Key

A parameter that determines the transformation from plaintext to ciphertext and vice versa. (A DEA key is a 64-bit parameter consisting of 56 independent bits and 8 parity bits). Multiple (1, 2 or 3) keys may be used in the Triple Data Encryption Algorithm. 

See NIST SP 800-20 under Cryptographic key for more information. 
 
The parameter of the block cipher that determines the selection of the forward cipher function from the family of permutations. 

See the following under Key for more information: 
NIST SP 800-38B under Key  
NIST SP 800-38D under Key 
 
A numerical value used to control cryptographic operations, such as decryption, encryption, signature generation, or signature verification. Usually a sequence of random or pseudorandom bits used initially to set up and periodically change the operations performed in cryptographic equipment for the purpose of encrypting or decrypting electronic signals, or for determining electronic counter-countermeasures (ECCM) patterns, or for producing other key. 
 
See CNSSI 4009-2015 (CNSSI 4005) for more information. 
 
A  binary  string  used  as  a  secret  parameter  by  a  cryptographic algorithm. In this Recommendation, a cryptographic key shall be either a truly random binary string of a length specified by the cryptographic algorithm or a pseudorandom binary string of the specified length that is computationally indistinguishable from one selected uniformly at random from the set of all binary strings of that length. 
 
See NIST SP 800-108 under Cryptographic key for more information. 
 
A parameter that determines the transformation using DEA and TDEA forward and inverse operations. 
 
See NIST SP 800-67 Rev. 2  and NIST SP 800-38A under Cryptographic Key for more information. 
 
A parameter used with a cryptographic algorithm that determines its operation in such a way that an entity with knowledge of the key can reproduce or reverse the operation, while an entity without knowledge of the key cannot. Examples applicable to this Recommendation include: 1. The computation of a keyed-hash message authentication code. 2. The verification of a keyed-hash message authentication code. 3. The generation of a digital signature on a message. 4. The verification of a digital signature. 

See NIST SP 800-102 and NIST SP 800-107 Rev. 1 under Key for more information.

A cryptographic key. In this document, keys generally refer to public key cryptography key pairs used for authentication of users and/or machines (using digital signatures). Examples include identity key and authorized keys. The SSH protocol also uses host keys that are used for authenticating SSH servers to SSH clients connecting them. 

See NISTIR 7966 under Key for more information.