--- 1/draft-ietf-uta-smtp-require-tls-05.txt 2018-12-04 11:13:12.100906663 -0800 +++ 2/draft-ietf-uta-smtp-require-tls-06.txt 2018-12-04 11:13:12.132907429 -0800 @@ -1,18 +1,18 @@ Internet Engineering Task Force J. Fenton Internet-Draft Altmode Networks -Intended status: Standards Track November 20, 2018 -Expires: May 24, 2019 +Intended status: Standards Track December 4, 2018 +Expires: June 7, 2019 SMTP Require TLS Option - draft-ietf-uta-smtp-require-tls-05 + draft-ietf-uta-smtp-require-tls-06 Abstract The SMTP STARTTLS option, used in negotiating transport-level encryption of SMTP connections, is not as useful from a security standpoint as it might be because of its opportunistic nature; message delivery is, by default, prioritized over security. This document describes an SMTP service extension, REQUIRETLS, and message header field, RequireTLS. If the REQUIRETLS option or RequireTLS message header field is used when sending a message, it asserts a @@ -30,21 +30,21 @@ 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 May 24, 2019. + This Internet-Draft will expire on June 7, 2019. Copyright Notice Copyright (c) 2018 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 @@ -69,29 +69,30 @@ 4.4. Delivery of REQUIRETLS messages . . . . . . . . . . . . . 7 5. Non-delivery message handling . . . . . . . . . . . . . . . . 7 6. Mailing list considerations . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8.1. Passive attacks . . . . . . . . . . . . . . . . . . . . . 10 8.2. Active attacks . . . . . . . . . . . . . . . . . . . . . 10 8.3. Bad Actor MTAs . . . . . . . . . . . . . . . . . . . . . 10 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 10. Revision History . . . . . . . . . . . . . . . . . . . . . . 11 - 10.1. Changes since -04 Draft . . . . . . . . . . . . . . . . 11 - 10.2. Changes since -03 Draft . . . . . . . . . . . . . . . . 11 - 10.3. Changes since -02 Draft . . . . . . . . . . . . . . . . 11 - 10.4. Changes since -01 Draft . . . . . . . . . . . . . . . . 12 - 10.5. Changes since -00 Draft . . . . . . . . . . . . . . . . 12 - 10.6. Changes since fenton-03 Draft . . . . . . . . . . . . . 12 - 10.7. Changes Since -02 Draft . . . . . . . . . . . . . . . . 12 - 10.8. Changes Since -01 Draft . . . . . . . . . . . . . . . . 12 - 10.9. Changes Since -00 Draft . . . . . . . . . . . . . . . . 13 + 10.1. Changes since -05 Draft . . . . . . . . . . . . . . . . 11 + 10.2. Changes since -04 Draft . . . . . . . . . . . . . . . . 11 + 10.3. Changes since -03 Draft . . . . . . . . . . . . . . . . 11 + 10.4. Changes since -02 Draft . . . . . . . . . . . . . . . . 11 + 10.5. Changes since -01 Draft . . . . . . . . . . . . . . . . 12 + 10.6. Changes since -00 Draft . . . . . . . . . . . . . . . . 12 + 10.7. Changes since fenton-03 Draft . . . . . . . . . . . . . 12 + 10.8. Changes Since -02 Draft . . . . . . . . . . . . . . . . 12 + 10.9. Changes Since -01 Draft . . . . . . . . . . . . . . . . 12 + 10.10. Changes Since -00 Draft . . . . . . . . . . . . . . . . 13 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . 13 11.2. Informative References . . . . . . . . . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15 1. Introduction The SMTP [RFC5321] STARTTLS service extension [RFC3207] provides a means by which an SMTP server and client can establish a Transport Layer Security (TLS) protected session for the transmission of email @@ -163,21 +164,21 @@ o If the SMTP server to which the message is being transmitted is identified through an MX record lookup, its name MUST be validated via a DNSSEC signature on the recipient domain's MX record, or the MX hostname MUST be validated by an MTA-STS policy as described in Section 4.1 of RFC 8461 [RFC8461]. DNSSEC is defined in RFC 4033 [RFC4033], RFC 4034 [RFC4034], and RFC 4035 [RFC4035]. o The certificate presented by the SMTP server MUST either verify successfully in a trust chain leading to a certificate trusted by - the SMTP client or it MUST verify succesfully using DANE as + the SMTP client or it MUST verify successfully using DANE as specified in RFC 7672 [RFC7672]. For trust chains, the choice of trusted (root) certificates is at the discretion of the SMTP client. o Following the negotiation of STARTTLS, the SMTP server MUST advertise in the subsequent EHLO response that it supports REQUIRETLS. 