A NOTE ON “ON CIPHERTEXT UNDETECTABILITY”

The notion of ciphertext undetectability was introduced in [Gaˇzi, P. - Stanek, M.: On ciphertext undetectability, Tatra Mt. Math. Publ. 41 (2008), 133-151] as a steganographic property of an encryption scheme. While finding the relationship between ciphertext undetectability and indistinguishability of encryptions, authors showed that ciphertext undetectability does not imply indistinguishability. Though the proposition is correct, the proof is not. In this note, we provide a correct proof of the above-mentioned result by a slight modification of the construction used in original paper cited above.