### NAME

RSA_generate_key_ex, RSA_generate_key - generate RSA key pair

### SYNOPSIS

```
#include <openssl/rsa.h>
int RSA_generate_key_ex(RSA *rsa, int bits, BIGNUM *e, BN_GENCB *cb);
```

Deprecated:

```
#if OPENSSL_API_COMPAT < 0x00908000L
RSA *RSA_generate_key(int num, unsigned long e,
void (*callback)(int,int,void *), void *cb_arg);
#endif
```

### DESCRIPTION

RSA_generate_key_ex() generates a key pair and stores it in the **RSA** structure provided in **rsa**. The pseudo-random number generator must be seeded prior to calling RSA_generate_key_ex().

The modulus size will be of length **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 **cb** is not **NULL**, it will be called as follows using the BN_GENCB_call() function described on the BN_generate_prime page.

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,

**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 with **BN_GENCB_call(cb, 3, 1)**.

RSA_generate_key is deprecated (new applications should use RSA_generate_key_ex instead). RSA_generate_key works in the same was as RSA_generate_key_ex except it uses "old style" call backs. See BN_generate_prime for further details.

### RETURN VALUE

If key generation fails, RSA_generate_key() returns **NULL**.

The error codes can be obtained by ERR_get_error.

### BUGS

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

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