Internet DRAFT - draft-ietf-uta-use-san
draft-ietf-uta-use-san
UTA R. Salz
Internet-Draft Akamai Technologies
Updates: 6125 (if approved) 1 April 2021
Intended status: Standards Track
Expires: 3 October 2021
Update to Verifying TLS Server Identities with X.509 Certificates
draft-ietf-uta-use-san-00
Abstract
In the decade since [RFC6125] was published, the
subjectAlternativeName extension (SAN), as defined in [RFC5280] has
become ubiquitous. This document updates [RFC6125] to specify that
the fall-back techniques of using the commonName attribute to
identify the service must not be used. This document also places
some limitations on the use of wildcards in SAN fields.
The original context of [RFC6125] using X.509 certificates for server
identity with Transport Layer Security (TLS), is not changed.
Discussion Venues
This note is to be removed before publishing as an RFC.
This draft is discussed in the UTA working group,
https://datatracker.ietf.org/wg/uta/.
Source for this draft and an issue tracker can be found at
https://github.com/richsalz/draft-rsalz-use-san.
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 https://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 3 October 2021.
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Copyright Notice
Copyright (c) 2021 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 (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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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. The New Rules . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Designing Application Protocols . . . . . . . . . . . . . 3
3.2. Representing Server Identity . . . . . . . . . . . . . . 3
3.3. Verifying Service Identity . . . . . . . . . . . . . . . 3
4. Constraints on Wildcards . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 4
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
In the decade since [RFC6125] was published, the
subjectAlternativeName extension (SAN), as defined in [RFC5280] has
become ubiquitous. This document updates [RFC6125] to specify that
the fall-back techniques of using the commonName attribute to
identify the service must not be used. This document also places
some limitations on the use of wildcards in SAN fields.
The original context of [RFC6125] using X.509 certificates for server
identity with Transport Layer Security (TLS), is not changed. In
addition to the examples in that document, the Baseline Requirements
of the CA/Browser Forum, [CABBR], might also be useful.
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2. Conventions and Definitions
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.
The terminology from [RFC6125] is used here. Specifically, the
following terms and brief definition (as a reminder):
* CN-ID: the Common Name element of a Distingiushed Name.
* DNS-ID: a domain name entry in a SAN extension.
3. The New Rules
The CN-ID MUST NOT be used. The appropriate value in the SAN
extension MUST be used to get the presented identity of the server.
While not discussed in [RFC6125] this section also implicitly
prohibits the use of the Domain Component or emailAddress RDN's.
The following sections repeat the above rule in other forms, for the
purpose of updating [RFC6125]
3.1. Designing Application Protocols
Applications should determine which form of name they want to use,
and specify the appropriate SAN extension. Unless there are reasons
to do otherwise, applications SHOULD use the DNS-ID form.
3.2. Representing Server Identity
Servers MUST NOT request certificates that contain CN-ID in the
subject. If the Common Name RDN must be present in the certificate,
it MUST be in a form that cannot be mistaken for a CN-ID.
3.3. Verifying Service Identity
When constructing a list of reference identifiers, the client MUST
NOT include any CN-ID present in the certificate. This means that
section 6.4.4 of [RFC6125] MUST be ignored.
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4. Constraints on Wildcards
Wildcard certificates are discussed in section 7.2 of [RFC6125] which
says that the specifications "are not clear or consistent" about
where a wildcard can appear.
This documents specifies that a wildcard can appear
* only as the left-most label; or
* as the last character in a left-most label
Clients that receive a DNS-ID that does not meet these criteria
SHOULD ignore it.
5. Security Considerations
The CN-ID, domainComponent, and emailAddress RDN fields are
unstructured free text, and using them is dependant on ordering and
encoding concerns. In addition, their evaluation when PKIX
nameConstraints are present is ambiguous. This document removes
those fields from use, so a source of possible errors is removed.
Because of the ambiguity around wildcards, [RFC6125] mentions that it
is possible to have exploitable differences in behavior. By
simplifying those practices to one rule, this source of errors should
be avoided.
All other security considerations of [RFC6125] and its dependant
documents are still relevant.
6. IANA Considerations
This document has no IANA actions.
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,
<https://www.rfc-editor.org/rfc/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/rfc/rfc5280>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/rfc/rfc6125>.
[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/rfc/rfc8174>.
7.2. Informative References
[CABBR] CA/Browser Forum, "Baseline Requirements for the Issuance
and Management of Publicly-Trusted Certificates", 2020,
<https://cabforum.org/wp-content/uploads/CA-Browser-Forum-
BR-1.7.3.pdf>.
Author's Address
Rich Salz
Akamai Technologies
United States of America
Email: rsalz@akamai.com
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