# Swap the encryption function with the decryption function

For any given one-key cipher (M,C,K,Ek,Dk), we may modify it into (M,C,K,Dk,Ek). In other words, we swap the encryption function with the decryption in the modified cipher. Prove that the two ciphers have the same level of security with respect to known- plaintext attacks.

Can anyone give me some helps to prove this? Thank you.

• If $(x,y)$ is a plain text/crypto text pair for one then $(y,x)$ is for the other – Hagen von Eitzen Mar 2 '17 at 7:35
• This means that they would be the same result? How can I prove that ? – Ng Clement Mar 2 '17 at 7:43