AES (Advanced Encryption Standard)
AES (Advanced Encryption Standard), standardised as NIST FIPS 197 in 2001, is the symmetric block cipher that underlies virtually all data encryption in modern infrastructure. It was selected through a five-year open competition that evaluated 15 candidate algorithms; the winner, Rijndael (designed by Joan Daemen and Vincent Rijmen), became AES. A block cipher takes a fixed-size block of plaintext and a key and produces a fixed-size block of ciphertext — AES always operates on 128-bit (16-byte) blocks, regardless of key size. Three key lengths are standardised: AES-128 (128-bit key, 10 rounds), AES-192 (192-bit key, 12 rounds), and AES-256 (256-bit key, 14 rounds), providing 128, 192, and 256 bits of security respectively against classical attacks. AES-256 is the conservative choice for data with long confidentiality requirements and is mandated by CNSA 2.0 for national security systems; AES-128 is widely deployed in TLS and provides adequate security for most workloads. The internal structure — SubBytes, ShiftRows, MixColumns, AddRoundKey — is fully public and has withstood over two decades of cryptanalysis; the best known attacks against full-round AES are theoretical and computationally infeasible, requiring work far beyond brute force but not threatening practical security.