| Internet-Draft | Update to Verifying TLS Server Identitie | March 2021 |
| Salz | Expires 14 September 2021 | [Page] |
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.¶
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.¶
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 14 September 2021.¶
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 and restrictions with respect 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.¶
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.¶
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):¶
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].¶
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.¶
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.¶
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.¶
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¶
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.¶
This document has no IANA actions.¶