Alternative Challenge Password Attributes for Enrollment over Secure Transport
draft-wallace-est-alt-challenge-00

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Last updated 2015-10-16 (latest revision 2015-08-03)
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Network Working Group                                        M. Pritikin
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                              C. Wallace
Expires: February 4, 2016                       Red Hound Software, Inc.
                                                          August 3, 2015

  Alternative Challenge Password Attributes for Enrollment over Secure
                               Transport
                   draft-wallace-est-alt-challenge-00

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 PKCS #9 challengePassword attribute.  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
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   This Internet-Draft will expire on February 4, 2016.

Copyright Notice

   Copyright (c) 2015 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
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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

1.  Introduction

   PKCS #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 SCEP implementations as indicated by
   [I-D.gutmann-scep].  Continuing this trend, Enrollment over Secure
   Transport [RFC7030] defines an additional semantic for the
   challengePassword attribute in Section 3.5, in order to provide a
   linking of the Certificate Signing Request 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
   might require the client to authenticate itself using the existing
   client x509 certificate, the user's username and password and to

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   include a One Time Password within the Certificate Signing Request
   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 is 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
   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 RFC 2119.

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.

3.1.  OTP Challenge Attribute

   The otpChallenge attribute is defined as a DirectoryString with an
   upper bound of 255.  This is consistent with the challengePassword
   attribute as originally defined in PKCS#9.  The otpChallenge
   attribute is identified by the id-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 an CSR request.  Generation,
   verification, storage, etc.  of the values is not addressed by this
   specification.

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

3.2.  PKCS #9 Challenge Password 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 revocation Challenge attribute
   is identified by the id-revocationChallenge object identifier.
   [RFC2985] discusses the original semantics for the PKCS #9 challenge
   password attribute.

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

3.3.  EST Identity Linking Attribute

   EST defines a mechanism for association 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 using of the PKCS #9 challenge password
   attribute for their purposes, a new object identifier is defined here
   and associated with the semantics described in section 3.5 of
   [RFC7030].

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

4.  Indicating Support for the Alternative Challenge Password Attributes

   The EST server MAY indicate any or all of these in the /csrattrs.
   The EST client SHOULD include the indicated attributes in the
   subsequent CSR.  The EST server can of course refuse enrollment
   requests that are not encoded according to the CA's policy.

   Note that the "estIdentityLinking" attribute is a disambiguated
   alternative to the overloading of the "challengePassword" in section
   3.5 of [RFC7030], therefore any EST server that requests
   "estIdentityLinking" MUST check the [RFC7030] "challengePassword" as
   specified in [RFC7030] as well as the "estIdentityLinking" requested
   in order to support legacy EST clients.  EST clients that include the
   "estIdentityLinking" attribute SHOULD NOT also include the
   "challengePassword" attribute.

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 [RFC4226] or TOTP [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 an OID (id-otpChallenge) that should be assigned in
   the S/MIME arc maintained by IANA as described in section 3.5 of
   [RFC7107].

   Appendix A defines an OID (EST-Alt-Challenge-Module) that should be
   assigned in the PKIX arc maintained by IANA as described in section
   3.3 of [RFC7299].

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               Value     Description                        Reference
               --------  ---------------------------------  ---------
               TBD1      id-otpChallenge                    [RFC7107]
               TBD2      id-revocationChallenge             [RFC7107]
               TBD3      id-estIdentityLinking              [RFC7107]
               TBD4      EST-Alt-Challenge-Module           [RFC7299]

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>.

   [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>.

7.2.  Informative References

   [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>.

   [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>.

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   [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>.

   [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., Pritikin, M., Nourse, A., and J. Vilhuber,
              "Simple Certificate Enrolment Protocol", draft-gutmann-
              scep-00 (work in progress), March 2015.

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].

   EST-Alt-Challenge-Module {
      id-pkix 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-otpChallenge INTEGER ::= 255
   id-otpChallenge OBJECT IDENTIFIER ::= {

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      iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
      smime(16) aa(2) TBD
   }
   otpChallenge ATTRIBUTE ::= {
      WITH SYNTAX DirectoryString {ub-otpChallenge}
      EQUALITY MATCHING RULE caseExactMatch
      SINGLE VALUE TRUE
      ID id-otpChallenge
   }
   ub-revocationChallenge INTEGER ::= 255
   id-revocationChallenge OBJECT IDENTIFIER ::= {
      id-smime TBD2
   }
   revocationChallenge ATTRIBUTE ::= {
      WITH SYNTAX DirectoryString {ub-revocationChallenge}
      EQUALITY MATCHING RULE caseExactMatch
      SINGLE VALUE TRUE
      ID id-revocationChallenge
   }
   ub-est-identity-linking INTEGER ::= 255
   id-estIdentityLinking OBJECT IDENTIFIER ::= {
      id-smime TBD3
   }
   estIdentityLinking ATTRIBUTE ::= {
      WITH SYNTAX DirectoryString {ub-est-identity-linking}
      EQUALITY MATCHING RULE caseExactMatch
      SINGLE VALUE TRUE
      ID id-estIdentityLinking
   }
   END

Appendix B.  Acknowledgements

   Thanks to 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

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   Carl Wallace
   Red Hound Software, Inc.

   Email: carl@redhoundsoftware.com

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