RSA_GENERATE_KEY(3SSL) OpenSSL RSA_GENERATE_KEY(3SSL)
NAME
EVP_RSA_gen, RSA_generate_key_ex, RSA_generate_key,
RSA_generate_multi_prime_key - generate RSA key pair
SYNOPSIS
#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);
DESCRIPTION
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.
RETURN VALUES
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.
BUGS
BN_GENCB_call(cb, 2, x) is used with two different meanings.
SEE ALSO
EVP_PKEY_Q_keygen(3) BN_generate_prime(3), ERR_get_error(3),
RAND_bytes(3), RAND(7)
HISTORY
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).
COPYRIGHT
Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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>.
3.5.7 2026-06-09 RSA_GENERATE_KEY(3SSL)
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