Round structure
SubBytes (S-box lookup), ShiftRows (byte permutation), MixColumns (matrix multiply in GF(2^8)), AddRoundKey. Final round skips MixColumns.
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Key schedule
Expand initial key to round keys via rotations + S-box + round constants. Deterministic derivation.
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AES-NI
Modern CPUs have AES instructions: single instruction per round. ~10 GB/s per core. Hardware-accelerated cryptography.
Modes of operation
ECB (bad), CBC (needs IV), CTR (parallel), GCM (authenticated). Never use raw ECB.