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=pod
=head1 NAME
RSA_generate_key - generate RSA key pair
=head1 SYNOPSIS
#include <openssl/rsa.h>
RSA *RSA_generate_key(int num, unsigned long e,
void (*callback)(int,int,void *), void *cb_arg);
=head1 DESCRIPTION
RSA_generate_key() generates a key pair and returns it in a newly
allocated B<RSA> structure. The pseudo-random number generator must
be seeded prior to calling RSA_generate_key().
The modulus size will be B<num> bits, 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.
A callback function may be used to provide feedback about the
progress of the key generation. If B<callback> is not B<NULL>, it
will be called as follows:
=over 4
=item *
While a random prime number is generated, it is called as
described in L<BN_generate_prime(3)|BN_generate_prime(3)>.
=item *
When the n-th randomly generated prime is rejected as not
suitable for the key, B<callback(2, n, cb_arg)> is called.
=item *
When a random p has been found with p-1 relatively prime to B<e>,
it is called as B<callback(3, 0, cb_arg)>.
=back
The process is then repeated for prime q with B<callback(3, 1, cb_arg)>.
=head1 RETURN VALUE
If key generation fails, RSA_generate_key() returns B<NULL>; the
error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
=head1 BUGS
B<callback(2, x, cb_arg)> is used with two different meanings.
RSA_generate_key() goes into an infinite loop for illegal input values.
=head1 SEE ALSO
L<ERR_get_error(3)|ERR_get_error(3)>, L<rand(3)|rand(3)>, L<rsa(3)|rsa(3)>,
L<RSA_free(3)|RSA_free(3)>
=head1 HISTORY
The B<cb_arg> argument was added in SSLeay 0.9.0.
=cut