Hardening DNSSEC against collision weaknesses in SHA-1 and other cryptographic hash algorithms
draft-fanf-dnsop-sha-ll-not-00

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Last updated 2020-03-09
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DNS Operations                                                  T. Finch
Internet-Draft                                   University of Cambridge
Updates: 8624 (if approved)                                March 9, 2020
Intended status: Standards Track
Expires: September 10, 2020

    Hardening DNSSEC against collision weaknesses in SHA-1 and other
                     cryptographic hash algorithms
                     draft-fanf-dnsop-sha-ll-not-00

Abstract

   DNSSEC deployments have often used the SHA-1 cryptographic hash
   algorithm to provide authentication of DNS data.  This document
   explains why SHA-1 is no longer secure for this purpose, and
   deprecates its use in DNSSEC signatures.  This document updates RFC
   8624.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 10, 2020.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   include Simplified BSD License text as described in Section 4.e of

Finch                  Expires September 10, 2020               [Page 1]
Internet-Draft         DNSSEC vs collision attacks            March 2020

   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Deprecating SHA-1 in DNSSEC . . . . . . . . . . . . . . . . .   3
     2.1.  DNSSEC signing software . . . . . . . . . . . . . . . . .   4
     2.2.  DNS hosting services  . . . . . . . . . . . . . . . . . .   4
     2.3.  DNSSEC validating software  . . . . . . . . . . . . . . .   4
     2.4.  DNS resolver services . . . . . . . . . . . . . . . . . .   5
   3.  Collision attacks against DNSSEC  . . . . . . . . . . . . . .   5
     3.1.  Chosen-prefix collisions  . . . . . . . . . . . . . . . .   5
     3.2.  Collision attacks and signatures  . . . . . . . . . . . .   5
     3.3.  Breaking DNSSEC . . . . . . . . . . . . . . . . . . . . .   6
     3.4.  Collision attacks and RRSIG records . . . . . . . . . . .   6
   4.  Hardening RRSIG records . . . . . . . . . . . . . . . . . . .   7
     4.1.  Predicting inception and expiration times . . . . . . . .   8
     4.2.  Unpredictable X.509 certificates  . . . . . . . . . . . .   8
     4.3.  Less predictable RRSIG records  . . . . . . . . . . . . .   9
   5.  Collision attacks and other DNS record types  . . . . . . . .   9
     5.1.  TXT records . . . . . . . . . . . . . . . . . . . . . . .   9
       5.1.1.  Syntax of TXT records . . . . . . . . . . . . . . . .  10
       5.1.2.  Mitigating TXT record attacks . . . . . . . . . . . .  10
     5.2.  CAA records . . . . . . . . . . . . . . . . . . . . . . .  10
     5.3.  SSHFP records . . . . . . . . . . . . . . . . . . . . . .  11
     5.4.  DNSKEY records  . . . . . . . . . . . . . . . . . . . . .  11
       5.4.1.  Shared keys . . . . . . . . . . . . . . . . . . . . .  11
       5.4.2.  Combined signing keys . . . . . . . . . . . . . . . .  11
     5.5.  DS records  . . . . . . . . . . . . . . . . . . . . . . .  12
   6.  Other uses of SHA-1 in the DNS  . . . . . . . . . . . . . . .  12
     6.1.  DS and CDS records  . . . . . . . . . . . . . . . . . . .  12
     6.2.  NSEC3 records . . . . . . . . . . . . . . . . . . . . . .  13
     6.3.  SSHFP records . . . . . . . . . . . . . . . . . . . . . .  13
     6.4.  TSIG authentication . . . . . . . . . . . . . . . . . . .  13
   7.  Security considerations . . . . . . . . . . . . . . . . . . .  13
     7.1.  Staying secure  . . . . . . . . . . . . . . . . . . . . .  14
     7.2.  When to declare SHA-1 insecure  . . . . . . . . . . . . .  14
     7.3.  Avoiding unwanted insecurity  . . . . . . . . . . . . . .  14
   8.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  14
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
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