# Security of a cryptosystem where the encryption is swapped with decryption

For any given one-key cipher $(M,C,K,E_k,D_k)$, we may modify it into $(M,C,K,D_k,E_k)$. In other words, we swap the encryption function with the decryption in the modified cipher.

Are the two ciphers have the same level of security with respect to known- plaintext attacks?

• looks like homework, what have you tried? – kodlu Mar 4 '17 at 1:54
• Yes. I don't how to tackle this. Would you mind to give me some hints, please? – Ng Clement Mar 4 '17 at 1:58
• Known plaintext means you have both plaintext and ciphertext. So you can go from either to the other,... – kodlu Mar 4 '17 at 2:34
• Suppose you could break the new scheme. Show how this would allow you to break the old. Conclude. – SEJPM Mar 4 '17 at 10:16
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