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XOR cipher preserves bit length, but depending on the accepted cleartext alphabet will result in longer ciphertexts. So if you have a 1 byte cleartext, XOR will result in a 1 byte ciphertext. Edit: Yes well you asked if you can do better than 32 bytes for a 1 byte message, and if so which algorithm would give the shortest ;) Technically you can encrypt 1 ...


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@fgrieu gives an excellent answer. One more option. Suppose you know that the plaintext has redundancy (due to some message formatting or something), and you know how to verify that its redundancy is correct (e.g., to check the formatting), but you don't know how to compress it or how to remove the redundancy. Then a reasonable solution is the following: ...


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If the data to protect has no built-in redundancy at all (for example, has each of its bit determined by fair coin toss), there is no way to protect integrity without expansion (Proof sketch: there are as many distinct possibilities for valid plaintext as there as possibilities for valid enciphered-and-protected data, hence every possible ...



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