What is S-Box Substitution?

Information SecuritySafe & SecurityData Structure

S-Box Substitution is a procedure that accepts the 48-bit input from the XOR operation containing the compressed key and expanded RPT and creates a 32-bit output utilizing the substitution technique.

The substitution is implemented by the eight substitution boxes (also known as the S-boxes). Each 8-S-boxes has a 6-bit input and a 4-bit output. The 48-bit input block is divided into 8 sub-blocks (each including 6 bits), and each sub-blocks is provided to an S-box.

The substitution in each box follows a pre-decided rule depends on a 4-row by 16- column table. The sequence of bits one and six of the input represent four rows and the sequence of bits two through five represent sixteen columns.

Because each S-box has its own table, we require eight tables, as display in table 1 to table 8, to represent the output of these boxes. The values of the inputs (row number and column number) and the values of the outputs are given as decimal numbers to store space. These need to be changed to binary.

S-Box 1

1441312151183106125907
0157414213110612119538
4114813621115129731050
1512824917511314100613

S-Box 2

1518146113497213120510
3134715281412011069115
0147111041315812693215
1381013154211671205149

S-Box 3

1009146315511312711428
1370934610285141211151
1364981530111212510147
1101306987415143115212

S-Box 4

7131430691012851112415
1381156150347212110149
1069012117131513145284
3150610113894511127214

S-Box 5

2124171011685315130149
1411212471315015103986
4211110137815912563014
1181271142136150910453

S-Box 6

1211015926801334147511
1015427129561131401138
9141552812370410113116
4321295151011141760813

S-Box 7

4112141508133129751061
1301174911014351221586
14111312371410156801092
6111381410795015140312

S-Box 8

1328461511110931450127
1151381037412561101492
7114191214206101315358
2114741081315129035611
raja
Updated on 16-Mar-2022 07:26:42

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