Salted Challenge Response HTTP Authentication Mechanism
RFC 7804

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Internet Engineering Task Force (IETF)                       A. Melnikov
Request for Comments: 7804                                     Isode Ltd
Category: Experimental                                        March 2016
ISSN: 2070-1721

        Salted Challenge Response HTTP Authentication Mechanism

Abstract

   This specification describes a family of HTTP authentication
   mechanisms called the Salted Challenge Response Authentication
   Mechanism (SCRAM), which provides a more robust authentication
   mechanism than a plaintext password protected by Transport Layer
   Security (TLS) and avoids the deployment obstacles presented by
   earlier TLS-protected challenge response authentication mechanisms.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7804.

Melnikov                      Experimental                      [Page 1]
RFC 7804                       HTTP SCRAM                     March 2016

Copyright Notice

   Copyright (c) 2016 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
   (http://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 and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.  Conventions Used in This Document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Notation  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  SCRAM Algorithm Overview  . . . . . . . . . . . . . . . . . .   6
   4.  SCRAM Mechanism Names . . . . . . . . . . . . . . . . . . . .   7
   5.  SCRAM Authentication Exchange . . . . . . . . . . . . . . . .   7
     5.1.  One Round-Trip Reauthentication . . . . . . . . . . . . .  10
   6.  Use of the Authentication-Info Header Field with SCRAM  . . .  12
   7.  Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . .  13
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   10. Design Motivations  . . . . . . . . . . . . . . . . . . . . .  15
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     11.2.  Informative References . . . . . . . . . . . . . . . . .  17
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  18
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   The authentication mechanism most widely deployed and used by
   Internet application protocols is the transmission of clear-text
   passwords over a channel protected by Transport Layer Security (TLS).
   There are some significant security concerns with that mechanism,
   which could be addressed by the use of a challenge response
   authentication mechanism protected by TLS.  Unfortunately, the HTTP
   Digest challenge response mechanism presently on the Standards Track
   failed widespread deployment and has had only limited success.

Melnikov                      Experimental                      [Page 2]
RFC 7804                       HTTP SCRAM                     March 2016

   This specification describes a family of authentication mechanisms
   called the Salted Challenge Response Authentication Mechanism
   (SCRAM), which addresses the requirements necessary to deploy a
   challenge response mechanism more widely than past attempts (see
   [RFC5802]).  In particular, it addresses some of the issues
   identified with HTTP Digest, as described in [RFC6331], such as the
   complexity of implementation and protection of the whole
   authentication exchange in order to protect against certain man-in-
   the-middle attacks.

   HTTP SCRAM is an adaptation of [RFC5802] for use in HTTP.  The SCRAM