 7]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 MS-CHAPv2-ID The MS-CHAPv2-ID field is one octet and aids in matching MSCHAP-v2 responses with requests. Typically, the MS-CHAPv2-ID field is the same as the Identifier field. MS-Length The MS-Length field is two octets and MUST be set to the value of the Length field minus 5. Value-Size This field is one octet and indicates the length of the Response field. It is set to 0x31 (Decimal 49). Response The Response field is 49 octets. The most significant octet is transmitted first. It is sub-formatted 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 [RFC1750] SHOULD be observed. The NT-Response field is an encoded function of the password, the Name field of the Response packet, the contents of the Peer-Challenge field and the received Challenge as output by the routine GenerateNTResponse() defined in [RFC2759], Section 8.1. The Windows NT password is a string of 0 to (theoretically) 256 case- sensitive Unicode [UNICODE] 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. Kamath & Palekar Informational [Page 8]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 Whenever a Response packet is received, the authenticator compares the Response Value with its own calculation of the expected value. If the values match, then the authenticator MUST send a Success-Request packet, as described in Section 2.3. If the values do not match, and if the error is retryable, then a Failure-Request packet MUST be sent as described in Section 2.5. If the values do not match, and the error is not retryable, then a Failure-Request packet (described in Section 2.5) SHOULD be sent, or alternatively, the authentication MAY be terminated (as described in Section 2.8) such as by sending an EAP Failure. Name 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). The Name SHOULD NOT be NUL or CR/LF terminated. The size of the Name field is determined from the Length - Value-Size - 10. 2.3. Success Request packet If the value received in the Response field of the EAP MS-CHAP-V2 Response packet is equal to the expected value, then the implementation MUST transmit an EAP MS-CHAP-V2 Request packet with the OpCode field set to 3 (Success). The format of the EAP MS-CHAP-v2 Success Request packet is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | OpCode | MS-CHAPv2-ID | MS-Length... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MS-Length | Message... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 1 - Request Kamath & Palekar Informational [Page 9]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 Identifier The Identifier field is one octet. The Identifier field MUST be the same if a Request packet is retransmitted due to a timeout while waiting for a Response. Any new (non-retransmission) Requests MUST modify the Identifier field. If a peer receives a duplicate Request for which it has already sent a Response, it MUST resend it's Response. If a peer receives a duplicate Request before it has sent a Response to the initial Request (i.e. it's waiting for user input), it MUST silently discard the duplicate Request. Length The Length field is two octets and indicates the length of the EAP packet including the Code, Identifier, Length, Type, OpCode, MS- CHAPv2-ID, MS-Length, and Message fields. Octets outside the range of the Length field should be treated as Data Link Layer padding and should be ignored on reception. Type 26 - EAP MS-CHAP-V2 OpCode 3 - Success MS-CHAPv2-ID The MS-CHAPv2-ID field is one octet and aids in matching MSCHAP-v2 responses with requests. Typically, the MS-CHAPv2-ID field is the same as the Identifier field. MS-Length The MS-Length field is two octets and MUST be set to the value of the Length field minus 5. Message 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>" The <auth_string> quantity is a 20 octet number encoded in ASCII as 40 hexadecimal digits. The hexadecimal digits A-F (if present) MUST Kamath & Palekar Informational [Page 10]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 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() defined in [RFC2759], Section 8.7. The authenticating peer MUST verify the authenticator response when a Success packet is received. The method for verifying the authenticator is described in [RFC2759], section 8.8. If the authenticator response is either missing or incorrect, the peer MUST end the session without sending a response. The <message> quantity is human-readable text in the appropriate charset and language [RFC2484]. 