regardingg the XXXing on receipts it turns out that things aren't as grim as i thought. i anlayzed the checksum algorithm and if you are missing n digits there are 10^(n-1) clashes.
i verified this with a brute force program. but in the "photograph the card" scenario ... if one digit is blurry then you still win because 10^(n-1) is 1. if two are unknown then mr nasty could try buying stuff from 10 diferent sites. brucee --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]