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Versions: 00 01 02 03 04 05 06 07 08 RFC 7894

Network Working Group                                        M. Pritikin
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                              C. Wallace
Expires: October 15, 2016                       Red Hound Software, Inc.
                                                          April 13, 2016


  Alternative Challenge Password Attributes for Enrollment over Secure
                               Transport
                   draft-wallace-est-alt-challenge-08

Abstract

   This document defines a set of new Certificate Signing Request
   attributes for use with the Enrollment over Secure Transport (EST)
   protocol.  These attributes provide disambiguation of the existing
   overloaded uses for the challengePassword attribute defined in PKCS
   (Public-Key Cryptography Standards) #9 (RFC2985).  Uses include the
   original certificate revocation password, common authentication
   password uses, and EST-defined linking of transport security
   identity.

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 October 15, 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



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   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Alternative Challenge Password Attributes . . . . . . . . . .   3
     3.1.  OTP Challenge Attribute . . . . . . . . . . . . . . . . .   4
     3.2.  Revocation Challenge Attribute  . . . . . . . . . . . . .   4
     3.3.  EST Identity Linking Attribute  . . . . . . . . . . . . .   5
   4.  Indicating Support for the Alternative Challenge Attributes .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  ASN.1 Module . . . . . . . . . . . . . . . . . . . .   8
   Appendix B.  Acknowledgements . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   PKCS (Public-Key Cryptography Standards) #9 [RFC2985] defined a
   challengePassword attribute that has been overloaded by modern
   protocol usage with the appropriate interpretation being provided by
   context rather than OID definition.  PKCS #9 defines the
   challengePassword attribute as "a password by which an entity may
   request certificate revocation".  The parsing and embedding of this
   attribute within Certificate Signing Requests is well supported by
   common PKI tool sets, but many work-flows leverage this supported
   field as a one-time password for authentication.  For example this is
   codified in many Simple Certificate Enrollment Protocol (SCEP)
   implementations as indicated by [I-D.gutmann-scep].  Continuing this
   trend, Enrollment over Secure Transport (EST) [RFC7030] defines an
   additional semantic for the challengePassword attribute in
   Section 3.5, in order to provide a linking of the Certificate Signing
   Request (CSR) to the secure transport.

   Where the context of the protocol operation fully defined the proper
   semantic, and when only one use was required at a time, the
   overloading of this field did not cause difficulties.  Implementation
   experience with EST has shown this to be a limitation though.  There
   are plausible use cases where it is valuable to use either of the
   existing methods separately or in concert.  For example an EST server



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   might require the client to authenticate itself using the existing
   client X.509 certificate, the user's username and password and to
   include a one-time password within the CSR all while maintaining
   identity linking to bind the CSR to the secure transport.  The
   overloading of a single attribute type should not be the limiting
   factor for administrators attempting to meet their security
   requirements.

   This document defines the otpChallenge attribute for use when a one-
   time password (OTP) value within the CSR is a requirement.  The
   revocationChallenge attribute is defined to allow disambiguated usage
   of the original challenge password attribute semantics for
   certificate revocation.  The estIdentityLinking attribute is defined
   to reference existing EST challenge password semantics with no
   potential for confusion with legacy challenge password practices.

   The attributes defined in this specification supplement existing EST
   mechanisms and are not intended to displace current usage of any
   existing EST authentication mechanisms.  Conveying the authentication
   value itself as an attribute may be preferable to using an HTTP or
   Transport Layer Security (TLS) password or other TLS authentication
   mechanism in environments where the certificate request processing
   component is removed from the HTTP/TLS termination point, for
   example, when a web application firewall is used.

2.  Terminology

   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 [RFC2119].

3.  Alternative Challenge Password Attributes

   The following sections describe three alternative challenge password
   attributes for use with EST [RFC7030].  Appendix A provides an ASN.1
   module containing the new definitions.

   Each attribute described below is defined as a DirectoryString with
   maximum length 255, which features several possible encoding options.
   Attribute values generated in accordance this document SHOULD use the
   PrintableString encoding whenever possible.  If internationalization
   issues make this impossible, the UTF8String alternative SHOULD be
   used.  Attribute processing systems MUST be able to recognize and
   process the PrintableString and UTF8String string types in
   DirectoryString values.  Support for other string types is OPTIONAL.






