Semi-OT, but PLEASE, read tirwan's second paragraph over ...and over again!!! And then, if necessary, read up on dictionary-based attacks.

Yes, I noted your comment that this is preliminary and hope that it means you really have no intention of doing the job this way, but -- even if so -- to future casual readers, please re-read and heed tirwan's second paragraph again.

Unless the "words" in the input file are themselves random strings, using them and appending three digits is about as safe as using the "Captain Midnight decoder ring" that I so desired, ca. 1948... back when it cost a boxtop from Chex (which I don't think were called Chex, then) and a dime (no self-addressed envelope required).