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Versions: (draft-popov-tokbind-negotiation) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14

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
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of



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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  . . . . . .   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.






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   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.



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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




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   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



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   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



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   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>.




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   [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











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