focal (3) RAND_priv_bytes.3ssl.gz

Provided by: libssl-doc_1.1.1f-1ubuntu2.24_all bug

NAME
       RAND_bytes, RAND_priv_bytes, RAND_pseudo_bytes - generate random data


SYNOPSIS
        #include <openssl/rand.h>

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

       Deprecated:

        #if OPENSSL_API_COMPAT < 0x10100000L
        int RAND_pseudo_bytes(unsigned char *buf, int num);
        #endif


DESCRIPTION
       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 RAND_DRBG(7).


NOTES
       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.


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 ERR_get_error(3).


SEE ALSO
       RAND_add(3), RAND_bytes(3), RAND_priv_bytes(3), ERR_get_error(3), RAND(7), RAND_DRBG(7)


HISTORY
       • 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.


       Copyright 2000-2020 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
       <https://www.openssl.org/source/license.html>.