You don’t need a password. Posterous fail.

Re:You don’t need a password. Posterous fail. by adamsmith on Friday June 18, 2010 @12:39PM (#1442769)

But most major domains use domain keys / DKIM.

http://en.wikipedia.org/wiki/DKIM

As far as I understand it, you can't fake being an SMTP server sending mail from such a domain because their emails get signed with a private key whose matching public key is published by DNS.

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Re:You don’t need a password. Posterous fail. by geocar on Friday June 18, 2010 @01:26PM (#1442971)

There are several ways to defeat DKIM here:

• If you can break DNS, you can get an NXDOMAIN reply, making recipients think there aren't any domainkeys

• If the domainkey private key is small, you can factor it. There's an article on HN's frontpage right now about this.

• If the server uses domainkeys, but it doesn't specifically verify the From: header, an attacker can still forge a message if they share a popular mail provider with their target. I don't know if this is still practical.

• Stupidity. DKIM is difficult to test, and as a security measure it would need to be tested.

An autoreponse confirmation would be immune to all of these attacks and would be trivial to implement correctly.

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Re:You don’t need a password. Posterous fail. by apphacker on Friday June 18, 2010 @01:48PM (#1443039)

An auto-response confirmation would make posterous suck.

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Re:You don’t need a password. Posterous fail. by geocar on Sunday June 20, 2010 @08:18PM (#1447497)

and yet DKIM is insecure for sender authentication.

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