keydependent

Keydependent, often written as key-dependent or keyed, describes functions, algorithms, or systems whose behavior or output is determined by a secret cryptographic key. In keydependent designs, the key is an integral input to the transformation, and without the key correct operation is impossible or results appear random.

In practice, key dependence is central to most cryptographic primitives. Encryption and decryption are naturally keydependent, with the key guiding how plaintext is mapped to ciphertext and back. Signatures rely on a private key to generate valid signatures, while verification uses public information. Key derivation functions produce new keys from a master secret, and pseudorandom functions or MACs produce keyed outputs that appear random to observers lacking the key. Block ciphers and stream ciphers also employ a key schedule that makes internal state and outputs depend on the key.

Security implications follow directly from key dependence. The secrecy and integrity of the key determine the system’s security; key compromise often leads to data exposure or loss of authentication guarantees. Consequently, key management, secure storage, access controls, and resistance to side-channel attacks are critical design considerations. Some designs aim to minimize key exposure or rotate keys to limit risk.

Terminology varies; the concept is the same whether described as keydependent, key-dependent, or keyed. The term highlights that the function’s behavior is parameterized by a key, distinguishing it from keyless or public operations in cryptography.

See also: cryptography, encryption, decryption, digital signatures, MACs, HMAC, PRFs, key derivation functions, key management.