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The Advanced Encryption Standard (AES) is a symmetric-key block cipher algorithm and U.S. government standard for secure and classified data encryption and decryption.
In December 2001, the National Institute of Standards (NIST) approved the AES as Federal Information Processing Standards Publication (FIPS PUB) 197, which specifies application of the Rijndael algorithm to all sensitive classified data.
The Advanced Encryption Standard was originally known as Rijndael.
The AES has three fixed 128-bit block ciphers with cryptographic key sizes of 128, 192 and 256 bits. Key size is unlimited, whereas the block size maximum is 256 bits. The AES design is based on a substitution-permutation network (SPN) and does not use the Data Encryption Standard (DES) Feistel network.
In 1997, the NIST initiated a five-year algorithm development process to replace the DES and Triple DES. The NIST algorithm selection process facilitated open collaboration and communication and included a close review of 15 candidates. After an intense evaluation, the Rijndael design, created by two Belgian cryptographers, was the final choice.
The AES replaced the DES with new and updated features: