hkdf.h

All headers

HKDF.

  1. HKDF
  2. HKDF_extract
  3. HKDF_expand

HKDF computes HKDF (as specified by RFC 5869) of initial keying material secret with salt and info using digest, and outputs out_len bytes to out_key. It returns one on success and zero on error.

HKDF is an Extract-and-Expand algorithm. It does not do any key stretching, and as such, is not suited to be used alone to generate a key from a password.

OPENSSL_EXPORT int HKDF(uint8_t *out_key, size_t out_len, const EVP_MD *digest,
                        const uint8_t *secret, size_t secret_len,
                        const uint8_t *salt, size_t salt_len,
                        const uint8_t *info, size_t info_len);

HKDF_extract computes a HKDF PRK (as specified by RFC 5869) from initial keying material secret and salt salt using digest, and outputs out_len bytes to out_key. The maximum output size is EVP_MAX_MD_SIZE. It returns one on success and zero on error.

WARNING: This function orders the inputs differently from RFC 5869 specification. Double-check which parameter is the secret/IKM and which is the salt when using.

OPENSSL_EXPORT int HKDF_extract(uint8_t *out_key, size_t *out_len,
                                const EVP_MD *digest, const uint8_t *secret,
                                size_t secret_len, const uint8_t *salt,
                                size_t salt_len);

HKDF_expand computes a HKDF OKM (as specified by RFC 5869) of length out_len from the PRK prk and info info using digest, and outputs the result to out_key. It returns one on success and zero on error.

OPENSSL_EXPORT int HKDF_expand(uint8_t *out_key, size_t out_len,
                               const EVP_MD *digest, const uint8_t *prk,
                               size_t prk_len, const uint8_t *info,
                               size_t info_len);