draft-ietf-uta-smtp-require-tls-05.txt		draft-ietf-uta-smtp-require-tls-06.txt
	Internet Engineering Task Force J. Fenton		Internet Engineering Task Force J. Fenton
	Internet-Draft Altmode Networks		Internet-Draft Altmode Networks
	Intended status: Standards Track November 20, 2018		Intended status: Standards Track December 4, 2018
	Expires: May 24, 2019		Expires: June 7, 2019
	SMTP Require TLS Option		SMTP Require TLS Option
	draft-ietf-uta-smtp-require-tls-05		draft-ietf-uta-smtp-require-tls-06
	Abstract		Abstract
	The SMTP STARTTLS option, used in negotiating transport-level		The SMTP STARTTLS option, used in negotiating transport-level
	encryption of SMTP connections, is not as useful from a security		encryption of SMTP connections, is not as useful from a security
	standpoint as it might be because of its opportunistic nature;		standpoint as it might be because of its opportunistic nature;
	message delivery is, by default, prioritized over security. This		message delivery is, by default, prioritized over security. This
	document describes an SMTP service extension, REQUIRETLS, and message		document describes an SMTP service extension, REQUIRETLS, and message
	header field, RequireTLS. If the REQUIRETLS option or RequireTLS		header field, RequireTLS. If the REQUIRETLS option or RequireTLS
	message header field is used when sending a message, it asserts a		message header field is used when sending a message, it asserts a
	skipping to change at page 1, line 41 ¶		skipping to change at page 1, line 41 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		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 Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 34 ¶		skipping to change at page 2, line 34 ¶
	4.4. Delivery of REQUIRETLS messages . . . . . . . . . . . . . 7		4.4. Delivery of REQUIRETLS messages . . . . . . . . . . . . . 7
	5. Non-delivery message handling . . . . . . . . . . . . . . . . 7		5. Non-delivery message handling . . . . . . . . . . . . . . . . 7
	6. Mailing list considerations . . . . . . . . . . . . . . . . . 8		6. Mailing list considerations . . . . . . . . . . . . . . . . . 8
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 9		8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
	8.1. Passive attacks . . . . . . . . . . . . . . . . . . . . . 10		8.1. Passive attacks . . . . . . . . . . . . . . . . . . . . . 10
	8.2. Active attacks . . . . . . . . . . . . . . . . . . . . . 10		8.2. Active attacks . . . . . . . . . . . . . . . . . . . . . 10
	8.3. Bad Actor MTAs . . . . . . . . . . . . . . . . . . . . . 10		8.3. Bad Actor MTAs . . . . . . . . . . . . . . . . . . . . . 10
	9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
	10. Revision History . . . . . . . . . . . . . . . . . . . . . . 11		10. Revision History . . . . . . . . . . . . . . . . . . . . . . 11
	10.1. Changes since -04 Draft . . . . . . . . . . . . . . . . 11		10.1. Changes since -05 Draft . . . . . . . . . . . . . . . . 11
	10.2. Changes since -03 Draft . . . . . . . . . . . . . . . . 11		10.2. Changes since -04 Draft . . . . . . . . . . . . . . . . 11
	10.3. Changes since -02 Draft . . . . . . . . . . . . . . . . 11		10.3. Changes since -03 Draft . . . . . . . . . . . . . . . . 11
	10.4. Changes since -01 Draft . . . . . . . . . . . . . . . . 12		10.4. Changes since -02 Draft . . . . . . . . . . . . . . . . 11
	10.5. Changes since -00 Draft . . . . . . . . . . . . . . . . 12		10.5. Changes since -01 Draft . . . . . . . . . . . . . . . . 12
	10.6. Changes since fenton-03 Draft . . . . . . . . . . . . . 12		10.6. Changes since -00 Draft . . . . . . . . . . . . . . . . 12
	10.7. Changes Since -02 Draft . . . . . . . . . . . . . . . . 12		10.7. Changes since fenton-03 Draft . . . . . . . . . . . . . 12
