=pod

=head1 NAME

RSA_generate_key_ex, RSA_generate_key,
RSA_generate_multi_prime_key - generate RSA key pair

=head1 SYNOPSIS

 #include <openssl/rsa.h>

 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);

Deprecated since OpenSSL 0.9.8, can be hidden entirely by defining
B<OPENSSL_API_COMPAT> with a suitable version value, see
L<openssl_user_macros(7)>:

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

=head1 DESCRIPTION

RSA_generate_key_ex() generates a 2-prime RSA key pair and stores it in the
B<RSA> structure provided in B<rsa>. The pseudo-random number generator must
be seeded prior to calling RSA_generate_key_ex().

RSA_generate_multi_prime_key() generates a multi-prime RSA key pair and stores
it in the B<RSA> structure provided in B<rsa>. The number of primes is given by
the B<primes> parameter. The random number generator must be seeded when
calling RSA_generate_multi_prime_key().
If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
external circumstances (see L<RAND(7)>), the operation will fail.

The modulus size will be of length B<bits>, the number of primes to form the
modulus will be B<primes>, and the public exponent will be B<e>. Key sizes
with B<num> E<lt> 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
B<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 B<cb> is not B<NULL>, it
will be called as follows using the BN_GENCB_call() function
described on the L<BN_generate_prime(3)> page.

RSA_generate_key() is similar to RSA_generate_key_ex() but
expects an old-style callback function; see
L<BN_generate_prime(3)> for information on the old-style callback.

=over 2

=item *

While a random prime number is generated, it is called as
described in L<BN_generate_prime(3)>.

=item *

When the n-th randomly generated prime is rejected as not
suitable for the key, B<BN_GENCB_call(cb, 2, n)> is called.

=item *

When a random p has been found with p-1 relatively prime to B<e>,
it is called as B<BN_GENCB_call(cb, 3, 0)>.

=back

The process is then repeated for prime q and other primes (if any)
with B<BN_GENCB_call(cb, 3, i)> where B<i> indicates the i-th prime.

=head1 RETURN VALUES

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 L<ERR_get_error(3)>.

RSA_generate_key() returns a pointer to the RSA structure or
B<NULL> if the key generation fails.

=head1 BUGS

B<BN_GENCB_call(cb, 2, x)> is used with two different meanings.

=head1 SEE ALSO

L<ERR_get_error(3)>, L<RAND_bytes(3)>, L<BN_generate_prime(3)>,
L<RAND(7)>

=head1 HISTORY

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

=head1 COPYRIGHT

Copyright 2000-2018 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
L<https://www.openssl.org/source/license.html>.

=cut
