Network Working Group N. Cam-Winget Internet-Draft H. Zhou Intended status: Informational Cisco Systems Expires: May 5, 2009 November 1, 2008 Basic Password Exchange within the Flexible Authentication via Secure Tunneling Extensible Authentication Protocol (EAP-FAST) draft-zhou-emu-fast-gtc-05 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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. This Internet-Draft will expire on May 5, 2009. Cam-Winget & Zhou Expires May 5, 2009 [Page 1] Internet-Draft EAP-FAST with GTC November 2008 Abstract The flexible authentication via secure tunneling EAP method (EAP- FAST) enables secure communication between a peer and a server by using Transport Layer Security (TLS) to establish a mutually authenticated tunnel. Within this tunnel a basic password exchange, based on the generic token card method (EAP-GTC), may be executed to authenticate the peer. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Specification Requirements . . . . . . . . . . . . . . . . 3 2. EAP-FAST GTC Authentication . . . . . . . . . . . . . . . . . 4 3. Security Considerations . . . . . . . . . . . . . . . . . . . 8 3.1. Security Claims . . . . . . . . . . . . . . . . . . . . . 8 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1. Normative References . . . . . . . . . . . . . . . . . . . 11 6.2. Informative References . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Intellectual Property and Copyright Statements . . . . . . . . . . 13 Cam-Winget & Zhou Expires May 5, 2009 [Page 2] Internet-Draft EAP-FAST with GTC November 2008 1. Introduction EAP-FAST [RFC4851] is an EAP method that can be used to mutually authenticate peer and server. This document describes the EAP-FAST inner EAP method, EAP-FAST-GTC, which is used to authenticate the peer through a basic password exchange. EAP-FAST-GTC was developed to support using clear text passwords to authenticate to legacy user databases, to facilitate password change and to support one time password features such as new pin mode. Message exchanges, including user credentials, are clear text strings transferred within the encrypted TLS tunnel and thus are considered secure. For historical reasons, EAP-FAST-GTC uses EAP Type 6, originally allocated to EAP- GTC [RFC3748]. Note that EAP-FAST-GTC payloads used in EAP-FAST require specific formatting and therefore will not necessarily be compatible with EAP-GTC mechanisms used outside of EAP-FAST. To avoid interference between these two methods, EAP-FAST-GTC MUST NOT be used outside an EAP-FAST tunnel, and EAP-GTC MUST NOT be used inside an EAP-FAST tunnel. All EAP-FAST-GTC packets sent within the TLS tunnel must be encapsulated in EAP Payload TLVs, described in [RFC4851]. It is assumed that reader of this document is familiar with EAP-FAST [RFC4851]. 1.1. Specification Requirements 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]. Cam-Winget & Zhou Expires May 5, 2009 [Page 3] Internet-Draft EAP-FAST with GTC November 2008 2. EAP-FAST GTC Authentication All EAP-FAST-GTC packets inside EAP-FAST other than the empty acknowledgment packet MUST follow the "LABEL=Value" format. All Labels are in ASCII text and SHALL NOT contain the space character. Currently, three Labels are defined: o "CHALLENGE", the server request packet MUST be in the form of "CHALLENGE=Value", where Value is the server challenge, such as "please enter your password." o "RESPONSE", the peer response packet MUST be in the form of "RESPONSE=Value", where Value is the peer response. o "E", the server failure packet MUST be in the form of "E=Value", where Value is the error message generated by the server. If the peer or the server receives an EAP-FAST-GTC request or response that is not in the format specified above, it SHOULD fail the authentication by sending a Result TLV with a failure. After the TLS encryption tunnel is established and EAP-FAST Authentication Phase 2 starts, the EAP Server sends an EAP-FAST-GTC Request, which contains a server challenge. The server challenge is a displayable message for use by the peer to prompt the user. A peer MAY prompt the user for the user credentials, or decide to use the user credentials gained through some other means without prompting the user. The peer sends the user credentials back in the EAP-FAST-GTC Response using the following format: "RESPONSE=user@example.com\0secret" where "user@example.com" is the actual user name and "secret" is the actual password. The NULL character "\0" is used to separate the user name and password. The username and password are included in a single message in the first response packet as an optimization by eliminating the inner method EAP-Identity exchange to save an extra round trip. Once the EAP-FAST server receives the user credentials, it SHOULD first validate the user identity with the I-ID [I-D.cam-winget-eap-fast-provisioning] in the PAC-Opaque and if it matches, it will continue to authenticate the user with internal or external user databases. Additional exchanges MAY occur between the EAP-FAST server and peer Cam-Winget & Zhou Expires May 5, 2009 [Page 4] Internet-Draft EAP-FAST with GTC November 2008 to facilitate various user authentications. The EAP-FAST server might send