2.4. Success Response packet In the peer successfully validates the EAP MS-CHAP-V2 Success Request packet sent by the authenticator, then it MUST respond with an EAP MS- CHAP-V2 Success Response packet with the OpCode field set to 3 (Success). The format of the EAP MS-CHAP-v2 Success Response packet is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | OpCode | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 2 - Response Identifier The Identifier field is one octet and contains the value included in the EAP Request to which it responds. Length 6 Kamath & Palekar Informational [Page 11]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 Type 26 - EAP MS-CHAP-V2 OpCode 3 - Success 2.5. Failure Request packet If the Value received in a Response is not equal to the expected value, and the error is retryable, then the implementation MUST transmit an EAP MS-CHAP-v2 Request packet with the OpCode field set to 4 (Failure). If the error is not retryable, then the implementation SHOULD transmit an EAP MS-CHAP-v2 Failure Request packet, or it MAY terminate the authentication (e.g. send an EAP Failure packet). The former approach is preferable, since this enables the cause of the error to be communicated. The format of the EAP MS-CHAP-v2 Failure Request packet is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | OpCode | MS-CHAPv2-ID | MS-Length... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MS-Length | Message... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 1 - Request Identifier The Identifier field is one octet. The Identifier field MUST be the same if a Request packet is retransmitted due to a timeout while waiting for a Response. Any new (non-retransmission) Requests MUST modify the Identifier field. If a peer receives a duplicate Request for which it has already sent a Response, it MUST resend it's Response. If a peer receives a duplicate Request before it has sent a Response to the initial Request (i.e. it's waiting for user input), it MUST silently discard the duplicate Request. Kamath & Palekar Informational [Page 12]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 Length The Length field is two octets and indicates the length of the EAP packet including the Code, Identifier, Length, Type, OpCode, MS- CHAPv2-ID, MS-Length, and Message fields. Octets outside the range of the Length field should be treated as Data Link Layer padding and should be ignored on reception. Type 26 - EAP MS-CHAP-V2 OpCode 4 - Failure MS-CHAPv2-ID The MS-CHAPv2-ID field is one octet and aids in matching MSCHAP-v2 responses with requests. Typically, the MS-CHAPv2-ID field is the same as the Identifier field. MS-Length The MS-Length field is two octets and MUST be set to the value of the Length field minus 5. Message 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 corresponding to one of those listed below, though implementations should deal with codes not on this list gracefully. The error code need not be 10 digits long. 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 single character ASCII flag set to '1' if a retry is Kamath & Palekar Informational [Page 13]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 allowed, and '0' if not. Typically, errors 646, 647, and 649 are non-retryable (R=0). 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. 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 EAP MS-CHAP-V2, this value MUSTalways be 3. <msg> is human-readable text in the appropriate charset and language [RFC2484]. 2.6. Failure Response packet When the peer receives a Failure Request packet that is retryable (R=1), the authentication MAY be retried. For example, a new Response packet, or Change Password packet MAY be sent. In these cases a Failure Response packet is not sent. However, if the EAP MS-CHAPv2 Failure Request is non-retryable (R=0), then the peer SHOULD transmit an EAP MS-CHAP-v2 Response packet with the OpCode field set to 4 (Failure). The format of the EAP MS-CHAP-v2 Failure Response packet is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | OpCode | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 2 - Response Identifier The Identifier field is one octet and contains the value included in the EAP Request to which it responds. Kamath & Palekar Informational [Page 14]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 Length 6 Type 26 - EAP MS-CHAP-V2 OpCode 4 - Failure 2.7. 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. The format of the EAP MS-CHAP-v2 Change Password packet is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | OpCode | MS-CHAPv2-ID | MS-Length... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MS-Length | Data... