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Title "RAND_BYTES 3" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
RAND_bytes, RAND_priv_bytes, RAND_pseudo_bytes - generate random data Header "SYNOPSIS" .Vb 1 #include <openssl/rand.h> \& int RAND_bytes(unsigned char *buf, int num); int RAND_priv_bytes(unsigned char *buf, int num); .Ve

Deprecated:

.Vb 3 #if OPENSSL_API_COMPAT < 0x10100000L int RAND_pseudo_bytes(unsigned char *buf, int num); #endif .Ve

Header "DESCRIPTION" \fBRAND_bytes() generates num random bytes using a cryptographically secure pseudo random generator (\s-1CSPRNG\s0) and stores them in buf.

\fBRAND_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 \s-1RAND_METHOD,\s0 this function uses a separate \*(L"private\*(R" \s-1PRNG\s0 instance so that a compromise of the \*(L"public\*(R" \s-1PRNG\s0 instance will not affect the secrecy of these private values, as described in \s-1RAND\s0\|(7) and \s-1RAND_DRBG\s0\|(7).

Header "NOTES" By default, the OpenSSL \s-1CSPRNG\s0 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 \s-1CSPRNG\s0 on first use using the operating systems's random generator.

If the entropy source fails or is not available, the \s-1CSPRNG\s0 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.

Header "RETURN VALUES" \fBRAND_bytes() and RAND_priv_bytes() return 1 on success, -1 if not supported by the current \s-1RAND\s0 method, or 0 on other failure. The error code can be obtained by ERR_get_error\|(3). Header "SEE ALSO" \fBRAND_add\|(3), \fBRAND_bytes\|(3), \fBRAND_priv_bytes\|(3), \fBERR_get_error\|(3), \s-1RAND\s0\|(7), \s-1RAND_DRBG\s0\|(7) Header "HISTORY" \fBRAND_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. Header "COPYRIGHT" Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at <https://www.openssl.org/source/license.html>.