Internet DRAFT - draft-wallace-est-alt-challenge
draft-wallace-est-alt-challenge
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
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Internet-Drafts are draft documents valid for a maximum of six months
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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
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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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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