Negotiated Finite Field Diffie-Hellman Ephemeral Parameters for TLS
draft-ietf-tls-negotiated-ff-dhe-10

Document Type Active Internet-Draft (tls WG)
Last updated 2015-10-14 (latest revision 2015-06-01)
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                         June 1, 2015
         approved)
Intended status: Standards Track
Expires: December 3, 2015

  Negotiated Finite Field Diffie-Hellman Ephemeral Parameters for TLS
                  draft-ietf-tls-negotiated-ff-dhe-10

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.

   This draft updates TLS versions 1.0 [RFC2246], 1.1 [RFC4346], and 1.2
   [RFC5246], as well as the TLS ECC extensions [RFC4492].

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
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   This Internet-Draft will expire on December 3, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Gillmor                 Expires December 3, 2015                [Page 1]
Internet-Draft          Negotiated-FF-DHE-for-TLS              June 2015

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Vocabulary  . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Named Group Overview  . . . . . . . . . . . . . . . . . . . .   4
   3.  Client Behavior . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Client Local Policy on Custom Groups  . . . . . . . . . .   6
   4.  Server Behavior . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Optimizations . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Checking the Peer's Public Key  . . . . . . . . . . . . .   8
     5.2.  Short Exponents . . . . . . . . . . . . . . . . . . . . .   8
     5.3.  Table Acceleration  . . . . . . . . . . . . . . . . . . .   8
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .   8
     6.1.  Preference Ordering . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
     9.1.  Negotiation resistance to active attacks  . . . . . . . .  10
     9.2.  Group strength considerations . . . . . . . . . . . . . .  11
     9.3.  Finite-Field DHE only . . . . . . . . . . . . . . . . . .  12
     9.4.  Deprecating weak groups . . . . . . . . . . . . . . . . .  12
     9.5.  Choice of groups  . . . . . . . . . . . . . . . . . . . .  12
     9.6.  Timing attacks  . . . . . . . . . . . . . . . . . . . . .  13
     9.7.  Replay attacks from non-negotiated FFDHE  . . . . . . . .  13
     9.8.  Forward Secrecy . . . . . . . . . . . . . . . . . . . . .  13
     9.9.  False Start . . . . . . . . . . . . . . . . . . . . . . .  14
   10. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  14
     10.1.  Client fingerprinting  . . . . . . . . . . . . . . . . .  14
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  15
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