title: Reducing size of hash
body: <p>If I have some data I hash with SHA256 like this :- hash=SHA256(data) </p>
  
  <p>And then copy only the first 8 bytes of the hash instead of the whole 32 bytes, how easy is it to find a hash collision with different data? Is it 2^64 or 2^32 ?</p>
  
  <p>If I need to reduce a hash of some data to a smaller size (n bits) is there any way to ensure the search space 2^n ?</p>