# Botan

# Key Derivation Functions

Key derivation functions are used to turn some amount of shared secret material into uniform random keys suitable for use with symmetric algorithms. An example of an input which is useful for a KDF is a shared secret created using Diffie-Hellman key agreement.

class ```KDF`
  SecureVector<byte> ```derive_key`(size_t key_len, const MemoryRegion<byte> &secret, const std::string &salt = "") const
  SecureVector<byte> ```derive_key`(size_t key_len, const MemoryRegion<byte> &secret, const MemoryRegion<byte> &salt) const
  SecureVector<byte> ```derive_key`(size_t key_len, const MemoryRegion<byte> &secret, const byte *salt, size_t salt_len) const
  SecureVector<byte> ```derive_key`(size_t key_len, const byte *secret, size_t secret_len, const std::string &salt) const

    All variations on the same theme. Deterministically creates a uniform random value from secret and salt. Typically salt is a lable or identifier, such as a session id.

You can create a `KDF` using

KDF *```get_kdf`(const std::string &algo_spec)