Internet DRAFT - draft-popov-tokbind-negotiation
draft-popov-tokbind-negotiation
Internet Engineering Task Force A. Popov, Ed.
Internet-Draft M. Nystroem
Intended status: Standards Track Microsoft Corp.
Expires: November 30, 2015 D. Balfanz
A. Langley
Google Inc.
May 29, 2015
Transport Layer Security (TLS) Extension for Token Binding Protocol
Negotiation
draft-popov-tokbind-negotiation-00
Abstract
This document specifies a Transport Layer Security (TLS) [RFC5246]
extension for the negotiation of Token Binding protocol [TBPROTO]
version and key parameters.
Status of This Memo
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This Internet-Draft will expire on November 30, 2015.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Token Binding Negotiation Client Hello Extension . . . . . . 2
3. Token Binding Negotiation Server Hello Extension . . . . . . 3
4. Negotiating Token Binding Protocol Version and Key Parameters 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6.1. Downgrade Attacks . . . . . . . . . . . . . . . . . . . . 6
6.2. Triple Handshake Vulnerability in TLS . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
In order to use the Token Binding protocol [TBPROTO], the client and
server need to agree on the Token Binding protocol version and the
parameters (signature and hash algorithm, length) of the Token
Binding key. This document specifies a new TLS extension to
accomplish this negotiation without introducing additional network
round-trips.
1.1. Requirements Language
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. Token Binding Negotiation Client Hello Extension
The client uses the "token_binding" TLS extension to indicate
supported Token Binding protocol version and key parameters.
enum {
token_binding(TBD), (65535)
} ExtensionType;
The "extension_data" field of this extension contains a
"TokenBindingParameters" value.
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struct {
uint8 major;
uint8 minor;
} ProtocolVersion;
enum {
rsa2048_pkcs1.5_sha256(0), rsa2048_pss_sha256(1), ecdsap256_sha256(2), (255)
} TokenBindingKeyParameters;
struct {
ProtocolVersion token_binding_version;
TokenBindingKeyParameters key_parameters_list<2..2^16-1>
} TokenBindingParameters;
"token_binding_version" indicates the supported version of the Token
Binding protocol. [TBPROTO] describes version {1, 0} of the
protocol. Protype implementations of Token Binding drafts can
indicate support of a specific draft version, e.g. {0, 0} or {0, 1}.
"key_parameters_list" contains the list of identifiers of the Token
Binding key parameters supported by the client, in descending order
of preference.
3. Token Binding Negotiation Server Hello Extension
The server uses the "token_binding" TLS extension to indicate support
for the Token Binding protocol version offered by the client and to
select key parameters.
The server that supports Token Binding and receives a client hello
message containing the "token_binding" extension, will include the
"token_binding" extension in the server hello if all of the following
conditions are satisfied:
1. The server supports the Token Binding protocol version offered by
the client.
2. The server finds acceptable Token Binding key parameters on the
client's list.
3. The server is also negotiating Extended Master Secret TLS
extension [I-D.ietf-tls-session-hash] (see security
considerations section below for more details).
The server will ignore any key parameters that it does not recognize.
The "extension_data" field of the "token_binding" extension is
structured the same as described above for the client
"extension_data".
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"token_binding_version" echos the Token Binding protocol version
advertised by the client.
"key_parameters_list" contains exactly one Token Binding key
parameters identifier selected by the server from the client's list.
4. Negotiating Token Binding Protocol Version and Key Parameters
It is expected that a server will have a list of Token Binding key
parameters identifiers that it supports, in preference order. The
server MUST only select an identifier that the client offered. The
server SHOULD select the most highly preferred key parameters
identifier it supports which is also advertised by the client. In
the event that the server supports none of the key parameters that
the client advertises, then the server MUST NOT include
"token_binding" extension in the server hello.
The client receiving the "token_binding" extension MUST terminate the
handshake with a fatal "unsupported_extension" alert if any of the
following conditions are true:
1. The client did not include the "token_binding" extension in the
client hello.
