Write the decryption of a 2-round generalized Feistel network given below.

$P_i$ denotes plaintext blocks of each 32-bits.
$RK_i$ denotes the round keys.
$WK_i$ denotes 32-bit keys applied only at the first round (whitening keys)

Continue the lines for the decryption.

The whole figure will input 4, 32-bit plaintext, encrypt it for 2 rounds and continue with decryption and will output the same input

feistel diagram

Can anyone help me for this question?

  • 2
    $\begingroup$ What have you tried? We generally don't provide much help for people who just do homework dumps on us, with no sign of effort on their part. $\endgroup$
    – poncho
    Dec 29, 2016 at 18:55
  • $\begingroup$ @poncho İ didn't do so i want to learn. $\endgroup$
    – Extraloob
    Dec 29, 2016 at 18:59
  • 1
    $\begingroup$ If two rounds are too tough, why don't you try to invert a single round? $\endgroup$
    – poncho
    Dec 29, 2016 at 19:41
  • $\begingroup$ I didnt do anything i tried but $\endgroup$
    – Extraloob
    Dec 30, 2016 at 21:12

1 Answer 1


I will give the 1 round answer which will help complete the question.

Let $X_{1,i},i=0,\ldots,3$ be the 32-bit outputs of the first round, before the swap, numbered left to right. Then,

$$P_2=X_{1,2}, \quad P_0=X_{1,0}$$ and $$P_1=WK_0\oplus F_0(RK_0,X_{1,0})\quad P_3=WK_0\oplus F_0(RK_1,X_{1,2}), $$ The equations for the $P_{i}$ are as above.


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