Editing Unicity distance (section)

==Practical application==
Unicity distance is a useful theoretical measure, but it does not say much about the security of a block cipher when attacked by an adversary with real-world (limited) resources. Consider a block cipher with a unicity distance of three ciphertext blocks.  Although there is clearly enough information for a computationally unbounded adversary to find the right key (simple exhaustive search), this may be computationally infeasible in practice.

The unicity distance can be increased by reducing the plaintext redundancy. One way to do this is to deploy [[data compression]] techniques prior to encryption, for example by removing redundant vowels while retaining readability. This is a good idea anyway, as it reduces the amount of data to be encrypted.

Ciphertexts greater than the unicity distance can be assumed to have only one meaningful decryption. Ciphertexts shorter than the unicity distance may have multiple plausible decryptions. Unicity distance is not a measure of how much ciphertext is required for cryptanalysis,{{why|date=November 2014}} but how much ciphertext is required for there to be only one reasonable solution for cryptanalysis.