Basic Password Exchange within the Flexible Authentication via Secure Tunneling Extensible Authentication Protocol (EAP-FAST)
draft-zhou-emu-fast-gtc-05
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 5421.
|
|
|---|---|---|---|
| Authors | Hao Zhou , Nancy Cam-Winget | ||
| Last updated | 2015-10-14 (Latest revision 2008-11-02) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
| Formats | |||
| Reviews | |||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 5421 (Informational) | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Tim Polk | ||
| Send notices to | (None) |
draft-zhou-emu-fast-gtc-05
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
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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
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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].
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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
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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=<msg>"
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.
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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 <msg> 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 <msg> 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]
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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.
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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.
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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.
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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.
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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.
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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
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