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9.2 Public key algorithms

Public key cryptography algorithms such as RSA, DSA and ECDSA, are accessed using the abstract key API in Abstract key types. This is a high level API with the advantage of transparently handling keys stored in memory and keys present in smart cards.

int gnutls_privkey_init (gnutls_privkey_t * key)
int gnutls_privkey_import_url (gnutls_privkey_t key, const char * url, unsigned int flags)
int gnutls_privkey_import_x509_raw (gnutls_privkey_t pkey, const gnutls_datum_t * data, gnutls_x509_crt_fmt_t format, const char * password, unsigned int flags)
int gnutls_privkey_sign_data (gnutls_privkey_t signer, gnutls_digest_algorithm_t hash, unsigned int flags, const gnutls_datum_t * data, gnutls_datum_t * signature)
int gnutls_privkey_sign_hash (gnutls_privkey_t signer, gnutls_digest_algorithm_t hash_algo, unsigned int flags, const gnutls_datum_t * hash_data, gnutls_datum_t * signature)
void gnutls_privkey_deinit (gnutls_privkey_t key)
int gnutls_pubkey_init (gnutls_pubkey_t * key)
int gnutls_pubkey_import_url (gnutls_pubkey_t key, const char * url, unsigned int flags)
int gnutls_pubkey_import_x509 (gnutls_pubkey_t key, gnutls_x509_crt_t crt, unsigned int flags)
int gnutls_pubkey_verify_data2 (gnutls_pubkey_t pubkey, gnutls_sign_algorithm_t algo, unsigned int flags, const gnutls_datum_t * data, const gnutls_datum_t * signature)
int gnutls_pubkey_verify_hash2 (gnutls_pubkey_t key, gnutls_sign_algorithm_t algo, unsigned int flags, const gnutls_datum_t * hash, const gnutls_datum_t * signature)
void gnutls_pubkey_deinit (gnutls_pubkey_t key)

Keys stored in memory can be imported using functions like gnutls_privkey_import_x509_raw, while keys on smart cards or HSMs should be imported using their PKCS#11 URL with gnutls_privkey_import_url.

If any of the smart card operations require PIN, that should be provided either by setting the global PIN function (gnutls_pkcs11_set_pin_function), or better with the targeted to structures functions such as gnutls_privkey_set_pin_function.

9.2.1 Key generation

All supported key types (including RSA, DSA, ECDSA, Ed25519, Ed448) can be generated with GnuTLS. They can be generated with the simpler gnutls_privkey_generate or with the more advanced gnutls_privkey_generate2.

Function: int gnutls_privkey_generate2 (gnutls_privkey_t pkey, gnutls_pk_algorithm_t algo, unsigned int bits, unsigned int flags, const gnutls_keygen_data_st * data, unsigned data_size)

pkey: The private key

algo: is one of the algorithms in gnutls_pk_algorithm_t .

bits: the size of the modulus

flags: Must be zero or flags from gnutls_privkey_flags_t .

data: Allow specifying gnutls_keygen_data_st types such as the seed to be used.

data_size: The number of data available.

This function will generate a random private key. Note that this function must be called on an initialized private key.

The flag GNUTLS_PRIVKEY_FLAG_PROVABLE instructs the key generation process to use algorithms like Shawe-Taylor (from FIPS PUB186-4) which generate provable parameters out of a seed for RSA and DSA keys. On DSA keys the PQG parameters are generated using the seed, while on RSA the two primes. To specify an explicit seed (by default a random seed is used), use the data with a GNUTLS_KEYGEN_SEED type.

Note that when generating an elliptic curve key, the curve can be substituted in the place of the bits parameter using the GNUTLS_CURVE_TO_BITS() macro.

To export the generated keys in memory or in files it is recommended to use the PKCS8 form as it can handle all key types, and can store additional parameters such as the seed, in case of provable RSA or DSA keys. Generated keys can be exported in memory using gnutls_privkey_export_x509() , and then with gnutls_x509_privkey_export2_pkcs8() .

If key generation is part of your application, avoid setting the number of bits directly, and instead use gnutls_sec_param_to_pk_bits() . That way the generated keys will adapt to the security levels of the underlying GnuTLS library.

Returns: On success, GNUTLS_E_SUCCESS (0) is returned, otherwise a negative error value.

Since: 3.5.0

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