Cyphercard

Cyphercard is a simple but effective tool (a Hypercard stack) for encoding and decoding text documents. It uses no complex math, but simply encodes one document (the target) by using a second document as a reference document or a 'one time scratch pad', as they call it in the cypher biz. Cyphercard does not just use simple pointers into the reference document, but modulates those pointers using offsets which are also taken from that document. It uses various other encoding techniques as well. None of this is complicated or tricky. It doesn't need to be. The security of the code is not compromised at all by knowing exactly how it was coded. All the security comes from the fact that the code depends on the reference document and the password. The upshot is that anyone who knows which reference document and password to use can decode any document that was encoded with that reference document and password. Anyone who does not know that document and password will not be able to decode the target document. Cyphercard requires a PowerPC Macintosh and Hypercard 2.4.