Algorithm 2: The extracting algorithm

Input: Steganographic image C*, Encrypted key matrix Uw1′,Vw1′.

Output: The extracted Secret image C’.

1: [LLw2, HLw2, LHw2, HHw2, HLw, LHw, HHw] = DWT2level (C*) 2: RSw = [HHw2, HLw(1:128,129:256); LHw(129:256,1:128), HHw(1:128,1:128)] 2: RSw* = Arnold (RSw) 3: (Uw1, Vw1) = ChaoticDecrypt (Uw1′, Vw1′) 4: PwHwPwT = Hessenberg (RSw*) 5: HUw*HSbw*HVw*T = SVD (Hw) 6: Sw1* = (HSbw1*-HSw)/α 7: C1′ = Uw1 Sw1* Vw1T 8: C’ = Rearnold (C1′)