title: Using SHA-1 hash as AES key
body: <p>Let's say I would like to have "password-derived-bytes" as AES key.
  For example, I have a password "topsecret", I do calculate SHA-1 hash for it (160bit) and I want to feed those bytes as key for AES-128. </p>
  
  <p>Should I just truncate after 128 bits or do some kind of folding?
  What about AES-256? Should I repeat bytes, pad with 0's or do some "unfolding" operation?</p>
  
  <p>I know that in the later case security remains at 160-bit because the pool of 256-bit passwords is reduced to 2^160 possible combinations, but I'm just trying to overcome technical limitation (no AES-160).</p>
  
  <p>What theory says?
  (No, using MD5 for 128-bit and SHA-256 for 256-bit long hashes is not an option)</p>