19.5 The ShiftRow Transformation

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19.5 The ShiftRow Transformation

The next step in the cycle of a round consists in the permutation of a block at the byte level. To this end the bytes are exchanged within the individual lines (b_i,0, b_i,1, b_i,2,..., ) of a block according to the schemata depicted in Tables 19.11-19.13.

Table 19.11: ShiftRow for blocks of length 128 bits (L_b = 4)

Before ShiftRow				After ShiftRow
0	4	8	12	0	4	8	12
1	5	9	13	5	9	13	1
2	6	10	14	10	14	2	6
3	7	11	15	15	3	7	11

Table 19.12: ShiftRow for blocks of length 192 bits (L_b = 6)

Before ShiftRow						After ShiftRow
0	4	8	12	16	20	0	4	8	12	16	20
1	5	9	13	17	21	5	9	13	17	21	1
2	6	10	14	18	22	10	14	18	22	2	6
3	7	11	15	19	23	15	19	23	3	7	11

Table 19.13: ShiftRow for blocks of length 256 bits (L_b = 8)

Before ShiftRow								After ShiftRow
0	4	8	12	16	20	24	28	0	4	8	12	16	20	24	28
1	5	9	13	17	21	25	29	5	9	13	17	21	25	29	1
2	6	10	14	18	22	26	30	14	18	22	26	30	2	6	10
3	7	11	15	19	23	27	31	19	23	27	31	3	7	11	15

In each first row no exchange takes place. In lines i = 2, 3, 4 the bytes are rotated left by positions, from position j to position j − mod L_b, where is taken from Table 19.14

Table 19.14: Distances of line rotations in ShiftRow

Lb
4	1	2	3
6	1	2	3
8	1	3	4

For inverting this step positions j in rows i = 2, 3, 4 are shifted to positions j + mod L_b.

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