Unicity distance

Length of ciphertext needed to unambiguously break a cipher

In cryptography, unicity distance is the length of an original ciphertext needed to break the cipher by reducing the number of possible spurious keys to zero in a brute force attack. That is, after trying every possible key, there should be just one decipherment that makes sense, i.e. expected amount of ciphertext needed to determine the key completely, assuming the underlying message has redundancy.

This keyword could refer to multiple things. Here are some suggestions: