Question

Define a substitution box, So as following table

1	0	3	2
3	2	1	0
0	2	1	3
1	1	3	2

and a substitution scheme that if we denote a 4 bit number as “b1 b2 b3 b4”, the (b1 b4) forms a 2 bit binary number that specifies a row of the above matrix and the (b2 b3) forms another 2 bit binary number that specifies a column of the matrix. The row and column lead to a number in the matrix. Taking the number and translating it into binary, we get the substitution value for the original 4 bit number. Now given a 4 bit 1001, please give the substitute value.

Answer 1

as given in above question,

consider 4 bit value : 1001

first and last bit is 11 in this case, binary is 3

we can determine this as it specify 3rd row

and middle two bits are 00, and if we convert them in binary,we get 0

and this can be determine as 0th column.

if we substitute the value in above substitution box at 3rd row and 0th column we will get the answer is -----> 1

AND THIS IS OUR SUBSTITUTION VALUE