Cryptography: AES - THE ENCRYPTION KEY AND ITS EXPANSION

• Assuming a 128-bit key, the key is also arranged in the form of a matrix of 4 × 4 bytes. As with the input block, the first word from the key fills the first column of the matrix, and so on.
• The four column words of the key matrix are expanded into a schedule of 44 words.Each round consumes four words from the key schedule.
• Figure 1 on the next page depicts the arrangement of the encryption key in the form of 4-byte words and the expansion of the key into a key schedule consisting of 44 4-byte words.