Key Derivation Function (KDF)
What is Key Derivation Function (KDF)?
Key Derivation Function (KDF)A cryptographic function that derives one or more strong cryptographic keys from a secret input such as a password, shared secret or master key.
A Key Derivation Function (KDF) takes a source of secret material — a password, a Diffie–Hellman shared secret, or an existing master key — and produces one or more cryptographically strong keys of a fixed length. KDFs split into two families: password-based KDFs designed to be slow and memory-hard (Argon2id, scrypt, bcrypt, PBKDF2) and extract-and-expand KDFs designed for high-entropy inputs (HKDF, defined in RFC 5869). HKDF is widely used in TLS 1.3, Signal, WireGuard, and Noise to derive multiple session keys from a single shared secret using HMAC. Good KDFs include salts and optional info/context strings to provide domain separation between derived keys, ensuring that derived keys cannot be linked or reused across contexts.
● Examples
- 01
HKDF-Extract+Expand is used in TLS 1.3 to derive handshake and traffic secrets.
- 02
Argon2id derives a 32-byte AES key from a user passphrase to unlock an encrypted vault.
● Frequently asked questions
What is Key Derivation Function (KDF)?
A cryptographic function that derives one or more strong cryptographic keys from a secret input such as a password, shared secret or master key. It belongs to the Cryptography category of cybersecurity.
What does Key Derivation Function (KDF) mean?
A cryptographic function that derives one or more strong cryptographic keys from a secret input such as a password, shared secret or master key.
How do you defend against Key Derivation Function (KDF)?
Defences for Key Derivation Function (KDF) typically combine technical controls and operational practices, as detailed in the full definition above.
What are other names for Key Derivation Function (KDF)?
Common alternative names include: KDF, Key derivation.