On Mar 30, 2008, at 3:12 PM, Leichter, Jerry wrote:
How would that help?

Unless I'm misunderstanding Zooko's writeup, he's worried about an attacker going from a partially-known plaintext (e.g. a form bank letter) to a completely-known plaintext by repeating the following process:

1. take partially known plaintext
2. make a guess, randomly or more intelligently where possible,
   about the unknown parts
3. take the current integrated partial+guessed plaintext, hash
   to obtain convergence key
4. verify whether that key exists in the storage index
5. if yes, you've found the full plaintext. if not, repeat from '2'.

That's a brute force search. If your convergence key, instead of being a simple file hash, is obtained through a deterministic but computationally expensive function such as PBKDF2 (or the OpenBSD bcrypt, etc), then step 3 makes an exhaustive search prohibitive in most cases while not interfering with normal filesystem operation. What am I missing?


Ivan Krstić <[EMAIL PROTECTED]> | http://radian.org

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