=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:

 #if OPENSSL_API_COMPAT < 0x00908000L
 RSA *RSA_generate_key(int bits, unsigned long e,
                       void (*callback)(int, int, void *), void *cb_arg);
 #endif

=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 2000-2019 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
L<https://www.openssl.org/source/license.html>.

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