The equations for the variables q and r for S-DES are defined in the section on

S-DES analysis. Provide the equations for s and t.

Using S-DES, decrypt the string 01000110 using the key 1010000010 by hand.

Show intermediate results after each function (IP, FK, SW, FK, IP-1

). Then decode

the first 4 bits of the plaintext string to a letter and the second 4 bits to another letter

where we encode A through P in base 2 (i.e., A = 0000, B = 0001, c, P = 1111).

Hint: As a midway check, after the xoring with K2, the string should be 11000001.