On 8/23/06, Dave Korn <[EMAIL PROTECTED]> wrote:
Given that, whatever passphrase you use, you will decrypt the EDK block and get /something/ that looks like a key, this comparison of hashes is a sanity test. If you bypass it but enter the wrong passphrase, you'll get an incorrectly-decrypted EDK, which will lead your disk to look like every sector is full of random garbage. Rather than decrypt the entire disk and run chkdsk to see if it looks sane, comparing the hashes of the passphrase is a quick and dirty way of testing if the resulting EDK is going to be the correct one.
The PGP email encryption has two known-plaintext bytes for that purpose. This only honors a bad key 2^16 of the time, but ensures that brute-forcing must do a more extensive unknown-plaintext attack at that rate for any potentially-correct key. This reminds me a little of the suggestions that MACs should be truncated, although it seems to me that it's better to encrypt a hash of the plaintext. -- "If you're not part of the solution, you're part of the precipitate." Unix "guru" for rent or hire -><- http://www.lightconsulting.com/~travis/ GPG fingerprint: 9D3F 395A DAC5 5CCC 9066 151D 0A6B 4098 0C55 1484 --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