	10.8. Changes Since -01 Draft . . . . . . . . . . . . . . . . 12		10.8. Changes Since -02 Draft . . . . . . . . . . . . . . . . 12
	10.9. Changes Since -00 Draft . . . . . . . . . . . . . . . . 13		10.9. Changes Since -01 Draft . . . . . . . . . . . . . . . . 12
			10.10. Changes Since -00 Draft . . . . . . . . . . . . . . . . 13
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
	11.1. Normative References . . . . . . . . . . . . . . . . . . 13		11.1. Normative References . . . . . . . . . . . . . . . . . . 13
	11.2. Informative References . . . . . . . . . . . . . . . . . 15		11.2. Informative References . . . . . . . . . . . . . . . . . 15
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
	1. Introduction		1. Introduction
	The SMTP [RFC5321] STARTTLS service extension [RFC3207] provides a		The SMTP [RFC5321] STARTTLS service extension [RFC3207] provides a
	means by which an SMTP server and client can establish a Transport		means by which an SMTP server and client can establish a Transport
	Layer Security (TLS) protected session for the transmission of email		Layer Security (TLS) protected session for the transmission of email
	skipping to change at page 4, line 37 ¶		skipping to change at page 4, line 37 ¶
	o If the SMTP server to which the message is being transmitted is		o If the SMTP server to which the message is being transmitted is
	identified through an MX record lookup, its name MUST be validated		identified through an MX record lookup, its name MUST be validated
	via a DNSSEC signature on the recipient domain's MX record, or the		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		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		Section 4.1 of RFC 8461 [RFC8461]. DNSSEC is defined in RFC 4033
	[RFC4033], RFC 4034 [RFC4034], and RFC 4035 [RFC4035].		[RFC4033], RFC 4034 [RFC4034], and RFC 4035 [RFC4035].
	o The certificate presented by the SMTP server MUST either verify		o The certificate presented by the SMTP server MUST either verify
	successfully in a trust chain leading to a certificate trusted by		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		specified in RFC 7672 [RFC7672]. For trust chains, the choice of
	trusted (root) certificates is at the discretion of the SMTP		trusted (root) certificates is at the discretion of the SMTP
	client.		client.
	o Following the negotiation of STARTTLS, the SMTP server MUST		o Following the negotiation of STARTTLS, the SMTP server MUST
	advertise in the subsequent EHLO response that it supports		advertise in the subsequent EHLO response that it supports
	REQUIRETLS.		REQUIRETLS.
	3. The RequireTLS Header Field		3. The RequireTLS Header Field
	skipping to change at page 9, line 39 ¶		skipping to change at page 9, line 39 ¶
	Reference: (this document)		Reference: (this document)
	Submitter: J. Fenton		Submitter: J. Fenton
	Change controller: IESG		Change controller: IESG
	If published as an RFC, this draft requests the addition of an entry		If published as an RFC, this draft requests the addition of an entry
	to the Permanent Message Header Field Names Registry		to the Permanent Message Header Field Names Registry
	[PermMessageHeaderFields]:		[PermMessageHeaderFields]:
	Header field name: RequireTLS		Header field name: RequireTLS
	Applicable protocol: mail		Applicable protocol: mail
	Status: provisional		Status: standard
	Author/change controller: IETF UTA Working Group		Author/change controller: IETF
	Specification document: (this document)		Specification document: (this document)
	This section is to be updated for publication by the RFC Editor.		This section is to be updated for publication by the RFC Editor.
