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Using Secure DNS to Associate Certificates with Domain Names For S/MIME
draft-ietf-dane-smime-05

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8162.
Authors Paul E. Hoffman , Jakob Schlyter
Last updated 2014-02-14
Replaces draft-hoffman-dane-smime
RFC stream Internet Engineering Task Force (IETF)
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Stream WG state WG Document
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IESG IESG state Became RFC 8162 (Experimental)
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draft-ietf-dane-smime-05
quot;) is a valid
   character in a local part, but would wreak havoc in a domain name
   unless the application using the name somehow quoted it.  Similarly,

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   RFC 6530 allows non-ASCII characters in local parts, and encoding a
   local part with non-ASCII characters with Base32 renders the name
   usable in applications that use the DNS.

   Wildcards can be more useful for SMIMEA than they are for TLSA.  If a
   site publishes a trust anchor certificate for all users on the site
   (certificate usage 0 or 2), it could make sense to use a wildcard
   resource record such as "*._smimecert.example.com".

4.  Mandatory-to-Implement Features

   S/MIME MUAs conforming to this specification MUST be able to
   correctly interpret SMIMEA records with certificate usages 0, 1, 2,
   and 3.  S/MIME MUAs conforming to this specification MUST be able to
   compare a certificate association with a certificate offered by
   another S/MIME MUA using selector types 0 and 1, and matching type 0
   (no hash used) and matching type 1 (SHA-256), and SHOULD be able to
   make such comparisons with matching type 2 (SHA-512).

5.  IANA Considerations

5.1.  SMIMEA RRtype

   This document uses a new DNS RRtype, SMIMEA, whose value will be
   allocated by IANA from the Resource Record (RR) TYPEs subregistry of
   the Domain Name System (DNS) Parameters registry.

   TODO: there needs to be new registries for certificate usages,
   selectors, and maching types, pre-populated with the values from
   TLSA.

6.  Security Considerations

   DNS zones that are signed with DNSSEC using NSEC for denial of
   existence are susceptible to zone-walking, a mechanism that allow
   someone to enumerate all the names in the zone.  Someone who wanted
   to collect email addresses from a zone that uses SMIMEA might use
   such a mechanism.  DNSSEC-signed zones using NSEC3 for denial of
   existence are significantly less susceptible to zone-walking.
   Someone could still attempt a dictionary attack on the zone to find
   SMIMEA records, just as they can use dictionary attacks on an SMTP
   server to see which addresses are valid.

   Client treatment of any information included in the trust anchor is a
   matter of local policy.  This specification does not mandate that
   such information be inspected or validated by the domain name
   administrator.

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7.  Acknowledgements

   Miek Gieben and Martin Pels contributed technical ideas and support
   to this document.

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, March 2005.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, March 2005.

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, March 2005.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, January 2010.

   [RFC5754]  Turner, S., "Using SHA2 Algorithms with Cryptographic
              Message Syntax", RFC 5754, January 2010.

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, August 2012.

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8.2.  Informative References

   [RFC2822]  Resnick, P., "Internet Message Format", RFC 2822, April
              2001.

   [RFC6530]  Klensin, J. and Y. Ko, "Overview and Framework for
              Internationalized Email", RFC 6530, February 2012.

Authors' Addresses

   Paul Hoffman
   VPN Consortium

   Email: paul.hoffman@vpnc.org

   Jakob Schlyter
   Kirei AB

   Email: jakob@kirei.se

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