2. "token_binding_version" does not match the Token Binding protocol
version advertised by the client.
3. "key_parameters_list" includes more than one Token Binding key
parameters identifier.
4. "key_parameters_list" includes an identifier that was not
advertised by the client.
5. Extended Master Secret [I-D.ietf-tls-session-hash] is not
negotiated (see security considerations section below for more
details).
If the "token_binding" extension is included in the server hello and
the TLS handshake succeeds, it means that the Token Binding protocol
version and key parameters have been negotiated between the client
and the server and SHALL be definitive for the TLS session. In this
case, the client MUST use the negotiated key parameters in the
"provided_token_binding" as described in [TBPROTO].
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5. IANA Considerations
This document defines a new TLS extension "token_binding", which
needs to be added to the IANA "Transport Layer Security (TLS)
Extensions" registry.
This document establishes a registry for identifiers of Token Binding
key parameters entitled "Token Binding Key Parameters" under the
"Token Binding Protocol" heading.
Entries in this registry require the following fields:
o Value: The octet value that identifies a set of Token Binding key
parameters (0-255).
o Description: The description of the Token Binding key parameters.
o Specification: A reference to a specification that defines the
Token Binding key parameters.
This registry operates under the "Expert Review" policy as defined in
[RFC5226]. The designated expert is advised to encourage the
inclusion of a reference to a permanent and readily available
specification that enables the creation of interoperable
implementations using the identified set of Token Binding key
parameters.
An initial set of registrations for this registry follows:
Value: 0
Description: rsa2048_pkcs1.5_sha256
Specification: this document
Value: 1
Description: rsa2048_pss_sha256
Specification: this document
Value: 2
Description: ecdsap256_sha256
Specification: this document
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6. Security Considerations
6.1. Downgrade Attacks
The Token Binding protocol version and key parameters are negotiated
via "token_binding" extension within the TLS handshake. TLS prevents
active attackers from modifying the messages of the TLS handshake,
therefore it is not possible for the attacker to remove or modify the
"token_binding" extension. The signature and hash algorithms and key
length used in the TokenBinding of type "provided_token_binding" MUST
match the parameters negotiated via "token_binding" extension.
6.2. Triple Handshake Vulnerability in TLS
The Token Binding protocol relies on the tls_unique value to
associate a TLS connection with a TLS Token Binding. The triple
handshake attack [TRIPLE-HS] is a known TLS protocol vulnerability
allowing the attacker to synchronize tls_unique values between TLS
connections. The attacker can then successfully replay bound tokens.
For this reason, the Token Binding protocol MUST NOT be negotiated
unless the Extended Master Secret TLS extension
[I-D.ietf-tls-session-hash] has also been negotiated.
7. Acknowledgements
This document incorporates comments and suggestions offered by Eric
Rescorla, Gabriel Montenegro, Martin Thomson, Vinod Anupam.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[TBPROTO] Popov, A., Nystroem, M., Balfanz, D., and A. Langley, "The
Token Binding Protocol Version 1.0", 2014.
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8.2. Informative References
[I-D.ietf-tls-session-hash]
Bhargavan, K., Delignat-Lavaud, A., Pironti, A., Langley,
A., and M. Ray, "Transport Layer Security (TLS) Session
Hash and Extended Master Secret Extension", draft-ietf-
tls-session-hash-05 (work in progress), April 2015.
[TRIPLE-HS]
Bhargavan, K., Delignat-Lavaud, A., Fournet, C., Pironti,
A., and P. Strub, "Triple Handshakes and Cookie Cutters:
Breaking and Fixing Authentication over TLS. IEEE
Symposium on Security and Privacy", 2014.
Authors' Addresses
Andrei Popov (editor)
Microsoft Corp.
USA
Email: andreipo@microsoft.com
Magnus Nystroem
Microsoft Corp.
USA
Email: mnystrom@microsoft.com
Dirk Balfanz
Google Inc.
USA
Email: balfanz@google.com
Adam Langley
Google Inc.
USA
Email: agl@google.com
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