	8. Security Considerations		8. Security Considerations
	The purpose of REQUIRETLS is to improve communications security for		The purpose of REQUIRETLS is to improve communications security for
	email by giving the originator of a message an expectation that it		email by giving the originator of a message an expectation that it
	will be transmitted in an encrypted form "over the wire". When used,		will be transmitted in an encrypted form "over the wire". When used,
	REQUIRETLS changes the traditional behavior of email transmission,		REQUIRETLS changes the traditional behavior of email transmission,
	skipping to change at page 11, line 25 ¶		skipping to change at page 11, line 25 ¶
	The author would like to acknowledge many helpful suggestions on the		The author would like to acknowledge many helpful suggestions on the
	ietf-smtp and uta mailing lists, in particular those of Viktor		ietf-smtp and uta mailing lists, in particular those of Viktor
	Dukhovni, Chris Newman, Tony Finch, Jeremy Harris, Arvel Hathcock,		Dukhovni, Chris Newman, Tony Finch, Jeremy Harris, Arvel Hathcock,
	John Klensin, John Levine, Rolf Sonneveld, and Per Thorsheim.		John Klensin, John Levine, Rolf Sonneveld, and Per Thorsheim.
	10. Revision History		10. Revision History
	To be removed by RFC Editor upon publication as an RFC.		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		Require validation of SMTP server hostname via DNSSEC or MTA-STS
	policy when TLS is required.		policy when TLS is required.
	10.2. Changes since -03 Draft		10.3. Changes since -03 Draft
	Working Group Last Call changes, including:		Working Group Last Call changes, including:
	o Correct reference for SMTP DANE		o Correct reference for SMTP DANE
	o Clarify that RequireTLS: NO applies to both MTA-STS and DANE		o Clarify that RequireTLS: NO applies to both MTA-STS and DANE
	policies		policies
	o Correct newly-defined status codes		o Correct newly-defined status codes
	o Update MTA-STS references to RFC		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 More complete documentation for IANA registration requests.
	o Changed bounce handling to use RET parameters of RFC 3461, along		o Changed bounce handling to use RET parameters of RFC 3461, along
	with slightly more liberal transmission of bounces even if		with slightly more liberal transmission of bounces even if
	REQUIRETLS can't be negotiated.		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 Converted DEEP references to RFC 8314.
	o Removed REQUIRETLS options: CHAIN, DANE, and DNSSEC.		o Removed REQUIRETLS options: CHAIN, DANE, and DNSSEC.
	o Editorial corrections, notably making the header field name		o Editorial corrections, notably making the header field name
	consistent (RequireTLS rather than Require-TLS).		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 Created new header field, Require-TLS, for use by "NO" option.
	o Removed "NO" option from SMTP service extension.		o Removed "NO" option from SMTP service extension.
	o Recommend DEEP requirements for delivery of messages requiring		o Recommend DEEP requirements for delivery of messages requiring
	TLS.		TLS.
	o Assorted copy edits		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 Wording improvements from Rolf Sonneveld review 22 July 2017
	o A few copy edits		o A few copy edits
	o Conversion from individual to UTA WG draft		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		o Incorporation of "MAY TLS" functionality as REQUIRETLS=NO per
	suggestion on UTA WG mailing list.		suggestion on UTA WG mailing list.
	o Additional guidance on bounce messages		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 Specified retries when multiple MX hosts exist for a given domain.
	o Clarified generation of non-delivery messages		o Clarified generation of non-delivery messages
	o Specified requirements for application of REQUIRETLS to mail		o Specified requirements for application of REQUIRETLS to mail
	forwarders and mailing lists.		forwarders and mailing lists.
	o Clarified DNSSEC requirements to include MX lookup only.		o Clarified DNSSEC requirements to include MX lookup only.
	o Corrected terminology regarding message retrieval vs. delivery.		o Corrected terminology regarding message retrieval vs. delivery.
	o Changed category to standards track.		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		o Conversion of REQUIRETLS from an SMTP verb to a MAIL FROM
	parameter to better associate REQUIRETLS requirements with		parameter to better associate REQUIRETLS requirements with
	transmission of individual messages.		transmission of individual messages.
	o Addition of an option to require DNSSEC lookup of the remote mail		o Addition of an option to require DNSSEC lookup of the remote mail
	server, since this affects the common name of the certificate that		server, since this affects the common name of the certificate that
	is presented.		is presented.
	o Clarified the wording to more clearly state that TLS sessions must		o Clarified the wording to more clearly state that TLS sessions must
End of changes. 15 change blocks.
	25 lines changed or deleted		30 lines changed or added
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