Internet DRAFT - draft-ietf-tokbind-negotiation
draft-ietf-tokbind-negotiation
Internet Engineering Task Force A. Popov, Ed.
Internet-Draft M. Nystroem
Intended status: Standards Track Microsoft Corp.
Expires: November 24, 2018 D. Balfanz
A. Langley
Google Inc.
May 23, 2018
Transport Layer Security (TLS) Extension for Token Binding Protocol
Negotiation
draft-ietf-tokbind-negotiation-14
Abstract
This document specifies a Transport Layer Security (TLS) extension
for the negotiation of Token Binding protocol version and key
parameters.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on November 24, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
Popov, et al. Expires November 24, 2018 [Page 1]
Internet-Draft Token Binding Negotiation TLS Extension May 2018
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 . . . . . . 4
4. Negotiating Token Binding Protocol Version and Key Parameters 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6.1. Downgrade Attacks . . . . . . . . . . . . . . . . . . . . 6
6.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS
Versions . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
In order to use the Token Binding protocol
[I-D.ietf-tokbind-protocol], the client and server need to agree on
the Token Binding protocol version and the parameters (signature
algorithm, length) of the Token Binding key. This document specifies
a new TLS [RFC5246] extension to accomplish this negotiation without
introducing additional network round-trips in TLS 1.2 and earlier
versions. The negotiation of the Token Binding protocol and key
parameters in combination with TLS 1.3 and later versions is beyond
the scope of this document.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Token Binding Negotiation Client Hello Extension
The client uses the "token_binding" TLS extension to indicate the
highest supported Token Binding protocol version and key parameters.
Popov, et al. Expires November 24, 2018 [Page 2]
Internet-Draft Token Binding Negotiation TLS Extension May 2018
enum {
token_binding(24), (65535)
} ExtensionType;
The "extension_data" field of this extension contains a
"TokenBindingParameters" value.
struct {
uint8 major;
uint8 minor;
} TB_ProtocolVersion;
enum {
rsa2048_pkcs1.5(0), rsa2048_pss(1), ecdsap256(2), (255)
} TokenBindingKeyParameters;
struct {
TB_ProtocolVersion token_binding_version;
TokenBindingKeyParameters key_parameters_list<1..2^8-1>
} TokenBindingParameters;
"token_binding_version" indicates the version of the Token Binding
protocol the client wishes to use during this connection. If the
client supports multiple Token Binding protocol versions, it SHOULD
indicate the latest supported version (the one with the highest
TB_ProtocolVersion.major and TB_ProtocolVersion.minor) in
TokenBindingParameters.token_binding_version. E.g. if the client
supports versions {1, 0} and {0, 13} of the Token Binding protocol,
it SHOULD indicate version {1, 0}. Please note that the server MAY
select any lower protocol version, see Section 3
"Token Binding Negotiation Server Hello Extension" for more details.
If the client does not support the Token Binding protocol version
selected by the server, then the connection proceeds without Token
Binding. [I-D.ietf-tokbind-protocol] describes version {1, 0} of the
protocol.
Please note that the representation of the Token Binding protocol
version using two octets ("major" and "minor") is for human
convenience only and carries no protocol significance.
RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH: Prototype
implementations of Token Binding drafts can indicate support of a
specific draft version, e.g. {0, 1} or {0, 2}.
"key_parameters_list" contains the list of identifiers of the Token
Binding key parameters supported by the client, in descending order
of preference. [I-D.ietf-tokbind-protocol] establishes an IANA
registry for Token Binding key parameter identifiers.
Popov, et al. Expires November 24, 2018 [Page 3]
Internet-Draft Token Binding Negotiation TLS Extension May 2018
3. Token Binding Negotiation Server Hello Extension
The server uses the "token_binding" TLS extension to indicate support
for the Token Binding protocol and to select the protocol version and
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 or a lower version.
2. The server finds acceptable Token Binding key parameters on the
client's list.
3. The server is also negotiating the Extended Master Secret
[RFC7627] and Renegotiation Indication [RFC5746] TLS extensions.
This requirement applies when TLS 1.2 or an older TLS version is
used (see Section 6 "Security Considerations" 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".
"token_binding_version" contains the lower of:
o the Token Binding protocol version offered by the client in the
"token_binding" extension and
o the highest Token Binding protocol version supported by the
server.
