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Salz 3 Internet-Draft Akamai Technologies 4 Intended status: Standards Track 4 February 2021 5 Expires: 8 August 2021 7 Use the SAN field 8 draft-rsalz-use-san-00 10 Abstract 12 In the decade since [RFC6125] was published, the subjectAltName 13 extension, as defined in [RFC5280] has become ubiquitous. This 14 document updates [RFC6125] to specify that the fall-back techniques 15 of using commonName attribute to identify the service MUST NOT be 16 used. 18 Discussion Venues 20 This note is to be removed before publishing as an RFC. 22 Source for this draft and an issue tracker can be found at 23 https://github.com/richsalz/draft-rsalz-use-san. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on 8 August 2021. 42 Copyright Notice 44 Copyright (c) 2021 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 49 license-info) in effect on the date of publication of this document. 50 Please review these documents carefully, as they describe your rights 51 and restrictions with respect to this document. Code Components 52 extracted from this document must include Simplified BSD License text 53 as described in Section 4.e of the Trust Legal Provisions and are 54 provided without warranty as described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 59 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 2 60 3. The New Rules . . . . . . . . . . . . . . . . . . . . . . . . 3 61 3.1. Designing Application Protocols . . . . . . . . . . . . . 3 62 3.2. Representing Server Identity . . . . . . . . . . . . . . 3 63 3.3. Verifying Service Identity . . . . . . . . . . . . . . . 3 64 4. Constraints on Wildcards . . . . . . . . . . . . . . . . . . 3 65 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 66 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 67 7. Normative References . . . . . . . . . . . . . . . . . . . . 4 68 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 71 1. Introduction 73 In the decade since [RFC6125] was published, the subjectAltName 74 extension, as defined in [RFC5280] has become ubiquitous. This 75 document updates [RFC6125] to specify that the fall-back techniques 76 of using commonName attribute to identify the service MUST NOT be 77 used. 79 2. Conventions and Definitions 81 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 82 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 83 "OPTIONAL" in this document are to be interpreted as described in BCP 84 14 [RFC2119] [RFC8174] when, and only when, they appear in all 85 capitals, as shown here. 87 The terminology from [RFC6125] is used here. Specifically, the 88 following terms and brief definition (as a reminder): 90 * CN-ID: the Common Name element from a Distingiushed Name. 92 * DNS-ID, SRV-ID, URI-ID: different types of entries in a 93 subjectAltName extension. 95 3. The New Rules 97 The CN-ID MUST NOT be used. The appropriate value in the 98 subjectAltName extension MUST be used to get the presented identity 99 of the server. 101 While not discussed in [RFC6125], this section also implicitly 102 prohibits the use of the Domain Component or emailAddress RDN's. 104 The following sections repeat the above rule in other forms, for the 105 purpose of updating [RFC6125]. 107 3.1. Designing Application Protocols 109 Applications should determine which form of name they want to use, 110 and specify the appropriate subjectAltName extension. Unless there 111 are reasons to do otherwise, applications SHOULD use the DNS-ID form. 113 3.2. Representing Server Identity 115 Severs either MUST NOT issue a CN-ID, or MUST use a form for the 116 Common Name RDN that cannot be mistaken for an identifier. Not using 117 Common Name is preferred. 119 3.3. Verifying Service Identity 121 When constructing a list of reference identifiers, the client MUST 122 NOT include any CN-ID present in the certificate. This means that 123 section 6.4.4 of [RFC6125] MUST be ignored. 125 4. Constraints on Wildcards 127 Wildcard certificates are discussed in section 7.2 of [RFC6125], 128 which says that the specifications "are not clear or consistent" 129 about where a wildcard can appear. 131 This documents specifies that a wildcard can appear 133 * only as the left-most label; or 135 * as the last character in a left-most label 137 5. Security Considerations 139 The CN-ID, domainComponent, and emailAddress RDN fields are 140 unstructured free text, and using them is dependant on ordering and 141 encoding concerns. In addition, their evaluation when PKIX 142 nameConstraints are present is ambiguous. This document removes 143 those fields from use, so a source of possible errors is removed. 145 Because of the ambiguity around wildcards, [RFC6125] mentions that it 146 is possible to have exploitable differences in behavior. By 147 simplifying those practices to one rule, this source of errors should 148 be avoided. 150 All other security considerations of [RFC6125] and its dependant 151 documents are still relevant. 153 6. IANA Considerations 155 This document has no IANA actions. 157 7. Normative References 159 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 160 Requirement Levels", BCP 14, RFC 2119, 161 DOI 10.17487/RFC2119, March 1997, 162 . 164 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 165 Housley, R., and W. Polk, "Internet X.509 Public Key 166 Infrastructure Certificate and Certificate Revocation List 167 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 168 . 170 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and 171 Verification of Domain-Based Application Service Identity 172 within Internet Public Key Infrastructure Using X.509 173 (PKIX) Certificates in the Context of Transport Layer 174 Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March 175 2011, . 177 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 178 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 179 May 2017, . 181 Acknowledgments 183 TODO acknowledge. 185 Author's Address 187 Rich Salz 188 Akamai Technologies 190 Email: rsalz@akamai.com