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 2 - Response Identifier The Identifier field is one octet and aids in matching responses with requests. The value is the Identifier of the received Failure packet to which this packet responds. Length The Length field is two octets and indicates the length of the EAP packet including the Code, Identifier, Length, Type, OpCode, MS- CHAPv2-ID, MS-Length and Data fields. Octets outside the range of Kamath & Palekar Informational [Page 15]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 the Length field should be treated as Data Link Layer padding and should be ignored on reception. For the Change Password packet, the length = 591. Type 26 - EAP MS-CHAP-V2 OpCode 7 - Change Password MS-CHAPv2-ID The MS-CHAPv2-ID field is one octet and aids in matching MSCHAP-v2 responses with requests. Typically, the MS-CHAPv2-ID field is the same as the Identifier field. MS-Length The MS-Length field is two octets and MUST be set to the value of the Length field minus 5. Data The Data field is 582 octets in length, and is subdivided as follows: 516 octets : Encrypted-Password 16 octets : Encrypted-Hash 16 octets : Peer-Challenge 8 octets : Reserved 24 octets : NT-Response 2-octet : Flags Encrypted-Password The Encrypted-Password field is 516 octets in length, and contains the PWBLOCK form of the new Windows NT password encrypted with the old Windows NT password hash, as output by the NewPasswordEncryptedWithOldNtPasswordHash() routine defined in [RFC2759], Section 8.9. Encrypted-Hash The Encrypted-Hash field is 16 octets in length and contains the old Windows NT password hash encrypted with the new Windows NT password hash, as output by the OldNtPasswordHashEncryptedWithNewNtPasswordHash() routine, defined in Kamath & Palekar Informational [Page 16]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 [RFC2759], Section 8.12. Peer-Challenge The Peer-Challenge field is 16 octets in length, and contains a 16-octet random quantity, as described in the Response packet description. Reserved 8 octets, must be zero. NT-Response The NT-Response field is 24 octets in length and is as described in the Response packet description. However it is calculated on the new password and the challenge received in the Failure packet. Flags The Flags 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Bits 0-15 Reserved, always clear (0). 2.8. Alternative failure behavior Rather than sending a Failure Request as described in Section 2.5, if the error is non-retryable (e.g. R=0), or if the maximum number of retries has been exhausted, then the Authenticator MAY terminate the authentication conversation. Where EAP MS-CHAP-V2 is running standalone (e.g. without PEAP), this will result in transmission of an EAP Failure message to the authenticator. Since EAP Failure packets do not carry additional data, no error message may be transmitted to the peer. 2.9. Known bugs In Windows XP SP1, Failure Request packets are only sent where the error is retryable (R=1). Rather than sending a Failure Request with a non- retryable error (R=0), a Windows XP SP1 authenticator will terminate Kamath & Palekar Informational [Page 17]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 authentication. This is undesirable, because it prevents non-retryable error messages from being received by the peer. A Windows XP SP1 host, on receiving a Failure Request packet with a non-retryable error (R=0), will silently discard the packet. Since a Windows XP SP1 peer will respond to a retryable (R=1) Failure Request by retrying authentication (such as by sending a Response or Change-Password packet), and non-retryable (R=0) Failure Requests are silently discarded, Windows XP SP1 peers do not send Failure Response packets. If a Windows XP SP1 authenticator receives a Failure Response packet, it will be silently discarded. 3. Normative references [RFC1320] Rivest, R., "MD4 Message Digest Algorithm", RFC 1320, April 1992. [RFC1994] Simpson, W., "PPP Challenge Handshake Authentication Protocol (CHAP)", RFC 1994, August 1996. [RFC1750] Eastlake, D., Crocker, S. and J. Schiller, "Randomness Recommendations for Security", RFC 1750, December 1994. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2284] Blunk, L., Vollbrecht, J., "PPP Extensible Authentication Protocol (EAP)", RFC 2284, March 1998. [RFC2433] Zorn, G. and Cobb, S., "Microsoft PPP CHAP Extensions", RFC 2433, October 1998. [RFC2484] Zorn, G., "PPP LCP Internationalization Configuration Option", RFC 2484, January 1999. [RFC2759] Zorn, G., "Microsoft PPP CHAP Extensions, Version 2", RFC 2759, January 2000. [RC4] 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 [IEEE8021X] IEEE Standards for Local and Metropolitan Area Networks: Port Based Network Access Control, IEEE Std 802.1X-2001, June 2001. Kamath & Palekar Informational [Page 18]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 [SHA1] "Secure Hash Standard", Federal Information Processing Standards Publication 180-1, National Institute of Standards and Technology, April 1995. [UNICODE] "The Unicode Standard, Version 2.0", The Unicode Consortium, Addison-Wesley, 1996. ISBN 0-201-48345-9. 