--- 1/draft-ietf-uta-email-tls-certs-04.txt 2015-09-20 14:15:22.504133172 -0700 +++ 2/draft-ietf-uta-email-tls-certs-05.txt 2015-09-20 14:15:22.524133658 -0700 @@ -1,76 +1,77 @@ Network Working Group A. Melnikov Internet-Draft Isode Ltd -Updates: 2595, 3207, 3501, 5804 (if August 6, 2015 +Updates: 2595, 3207, 3501, 5804 (if September 20, 2015 approved) Intended status: Standards Track -Expires: February 7, 2016 +Expires: March 23, 2016 Updated TLS Server Identity Check Procedure for Email Related Protocols - draft-ietf-uta-email-tls-certs-04 + draft-ietf-uta-email-tls-certs-05 Abstract This document describes TLS server identity verification procedure for SMTP Submission, IMAP, POP and ManageSieve clients. It replaces - Section 2.4 of RFC 2595. + Section 2.4 of RFC 2595, updates Section 4.1 of RFC 3207, updates + Section 11.1 of RFC 3501, updates Section 2.2.1 of RFC 5804. 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 http://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 February 7, 2016. + This Internet-Draft will expire on March 23, 2016. Copyright Notice Copyright (c) 2015 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 (http://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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 - 2. Conventions Used in This Document . . . . . . . . . . . . . . 2 + 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 3. Email Server Certificate Verification Rules . . . . . . . . . 3 4. Compliance Checklist for Certification Authorities . . . . . 4 5. Compliance Checklist for Mail Service Providers and Certificate Signing Request generation tools . . . . . . . . 4 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 9.2. Informative References . . . . . . . . . . . . . . . . . 7 - Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8 - Appendix B. Changes since draft-ietf-uta-email-tls-certs-00 . . 8 - Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 + Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9 + Appendix B. Changes since draft-ietf-uta-email-tls-certs-00 . . 9 + Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 1. Introduction Use of TLS by SMTP Submission, IMAP, POP and ManageSieve clients is described in [RFC3207], [RFC3501], [RFC2595] and [RFC5804] respectively. Each of the documents describes slightly different rules for server certificate identity verification (or doesn't define any rules at all). In reality, email client and server developers implement many of these protocols at the same time, so it would be good to define modern and consistent rules for verifying email server @@ -89,44 +90,53 @@ protocols. This should make it easier for Certification Authorities and ISPs to deploy TLS for email use, and would enable email client developers to write more secure code. 2. Conventions Used in This Document 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]. + The following terms or concepts are used through the document: + + reference identifier: (as defined in [RFC6125]) One of the domain + names associated by the email (i.e., an SMTP, IMAP, POP3 or + ManageSieve) client with the destination email server and + optionally an application service type for performing name checks + on the server certificate. When name checks are applicable, at + least one of the reference identifiers MUST match an [RFC6125] + DNS-ID or SRV-ID (or if none are present the [RFC6125] CN-ID) of + the server certificate. + 3. Email Server Certificate Verification Rules During a TLS negotiation, an email client (i.e., an SMTP, IMAP, POP3 or ManageSieve client) MUST check its understanding of the server hostname against the server's identity as presented in the server Certificate message, in order to prevent man-in-the-middle attacks. Matching is performed according to the rules specified in Section 6 of [RFC6125], including "certificate pinning" and the procedure on failure to match. The following inputs are used by the verification procedure used in [RFC6125]: - 1. For DNS-ID and CN-ID identifier types the client MUST use the - server hostname it used to open the connection as at least one of - the values to compare against (*) in the server certificate. The - client MUST NOT use any form of the server hostname derived from - an insecure remote source (e.g., insecure DNS lookup). CNAME - canonicalization is not done. + 1. For DNS-ID and CN-ID identifier types the client MUST use one or + more of the following as "reference identifiers": (a) the right + hand side of the email address, (b) the hostname it used to open + the connection (without CNAME canonicalization). The client MAY + also use (c) a value securely derived from (a) or (b), such as + using "secure" DNSSEC validated lookup. 2. When using email service discovery procedure specified in [RFC6186] the client MUST also use the right hand side of the email address as another "reference identifier" to compare - against in the server certificate. - - (*) - "reference identifier" (see the definition in [RFC6125]). + against SRV-ID identifier in the server certificate. The rules and guidelines defined in [RFC6125] apply to an email server certificates, with the following supplemental rules: 1. Support for the DNS-ID identifier type (subjectAltName of dNSName type [RFC5280]) is REQUIRED in Email client software implementations. 2. Support for the SRV-ID identifier type (subjectAltName of SRVName type [RFC4985]) is REQUIRED for email client software @@ -263,24 +273,20 @@ 9. References 9.1. 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, . - [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, - DOI 10.17487/RFC5321, October 2008, - . - [RFC6409] Gellens, R. and J. Klensin, "Message Submission for Mail", STD 72, RFC 6409, DOI 10.17487/RFC6409, November 2011, . [RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over Transport Layer Security", RFC 3207, DOI 10.17487/RFC3207, February 2002, . [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,