openssl/doc/man3/RAND_bytes.pod

=pod

=head1 NAME

RAND_bytes, RAND_priv_bytes, RAND_bytes_ex, RAND_priv_bytes_ex,
RAND_pseudo_bytes - generate random data

=head1 SYNOPSIS

 #include <openssl/rand.h>

 int RAND_bytes(unsigned char *buf, int num);
 int RAND_priv_bytes(unsigned char *buf, int num);

 int RAND_bytes_ex(OPENSSL_CTX *ctx, unsigned char *buf, int num);
 int RAND_priv_bytes_ex(OPENSSL_CTX *ctx, unsigned char *buf, int num);

Deprecated since OpenSSL 1.1.0, can be hidden entirely by defining
B<OPENSSL_API_COMPAT> with a suitable version value, see
L<openssl_user_macros(7)>:

 int RAND_pseudo_bytes(unsigned char *buf, int num);

=head1 DESCRIPTION

RAND_bytes() puts B<num> cryptographically strong pseudo-random bytes
into B<buf>.

RAND_priv_bytes() has the same semantics as RAND_bytes().  It is intended to
be used for generating values that should remain private. If using the
default RAND_METHOD, this function uses a separate "private" PRNG
instance so that a compromise of the "public" PRNG instance will not
affect the secrecy of these private values, as described in L<RAND(7)>
and L<RAND_DRBG(7)>.

RAND_bytes_ex() and RAND_priv_bytes_ex() are the same as RAND_bytes() and
RAND_priv_bytes() except that they both take an additional I<ctx> parameter.
The DRBG used for the operation is the public or private DRBG associated with
the specified I<ctx>. The parameter can be NULL, in which case
the default library context is used (see L<OPENSSL_CTX(3)>.
If the default RAND_METHOD has been changed then for compatibility reasons the
RAND_METHOD will be used in preference and the DRBG of the library context
ignored.

=head1 NOTES

Always check the error return value of RAND_bytes() and
RAND_priv_bytes() and do not take randomness for granted: an error occurs
if the CSPRNG has not been seeded with enough randomness to ensure an
unpredictable byte sequence.

=head1 RETURN VALUES

RAND_bytes() and RAND_priv_bytes()
return 1 on success, -1 if not supported by the current
RAND method, or 0 on other failure. The error code can be
obtained by L<ERR_get_error(3)>.

=head1 SEE ALSO

L<RAND_add(3)>,
L<RAND_bytes(3)>,
L<RAND_priv_bytes(3)>,
L<ERR_get_error(3)>,
L<RAND(7)>,
L<RAND_DRBG(7)>

=head1 HISTORY

=over 2

=item *

RAND_pseudo_bytes() was deprecated in OpenSSL 1.1.0; use RAND_bytes() instead.

=item *

The RAND_priv_bytes() function was added in OpenSSL 1.1.1.

=item *

The RAND_bytes_ex() and RAND_priv_bytes_ex() functions were added in OpenSSL 3.0

=back

=head1 COPYRIGHT

Copyright 2000-2019 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