- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUE
- BUGS
- SEE ALSO
- HISTORY

# NAME

RSA_generate_key - generate RSA key pair

# SYNOPSIS

     #include <openssl/rsa.h>

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

# DESCRIPTION

`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.

- 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).

# RETURN VALUE

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

# BUGS

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

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

# SEE ALSO

ERR_get_error, rand, rsa, RSA_free

# HISTORY

The cb_arg argument was added in SSLeay 0.9.0.