< draft-ietf-dane-smtp-with-dane-09.txt   draft-ietf-dane-smtp-with-dane-10.txt >
DANE V. Dukhovni DANE V. Dukhovni
Internet-Draft Two Sigma Internet-Draft Two Sigma
Intended status: Standards Track W. Hardaker Intended status: Standards Track W. Hardaker
Expires: November 7, 2014 Parsons Expires: November 26, 2014 Parsons
May 6, 2014 May 25, 2014
SMTP security via opportunistic DANE TLS SMTP security via opportunistic DANE TLS
draft-ietf-dane-smtp-with-dane-09 draft-ietf-dane-smtp-with-dane-10
Abstract Abstract
This memo describes a downgrade-resistant protocol for SMTP transport This memo describes a downgrade-resistant protocol for SMTP transport
security between Mail Transfer Agents (MTAs) based on the DNS-Based security between Mail Transfer Agents (MTAs) based on the DNS-Based
Authentication of Named Entities (DANE) TLSA DNS record. Adoption of Authentication of Named Entities (DANE) TLSA DNS record. Adoption of
this protocol enables an incremental transition of the Internet email this protocol enables an incremental transition of the Internet email
backbone to one using encrypted and authenticated Transport Layer backbone to one using encrypted and authenticated Transport Layer
Security (TLS). Security (TLS).
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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 http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 November 7, 2014. This Internet-Draft will expire on November 26, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://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
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clients elect to make use of the provider's TLSA records. clients elect to make use of the provider's TLSA records.
When the MX records are not (DNSSEC) signed, an active attacker can When the MX records are not (DNSSEC) signed, an active attacker can
redirect SMTP clients to MX hosts of his choice. Such redirection is redirect SMTP clients to MX hosts of his choice. Such redirection is
tamper-evident when SMTP servers found via "insecure" MX records are tamper-evident when SMTP servers found via "insecure" MX records are
recorded as the next-hop relay in the MTA delivery logs in their recorded as the next-hop relay in the MTA delivery logs in their
original (rather than CNAME expanded) form. Sending MTAs SHOULD log original (rather than CNAME expanded) form. Sending MTAs SHOULD log
unexpanded MX hostnames when these result from insecure MX lookups. unexpanded MX hostnames when these result from insecure MX lookups.
Any successful authentication via an insecurely determined MX host Any successful authentication via an insecurely determined MX host
MUST NOT be misrepresented in the mail logs as secure delivery to the MUST NOT be misrepresented in the mail logs as secure delivery to the
intended next-hop domain. When DANE TLS is mandatory (xref intended next-hop domain. When DANE TLS is mandatory (Section 6) for
target="madatory"/>) for a given destination, delivery MUST be a given destination, delivery MUST be delayed when the MX RRset is
delayed when the MX RRset is not "secure". not "secure".
Otherwise, assuming no DNS errors (Section 2.1.1), the MX RRset is Otherwise, assuming no DNS errors (Section 2.1.1), the MX RRset is
"secure", and the SMTP client MUST treat each MX hostname as a "secure", and the SMTP client MUST treat each MX hostname as a
separate non-MX destination for opportunistic DANE TLS as described separate non-MX destination for opportunistic DANE TLS as described
in Section 2.2.2. When, for a given MX hostname, no TLSA records are in Section 2.2.2. When, for a given MX hostname, no TLSA records are
found, or only "insecure" TLSA records are found, DANE TLSA is not found, or only "insecure" TLSA records are found, DANE TLSA is not
applicable with the SMTP server in question and delivery proceeds to applicable with the SMTP server in question and delivery proceeds to
that host as with pre-DANE opportunistic TLS. To avoid downgrade that host as with pre-DANE opportunistic TLS. To avoid downgrade
attacks, any errors during TLSA lookups MUST, as explained in attacks, any errors during TLSA lookups MUST, as explained in
Section 2.1.1, cause the SMTP server in question to be treated as Section 2.1.1, cause the SMTP server in question to be treated as
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