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.
derive_key(size_t key_len, const std::vector<uint8_t> &secret, const std::string &salt = "") const¶
derive_key(size_t key_len, const std::vector<uint8_t> &secret, const std::vector<uint8_t> &salt) const¶
derive_key(size_t key_len, const std::vector<uint8_t> &secret, const uint8_t *salt, size_t salt_len) const¶
derive_key(size_t key_len, const uint8_t *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
Botan includes many different KDFs simply because different protocols and standards have created subtly different approaches to this problem. For new code, use HKDF which is conservative, well studied, widely implemented and NIST approved.
Defined in RFC 5869, HKDF uses HMAC to process inputs. Also available are variants HKDF-Extract and HKDF-Expand. HKDF is the combined Extract+Expand operation. Use the combined HKDF unless you need compatability with some other system.
BOTAN_HAS_HKDF is defined.
KDF2 comes from IEEE 1363. It uses a hash function.
BOTAN_HAS_KDF2 is defined.
KDF1 from ISO 18033-2. Very similar to (but incompatible with) KDF2.
BOTAN_HAS_KDF1_18033 is defined.
KDF1 from IEEE 1363. It can only produce an output at most the length of the hash function used.
BOTAN_HAS_KDF1 is defined.
A KDF from ANSI X9.42. Sometimes used for Diffie-Hellman.
BOTAN_HAS_X942_PRF is defined.
KDFs from NIST SP 800-108. Variants include “SP800-108-Counter”, “SP800-108-Feedback” and “SP800-108-Pipeline”.
BOTAN_HAS_SP800_108 is defined.
KDF from NIST SP 800-56A.
BOTAN_HAS_SP800_56A is defined.
KDF from NIST SP 800-56C.
BOTAN_HAS_SP800_56C is defined.