Re: key length vs block length, most secure encryption algorithm today?

On Thu, 14 Aug 2008 04:12:05 -0700 (PDT), some guy <ncnlcss@xxxxxxxxx>
wrote:

I'm looking for the most secure encryption algorithm. I found AES-256,
blowfish-448 and twofish(-256?). Is there a more secure one?
Twofish is a development of Blowfish and more secure. Use Twofish in
preference to Blowfish. Both AES (Rijndael) and Twofish were
finalists in the AES competition. A third finalist, Serpent, was
generally considered the most secure and also the slowest. Rijndael
was fastest, which is probably why it won, and Twofish comes in
between, slower than AES/Rijndael but less secure than Serpent.


Speed doesn't really matter to me. I use it mostly to encrypt small
documents.
Use Serpent then as it is slow and more secure. Any one of AES,
Serpent and Twofish are probably going to be secure enough for you.


From what I gather AES-256 is the only one that has a 128-bit block
length.
No, all three AES, Twofish and Serpent have a 128 bit blocksize. If
you look back at the original (pre-AES) Rijndael design then there is
a 256 bit block version, but this is less well tested than AES.

Does this make AES-256 more secure than the other two, despite
the fact that blowfish has a 448 bit key? I also found that blowfish
needs just over 500 algorithm iterations to test a single key, to make
it resistant to bruteforce attacks.

Using the full key length of any of these encryption algorithm, random
characters, capital and non-capital, numbers and punctuation, are they
crackable in a lifetime?
Never ever use a passphrase directly as your key. Use a complex
passphrase (google for "diceware") to seed a key derivation function
(KDF). A simple KDF is just to feed the passphrase into a Hash
function (SHA-256 or similar), for more complex ones see PBKDF1 or
PBKDF2, as defined in RFC 2898 (http://tools.ietf.org/html/rfc2898)

rossum


Thanks

.

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