> sha1(md5(things)) Consider what would happen if the "md5" function was found to always return the number 3 for "things" greater than 999 - the "sha1" functio

> sha1(md5(things)) Consider what would happen if the "md5" function was found to always return the number 3 for "things" greater than 999 - the "sha1" function would be no help. The entire chain is only as strong as the weakest link. It doesn't matter how you mix the inputs, any biased input weakens the system.