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TLS Working Group Mohamad Badra
Internet Draft LIMOS Laboratory
Intended status: Standards Track February 24, 2008
Expires: August 2008
Password Extension for the TLS Client Authentication
draft-badra-tls-password-ext-01.txt
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
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Drafts.
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The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on August 24, 2008.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document specifies a new Transport Layer Security (TLS)
extension and a new TLS message providing TLS client authentication
using passwords. It provides client credential protection.
Badra Expires August 24, 2008 [Page 1]
Internet-Draft Password Extension for TLS February 2008
Table of Contents
1. Introduction...................................................3
1.1. Conventions used in this document.........................3
2. Password Extension.............................................3
2.1. Encrypted Password........................................3
3. Conformance Requirements.......................................6
3.1. Requirements for Management Interfaces....................6
4. Security Considerations........................................6
5. IANA Considerations............................................6
6. References.....................................................7
6.1. Normative References......................................7
6.2. Informative References....................................7
Author's Addresses................................................7
Intellectual Property Statement...................................7
Disclaimer of Validity............................................8
Badra Expires August 24, 2008 [Page 2]
Internet-Draft Password Extension for TLS February 2008
1. Introduction
This document defines a new extension and a new TLS message to the
Transport Layer Security (TLS) protocol to enable TLS client
authentication using passwords. It provides client credential
protection.
1.1. Conventions used in this document
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].
2. Password Extension
In order to negotiate the use of client password-based
authentication, clients MAY include an extension of type "password"
in the extended client hello. The "extension_data" field of this
extension SHALL be empty. The extension_type field is to be assigned
by IANA.
For servers aware of the password extension but not wishing to use
it, it will gracefully revert to an ordinary TLS handshake or stop
the negotiation.
Servers that receive an extended hello containing a "password"
extension MAY agree to authenticate the client using passwords by
including an extension of type "password", with empty
"extension_data", in the extended server hello. The
CertificateRequest payload is omitted from the server response.
Clients return a response along with their credentials by sending a
"EncryptedPassword" message immediately after the "ClientKeyExchange"
message. The encrypted password message is sent symmetrically
encrypted with the key client_write_key and the cipher algorithm
selected by the server in the ServerHello.cipher_suite.
The Certificate and CertificateVerify payloads are omitted from the
client response.
2.1. Encrypted Password
When this message will be sent:
The client MUST send this message immediately after the client key
exchange message.
Badra Expires August 24, 2008 [Page 3]
Internet-Draft Password Extension for TLS February 2008
Structure of this message:
struct {
uint16 length;
select (CipherSpec.cipher_type) {
case stream:
stream-ciphered struct {
opaque fresh_random<16..2^16-1>;
opaque username<1..2^16-1>;
opaque password<1..2^16-1>;
};
case block:
block-ciphered struct {
opaque IV[CipherSpec.block_length];
opaque username<1..2^16-1>;
opaque password<1..2^16-1>;
uint8 adding[EncryptedPassword.padding_length];
uint8 padding_length;
};
} EncryptedPassword;
fresh_random
A vector contains at least 16 bytes random value. It is RECOMMENDED
that implementations provide functionality for generating this
random, taking [RFC4086] into account.
length
The length (in bytes) of the EncryptedPassword structure.
padding
Padding that is added to force the length of the EncryptedPassword
structure to be an integral multiple of the block cipher's block
length. The padding MAY be any length up to 255 bytes, as long as
it results in the EncryptedPassword.length being an integral
multiple of the block length. Lengths longer than necessary might
be desirable to frustrate attacks on a protocol that are based on
analysis of the lengths of exchanged messages. Each uint8 in the
padding data vector MUST be filled with the padding length value.
The receiver MUST check this padding and SHOULD use the
bad_record_mac alert to indicate padding errors.
Badra Expires August 24, 2008 [Page 4]
Internet-Draft Password Extension for TLS February 2008
padding_length
The padding length MUST be such that the total size of the
EncryptedPassword structure is a multiple of the cipher's block
length. Legal values range from zero to 255, inclusive. This
length specifies the length of the padding field exclusive of the
padding_length field itself.
BulkCipherAlgorithm.null (e.g. TLS_RSA_WITH_NULL_MD5 and
RSA_WITH_NULL_SHA) MUST NOT be negotiated when password extension is
deployed, as it provides no more protection than an unsecured
connection.
Upon receipt of this message, the server symmetrically decrypts the
EncryptedPassword using the same key as the client to retrieve the
username and the password in clear text.
Next, the server will then check the authentication database to see
if the received username/password and those stored in the database
match. If a match is found, the server sends its change cipher spec
message and proceeds directly to finished message. If no match is
found, the server MUST send a fatal alert, results in the immediate
termination of the connection.
This documents doesn't specify how exactly the server checks the
username/password for a match. However, the server MAY consider
using of an AAA or RADIUS infrastructures. In this case, the server
calls into the local AAA client, which in turn contacts the AAA
server. The client's credentials (username and password) are
validated at the AAA server, which in turn responds to the AAA client
with an accept/reject message.
Client Server
------ ------
ExtendedClientHello -------->
ExtendedServerHello
Certificate
ServerKeyExchange*
<-------- ServerHelloDone
ClientKeyExchange
EncryptedPassword
ChangeCipherSpec
Finished -------->
ChangeCipherSpec
<-------- Finished
Badra Expires August 24, 2008 [Page 5]
Internet-Draft Password Extension for TLS February 2008
3. Conformance Requirements
This document does not specify how the server stores the password and
the username, or how exactly it verifies the password and the
username it receives. It is RECOMMENDED that before looking up the
password, the server processes the username with a SASLprep profile
[RFC4013] appropriate for the username in question.
3.1. Requirements for Management Interfaces
In the absence of an application profile specification specifying
otherwise, a management interface for entering the password and/or
the username MUST support the following:
o Entering usernames consisting of up to 128 printable Unicode
characters.
o Entering passwords up to 64 octets in length as ASCII strings
and in hexadecimal encoding. The management interface MAY
accept other encodings if the algorithm for translating the
encoding to a binary string is specified.
4. Security Considerations
The security considerations described throughout [RFC4346] and
[RFC4366] apply here as well.
5. IANA Considerations
This document defines a new TLS extension "password", assigned the
value to be allocated from the TLS ExtensionType registry defined in
[RFC4366].
This document defines a new handshake message, encrypted password,
whose value is to be allocated from the TLS HandshakeType registry
defined in [RFC4346].
Badra Expires August 24, 2008 [Page 6]
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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.
[RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
June 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol 1.1", RFC 4346, April 2006.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS) Extensions",
RFC 4366, April 2006.
6.2. Informative References
[RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names
and Passwords", RFC 4013, February 2005.
Author's Addresses
Mohamad Badra
LIMOS Laboratory - UMR6158, CNRS
France
Email: badra@isima.fr
Intellectual Property Statement
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Badra Expires August 24, 2008 [Page 7]
Internet-Draft Password Extension for TLS February 2008
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Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Badra Expires August 24, 2008 [Page 8]
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