1. Information (usually a sequence of random or pseudorandom binary digits) used initially to set up and periodically change the operations performed in crypto-equipment for the purpose of encrypting or decrypting electronic data, for determining electronic counter-countermeasures patterns (e. G. , frequency hopping or spread spectrum ,) or for producing other key. Note: "Key" has replaced the terms "variable," "key (ing) variable," and "cryptovariable. " 2. Usually a sequence of random or pseudorandom bits used initially to set up and periodically change the operations performed in crypto-equipment for the purpose of encrypting or decrypting electronic signals, or for determining electronic counter-countermeasures patterns (e. G. , frequency hopping or spread spectrum,) or for producing other key. 3. A sequence of symbols that controls the operations of encipherment and decipherment.