1. The problem statement, all variables and given/known data example: S(18 09 12 3d 11 17 38 39) = 5fd25e03 2. Relevant equations 3. The attempt at a solution So I know about DES that you split a 64 bit block into left and right halves 32 bits each. Where even bits are on the left and odd are on the right. Perform the round function of the 32 bit right side and 48 bit key. The round function works by expanding the bits the flowing them through a xor gate with the 48 bit key, which then flows into the substitution stage where the 48 bit expanded input is dropped to 32 bit. This then goes into permutation and goes into the XOR gate along with LI-1. Such that Li = RI-1 and Ri = LI-1 xor F(RI-1,Ki). So knowing that and only focusing on the substitution the 8 S boxes map the 6 bit to 4 bit, in which each each s box is 4 little 4 bit boxes where the outer bits select rows and the inner bits select the columns. Ok so I know all this and I have the table that it suggests using but I don't know what any of this means I have tried to find a pattern to no avail. More specifically what are the outer bits in this and what are the inner? Then once I figure this out how do I use the table provided?