Network Working Group M. Pritikin
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track C. Wallace
Expires: April 19, 2016 Red Hound Software, Inc.
October 17, 2015
Alternative Challenge Password Attributes for Enrollment over Secure
Transport
draft-wallace-est-alt-challenge-01
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.
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This Internet-Draft will expire on April 19, 2016.
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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 [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, 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 all string
types in DirectoryString values.
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
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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.
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
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attribute for their purposes, a new object identifier is defined here
and associated with the semantics described in section 3.5 of
[RFC7030].
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].
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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].
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>.
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[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>.
[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. and J. Marcon, "Simple Certificate Enrolment
Protocol", draft-gutmann-scep-01 (work in progress),
September 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)
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mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57)
};
ub-otpChallenge INTEGER ::= 255
id-otpChallenge OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) aa(2) TBD
}
otpChallenge ATTRIBUTE ::= {
TYPE DirectoryString {ub-otpChallenge}
COUNTS MIN 1 MAX 1
IDENTIFIED BY id-otpChallenge
}
ub-revocationChallenge INTEGER ::= 255
id-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-revocationChallenge}
COUNTS MIN 1 MAX 1
IDENTIFIED BY id-revocationChallenge
}
ub-est-identity-linking INTEGER ::= 255
id-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-est-identity-linking}
COUNTS MIN 1 MAX 1
IDENTIFIED BY id-estIdentityLinking
}
END
Appendix B. Acknowledgements
Thanks to Phil Scheffler, Geoff Beier, Mike Jenkins and Deb Cooley
for their feedback.
Authors' Addresses
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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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