The message is decoded by reversing the substitution rule. If the encryption changed S to Y, the decryption changes Y back to S, applying the inverse mapping to all characters.
Conditions: The receiver knows the substitution mapping for each character.; The example uses direct reversal, such as Y back to S.
The message is decoded by reversing the substitution rule. If the encryption changed S to Y, the decryption changes Y back to S, applying the inverse mapping to all characters.
Conditions: The receiver knows the substitution mapping for each character.; The example uses direct reversal, such as Y back to S.
Combining transposition and block substitution defeats simple cryptanalysis by first scrambling the letter positions and then applying different substitution keys to the resulting blocks. This ensures that guessing a single key yields completely unreadable gibberish, as the original word boundaries and letter frequencies are hidden.
Conditions: The method applies a transposition cipher first.; The method applies a block substitution cipher second.; The attacker attempts to decrypt using only one of the keys.
Combining transposition and block substitution defeats simple cryptanalysis by first scrambling the letter positions and then applying different substitution keys to the resulting blocks. This ensures that guessing a single key yields completely unreadable gibberish, as the original word boundaries and letter frequencies are hidden.
Conditions: The method applies a transposition cipher first.; The method applies a block substitution cipher second.; The attacker attempts to decrypt using only one of the keys.