additional challenges to prompt the peer for additional information, such as request for next token or new pin in the one time password case, or server failure packet to indicate error. The peer displays the prompt to the user again and sends back the needed information in an EAP-FAST-GTC Response. The exchange ends when a Result TLV is received. An EAP-FAST-GTC server implementation within EAP-FAST uses the following format to indicate error if an authentication fails: "E=eeeeeeeeee R=r M=" where The "eeeeeeeeee" is the ASCII representation of a decimal error code corresponding to one of those listed below, though peer implementations SHOULD deal with codes not on this list gracefully. The error code need not be 10 digits long. Below is a complete list of predefined error codes: o 646 ERROR_RESTRICTED_LOGON_HOURS Indicates that access is attempted outside the allowed hours. Peer implementation SHOULD display the error message to the user and ask the user to try in a later time. o 647 ERROR_ACCT_DISABLED Indicates the requested account is disabled. Peer implementation SHOULD display the error message to the user, which helps the user to resolve the issue with the administrator. o 648 ERROR_PASSWD_EXPIRED Indicates the password has expired and password change is required. Peer implementation SHOULD prompt user for a new password and send back the new password in the peer response packet. o 649 ERROR_NO_DIALIN_PERMISSION Indicates that access has been denied due to lack of dial in permission. Peer implementation SHOULD display the error message to the user, which helps the user to resolve the issue with the administrator. Cam-Winget & Zhou Expires May 5, 2009 [Page 5] Internet-Draft EAP-FAST with GTC November 2008 o 691 ERROR_AUTHENTICATION_FAILURE Indicates authentication failure due to incorrect user name or password. Base on the retry flag described below, peer implementation MAY prompt the user again for a new set of user name and password or simply send back an empty acknowledgment packet to acknowledge the failure and go into termination phase of the authentication session. o 709 ERROR_CHANGING_PASSWORD Indicates password change failed, most likely because the new password fails to meet the password complexity policy. Peer implementation SHOULD display the error message and prompt the user again for the new password. o 755 ERROR_PAC_I-ID_NO_MATCH Indicates that the PAC used to establish the EAP-FAST session cannot be used to authenticate to this user account. Base on the retry flag described below, peer implementation MAY prompt the user again for a new set of user name and password or simply send back an empty acknowledgment packet to acknowledge the failure and go into termination phase of the authentication session. The "r" is a single character ASCII flag set to '1' if a retry is allowed, and '0' if not. When the server sets this flag to '1' it disables short timeouts, expecting the peer to prompt the user for new credentials and resubmit the response. When the server sets this flag to '0' the peer SHOULD NOT prompt the user for new credentials to try again without restarting the EAP-FAST authentication from the beginning. The is human-readable ASCII text. Current implementations only support ASCII text. The server failure packet can be broken into label/value pair using the space character as the separator. The only value may contain the space character is the value, which is always the last value pair in the failure packet. Peer SHOULD ignore any unknown label/ value pair in the failure packet. The error format described above is similar to what are defined in MSCHAPv2 [RFC2759], except for the omission of server challenge. So if the EAP-FAST Server is distributing MSCHAPV2 exchanges to the backend inner method server, it can simply just return what the backend inner method server returns less the server challenge. In the case of connecting to an one time password or LDAP [RFC4511] Cam-Winget & Zhou Expires May 5, 2009 [Page 6] Internet-Draft EAP-FAST with GTC November 2008 server, the EAP-FAST Server can format the error message into this format. With the addition of the retry count, peer can potentially prompt the user for new credentials to try again without restarting the EAP-FAST authentication from the beginning. Peer will respond to the error code with another EAP-FAST-GTC Response packet with both the new user name and password or in case of other unrecoverable failures, an empty EAP-FAST-GTC packet for acknowledgement. Peer uses empty EAP-FAST-GTC payload as an acknowledgment to the unrecoverable failure. If the EAP-FAST server finishes authentication for EAP-FAST-GTC inner method, it will proceed to Protected Termination as described in [RFC4851]. In the case of an unrecoverable EAP-FAST-GTC authentication failure, the EAP server can send an EAP-FAST-GTC error code as described above, along with the Result TLV for protected termination. This way, no extra round trips will occur. The peer can acknowledge the EAP-FAST-GTC failure as well as the Result TLV within the same EAP-FAST packet. Once server receives the acknowledgement, the TLS tunnel will be torn down and a clear text EAP-Failure will be sent. The user name and password, as well