Negotiated Finite Field Diffie-Hellman Ephemeral Parameters for TLS
draft-ietf-tls-negotiated-ff-dhe-07

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Document Type Active Internet-Draft (tls WG)
Last updated 2015-03-16 (latest revision 2015-03-03)
Replaces draft-ietf-tls-negotiated-dl-dhe
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Internet Engineering Task Force                               D. Gillmor
Internet-Draft                                                      ACLU
Updates: 4492, 5246, 4346, 2246 (if                        March 4, 2015
         approved)
Intended status: Informational
Expires: September 5, 2015

  Negotiated Finite Field Diffie-Hellman Ephemeral Parameters for TLS
                  draft-ietf-tls-negotiated-ff-dhe-07

Abstract

   Traditional finite-field-based Diffie-Hellman (DH) key exchange
   during the TLS handshake suffers from a number of security,
   interoperability, and efficiency shortcomings.  These shortcomings
   arise from lack of clarity about which DH group parameters TLS
   servers should offer and clients should accept.  This document offers
   a solution to these shortcomings for compatible peers by using a
   section of the TLS "EC Named Curve Registry" to establish common
   finite-field DH parameters with known structure and a mechanism for
   peers to negotiate support for these groups.

Status of This Memo

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   This Internet-Draft will expire on September 5, 2015.

Copyright Notice

   Copyright (c) 2015 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
   (http://trustee.ietf.org/license-info) in effect on the date of

Gillmor                 Expires September 5, 2015               [Page 1]
Internet-Draft          Negotiated-FF-DHE-for-TLS             March 2015

   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Vocabulary  . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Named Group Overview  . . . . . . . . . . . . . . . . . . . .   4
   3.  Client Behavior . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Server Behavior . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Optimizations . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Checking the Peer's Public Key  . . . . . . . . . . . . .   7
     5.2.  Short Exponents . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  Table Acceleration  . . . . . . . . . . . . . . . . . . .   8
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .   8
     6.1.  Preference Ordering . . . . . . . . . . . . . . . . . . .   8
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     9.1.  Negotiation resistance to active attacks  . . . . . . . .  10
     9.2.  Group strength considerations . . . . . . . . . . . . . .  11
     9.3.  Finite-Field DHE only . . . . . . . . . . . . . . . . . .  11
     9.4.  Deprecating weak groups . . . . . . . . . . . . . . . . .  11
     9.5.  Choice of groups  . . . . . . . . . . . . . . . . . . . .  12
     9.6.  Timing attacks  . . . . . . . . . . . . . . . . . . . . .  12
     9.7.  Replay attacks from non-negotiated FFDHE  . . . . . . . .  12
     9.8.  Forward Secrecy . . . . . . . . . . . . . . . . . . . . .  13
     9.9.  False Start . . . . . . . . . . . . . . . . . . . . . . .  13
   10. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  14
     10.1.  Client fingerprinting  . . . . . . . . . . . . . . . . .  14
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     11.2.  Informative References . . . . . . . . . . . . . . . . .  14
     11.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  16
   Appendix A.  Named Group Registry . . . . . . . . . . . . . . . .  16
     A.1.  ffdhe2048 . . . . . . . . . . . . . . . . . . . . . . . .  16
     A.2.  ffdhe3072 . . . . . . . . . . . . . . . . . . . . . . . .  17
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