(What is the maximum key size (in bits) supported by AES?)

The Advanced Encryption Standard (AES), as defined by the National Institute of Standards and Technology (NIST) in FIPS PUB 197, specifies three possible key lengths for the algorithm. These are 128 bits, 192 bits, and 256 bits. The largest of these, and therefore the maximum key size supported by the standard, is 256 bits. While the underlying Rijndael algorithm could support other key and block sizes, the AES standard strictly defines these three options.

A. 128 bits is a valid and commonly used AES key size, but it is the minimum supported key length, not the maximum.

B. 192 bits is the intermediate AES key size specified in the standard, falling between the minimum and maximum options.

D. 512 bits is not a key size defined in the FIPS 197 standard for AES. It is not a valid option for AES.

1. National Institute of Standards and Technology (NIST). (2001). FIPS PUB 197: Advanced Encryption Standard (AES). Section 5, "Algorithm Specification," p. 13, Table 1.

2. Daemen, J., & Rijmen, V. (2002). The Design of Rijndael: AES - The Advanced Encryption Standard. Springer. Section 3.4, "Key-Block-Round Arrangements," p. 34.