# 2-round generalized Feistel network

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

Can anyone help me for this question?

• 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. – poncho Dec 29 '16 at 18:55
• @poncho İ didn't do so i want to learn. – Extraloob Dec 29 '16 at 18:59
• If two rounds are too tough, why don't you try to invert a single round? – poncho Dec 29 '16 at 19:41
• I didnt do anything i tried but – Extraloob Dec 30 '16 at 21:12

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.