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HKDF
HKDF is a standard method for turning one shared secret into several strong, purpose-specific keys.
HKDF (HMAC-based Key Derivation Function) takes input key material and, in an extract-then-expand process built on HMAC, produces one or more cryptographically strong output keys. TLS uses it as the backbone of its 'key schedule,' deriving distinct keys for distinct purposes from the handshake's shared secret. It ensures derived keys are well-mixed and independent rather than reused raw.
See also
- HMACHMAC is a way to attach a secret-keyed tag to a message so the receiver can verify it was not altered or forged.
- handshakeA handshake is the opening negotiation of a secure connection where both sides agree on keys before any data flows.
- initialisation vector (IV)An initialisation vector is a per-message random or unique value that makes encryption of the same data look different each time.