"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
Popov, et al. Expires November 24, 2018 [Page 4]
Internet-Draft Token Binding Negotiation TLS Extension May 2018
the client advertises, then the server MUST NOT include the
"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" is higher than 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. TLS 1.2 or an older TLS version is used, but the Extended Master
Secret [RFC7627] and TLS Renegotiation Indication [RFC5746]
extensions are not negotiated (see Section 6
"Security Considerations" below for more details).
If the "token_binding" extension is included in the server hello and
the client supports the Token Binding protocol version selected by
the server, it means that the version and key parameters have been
negotiated between the client and the server and SHALL be definitive
for the TLS connection. TLS 1.2 and earlier versions support
renegotiation, allowing the client and server to renegotiate the
Token Binding protocol version and key parameters on the same
connection. The client MUST use the negotiated key parameters in the
"provided_token_binding" as described in [I-D.ietf-tokbind-protocol].
If the client does not support the Token Binding protocol version
selected by the server, then the connection proceeds without Token
Binding. There is no requirement for the client to support any Token
Binding versions other than the one advertised in the client's
"token_binding" extension.
Client and server applications can choose to handle failure to
negotiate Token Binding in a variety of ways, e.g.: continue using
the connection as usual, shorten the lifetime of tokens issued during
this connection, require stronger authentication, terminate the
connection, etc.
The Token Binding protocol version and key parameters are negotiated
for each TLS connection, which means that the client and server
Popov, et al. Expires November 24, 2018 [Page 5]
Internet-Draft Token Binding Negotiation TLS Extension May 2018
include their "token_binding" extensions both in the full TLS
handshake that establishes a new TLS session and in the subsequent
abbreviated TLS handshakes that resume the TLS session.
5. IANA Considerations
This document updates the TLS "ExtensionType Values" registry. IANA
has provided the following temporary registration for the
"token_binding" TLS extension:
Value: 24
Extension name: token_binding
Reference: this document
Recommended: Yes
IANA is requested to make this registration permanent, keeping the
value of 24, which has been used by the prototype implementations of
the Token Binding protocol.
This document uses "Token Binding Key Parameters" registry originally
created in [I-D.ietf-tokbind-protocol]. This document creates no new
registrations in this registry.
6. Security Considerations
6.1. Downgrade Attacks
The Token Binding protocol version and key parameters are negotiated
via the "token_binding" extension within the TLS handshake. TLS
detects handshake message modification by active attackers, therefore
it is not possible for an attacker to remove or modify the
"token_binding" extension without breaking the TLS handshake. The
signature algorithm and key length used in the Token Binding of type
"provided_token_binding" MUST match the parameters negotiated via the
"token_binding" extension.
6.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS Versions
The Token Binding protocol relies on the TLS Exporters [RFC5705] to
associate a TLS connection with a Token Binding. The triple
handshake attack [TRIPLE-HS] is a known vulnerability in TLS 1.2 and
older TLS versions, allowing an attacker to synchronize keying
material between TLS connections. The attacker can then successfully
replay bound tokens. For this reason, the Token Binding protocol
MUST NOT be negotiated with these TLS versions, unless the Extended
Popov, et al. Expires November 24, 2018 [Page 6]
Internet-Draft Token Binding Negotiation TLS Extension May 2018
Master Secret [RFC7627] and Renegotiation Indication [RFC5746] TLS
extensions have also been negotiated.
7. Acknowledgements
This document incorporates comments and suggestions offered by Eric
Rescorla, Gabriel Montenegro, Martin Thomson, Vinod Anupam, Anthony
Nadalin, Michael B. Jones, Bill Cox, Nick Harper, Brian Campbell,
Benjamin Kaduk, Alexey Melnikov and others.
This document was produced under the chairmanship of John Bradley and
Leif Johansson. The area directors included Eric Rescorla, Kathleen
Moriarty and Stephen Farrell.
8. References
8.1. Normative References
[I-D.ietf-tokbind-protocol]
Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J.
Hodges, "The Token Binding Protocol Version 1.0", draft-
ietf-tokbind-protocol-18 (work in progress), May 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5705] Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705,
March 2010, <https://www.rfc-editor.org/info/rfc5705>.
[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010,
<https://www.rfc-editor.org/info/rfc5746>.
[RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A.,
Langley, A., and M. Ray, "Transport Layer Security (TLS)
Session Hash and Extended Master Secret Extension",
RFC 7627, DOI 10.17487/RFC7627, September 2015,
<https://www.rfc-editor.org/info/rfc7627>.
Popov, et al. Expires November 24, 2018 [Page 7]
Internet-Draft Token Binding Negotiation TLS Extension May 2018
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References
[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
Popov, et al. Expires November 24, 2018 [Page 8]
