RAND_bytes

RAND_BYTES(3)                        OpenSSL                       RAND_BYTES(3)



NAME
       RAND_bytes, RAND_priv_bytes, RAND_bytes_ex, RAND_priv_bytes_ex,
       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);

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

       Deprecated since OpenSSL 1.1.0, 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);

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
       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 an additional ctx parameter.
       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.

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), EVP_RAND(7)

HISTORYRAND_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
       Copyright 2000-2020 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>.



3.0.0-alpha12                      2021-02-18                      RAND_BYTES(3)