Internet Engineering Task Force P. Hallam-Baker
Internet-Draft VeriSign Inc
Intended status: Informational July 13, 2008
Expires: January 14, 2009
DKIM Extensions
draft-hallambaker-dkim-extensions-01
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Abstract
Optional extensions for DKIM are described. A DKIM Policy statement
is defined for the policy 'this zone never sends mail'. The NULL Key
Algorithm is defined to simplify management of large zones where most
mail is signed but with important exceptions. The X509 key record
extension allows the location from which an X.509v3 certificate for
the key specified in the record may be obtained.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. NoMail Policy . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. NULL Signature Algorithm . . . . . . . . . . . . . . . . . . . 3
4. X509 Certificate Location Extension . . . . . . . . . . . . . . 3
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
8. Normative References . . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 4
Intellectual Property and Copyright Statements . . . . . . . . . . 5
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1. Introduction
1.1. Requirements Language
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 RFC 2119 [RFC2119].
2. NoMail Policy
The NOMAIL policy is declared in an SSP record using the tag
"NOMAIL".
No parameters are specified for the NOMAIL policy.
If specified the NOMAIL policy states that no mail is sent from the
domain to which it is attached. All mail that purports to have been
sent by that domain MUST be considered suspicious.
3. NULL Signature Algorithm
The NULL Signature algorithm is a DKIM signature algorithm that
always produces the same signature value regardless of the message
contents.
A message signed with the NULL signature MUST be treated as if it
were unsigned for all purposes other than verifying compliance with a
DKIM policy. For purposes of policy compliance, a message that
carries a NULL signature is considered to be compliant if and only if
it is consistent with the signing restrictions specified in the key
record.
A key record that specifies the NULL signature algorithm SHOULD
specify usage restricted to specific senders.
4. X509 Certificate Location Extension
The x509 key record extension specifies a URL from which a
certificate chain corresponding to the key specified in the key
record may be obtained.
The key chain is specified as a CMS SignedData structure with no
data.
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5. Acknowledgements
The ideas in this document arose from extensive discussions with the
DKIM working group, in particular Hector Santos and others.
6. IANA Considerations
This document requests allocation of a DKIM SSP tag 'NOMAIL'
7. Security Considerations
The NOMAIL policy MAY be employed to perform a denial of service
attack.
8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Author's Address
Phillip Hallam-Baker
VeriSign Inc
Email: pbaker@verisign.com
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