Editing Advanced Encryption Standard (section)

=== The {{mono|ShiftRows}} step ===
[[Image:AES-ShiftRows.svg|right|320px|thumbnail|In the {{mono | ShiftRows}} step, bytes in each row of the state are shifted cyclically to the left. The number of places each byte is shifted differs incrementally for each row.]]
The {{mono | ShiftRows}} step operates on the rows of the state; it cyclically shifts the bytes in each row by a certain [[Offset (computer science)|offset]]. For AES, the first row is left unchanged. Each byte of the second row is shifted one to the left. Similarly, the third and fourth rows are shifted by offsets of two and three respectively.<ref group="note">Rijndael variants with a larger block size have slightly different offsets. For blocks of sizes 128 bits and 192 bits, the shifting pattern is the same. Row <math>n</math> is shifted left circular by <math>n-1</math> bytes.  For a 256-bit block, the first row is unchanged and the shifting for the second, third and fourth row is 1 byte, 3 bytes and 4 bytes respectively—this change only applies for the Rijndael cipher when used with a 256-bit block, as AES does not use 256-bit blocks.</ref> In this way, each column of the output state of the {{mono | ShiftRows}} step is composed of bytes from each column of the input state. The importance of this step is to avoid the columns being encrypted independently, in which case AES would degenerate into four independent block ciphers.