Hardware Security
Besides speed, what advantage comes from giving CPUs dedicated AES instructions (such as AES-NI)?
- AAES keys automatically become longer
- BIt eliminates the table lookups used by software implementations, preventing cache-timing leaks caused by key-dependent memory accesses
- CAnyone can read AES ciphertext without the key
Show answer and explanation
Answer: B. It eliminates the table lookups used by software implementations, preventing cache-timing leaks caused by key-dependent memory accesses
Fast software AES often used large precomputed tables, reading them at locations determined by the data and key. Because the access location depended on the key, attacks inferring the key from cache hit and miss timing became known. Dedicated instructions compute in constant time inside the circuit without tables, so they are both faster and immune to this kind of side-channel leakage.
- A. The key length does not change.
- B. Correct. Computation happens in constant time inside the circuit.
- C. Cryptographic strength is unchanged.