Decryption with RC6-w/r/b

Input: Ciphertext stored in four w-bit input registers A,B,C,D; Number r of rounds

w-bit round keys S[0,…,2r+3]

Output: Plainrtext stored in A,B,C,D

Procedure: C=C - S[2r+3] A=A - S[2r+2]

for I = r downto 1 do

{

(A,B,C,D)=(D,A,B,C)

u=(D ? (2D + 1)) <<< lg w

t=(B ? (2B + 1 )) <<< lg w

C=((C - S[2i+1]) >>> t) ? u

A=((A - S[2i]) >>> u ) ? t

}

D=D-S[1] B=B-S[0]

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