Clarification of RFC7030 CSR Attributes definition
draft-ietf-lamps-rfc7030-csrattrs-00
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| Authors | Michael Richardson , Owen Friel , David von Oheimb , Dan Harkins | ||
| Last updated | 2022-09-16 (Latest revision 2022-08-15) | ||
| Replaces | draft-richardson-lamps-rfc7030-csrattrs | ||
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draft-ietf-lamps-rfc7030-csrattrs-00
LAMPS Working Group M. Richardson, Ed.
Internet-Draft Sandelman Software Works
Intended status: Standards Track O. Friel
Expires: 16 February 2023 Cisco
D. von Oheimb
Siemens
D. Harkins
The Industrial Lounge
15 August 2022
Clarification of RFC7030 CSR Attributes definition
draft-ietf-lamps-rfc7030-csrattrs-00
Abstract
The Enrollment over Secure Transport (EST, RFC7030) is ambiguous in
its specification of the CSR Attributes Response. This has resulted
in implementation challenges and implementor confusion.
This document updates RFC7030 (EST) and clarifies how the CSR
Attributes Response can be used by an EST server to specify both CSR
attribute OIDs and also CSR attribute values, in particular X.509
extension values, that the server expects the client to include in
subsequent CSR request.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 16 February 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CSR Attributes Handling . . . . . . . . . . . . . . . . . . . 3
3.1. Extensions to RFC 7030 section 2.6. . . . . . . . . . . . 3
3.2. Extensions to RFC 7030 section 4.5.2. . . . . . . . . . . 3
4. Co-existence with existing implementations . . . . . . . . . 5
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. RFC8994/ACP subjectAltName with specific otherName and
other extensions included . . . . . . . . . . . . . . . . 5
5.2. EST server requires public keys of a specific size . . . 6
5.3. EST server requires a public key of a specific algorithm/
curve . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.4. EST server requires a specific extension to be present . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6.1. Identity and Privacy Considerations . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
9. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Enrollment over Secure Transport [RFC7030] (EST) has been used in a
wide variety of applications. In particular, [RFC8994] and [RFC8995]
describe a way to use it in order to build out an autonomic control
plane (ACP) [RFC8368].
The ACP requires that each node be given a very specific
subjectAltName. In the ACP specification, the solution was for the
EST server to use section 2.6 of [RFC7030] to convey to the EST
client the actual subjectAltName that will end up in its certificate.
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As a result of some implementation challenges, it came to light that
this particular way of using the CSR attributes was not universally
agreed upon, and it was suggested that it went contrary to section
2.6.
Section 2.6 says that the CSR attributes "can provide additional
descriptive information that the EST server cannot access itself".
This is extened to mention also values that the EST server demands to
use.
After significant discussion, it has been determined that Section 4.5
of [RFC7030] specification is sufficiently difficult to read and
ambiguous to interpret that clarification is needed.
This document motivates the different use cases, and provides
additional worked out examples.
Also section 4.5.2 is extended to clarify the use of the existing
ASN.1 syntax. This covers all uses and is fully backward compatible
with the existing use.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. CSR Attributes Handling
3.1. Extensions to RFC 7030 section 2.6.
Replace the second paragraph with the following text.
These attributes can provide additional descriptive information that
the EST server cannot access itself, such as the Media Access Control
(MAC) address of an interface of the EST client. The EST server can
also provide concrete values that it tells the client to include in
the CSR, such as a specific X.509 Subject Alternative Name extension.
Moreover, these attributes can indicate the kind of enrollment
request, such as a specific elliptic curve or a specific hash
function that the client is expected to use when generating the CSR.
3.2. Extensions to RFC 7030 section 4.5.2.
The ASN.1 for CSR Attributes as defined in EST section 4.5.2 is:
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CsrAttrs ::= SEQUENCE SIZE (0..MAX) OF AttrOrOID
AttrOrOID ::= CHOICE (oid OBJECT IDENTIFIER, attribute Attribute }
Attribute { ATTRIBUTE:IOSet } ::= SEQUENCE {
type ATTRIBUTE.&id({IOSet}),
values SET SIZE(1..MAX) OF ATTRIBUTE.&Type({IOSet}{@type}) }
This remains unchanged, such that bits-on-the-wire compatibility is
maintained.
Key parts that were unclear were which OID to use in the 'type' field
and that the 'values' field can contain an entire sequence of X.509
extensions.
