Recognized Transformations of Messages Bearing DomainKeys Identified Mail (DKIM) Signatures

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Document Type Expired Internet-Draft (individual)
Author Murray Kucherawy 
Last updated 2015-10-07 (latest revision 2015-04-05)
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DomainKeys Identified Mail (DKIM) introduced a mechanism whereby a mail operator can affix a signature to a message that validates at the level of the signer's domain name. It specified two possible ways of converting the message body to a canonical form, one intolerant of changes and the other tolerant of simple changes to whitespace within the message body. The provided canonicalization schemes do not tolerate changes in a message such as conversion between transfer encodings or addition of new message content. It is useful to have these capabilities to allow for transport through gateways, and also for transport through handlers (such as mailing list services) that might add content that would invalidate a signature generated using the existing canonicalization schemes. This document presents a mechanism for declaring that a message underwent one of a handful of well-defined transformations, so that a verifier might rewind such a modification and thereby confirm that the signature still verifies against the original content.


Murray Kucherawy (

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