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Can one create a cipher with two meanings? Not two layers, two phrases in the same cipher in the way that it would have a meaning X, for example, if deciphered using Transposition cipher and meaning Y if deciphered with the Playfair chipher. Is it possible?

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  • $\begingroup$ Does the OTP (using letter addition) count (one keys gives one word "ABC", another another word "XYZ")? $\endgroup$ – SEJPM Feb 13 '16 at 18:03
  • $\begingroup$ Simliar question here.. Essence: its not possible in a secure way. $\endgroup$ – marstato Feb 13 '16 at 18:26
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This is possible, and it's called deniable encryption. The idea behind this type of encryption is that if you are required (e.g., under subpoena) to provide a key to decrypt your ciphertext, then you can provide an "alternative key" that decrypts it to something else.

However, this is complex, and you cannot do it by hand. In general, it's difficult to do, even by machine.

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  • $\begingroup$ Although it might be possible, I don't know any (unbroken and practical) ciphers that support this, nor does the page you link to name any. Could you give an example? $\endgroup$ – Aleph Feb 14 '16 at 11:54
  • $\begingroup$ To the best of my knowledge, deniable encryption is not very practical, but I'm not sure. I guess it's a good thing to research :-). $\endgroup$ – Yehuda Lindell Feb 14 '16 at 15:28

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