>
>Here's a purely software question...
>
>I am implementing a data block encryption algorithm using a CRC-CCITT
>style filter. The SR is preloaded with a key. The clear text is shifted
>into the SR one bit at a time, and the msb of the SR gives each clear
>text bit it's encrypted equivelant.
>
>Now here's the question: If I use the above algorithm what is the
>inverse method? How does one convert it back? I'm pretty sure that it is
>possible as their are no folded (lost) states.
>
>I hope someone has a pointer to a solution for me. Thanks.
>
>--
>Regards, Dana Frank Raymond

As no-one else has commented, here is my first thought.
I would have assumed that the inverse function (decryption) was the same as
for
the encryption.  Whenever I have used CRC in the past the same polynomial
is used to recover the clear text.  (maybe I have misunderstood the question?)

A trap-door (one-way) encryption would require a key to reverse. (aka DES).



Ray Gardiner, Shepparton, Victoria, Australia, ray@netspace.net.au