RAND_bytes, RAND_priv_bytes, RAND_bytes_ex, RAND_priv_bytes_ex,
RAND_pseudo_bytes - generate random data
#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(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num,
unsigned int strength);
int RAND_priv_bytes_ex(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num,
unsigned int strength);
The following function has been deprecated since OpenSSL 1.1.0, and can be
hidden entirely by defining
OPENSSL_API_COMPAT with a suitable version
value, see
openssl_user_macros(7):
int RAND_pseudo_bytes(unsigned char *buf, int num);
RAND_bytes() generates
num random bytes using a cryptographically
secure pseudo random generator (CSPRNG) and stores them in
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
RAND(7) and
EVP_RAND(7).
RAND_bytes_ex() and
RAND_priv_bytes_ex() are the same as
RAND_bytes() and
RAND_priv_bytes() except that they both take
additional
strength and
ctx parameters. The bytes generated will
have a security strength of at least
strength bits. The DRBG used for
the operation is the public or private DRBG associated with the specified
ctx. The parameter can be NULL, in which case the default library
context is used (see
OSSL_LIB_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.
By default, the OpenSSL CSPRNG supports a security level of 256 bits, provided
it was able to seed itself from a trusted entropy source. On all major
platforms supported by OpenSSL (including the Unix-like platforms and
Windows), OpenSSL is configured to automatically seed the CSPRNG on first use
using the operating systems's random generator.
If the entropy source fails or is not available, the CSPRNG will enter an error
state and refuse to generate random bytes. For that reason, it is important to
always check the error return value of
RAND_bytes() and
RAND_priv_bytes() and not take randomness for granted.
On other platforms, there might not be a trusted entropy source available or
OpenSSL might have been explicitly configured to use different entropy
sources. If you are in doubt about the quality of the entropy source, don't
hesitate to ask your operating system vendor or post a question on GitHub or
the openssl-users mailing list.
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
ERR_get_error(3).
RAND_add(3), ,
RAND_priv_bytes(3),
ERR_get_error(3),
RAND(7),
EVP_RAND(7)
- •
-
RAND_pseudo_bytes() was deprecated in OpenSSL 1.1.0;
use RAND_bytes() instead.
- •
- The RAND_priv_bytes() function was added in OpenSSL
1.1.1.
- •
- The RAND_bytes_ex() and RAND_priv_bytes_ex()
functions were added in OpenSSL 3.0
Copyright 2000-2023 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
<
https://www.openssl.org/source/license.html>.