MD5, like all hash functions, are many-to-one functions. This means that theoretically there are an infinite number of messages that will hash to the same value. This also means that reverting from the hash back to your original message is nigh impossible. The security of MD5 is based upon the fact that *finding* two messages that hash to the same value is as difficult as a brute-force attack, which requires 2^128 trials (maybe it's 2^127, but I don't think that really matters). I dion't believe that multiple iterations of MD5 will cause you to lose entropy. Actually, you will lose entropy on teh *first* iteration, since MD5 will \*only\* let you have 128 bits of Entropy, since there are only 128 bits in the output. In subsequent iterations, you just move those bits around. Does this answer your question? -derek Derek Atkins, SB '93 MIT EE, G MIT Media Laboratory Member, MIT Student Information Processing Board (SIPB) Home page: http://www.mit.edu:8001/people/warlord/home_page.html warlord@MIT.EDU PP-ASEL N1NWH PGP key available