RSA_generate_key.3ossl - Man Page

generate RSA key pair


 #include <openssl/rsa.h>

 EVP_PKEY *EVP_RSA_gen(unsigned int bits);

Deprecated since OpenSSL 3.0, can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

 int RSA_generate_key_ex(RSA *rsa, int bits, BIGNUM *e, BN_GENCB *cb);
 int RSA_generate_multi_prime_key(RSA *rsa, int bits, int primes, BIGNUM *e, BN_GENCB *cb);

Deprecated since OpenSSL 0.9.8:

 RSA *RSA_generate_key(int bits, unsigned long e,
                       void (*callback)(int, int, void *), void *cb_arg);


EVP_RSA_gen() generates a new RSA key pair with modulus size bits.

All of the functions described below are deprecated. Applications should instead use EVP_RSA_gen(), EVP_PKEY_Q_keygen(3), or EVP_PKEY_keygen_init(3) and EVP_PKEY_keygen(3).

RSA_generate_key_ex() generates a 2-prime RSA key pair and stores it in the RSA structure provided in rsa.

RSA_generate_multi_prime_key() generates a multi-prime RSA key pair and stores it in the RSA structure provided in rsa. The number of primes is given by the primes parameter. If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to external circumstances (see RAND(7)), the operation will fail.

The modulus size will be of length bits, the number of primes to form the modulus will be primes, and the public exponent will be e. Key sizes with num < 1024 should be considered insecure. The exponent is an odd number, typically 3, 17 or 65537.

In order to maintain adequate security level, the maximum number of permitted primes depends on modulus bit length:

   <1024 | >=1024 | >=4096 | >=8192
     2   |   3    |   4    |   5

A callback function may be used to provide feedback about the progress of the key generation. If cb is not NULL, it will be called as follows using the BN_GENCB_call() function described on the BN_generate_prime(3) page.

RSA_generate_key() is similar to RSA_generate_key_ex() but expects an old-style callback function; see BN_generate_prime(3) for information on the old-style callback.

The process is then repeated for prime q and other primes (if any) with BN_GENCB_call(cb, 3, i) where i indicates the i-th prime.

Return Values

EVP_RSA_gen() returns an EVP_PKEY or NULL on failure.

RSA_generate_multi_prime_key() returns 1 on success or 0 on error. RSA_generate_key_ex() returns 1 on success or 0 on error. The error codes can be obtained by ERR_get_error(3).

RSA_generate_key() returns a pointer to the RSA structure or NULL if the key generation fails.


BN_GENCB_call(cb, 2, x) is used with two different meanings.

See Also

EVP_PKEY_Q_keygen(3) BN_generate_prime(3), ERR_get_error(3), RAND_bytes(3), RAND(7)


EVP_RSA_gen() was added in OpenSSL 3.0. All other functions described here were deprecated in OpenSSL 3.0. For replacement see EVP_PKEY-RSA(7).

Referenced By

BN_generate_prime.3ossl(3), RSA_new.3ossl(3).

The man pages EVP_RSA_gen.3ossl(3), RSA_generate_key_ex.3ossl(3) and RSA_generate_multi_prime_key.3ossl(3) are aliases of RSA_generate_key.3ossl(3).

2021-09-09 3.0.0 OpenSSL