Adding Support for Salted Password Databases to EAP-pwd
draft-harkins-salted-eap-pwd-00

Internet Engineering Task Force                               D. Harkins
Internet-Draft                                            Aruba Networks
Updates: RFC5931 (if approved)                        September 30, 2014
Intended status: Informational
Expires: April 3, 2015

        Adding Support for Salted Password Databases to EAP-pwd
                    draft-harkins-salted-eap-pwd-00

Abstract

   EAP-pwd is an EAP method that uses a shared password for
   authentication using a technique that is resistant to dictionary
   attack.  It included support for raw keys and RFC2751-style double
   hashing of a password but did include support for salted passwords.
   There are many existing databases of salted passwords and it is
   desirable to allow their use with EAP-pwd.

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 http://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 April 3, 2015.

Copyright Notice

   Copyright (c) 2014 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

Harkins                   Expires April 3, 2015                 [Page 1]
Internet-Draft              Abbreviated Title             September 2014

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Background  . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Keyword Definition  . . . . . . . . . . . . . . . . . . .   2
   2.  Salted Passwords in EAP-pwd . . . . . . . . . . . . . . . . .   3
     2.1.  Password Pre-Processing . . . . . . . . . . . . . . . . .   3
     2.2.  The Salting of a Password . . . . . . . . . . . . . . . .   3
     2.3.  Using UNIX crypt  . . . . . . . . . . . . . . . . . . . .   3
     2.4.  Protocol Modifications  . . . . . . . . . . . . . . . . .   4
     2.5.  Payload Modifications . . . . . . . . . . . . . . . . . .   4
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

1.1.  Background

   Databases of stored passwords present an attractive target for
   attack-- get access to the database, learn the passwords.  To
   confound such attacks a random "salt" is hashed with the password and
   the resulting digest is stored, along with the salt, instead of the
   raw password.  This has the effect of randomizing the password so if
   two distinct users have chosen the same password the stored, and
   salted, password will be different.  It also requires an adversary
   who has compromized the security of the stored database to launch a
   dictionary attack per entry to recover passwords.

   The popularity of password salting means there are a large number of
   such databases deployed and EAP-pwd needs to be able to support them.
   EAP-pwd imposes an additional security requirement on a database of
   salted passwords that otherwise would not exist, see Section 5.

1.2.  Keyword Definition

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

Harkins                   Expires April 3, 2015                 [Page 2]
Internet-Draft              Abbreviated Title             September 2014

2.  Salted Passwords in EAP-pwd

2.1.  Password Pre-Processing

   EAP-pwd requires that each party to the protocol obtain an identical
   representation of a processed password (see Section 5).  Salting of a
   password is therefore treated as additional password pre-processing
   techniques of EAP-pwd.  The salt and digest to use is conveyed to the
   peer by the server and the password is processed prior to fixing the
   password element (see Section 2.8.3 of [RFC5931]).

   This memo defines four (4) new password pre-processing techniques for
   EAP-pwd:

   1.  TBD1: a random salt with SHA-1 ([SHS])

   2.  TBD2: a random salt with SHA-256 ([SHS])

   3.  TBD3: a random salt with SHA-512 ([SHS])

   4.  TBD4: UNIX crypt() ([CRY])

   When passing salt, the size of the salt SHOULD be at least as long as
   the message digest of the hash algorithm used.  There is no guarantee
   that deployed salted databases have followed this rule, and in the
   interest of interoperability, an EAP peer SHOULD NOT abort an EAP-pwd
   exchange if the salt conveyed during the exchange is less than the
   message digest of the indicated hash algorithm.

2.2.  The Salting of a Password

   For both parties to derive the same salted password there needs to be
   a canonical method of salting a password.  When using EAP-pwd, a
   password SHALL be salted by hashing the password followed by the salt
   using the designated hash function:

      salted-password = Hash(password | salt)

   The server stores the salted-password, and the salt, in its database
   and the client derives the salted-password on-the-fly.

2.3.  Using UNIX crypt

   Different algorithms are supported with the UNIX crypt() function.
   The particular algorithm used is indicated by prepending an encoding
   of "setting" to the passed salt.  The specific algorithm used is
   opaque to EAP-pwd as the entire salt, including the encoded
   "setting", is passed as an opaque string for interpretation by

Harkins                   Expires April 3, 2015                 [Page 3]
Internet-Draft              Abbreviated Title             September 2014

   crypt().  The salted password used for EAP-pwd SHALL be the output of
   crypt():

      salted-password = crypt(password, salt)

   The server stores the salted-password, and the encoded algorithm plus
   salt, in its database and the client derives the salted-password on-
   the-fly.

