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DKIM Seen Through a PKIX-Focused Lens

DKIM Seen Through a PKIX-Focused Lens. April 5, 2006 Tim Polk tim.polk@nist.gov. Observations on E-Mail. Spam is rapidly overwhelming all that is good about email I delete 90% of my mail unread Much of what is left is garbage

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DKIM Seen Through a PKIX-Focused Lens

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  1. DKIM Seen Through a PKIX-Focused Lens April 5, 2006 Tim Polk tim.polk@nist.gov

  2. Observations on E-Mail • Spam is rapidly overwhelming all that is good about email • I delete 90% of my mail unread • Much of what is left is garbage • A small percentage of what I deleted was probably important (I’ll never know!) • Anything that helps me identify messages I should read is awesome

  3. Does DKIM Solve The Right Problem? • While the techniques specified by the DKIM working group will not prevent fraud or spam, they will provide a tool for defense against them by assisting receiving domains in detecting some spoofing of known domains • Solve may be too strong a word, but I think it is on target

  4. Observations on DKIM • In DKIM, there is no dependency on public and private key pairs being issued by well-known, trusted certificate authorities • A feature for deployment, but perhaps also the Achilles heel • In DKIM, the verifier requests the public key from the claimed signer directly • And trusts it because it got it from the DNS?

  5. Is The Foundation Sufficient? • DKIM relies on DNS as the initial mechanism for publishing public keys • DNS poisoning is not that difficult, it just isn’t that interesting in most cases. DKIM makes it interesting. • DKIM sender signing policy statements are expected to be very simplistic • Fine to start, but experience shows one-size-fits-all policies don’t fit anyone

  6. DKIM Solution Strength • IMHO, DKIM provides an incremental improvement in security • For the near term, that is all we can ask or expect • For the long term, it isn’t nearly good enough

  7. Conclusions • DKIM will be far better than nothing, and really ought to be deployed aggressively. • DKIM’s success will provide real incentives for attackers • Spammers will exploit the DNS-based key distribution and weak policy schemes to alter recipient behavior • The good news: DKIM is designed to be extensible to other key fetching services • An X.509 PKI based solution should be one of the well defined services

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