simplifid DES
salman tahir

San Jose, CA

#1 Apr 2, 2013
plz help
S0y =(P0,0 P0,3)=(11)= 3
S0x =(P0,1 P0,2)=(10)= 2
S0(y,x)= 3 (dec)= 11 (bin)
S1y =(P1,0 P1,3)=(11)= 3
S1x =(P1,1 P1,2)=(00)= 0
S1(y,x)= 2 (dec)= 10 (bin)

what is the role for calculating
S1(y,x)= 2 (dec)= 10 (bin)
S0(y,x)= 3 (dec)= 11 (bin
from the above .this is actually a subsituation process
ibrahiem albarki

Misr, Egypt

#2 Apr 26, 2013
hi salman

first the S- box receive 4 bits as input and produce 2-bit output

the s-box has a known 4*4 matrix that depends in its equation

So if the S-box matrix is 1 0 3 2
3 2 1 0
0 2 1 3
3 1 3 2

suppose the input of the S-box is 0100
the first and fourth bit (00)specify the row of the matrix, the the row is 0
and the second and third bit(10) specify the column , the column is 2

So the output of the s-box lies at row 0 and column 2, thus the output is 3 (11 in binary)

that is it , hope to understand me
thanks
ibrahiem Egypt

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