4. Informative references [RFC1570] Simpson, W., Editor, "PPP LCP Extensions", RFC 1570, January 1994. [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, July 1994. [DES] "Data Encryption Standard (DES)", Federal Information Processing Standard Publication 46-2, National Institute of Standards and Technology, December 1993. [DESMODES] "DES Modes of Operation", Federal Information Processing Standards Publication 81, National Institute of Standards and Technology, December 1980. [RFC3079] Zorn, G., "Deriving Keys for use with Microsoft Point-to-Point Encryption (MPPE)", RFC 3079, March 2001. Kamath & Palekar Informational [Page 19]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 Appendix A - Examples In the case where the EAP-MS-CHAP-V2 authentication is successful, the conversation will appear as follows: Peer Authenticator ---- ------------- <- EAP-Request/Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Type=EAP MS-CHAP-V2 (Challenge) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Response)-> <- EAP-Request/ EAP-Type=EAP-MS-CHAP-V2 (Success) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Success) -> <- EAP-Success In the case where the EAP MS-CHAP-V2 authentication is unsuccessful, due to a retryable error, the conversation will appear as follows (assuming a maximum of two retries): Peer Authenticator ---- ------------- <- EAP-Request/Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Type=EAP MS-CHAP-V2 (Challenge) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Response)-> <- EAP-Request/ EAP-Type=EAP-MS-CHAP-V2 (Failure, R=1) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Response) -> <- EAP-Request/ EAP-Type=EAP-MS-CHAP-V2 (Failure, R=1) Kamath & Palekar Informational [Page 20]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Response) -> <- EAP-Failure In the case where the EAP MS-CHAP-V2 authentication is unsuccessful, due to a non-retryable error, the conversation will appear as follows (Windows XP SP1): Peer Authenticator ---- ------------- <- EAP-Request/Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Type=EAP MS-CHAP-V2 (Challenge) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Response)-> <- EAP-Failure In the case where the EAP MS-CHAP-V2 authentication is unsuccessful, due to a non-retryable error, and a Failure Request packet is sent, the conversation will appear as follows (behavior not exhibited by Windows XP SP1): Peer Authenticator ---- ------------- <- EAP-Request/Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Type=EAP MS-CHAP-V2 (Challenge) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Response)-> <- EAP-Request/ EAP-Type=EAP MS-CHAP-V2 (Failure, R=0) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Failure)-> <- EAP-Failure In the case where the EAP MS-CHAP-V2 authentication is initially Kamath & Palekar Informational [Page 21]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 unsuccessful due to password expiration, but the subsequent Change Password operation succeeds, the conversation will appear as follows: Peer Authenticator ---- ------------- <- EAP-Request/Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Type=EAP MS-CHAP-V2 (Challenge) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Response)-> <- EAP-Request/ EAP-Type=MS-CHAP-V2 (Failure, R=1, Message=ERROR_PASSWD_EXPIRED (E=648)) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Change-Password) -> <- EAP-Request/ EAP-Type=MS-CHAP-V2 (Success) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Success) -> <- EAP-Success In the case where the EAP MS-CHAP-V2 authentication is unnsuccessful due to password failure and a successful retry occurs, the conversation appears as follows: Peer Authenticator ---- ------------- <- EAP-Request/Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Type=EAP MS-CHAP-V2 (Challenge) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Response)-> <- EAP-Request/ EAP-Type=MS-CHAP-V2 (Failure, R=1, Message=ERROR_AUTHENTICATION_FAILURE (E=691) Kamath & Palekar Informational [Page 22]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Response)-> <- EAP-Request/ EAP-Type=MS-CHAP-V2 (Success) EAP-Response/ EAP-Type=EAP-MS-CHAP-V2 (Success) -> <- EAP-Success Acknowledgments Thanks to Mark Wodrich and Narendra Gidwani of Microsoft for discussions relating to this document. Authors' Addresses Vivek Kamath Ashwin Palekar Microsoft Corporation One Microsoft Way Redmond, WA 98052 EMail: {vivek, ashwinp}@microsoft.com Phone: +1 425 882 8080 Fax: +1 425 936 7329 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE Kamath & Palekar Informational [Page 23]
INTERNET-DRAFT EAP MS-CHAPv2 2 September 2002 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." Expiration Date This memo is filed as <draft-kamath-pppext-eap-mschapv2-00.txt>, and expires March 19, 2003. Kamath & Palekar Informational [Page 24]