Randomness Improvements for Security Protocols
draft-irtf-cfrg-randomness-improvements-03

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Last updated 2018-10-21
Replaces draft-sullivan-randomness-improvements
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Network Working Group                                         C. Cremers
Internet-Draft                                                L. Garratt
Intended status: Informational                      University of Oxford
Expires: April 24, 2019                                    S. Smyshlyaev
                                                               CryptoPro
                                                             N. Sullivan
                                                              Cloudflare
                                                                 C. Wood
                                                              Apple Inc.
                                                        October 21, 2018

             Randomness Improvements for Security Protocols
               draft-irtf-cfrg-randomness-improvements-03

Abstract

   Randomness is a crucial ingredient for TLS and related security
   protocols.  Weak or predictable "cryptographically-strong"
   pseudorandom number generators (CSPRNGs) can be abused or exploited
   for malicious purposes.  The Dual EC random number backdoor and
   Debian bugs are relevant examples of this problem.  An initial
   entropy source that seeds a CSPRNG might be weak or broken as well,
   which can also lead to critical and systemic security problems.  This
   document describes a way for security protocol participants to
   augment their CSPRNGs using long-term private keys.  This improves
   randomness from broken or otherwise subverted CSPRNGs.

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
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   This Internet-Draft will expire on April 24, 2019.

Cremers, et al.          Expires April 24, 2019                 [Page 1]
Internet-Draft           Randomness Improvements            October 2018

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Randomness Wrapper  . . . . . . . . . . . . . . . . . . . . .   3
   3.  Tag Generation  . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Application to TLS  . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Comparison to RFC 6979  . . . . . . . . . . . . . . . . . . .   6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Randomness is a crucial ingredient for TLS and related transport
   security protocols.  TLS in particular uses random number generators
   (generally speaking, CSPRNGs) to generate several values: session
   IDs, ephemeral key shares, and ClientHello and ServerHello random
   values.  CSPRNG failures such as the Debian bug described in
   [DebianBug] can lead to insecure TLS connections.  CSPRNGs may also
   be intentionally weakened to cause harm [DualEC].  Initial entropy
   sources can also be weak or broken, and that would lead to insecurity
   of all CSPRNG instances seeded with them.  In such cases where
   CSPRNGs are poorly implemented or insecure, an adversary may be able
   to predict its output and recover secret Diffie-Hellman key shares
   that protect the connection.

   This document proposes an improvement to randomness generation in
   security protocols inspired by the "NAXOS trick" [NAXOS].
   Specifically, instead of using raw randomness where needed, e.g., in
   generating ephemeral key shares, a party's long-term private key is
   mixed into the entropy pool.  In the NAXOS key exchange protocol, raw
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