I don't know. You can easily get sdhc cards that are 128GB, ditto for usb sticks. You'd need a high-bandwidth source of random data - or possibly proxy that wit

I don't know. You can easily get sdhc cards that are 128GB, ditto for usb sticks. You'd need a high-bandwidth source of random data - or possibly proxy that with high-quality seed for a stream/bloc cipher (conceivably, it's easier to guarantee a one-time, controlled secure generation of a 256 bit symmetric key that's thrown away after generating your stream, than handling of session keys and complicated calculations on a message by message basis) - but I'm not aware of any secure system designed to work with such a one-time pad. You'd need a way to keep track of sections of the pad [probably framing the message, maybe a start keyword could work - it'd give away the section of the pad, but as that section is never re-used... or, if you can assume few messages will be lost, just keep a local counter, and do a sliding search] - and there are other issues. Split the pad into sender/receiver sections (A only encrypt and send with a-apd, B only encrypts with b-pad - to avoid two messages encrypted with the same section of pad, crossing each other). Still, if Eve gets a hold of a plaintext message from Bob, and can intercept the ciphertext before it gets to Alice - Eve gains access to a section of the otp by xoring - and can send anything to Bob (up to the same message length). I'd be interesting to hear if there are modern cryptosystems /research based around one time pads?