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0 pointsadamsmith15y ago0 comments

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.

0 comments

geocar15y ago

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.

apphacker15y ago

An auto-response confirmation would make posterous suck.

geocar15y ago

and yet DKIM is insecure for sender authentication.

j / k navigate · click thread line to collapse

0 pointsadamsmith15y ago0 comments

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.

0 comments

geocar15y ago

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.

• 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.

apphacker15y ago

An auto-response confirmation would make posterous suck.

geocar15y ago

and yet DKIM is insecure for sender authentication.

j / k navigate · click thread line to collapse