On 09/06/11 18:14, Paul Hoffman wrote:
Greetings again. I am helping someone design a system that will involve giving
someone a randomly-generated key that they have to type in order to unlock data
that is private but not terribly valuable. Thus, we want to keep the key as
short as practical to reduce typing and mis-typing, but long enough to prevent
trivial brute-force attacks. The encryption will be AES-128 in CBC mode.
You can make this stronger by stretching the key: repeatedly hashing the
passphrase before using it as a key to make brute-force attacks harder.
http://www.schneier.com/paper-low-entropy.html
We know *lots* about how fast SHA-256 can be run because of its use in
BitCoin:
https://en.bitcoin.it/wiki/Mining_hardware_comparison
On an unrelated note, if I have to enter a randomly-generated passphrase
with 80 bits of entropy, I'd personally rather enter a 25-character all
lower case passphrase than a 19 character mixed-case passphrase with
special characters.
--
__
\/ o\ Paul Crowley, [email protected]
/\__/ http://www.ciphergoth.org/
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