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3.1.  OTP Challenge Attribute

   The otpChallenge attribute is defined as a DirectoryString with an
   maximum length of 255.  This is consistent with the challengePassword
   attribute as originally defined in PKCS#9 [RFC2985].  The
   otpChallenge attribute is identified by the id-aa-otpChallenge object
   identifier.  This facilitates reuse of existing challengePassword
   code by associating the new object identifiers with the existing
   parsing and generation code.  This attribute provides a means of
   conveying a one-time password value as part of a CSR request.
   Generation, verification, storage, etc. of the value is not addressed
   by this specification.  [RFC4226] and [RFC6238] define one-time
   password mechanisms that MAY be used with this attribute.

      ub-aa-otpChallenge INTEGER ::= 255
      id-aa-otpChallenge OBJECT IDENTIFIER ::= {
          id-smime TBD1
      }
      otpChallenge ATTRIBUTE ::= {
          WITH SYNTAX DirectoryString {ub-aa-otpChallenge}
          EQUALITY MATCHING RULE caseExactMatch
          SINGLE VALUE TRUE
          ID id-aa-otpChallenge
      }

3.2.  Revocation Challenge Attribute

   The original PKCS#9 challengePassword field has been overloaded and
   the common use is unclear.  The revocationChallenge attribute defined
   here provides an unambiguous method of indicating the original PKCS#9
   intent for this attribute type.  The revocationChallenge attribute is
   identified by the id-aa-revocationChallenge object identifier.
   [RFC2985] discusses the original semantics for the PKCS #9 challenge
   password attribute.

      ub-aa-revocationChallenge INTEGER ::= 255
      id-aa-revocationChallenge OBJECT IDENTIFIER ::= {
          id-smime TBD2
      }
      revocationChallenge ATTRIBUTE ::= {
          WITH SYNTAX DirectoryString {ub-aa-revocationChallenge}
          EQUALITY MATCHING RULE caseExactMatch
          SINGLE VALUE TRUE
          ID id-aa-revocationChallenge
      }






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3.3.  EST Identity Linking Attribute

   EST defines a mechanism for associating identity information from an
   authenticated TLS session with proof-of-possession information in a
   certificate request.  The mechanism was labeled using the pkcs-9-at-
   challengePassword identifier from [RFC2985].  To avoid any confusion
   with the semantics described in [RFC2985] or any other specifications
   that similarly defined use of the PKCS #9 challenge password
   attribute for their own purposes, a new object identifier is defined
   here and associated with the semantics described in section 3.5 of
   [RFC7030].

      ub-aa-est-identity-linking INTEGER ::= 255
      id-aa-estIdentityLinking OBJECT IDENTIFIER ::= {
          id-smime TBD3
      }
      estIdentityLinking ATTRIBUTE ::= {
          WITH SYNTAX DirectoryString {ub-aa-est-identity-linking}
          EQUALITY MATCHING RULE caseExactMatch
          SINGLE VALUE TRUE
          ID id-aa-estIdentityLinking
      }

4.  Indicating Support for the Alternative Challenge Attributes

   The EST server MUST indicate these attributes, as the particular use
   case requires, in every CSR Attributes Response.  An EST server MAY
   send both the "estIdentityLinking" and also the [RFC7030]
   "challengePassword" in a CSR Attrs response to ensure support for
   legacy [RFC7030] clients.

   The client MUST include every indicated attribute for which it has
   values in the subsequent CSR.  If a client sees "estIdentityLinking"
   in a CSR Attributes Response it SHOULD prefer that and not include an
   [RFC7030] "challengePassword" in the resulting CSR.  EST clients that
   include an unsolicited "estIdentityLinking" attribute MAY also
   include the [RFC7030] "challengePassword" attribute to ensure support
   for legacy [RFC7030] servers.

   EST servers MUST evaluate each challenge attribute independently.
   All challenge attributes included by an EST client MUST be
   successfully processed by an EST server for a request to be
   considered valid.  The EST server MAY ignore challenge attributes
   according to local policy, for example if the EST client is an
   authenticated Registration Authority the EST server ignores the
   "estIdentityLinking" within a CSR (see Section 3.7 of [RFC7030]).
   The EST server MAY refuse enrollment requests that are not encoded
   according to the CA's policy.



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5.  Security Considerations

   In addition to the security considerations expressed in the EST
   specification [RFC7030], additional security considerations may be
   associated with the mechanism used to generate and verify the
   otpChallenge value.  Where a one-time password is used, the security
   considerations expressed in the "HOTP: An HMAC-Based One-Time
   Password Algorithm" [RFC4226] or "TOTP: Time-Based One-Time Password
   Algorithm" [RFC6238] specifications may be relevant.  Similarly, the
   security considerations from [RFC2985] that apply to the challenge
   attribute are relevant as well.

6.  IANA Considerations

   Section 3 defines three attributes that need object identifier
   assignments from the SMI Security for S/MIME Attributes
   (1.2.840.113549.1.9.16.2) registry [RFC7107].

   [RFC Editor: please replace the TBDx references below, in section
   3.1, in section 3.2, in section 3.3 and in Appendix A.]

            Value     Description                        Reference
            --------  ---------------------------------  ---------
            TBD1      id-aa-otpChallenge                 [this document]
            TBD2      id-aa-revocationChallenge          [this document]
            TBD3      id-aa-estIdentityLinking           [this document]

   Appendix A contains an ASN.1 module, and a module identifier needs to
   be assigned from the SMI Security for PKIX Module Identifier registry
   [RFC7299].

