[Bcrypt-users] bcrypt 1.1 encryption mode

[Michael M. <mg...@es...>]

Hi there,

I've just found bcrypt on freshmeat, whilst looking for utilities for
encrypting files with a view to using rsync to store encrypted offsite
backups. I'm interested in encryption that doesn't break rsync's remote
diff behaviour, whilst still being strong crypto. I've run a few tests on
the output from bcrypt and was wondering if anyone could comment on the
following:

 - if I encrypt identical files with the same passphrase, I get the same
output. Have I just been lucky or is this guaranteed? (You can avoid it by
"seeding" the blocks to encrypt with a random starting block which you
discard when decrypting).

 - if I encrypt two files which are identical except for a new block of
2048 bytes in the middle, bdiff tells me that the encrypted files differ
by around 4000 bytes (i.e. a value close to the difference between the
files). Does this make sense?

What I think is that the encryption works in some sort of mode where the
results of encrypting previous blocks does not affect encryption of future
blocks. Is this correct?

Finally, does anyone have comments on the security of the bcrypt utility?
Is the security roughly as good as my key choice?

Thanks,
Mike.