3. The RequireTLS Header Field @@ -405,22 +406,22 @@ Reference: (this document) Submitter: J. Fenton Change controller: IESG If published as an RFC, this draft requests the addition of an entry to the Permanent Message Header Field Names Registry [PermMessageHeaderFields]: Header field name: RequireTLS Applicable protocol: mail - Status: provisional - Author/change controller: IETF UTA Working Group + Status: standard + Author/change controller: IETF Specification document: (this document) This section is to be updated for publication by the RFC Editor. 8. Security Considerations The purpose of REQUIRETLS is to improve communications security for email by giving the originator of a message an expectation that it will be transmitted in an encrypted form "over the wire". When used, REQUIRETLS changes the traditional behavior of email transmission, @@ -486,97 +487,101 @@ The author would like to acknowledge many helpful suggestions on the ietf-smtp and uta mailing lists, in particular those of Viktor Dukhovni, Chris Newman, Tony Finch, Jeremy Harris, Arvel Hathcock, John Klensin, John Levine, Rolf Sonneveld, and Per Thorsheim. 10. Revision History To be removed by RFC Editor upon publication as an RFC. -10.1. Changes since -04 Draft +10.1. Changes since -05 Draft + + Corrected IANA Permanent Message Header Fields Registry request. + +10.2. Changes since -04 Draft Require validation of SMTP server hostname via DNSSEC or MTA-STS policy when TLS is required. -10.2. Changes since -03 Draft +10.3. Changes since -03 Draft Working Group Last Call changes, including: o Correct reference for SMTP DANE o Clarify that RequireTLS: NO applies to both MTA-STS and DANE policies o Correct newly-defined status codes o Update MTA-STS references to RFC -10.3. Changes since -02 Draft +10.4. Changes since -02 Draft o More complete documentation for IANA registration requests. o Changed bounce handling to use RET parameters of RFC 3461, along with slightly more liberal transmission of bounces even if REQUIRETLS can't be negotiated. -10.4. Changes since -01 Draft +10.5. Changes since -01 Draft o Converted DEEP references to RFC 8314. o Removed REQUIRETLS options: CHAIN, DANE, and DNSSEC. o Editorial corrections, notably making the header field name consistent (RequireTLS rather than Require-TLS). -10.5. Changes since -00 Draft +10.6. Changes since -00 Draft o Created new header field, Require-TLS, for use by "NO" option. o Removed "NO" option from SMTP service extension. o Recommend DEEP requirements for delivery of messages requiring TLS. o Assorted copy edits -10.6. Changes since fenton-03 Draft +10.7. Changes since fenton-03 Draft o Wording improvements from Rolf Sonneveld review 22 July 2017 o A few copy edits o Conversion from individual to UTA WG draft -10.7. Changes Since -02 Draft +10.8. Changes Since -02 Draft o Incorporation of "MAY TLS" functionality as REQUIRETLS=NO per suggestion on UTA WG mailing list. o Additional guidance on bounce messages -10.8. Changes Since -01 Draft +10.9. Changes Since -01 Draft o Specified retries when multiple MX hosts exist for a given domain. o Clarified generation of non-delivery messages o Specified requirements for application of REQUIRETLS to mail forwarders and mailing lists. o Clarified DNSSEC requirements to include MX lookup only. o Corrected terminology regarding message retrieval vs. delivery. o Changed category to standards track. -10.9. Changes Since -00 Draft +10.10. Changes Since -00 Draft o Conversion of REQUIRETLS from an SMTP verb to a MAIL FROM parameter to better associate REQUIRETLS requirements with transmission of individual messages. o Addition of an option to require DNSSEC lookup of the remote mail server, since this affects the common name of the certificate that is presented. o Clarified the wording to more clearly state that TLS sessions must