as server challenges MAY support non-ASCII characters. In this case, international user name, password, and messages are based on the use of Unicode characters, encoded as UTF-8 [RFC3629] and processed with a certain algorithm to ensure a canonical representation. The input SHOULD be processed according to [RFC5198]. Since EAP-FAST-GTC does not generate session keys, the MSKi used for crypto-binding for EAP-FAST will be filled with all zeros. Cam-Winget & Zhou Expires May 5, 2009 [Page 7] Internet-Draft EAP-FAST with GTC November 2008 3. Security Considerations The EAP-FAST-GTC method sends password information in the clear and MUST NOT be used outside of a protected tunnel providing strong protection such as the one provided by EAP-FAST. Weak encryption such as, 40-bit encryption or NULL cipher, MUST NOT be used. In addition, the peer MUST authenticate the server before disclosing its credentials. Since EAP-FAST Server-Unauthenticated Provisioning Mode does not authenticate the server, EAP-FAST-GTC MUST NOT be used as the inner method in this mode. EAP-FAST-GTC MAY be used in EAP-FAST authentication and Server-Authenticated Provisioning Mode [I-D.cam-winget-eap-fast-provisioning], where the server is authenticated. Since EAP-FAST-GTC requires the server to have access to the actual authentication secret, it is RECOMMENDED to vary the stored authentication validation data by domain so that a compromise of a server at one location does not compromise others. 3.1. Security Claims This section provides the needed security claim requirement for EAP [RFC3748]. Auth. mechanism: Password based. Ciphersuite negotiation: Yes. Provided by the EAP-FAST Tunnel. Mutual authentication: Yes. Peer is authenticated by the password and server is authenticated by certificate or shared secret. Integrity protection: Yes, Any method executed within the EAP-FAST tunnel is integrity protected. The cleartext EAP headers outside the tunnel are not integrity protected. Replay protection: Yes. Provided by the EAP-FAST Tunnel. Confidentiality: Yes. Provided by the EAP-FAST Tunnel. Key derivation: Yes. Provided by the EAP-FAST Tunnel. Key strength: See Section 7.8 of [RFC4851]. Dictionary attack prot.: Yes. Provided by the EAP-FAST Tunnel. Fast reconnect: Yes. Cryptographic binding: Yes. Provided by the EAP-FAST Tunnel. Session independence: Yes. Provided by the EAP-FAST Tunnel. Fragmentation: Yes. Provided by the EAP-FAST Tunnel. Key Hierarchy: Yes. Provided by the EAP-FAST Tunnel. Channel binding: No, but TLVs could be defined for this. Cam-Winget & Zhou Expires May 5, 2009 [Page 8] Internet-Draft EAP-FAST with GTC November 2008 4. IANA Considerations EAP-FAST-GTC uses the assigned value of 6 (EAP-GTC) for the EAP Type in [RFC3748]. The document defines a registry for EAP-FAST-GTC error codes when running inside EAP-FAST, named "EAP-FAST GTC Error Codes". It may be assigned by Specification Required as defined in [RFC5226]. A summary of the error codes defined so far is given below: o 646 ERROR_RESTRICTED_LOGON_HOURS o 647 ERROR_ACCT_DISABLED o 648 ERROR_PASSWD_EXPIRED o 649 ERROR_NO_DIALIN_PERMISSION o 691 ERROR_AUTHENTICATION_FAILURE o 709 ERROR_CHANGING_PASSWORD o 755 ERROR_PAC_I-ID_NO_MATCH No IANA registry will be created for Labels, as current implementations only support the Labels defined in this document and new Labels are not expected; if necessary, new Labels can be defined in documents updating this document. Cam-Winget & Zhou Expires May 5, 2009 [Page 9] Internet-Draft EAP-FAST with GTC November 2008 5. Acknowledgments The authors would like thank Joe Salowey, Amir Naftali for their contributions of the problem space, and Jouni Malinen, Pasi Eronen, Jari Arkko, Chris Newman for reviewing this document. Cam-Winget & Zhou Expires May 5, 2009 [Page 10] Internet-Draft EAP-FAST with GTC November 2008 6. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC4851] Cam-Winget, N., McGrew, D., Salowey, J., and H. Zhou, "The Flexible Authentication via Secure Tunneling Extensible Authentication Protocol Method (EAP-FAST)", RFC 4851, May 2007. [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network Interchange", RFC 5198, March 2008. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. 6.2. Informative References [I-D.cam-winget-eap-fast-provisioning] Cam-Winget, N., McGrew, D., Salowey, J., and H. Zhou, "Dynamic Provisioning using Flexible Authentication via Secure Tunneling Extensible Authentication Protocol (EAP- FAST)", draft-cam-winget-eap-fast-provisioning-10 (work in progress), October 2008. [RFC2759] Zorn, G., "Microsoft PPP CHAP Extensions, Version 2", RFC 2759, January 2000. [RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol (LDAP): The Protocol", RFC 4511, June 2006. Cam-Winget & Zhou Expires May 5, 2009 [Page 11] Internet-Draft EAP-FAST with GTC November 2008 Authors' Addresses Nancy Cam-Winget Cisco Systems 3625 Cisco Way San Jose, CA 95134 US Email: ncamwing@cisco.com Hao Zhou Cisco Systems 4125 Highlander Parkway Richfield, OH 44286 US Email: hzhou@cisco.com Cam-Winget & Zhou Expires May 5, 2009 [Page 12] Internet-Draft EAP-FAST with GTC November 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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