            Value     Description                        Reference
            --------  ---------------------------------  ---------
            TBD4      id-mod-EST-Alt-Challenge           [this document]

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2985]  Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
              Classes and Attribute Types Version 2.0", RFC 2985,
              DOI 10.17487/RFC2985, November 2000,
              <http://www.rfc-editor.org/info/rfc2985>.



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   [RFC5272]  Schaad, J. and M. Myers, "Certificate Management over CMS
              (CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
              <http://www.rfc-editor.org/info/rfc5272>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC5912]  Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
              Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
              DOI 10.17487/RFC5912, June 2010,
              <http://www.rfc-editor.org/info/rfc5912>.

   [RFC7030]  Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
              "Enrollment over Secure Transport", RFC 7030,
              DOI 10.17487/RFC7030, October 2013,
              <http://www.rfc-editor.org/info/rfc7030>.

7.2.  Informative References

   [RFC4226]  M'Raihi, D., Bellare, M., Hoornaert, F., Naccache, D., and
              O. Ranen, "HOTP: An HMAC-Based One-Time Password
              Algorithm", RFC 4226, DOI 10.17487/RFC4226, December 2005,
              <http://www.rfc-editor.org/info/rfc4226>.

   [RFC6238]  M'Raihi, D., Machani, S., Pei, M., and J. Rydell, "TOTP:
              Time-Based One-Time Password Algorithm", RFC 6238,
              DOI 10.17487/RFC6238, May 2011,
              <http://www.rfc-editor.org/info/rfc6238>.

   [RFC7107]  Housley, R., "Object Identifier Registry for the S/MIME
              Mail Security Working Group", RFC 7107,
              DOI 10.17487/RFC7107, January 2014,
              <http://www.rfc-editor.org/info/rfc7107>.

   [RFC7299]  Housley, R., "Object Identifier Registry for the PKIX
              Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014,
              <http://www.rfc-editor.org/info/rfc7299>.

   [I-D.gutmann-scep]
              Gutmann, P. and J. Marcon, "Simple Certificate Enrolment
              Protocol", draft-gutmann-scep-01 (work in progress),
              September 2015.






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Appendix A.  ASN.1 Module

   The following ASN.1 module includes the definitions to support usage
   of the attributes defined in this specification.  Modules from
   [RFC5912] are imported (original standards-track source for the
   imported structures is [RFC5280] and [RFC5272].

   Mod-EST-Alt-Challenge {
      iso(1) identified-organization(3) dod(6) internet(1) security(5)
         mechanisms(5) pkix(7) id-mod(0) TBD4
   }

   DEFINITIONS IMPLICIT TAGS ::=
   BEGIN
   IMPORTS

   DirectoryString{}
   FROM PKIX1Explicit-2009 {
      iso(1) identified-organization(3) dod(6) internet(1) security(5)
      mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51)
   }

   ATTRIBUTE
   FROM PKIX-CommonTypes-2009 {
      iso(1) identified-organization(3) dod(6) internet(1) security(5)
      mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57)
   };

   ub-aa-otpChallenge INTEGER ::= 255
   id-aa-otpChallenge OBJECT IDENTIFIER ::= {
      iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
      smime(16) aa(2) TBD1
   }
   otpChallenge ATTRIBUTE ::= {
      TYPE DirectoryString {ub-aa-otpChallenge}
      COUNTS MIN 1 MAX 1
      IDENTIFIED BY id-aa-otpChallenge
   }
   ub-aa-revocationChallenge INTEGER ::= 255
   id-aa-revocationChallenge OBJECT IDENTIFIER ::= {
      iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
      smime(16) aa(2) TBD2
   }
   revocationChallenge ATTRIBUTE ::= {
      TYPE DirectoryString {ub-aa-revocationChallenge}
      COUNTS MIN 1 MAX 1
      IDENTIFIED BY id-aa-revocationChallenge
   }



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   ub-aa-est-identity-linking INTEGER ::= 255
   id-aa-estIdentityLinking OBJECT IDENTIFIER ::= {
      iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
      smime(16) aa(2) TBD3
   }
   estIdentityLinking ATTRIBUTE ::= {
      TYPE DirectoryString {ub-aa-est-identity-linking}
      COUNTS MIN 1 MAX 1
      IDENTIFIED BY id-aa-estIdentityLinking
   }
   END

Appendix B.  Acknowledgements

   Thanks to Jim Schaad, Dan Harkins, Phil Scheffler, Geoff Beier, Mike
   Jenkins and Deb Cooley for their feedback.

Authors' Addresses

   Max Pritikin
   Cisco Systems, Inc.
   510 McCarthy Drive
   Milpitas, CA  95035
   USA

   Email: pritikin@cisco.com


   Carl Wallace
   Red Hound Software, Inc.

   Email: carl@redhoundsoftware.com



















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