RSA_generate_key

 #include <openssl/rsa.h>
 RSA *RSA_generate_key(int num, unsigned long e,
    void (*callback)(int,int,void *), void *cb_arg);

RSA_generate_key() generates a key pair and returns it in a newly allocated RSA structure. The pseudo-random number generator must be seeded prior to calling RSA_generate_key().

The modulus size will be num bits, 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.

A callback function may be used to provide feedback about the progress of the key generation. If callback is not NULL, it will be called as follows:

• 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, callback(2, n, cb_arg) is called.
• When a random p has been found with p-1 relatively prime to e, it is called as callback(3, 0, cb_arg).

The process is then repeated for prime q with callback(3, 1, cb_arg).

If key generation fails, RSA_generate_key() returns NULL; the error codes can be obtained by ERR_get_error(3).

callback(2, x, cb_arg) is used with two different meanings.

RSA_generate_key() goes into an infinite loop for illegal input values.

ERR_get_error(3), rand(3), rsa(3), RSA_free(3)

The cb_arg argument was added in SSLeay 0.9.0.