EVP_RSA_gen, RSA_generate_key_ex, RSA_generate_key, RSA_generate_multi_prime_key - generate RSA key pair

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

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       Licensed under the Apache License 2.0 (the "License").  You may not use this file  except  in  compliance
       with  the  License.   You  can  obtain  a  copy  in  the  file  LICENSE  in the source distribution or at
       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04                             RSA_GENERATE_KEY(3SSL)

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.

       • While a random prime number is generated, it is called as described in BN_generate_prime(3).

       • When the n-th randomly generated prime is rejected as not suitable for the key, BN_GENCB_call(cb,2,n)
         is called.

       • When a random p has been found with p-1 relatively prime to e, it is called as BN_GENCB_call(cb,3,0).

       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.

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).

       EVP_RSA_gen, RSA_generate_key_ex, RSA_generate_key, RSA_generate_multi_prime_key - generate RSA key pair

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.

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

        #include <openssl/rsa.h>

        EVP_PKEY *EVP_RSA_gen(unsigned int bits);

       The following functions have been deprecated since OpenSSL 3.0, and 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);

       The following function has been deprecated since OpenSSL 0.9.8, and can be hidden entirely by defining
       OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

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