Randomness Improvements for Security Protocols
draft-irtf-cfrg-randomness-improvements-00

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Last updated 2018-04-08 (latest revision 2018-03-23)
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: September 24, 2018                                S. Smyshlyaev
                                                               CryptoPro
                                                             N. Sullivan
                                                              Cloudflare
                                                                 C. Wood
                                                              Apple Inc.
                                                          March 23, 2018

             Randomness Improvements for Security Protocols
             draft-irtf-cfrg-randomness-improvements-00

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.  This document
   describes a way for security protocol participants to mix their long-
   term private key into the entropy pool(s) from which random values
   are derived.  This augments and 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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on September 24, 2018.

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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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

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

1.  Introduction

   Randomness is a crucial ingredient for TLS and related transport
   security protocols.  TLS in particular uses Random Number Generators
   (RNGs) to generate several values: session IDs, ephemeral key shares,
   and ClientHello and ServerHello random values.  RNG failures such as
   the Debian bug described in [DebianBug] can lead to insecure TLS
   connections.  RNGs may also be intentionally weakened to cause harm
   [DualEC].  In such cases where RNGs 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 entropy 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
   entropy output x is replaced by H(x, sk), where sk is the sender's
   private key.  Unfortunately, as private keys are often isolated in
   HSMs, direct access to compute H(x, sk) is impossible.  An alternate
   yet functionally equivalent construction is needed.

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