Delayed Password Disclosure

ET_Fleshy writes "Markus Jakobsson has an interesting article discussing a promising new security protocol called "Delayed Password Disclosure" that can validate a computers authenticity before exchanging passwords/keys. While nothing is ever truly secure, this seems to show promise in protecting users from a wide variety of stealth attacks (pdf) used today, specifically man in the middle (pdf) attacks."

Comments

And this is new how???

[SeanTobin]

Forgive me for not reading my latest issue of Cryptographer weekly but how on earth is this any different than RSA fingerprints? It looks like the "envelope" and "carbon paper" are just elements of a pre-shared key anyway.

If you know the fingerprint of the host you are connecting to, you are more or less immune from man-in-the-middle attacks. If you have never communicated with the host before, nothing is going to stop a man-in-the-middle - especially if you have to magically share locations of "carbon paper" without the man-in-the-middle knowing about it.

Sharing keys?

[nizo]

Thus spake the article:
Note that use of encryption software, such as SSH, does not address this problem, since the attacker simply can replace the public keys of the two parties with public keys for which it knows the secret keys. This results in the two parties sharing keys with the attacker, as opposed to with each other; as a consequence, the attacker will be able to read (and even modify) all traffic before re-encrypting it and forwarding it.

And this is why you always share public keys via some other secure means (USB drive, cd, floppy), at least in an ideal world. The article talks about this in regards to someone transmitting data to their bank, however if I am not mistaken SSL(not mentioned in the article) already takes care of this kind of attack. Somehow I doubt any joe user is using SSH to authenticate with their bank :-)