The GNU bc threaded code compiler, included with most Linux distributions, provides arbitrary precision arithmetic that can handle the large numbers used in modern cryptography. Here we use the bc compiler to explore Diffie-Hellman public key encryption.
Communicating "in the clear", Alice and Bob select two numbers, q and n. Alice then selects the secret number xa. Bob selects the secret number xb. From the two public numbers, q and n, and her secret number xa, Alice calculates ya and sends the number to Bob. Using the same two public numbers, q and n, and his secret number xb, Bob calculates yb and sends the number to Alice. Alice and Bob have completed step one of the Diffie-Hellman process.
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