Best practices for password hashing and storage
draft-ietf-kitten-password-storage-00

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Last updated 2020-05-20
Replaces draft-whited-kitten-password-storage
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Common Authentication Technology Next Generation               S. Whited
Internet-Draft                                               20 May 2020
Intended status: Best Current Practice                                  
Expires: 21 November 2020

            Best practices for password hashing and storage
                 draft-ietf-kitten-password-storage-00

Abstract

   This document outlines best practices for handling user passwords and
   other authenticator secrets in client-server systems making use of
   SASL.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 21 November 2020.

Copyright Notice

   Copyright (c) 2020 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 carefully, as they describe your rights
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   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Terminology . . . . . . . . . . . . . . .   2
   2.  SASL Mechanisms . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Client Best Practices . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Mechanism Pinning . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Storage . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Server Best Practices . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Additional SASL Requirements  . . . . . . . . . . . . . .   5
     4.2.  Storage . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Authentication and Rotation . . . . . . . . . . . . . . .   6
   5.  KDF Recommendations . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Argon2  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Bcrypt  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  PBKDF2  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.4.  Scrypt  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Password Complexity Requirements  . . . . . . . . . . . . . .   8
   7.  Internationalization Considerations . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   Following best practices when hashing and storing passwords for use
   with SASL impacts a great deal more than just a user's identity.  It
   also affects usability, backwards compatibility, and interoperability
   by determining what authentication and authorization mechanisms can
   be used.

1.1.  Conventions and Terminology

   Various security-related terms are to be understood in the sense
   defined in [RFC4949].  Some may also be defined in [NISTSP63-3]
   Appendix A.1 and in [NISTSP132] section 3.1.

   Throughout this document the term "password" is used to mean any
   password, passphrase, PIN, or other memorized secret.

   Other common terms used throughout this document include:

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   Pepper  A secret added to a password hash like a salt.  Unlike a
      salt, peppers are secret and not unique.  They must not be stored
      alongside the hashed password.

   Mechanism pinning  A security mechanism which allows SASL clients to
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