xref: /openssl/doc/man3/RSA_generate_key.pod (revision 3dbf8243)
1=pod
2
3=head1 NAME
4
5EVP_RSA_gen,
6RSA_generate_key_ex, RSA_generate_key,
7RSA_generate_multi_prime_key - generate RSA key pair
8
9=head1 SYNOPSIS
10
11 #include <openssl/rsa.h>
12
13 EVP_PKEY *EVP_RSA_gen(unsigned int bits);
14
15The following functions have been deprecated since OpenSSL 3.0, and can be
16hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
17see L<openssl_user_macros(7)>:
18
19 int RSA_generate_key_ex(RSA *rsa, int bits, BIGNUM *e, BN_GENCB *cb);
20 int RSA_generate_multi_prime_key(RSA *rsa, int bits, int primes, BIGNUM *e, BN_GENCB *cb);
21
22The following function has been deprecated since OpenSSL 0.9.8, and can be
23hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
24see L<openssl_user_macros(7)>:
25
26 RSA *RSA_generate_key(int bits, unsigned long e,
27                       void (*callback)(int, int, void *), void *cb_arg);
28
29=head1 DESCRIPTION
30
31EVP_RSA_gen() generates a new RSA key pair with modulus size I<bits>.
32
33All of the functions described below are deprecated.
34Applications should instead use EVP_RSA_gen(), L<EVP_PKEY_Q_keygen(3)>, or
35L<EVP_PKEY_keygen_init(3)> and L<EVP_PKEY_keygen(3)>.
36
37RSA_generate_key_ex() generates a 2-prime RSA key pair and stores it in the
38B<RSA> structure provided in I<rsa>.
39
40RSA_generate_multi_prime_key() generates a multi-prime RSA key pair and stores
41it in the B<RSA> structure provided in I<rsa>. The number of primes is given by
42the I<primes> parameter.
43If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
44external circumstances (see L<RAND(7)>), the operation will fail.
45
46The modulus size will be of length I<bits>, the number of primes to form the
47modulus will be I<primes>, and the public exponent will be I<e>. Key sizes
48with I<num> E<lt> 1024 should be considered insecure. The exponent is an odd
49number, typically 3, 17 or 65537.
50
51In order to maintain adequate security level, the maximum number of permitted
52I<primes> depends on modulus bit length:
53
54   <1024 | >=1024 | >=4096 | >=8192
55   ------+--------+--------+-------
56     2   |   3    |   4    |   5
57
58A callback function may be used to provide feedback about the
59progress of the key generation. If I<cb> is not NULL, it
60will be called as follows using the BN_GENCB_call() function
61described on the L<BN_generate_prime(3)> page.
62
63RSA_generate_key() is similar to RSA_generate_key_ex() but
64expects an old-style callback function; see
65L<BN_generate_prime(3)> for information on the old-style callback.
66
67=over 2
68
69=item *
70
71While a random prime number is generated, it is called as
72described in L<BN_generate_prime(3)>.
73
74=item *
75
76When the n-th randomly generated prime is rejected as not
77suitable for the key, I<BN_GENCB_call(cb, 2, n)> is called.
78
79=item *
80
81When a random p has been found with p-1 relatively prime to I<e>,
82it is called as I<BN_GENCB_call(cb, 3, 0)>.
83
84=back
85
86The process is then repeated for prime q and other primes (if any)
87with I<BN_GENCB_call(cb, 3, i)> where I<i> indicates the i-th prime.
88
89=head1 RETURN VALUES
90
91EVP_RSA_gen() returns an I<EVP_PKEY> or NULL on failure.
92
93RSA_generate_multi_prime_key() returns 1 on success or 0 on error.
94RSA_generate_key_ex() returns 1 on success or 0 on error.
95The error codes can be obtained by L<ERR_get_error(3)>.
96
97RSA_generate_key() returns a pointer to the RSA structure or
98NULL if the key generation fails.
99
100=head1 BUGS
101
102I<BN_GENCB_call(cb, 2, x)> is used with two different meanings.
103
104=head1 SEE ALSO
105
106L<EVP_PKEY_Q_keygen(3)>
107L<BN_generate_prime(3)>, L<ERR_get_error(3)>,
108L<RAND_bytes(3)>, L<RAND(7)>
109
110=head1 HISTORY
111
112EVP_RSA_gen() was added in OpenSSL 3.0.
113All other functions described here were deprecated in OpenSSL 3.0.
114For replacement see L<EVP_PKEY-RSA(7)>.
115
116=head1 COPYRIGHT
117
118Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
119
120Licensed under the Apache License 2.0 (the "License").  You may not use
121this file except in compliance with the License.  You can obtain a copy
122in the file LICENSE in the source distribution or at
123L<https://www.openssl.org/source/license.html>.
124
125=cut
126