Hector Santos: > > The problem is the mistaken belief that signatures make > > statements about 2822.From addresses. ... > So I am not sure why it is a mistaken belief to view DKIM as a Digital > Message Signature technology and protocol that attempts to make a strong > statement of assuring mail integrity by protecting the originating mail > author, its domain, its mail content from potential harm and abuse.
First, I trimmed a log of your reply, because I would not limit a discussion of DKIM usefulness to just the popular email exploit of the day (phishing). Allow me to get back to basics. Stated in simple terms, if a DKIM signature verifies, then the verifier knows two things: 1) The hash was signed by the purported signing party. This means that the verifier can trace the message back to the signing party. 2) The inputs to the hash were not modified. Specifically, some malicious or non-malicious party didn't modify the inputs at some later point in time. If mail doesn't have a valid signature, then the none of the above assurances exist. The mail may be authentic but some munging broke the DKIM seal, or it may be non-authentic (phishing etc). The verifier can not make a definitive statement about this. SSPs notwithstanding, because SSPs don't handle email munging. > After all, what is the purpose of DKIM? Thanks for asking. The purpose of DKIM is to trace back signed mail to signing parties. For example, suppose that you have confidence in your bank's DKIM signature. Then you can use it to distinguish between mail from the bank, and phishing mail that pretends to be. Note that it does not matter what their rfc822.from says. It's the bank's DKIM signature that forms the primary basis for trust. Another example: suppose that I receive mail from a mailing list. I trust the list server's DKIM signature, so I can distinguish between mail from the list server and mail that pretends to be. Again, note that it does not matter what their rfc822.from says. It's the list server's DKIM signature that forms the primary basis for trust. With first-party signatures, things simplify conceptually and technically to the point of elegance. This is one reason why I express preference for first-party signatures. But even in this special case, it is the DKIM signature that forms the primary basis for trust. The rfc822.from is secondary. Wietse _______________________________________________ NOTE WELL: This list operates according to http://mipassoc.org/dkim/ietf-list-rules.html