Who first presented the meet-in-the-middle attack for cryptanalysis?

• A. Diffie and Hellman.
• B. Rivest and Shamir.
• C. NIST researchers.
• D. Lamport and Deffie.

Answer: (A)

Meet-in-the-middle attacks split a two-stage process, like double encryption, into two halves and look for a match in the middle. You precompute all possible results from the first stage and store them, then work from the second stage and try to match those intermediates with the second-key outcomes. When a match is found, you’ve effectively identified the two keys with far less effort than trying every possible pair from start to finish. This trade of memory for time is what makes the technique so powerful for breaking two-key schemes.

This approach was first presented by Diffie and Hellman in their foundational cryptography work. Their presentation showed how a two-key cascade could be attacked by computing and comparing intermediate values, illustrating a fundamental vulnerability in naïve two-stage designs. The other names listed did not originate this technique, so the credit goes to Diffie and Hellman.