Algorithm 2: Pseudocode of Att()

Input: a carrier message (CMHM), an estimated secret key (EK) Output: a compromised carrier message (CM’HM), an estimated Secret Message (ESM) 1. HS← Estimates the hidden/invisible symbols from the CMHM; 2. for each $c_i\in HS=\left\{c_1,c_2,\dots ,c_n\right\}$ do 3. Estimated_SMbits ← Estimated_SMbits + Guess the binary string of each symbol based on the $HS[c_i]$; 4. EKbits← EKbits + Guess the secret key according to the $HS[c_i]$ using the conventional approaches; 5. end for 6. SMbits← Tries to decrypt the Estimated_SMbits based on the ESK; 7. ESM← If it is possible, estimates/decodes the SMbits using conventional approaches; 8. CM’HM← Manipulate the CM’HM in order to remove the HM; 9. Return CM’HM, ESM;