openssl/doc/man3/RAND_bytes.pod

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=pod
=head1 NAME
RAND_bytes, RAND_priv_bytes, RAND_pseudo_bytes - generate random data
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=head1 SYNOPSIS
#include <openssl/rand.h>
int RAND_bytes(unsigned char *buf, int num);
int RAND_priv_bytes(unsigned char *buf, int num);
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Deprecate RAND_pseudo_bytes The justification for RAND_pseudo_bytes is somewhat dubious, and the reality is that it is frequently being misused. RAND_bytes and RAND_pseudo_bytes in the default implementation both end up calling ssleay_rand_bytes. Both may return -1 in an error condition. If there is insufficient entropy then both will return 0, but RAND_bytes will additionally add an error to the error queue. They both return 1 on success. Therefore the fundamental difference between the two is that one will add an error to the error queue with insufficient entory whilst the other will not. Frequently there are constructions of this form: if(RAND_pseudo_bytes(...) <= 1) goto err; In the above form insufficient entropy is treated as an error anyway, so RAND_bytes is probably the better form to use. This form is also seen: if(!RAND_pseudo_bytes(...)) goto err; This is technically not correct at all since a -1 return value is incorrectly handled - but this form will also treat insufficient entropy as an error. Within libssl it is required that you have correctly seeded your entropy pool and so there seems little benefit in using RAND_pseudo_bytes. Similarly in libcrypto many operations also require a correctly seeded entropy pool and so in most interesting cases you would be better off using RAND_bytes anyway. There is a significant risk of RAND_pseudo_bytes being incorrectly used in scenarios where security can be compromised by insufficient entropy. If you are not using the default implementation, then most engines use the same function to implement RAND_bytes and RAND_pseudo_bytes in any case. Given its misuse, limited benefit, and potential to compromise security, RAND_pseudo_bytes has been deprecated. Reviewed-by: Richard Levitte <levitte@openssl.org>
2015-02-26 21:52:30 +08:00
Deprecated:
#if OPENSSL_API_COMPAT < 0x10100000L
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int RAND_pseudo_bytes(unsigned char *buf, int num);
#endif
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=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)>.
=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.
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=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 HISTORY
=over 2
=item *
RAND_pseudo_bytes() was deprecated in OpenSSL 1.1.0; use RAND_bytes() instead.
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=item *
RAND_priv_bytes() was added in OpenSSL 1.1.1.
=back
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=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)>
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=head1 COPYRIGHT
Copyright 2000-2018 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>.
=cut