The OID to use for such extensions in the 'type' field MUST be
extensionRequest, which has the numerical value
1.2.840.113549.1.9.14. There MUST be only one such attribute.
The 'values' field of this attribute MUST contain a set with exactly
one element, and this element MUST by of type Extensions, as per
Section 4.1 of [RFC5280]:
Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
Extension ::= SEQUENCE {
extnID OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING
-- contains the DER encoding of an ASN.1 value
-- corresponding to the extension type identified
-- by extnID
}
In each such Extensions sequence, an extnID OID MUST appear at most
once.
An Extension comprises of the OID of the specific X.509 extension
(extnID), optionally the 'critical' bit, and the extension value
(extnValue).
(TODO: Do we want to allow an empty extnValue (which is of type OCTET
STRING), which would mean that the client is told to include an X.509
extension of the given type and fill in the concrete value itself?)
With this understanding, the needs of [RFC8994] and [RFC8995] are
satisfied with no change to the bits on the wire.
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(TODO: Do we want to give the empty list of Extensions a specific
meaning, such as, no X.509 extensions should be included in the CSR?)
(TODO: Note that this mechanism does not support telling the client
to include in the CSR a specific subject DN, simply because there is
no OID for this. I think we should better make this clear, or we
have to define such an OID if setting a subject name should be
supported.)
4. Co-existence with existing implementations
5. Examples
5.1. RFC8994/ACP subjectAltName with specific otherName and other
extensions included
This is a CSR Attributes object with two non-critical
basicConstraints and extKeyUsage extensions and a critical X.509
subjectAltName extension that contains both an RFC8994/ACP Subject
Alternative Name with a specific otherName and an example Subject
Alternative Name value of type dNSName.
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SEQUENCE {
SEQUENCE {
OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14)
SET {
SEQUENCE {
SEQUENCE {
OBJECT IDENTIFIER basicConstraints (2 5 29 19)
OCTET STRING, encapsulates {
SEQUENCE {}
}
}
SEQUENCE {
OBJECT IDENTIFIER extKeyUsage (2 5 29 37)
OCTET STRING, encapsulates {
SEQUENCE {
OBJECT IDENTIFIER serverAuth (1 3 6 1 5 5 7 3 1)
}
}
}
SEQUENCE {
OBJECT IDENTIFIER subjectAltName (2 5 29 17)
BOOLEAN TRUE
OCTET STRING, encapsulates {
SEQUENCE {
[0] {
OBJECT IDENTIFIER '1 3 6 1 5 5 7 8 10'
[0] {
IA5String
'fd89b714f3db00000200000064000000+area51.research'
'@acp.example.com'
}
}
[2] 'domain.example'
}
}
}
}
}
}
}
5.2. EST server requires public keys of a specific size
TBD
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5.3. EST server requires a public key of a specific algorithm/curve
TBD
5.4. EST server requires a specific extension to be present
TBD
6. Security Considerations
The security considerations from EST [RFC7030] section 6 are
unchanged.
6.1. Identity and Privacy Considerations
An EST server may use this mechanism to instruct the EST client about
the identities it should include in the CSR it sends as part of
enrollment. The client may only be aware of its IDevID Subject,
which includes a manufacturer serial number. The EST server can use
this mechanism to tell the client to include a specific fully
qualified domain name in the CSR in order to complete domain
ownership proofs required by the CA. Additionally, the EST server
may deem the manufacturer serial number in an IDevID as personally
identifiable information, and may want to specify a new random opaque
identifier that the pledge should use in its CSR. This may be
desirable if the CA and EST server have different operators.
7. IANA Considerations
No requests are made to IANA.
8. Acknowledgements
TODO
9. Changelog
10. References
10.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
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[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,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8994] Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An
Autonomic Control Plane (ACP)", RFC 8994,
DOI 10.17487/RFC8994, May 2021,
<https://www.rfc-editor.org/info/rfc8994>.
[RFC8995] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, <https://www.rfc-editor.org/info/rfc8995>.
10.2. Informative References
[RFC8368] Eckert, T., Ed. and M. Behringer, "Using an Autonomic
Control Plane for Stable Connectivity of Network
Operations, Administration, and Maintenance (OAM)",
RFC 8368, DOI 10.17487/RFC8368, May 2018,
<https://www.rfc-editor.org/info/rfc8368>.
Authors' Addresses
Michael Richardson (editor)
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
Owen Friel
Cisco
Email: ofriel@cisco.com
Dr. David von Oheimb
Siemens
Email: dev@ddvo.net
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Dan Harkins
The Industrial Lounge
Email: dharkins@lounge.org
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