A Specification for Rijndael, the AES Algorithm

1.1 Rijndael Inputs and Outputs The input, the output and the cipher key for Rijndael are each bit sequences containing 128, 192 or 256 bits with the constraint that the input and output sequences have the same length. A bit is a binary digit, 0 or 1, while the term ‘length’ refers to the number of bits in a sequence. In general the length of the input and output sequences can be any of the three allowed values but for the Advanced Encryption Standard (AES) the only length allowed is 128. However, both Rijndael and AES allow cipher keys of all three lengths.