2.4.  Protocol Modifications

   Like all EAP methods, EAP-pwd is server initiated.  The server is
   required to indicate its intentions, including the password pre-
   processing it wishes to use, before it knows the identity of the
   client.

   The server uses the EAP-pwd-ID/Request to indicate the password pre-
   processing technique.  The client indicates its acceptance of the
   password pre-processing technique and identifies itself in the EAP-
   pwd-ID/Response.  Upon receipt of the EAP-pwd-ID/Response, the server
   knows the identity of the client and can look up the client's salted
   password and the salt from the database.  The server adds the length
   of the salt and the salt itself to the EAP-pwd-Commit/Request message
   (see Section 2.5).

   The server can fix the password element (Section 2.8.3 of [RFC5931])
   as soon as the salted password has been looked up in the database.
   The client, though, is required to wait until receipt of the server's
   EAP-pwd-Commit/Request before it begins fixing the password element.

2.5.  Payload Modifications

   When a salted password pre-processing technique is agreed upon during
   the EAP-pwd-ID exchange the EAP-pwd-Commit payload is modified to
   include the salt and salt length (see Figure 1).  The server passes
   the salt and salt length in the EAP-pwd-Commit/Request; the client's
   EAP-pwd-Commit/Response is unchanged and it MUST NOT echo the salt
   length and salt in its EAP-pwd-Commit/Response.

Harkins                   Expires April 3, 2015                 [Page 4]
Internet-Draft              Abbreviated Title             September 2014

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   salt-len    |                                               |
      +-+-+-+-+-+-+-+-+                                               ~
      ~                            Salt             +-+-+-+-+-+-+-+-+-+
      |                                             |                 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                 ~
      |                                                               |
      ~                           Element                             ~
      |                                                               |
      ~                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               ~
      |                                                               |
      ~                            Scalar             +-+-+-+-+-+-+-+-+
      |                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 1: Salted EAP-pwd-Commit/Request

   The "salt-len" SHALL be non-zero and indicates the length, in octets,
   of the salt that follows.  When using UNIX crypt for salting, the
   salt SHALL be an unterminated ASCII string.  For all other salting
   algorithms, the salt SHALL be a binary string with no additional
   encoding.  The Element and Scalar are encoded according to
   Section 3.3 of [RFC5931].

   Note: when a non-salted password pre-processing method is used, for
   example, any of the methods from [RFC5931] the EAP-pwd-Commit payload
   MUST NOT be modified to include the salt and salt length.

3.  Acknowledgements

   Thanks to the eduroam project for its continued interest in using
   EAP-pwd.

4.  IANA Considerations

   IANA is instructed to allocate four (4) values from the "password
   preprocessing method registry" established by [RFC5931] and replace
   TBD1, TBD2, TBD3, and TBD4 above with the values assigned.

5.  Security Considerations

   EAP-pwd requires each side to produce an identical representation of
   the (processed) password before the password element can be fixed.
   This symmetry undercuts one of the benefits to salting a password

Harkins                   Expires April 3, 2015                 [Page 5]
Internet-Draft              Abbreviated Title             September 2014

   database because the salted password from a compromised database can
   be used directly to impersonate the client-- there is no dictionary
   attack needed to recover the plaintext password.  Salted password
   databases used with EAP-pwd MUST be afforded the same level of
   protection as databases of plaintext passwords.

6.  Normative References

   [CRY]      "crypt(3) man page",
              <http://man7.org/linux/man-pages/man3/crypt.3.html>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5931]  Harkins, D. and G. Zorn, "Extensible Authentication
              Protocol (EAP) Authentication Using Only a Password", RFC
              5931, August 2010.

   [SHS]      National Institute of Standards and Technology, , "Federal
              Information Processing Standard Publication 180-4: Secure
              Hash Standard (SHS)", March 2012,
              <http://csrc.nist.gov/publications/fips/fips180-4/
              fips-180-4.pdf>.

Author's Address

   Dan Harkins
   Aruba Networks
   1322 Crossman Avenue
   Sunnyvale, CA  94089-1113
   United States of America

   Email: dharkins@arubanetworks.com

Harkins                   Expires April 3, 2015                 [Page 6]