title: CMAC why K1 and K2
body: <p><a href="http://en.wikipedia.org/wiki/CMAC" rel="nofollow noreferrer">http://en.wikipedia.org/wiki/CMAC</a></p>
  
  <p><a href="http://www.rfc-archive.org/getrfc.php?rfc=4493" rel="nofollow noreferrer">http://www.rfc-archive.org/getrfc.php?rfc=4493</a></p>
  
  <p>There are two keys K1 and K2. Are there any other reasons, beside that messages 1 differs from 10^127 (1 and 127 zeroes)</p>
  
  <p>If message carries length (and  length is also CMAC-ed whit message), are there any security weaknesses using only one randomly generated K?</p>