### 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(3) page.

RSA_generate_prime() is similar to RSA_generate_prime_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 with **BN_GENCB_call(cb, 3, 1)**.

### RETURN VALUE

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.

### BUGS

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

### SEE ALSO

ERR_get_error(3), RAND_bytes(3), RSA_generate_key_ex(3), BN_generate_prime(3)

### HISTORY

RSA_generate_key() was deprecated in OpenSSL 0.9.8; use RSA_generate_key_ex() intsead.

### COPYRIGHT

Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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.