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.\" ========================================================================
.\"
.IX Title "RAND_DRBG_generate 3"
.TH RAND_DRBG_generate 3 "2019-06-09" "1.1.1i" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
RAND_DRBG_generate,
RAND_DRBG_bytes
\&\- generate random bytes using the given drbg instance
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rand_drbg.h>
\&
\& int RAND_DRBG_generate(RAND_DRBG *drbg,
\&                        unsigned char *out, size_t outlen,
\&                        int prediction_resistance,
\&                        const unsigned char *adin, size_t adinlen);
\&
\& int RAND_DRBG_bytes(RAND_DRBG *drbg,
\&                     unsigned char *out, size_t outlen);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBRAND_DRBG_generate()\fR generates \fBoutlen\fR random bytes using the given
\&\s-1DRBG\s0 instance \fBdrbg\fR and stores them in the buffer at \fBout\fR.
.PP
Before generating the output, the \s-1DRBG\s0 instance checks whether the maximum
number of generate requests (\fIreseed interval\fR) or the maximum timespan
(\fIreseed time interval\fR) since its last seeding have been reached.
If this is the case, the \s-1DRBG\s0 reseeds automatically.
Additionally, an immediate reseeding can be requested by setting the
\&\fBprediction_resistance\fR flag to 1. See \s-1NOTES\s0 section for more details.
.PP
The caller can optionally provide additional data to be used for reseeding
by passing a pointer \fBadin\fR to a buffer of length \fBadinlen\fR.
This additional data is mixed into the internal state of the random
generator but does not contribute to the entropy count.
The additional data can be omitted by setting \fBadin\fR to \s-1NULL\s0 and
\&\fBadinlen\fR to 0;
.PP
\&\fBRAND_DRBG_bytes()\fR generates \fBoutlen\fR random bytes using the given
\&\s-1DRBG\s0 instance \fBdrbg\fR and stores them in the buffer at \fBout\fR.
This function is a wrapper around the \fBRAND_DRBG_generate()\fR call,
which collects some additional data from low entropy sources
(e.g., a high resolution timer) and calls
RAND_DRBG_generate(drbg, out, outlen, 0, adin, adinlen).
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBRAND_DRBG_generate()\fR and \fBRAND_DRBG_bytes()\fR return 1 on success,
and 0 on failure.
.SH "NOTES"
.IX Header "NOTES"
The \fIreseed interval\fR and \fIreseed time interval\fR of the \fBdrbg\fR are set to
reasonable default values, which in general do not have to be adjusted.
If necessary, they can be changed using \fBRAND_DRBG_set_reseed_interval\fR\|(3)
and \fBRAND_DRBG_set_reseed_time_interval\fR\|(3), respectively.
.PP
A request for prediction resistance can only be satisfied by pulling fresh
entropy from one of the approved entropy sources listed in section 5.5.2 of
[\s-1NIST SP 800\-90C\s0].
Since the default \s-1DRBG\s0 implementation does not have access to such an approved
entropy source, a request for prediction resistance will always fail.
In other words, prediction resistance is currently not supported yet by the \s-1DRBG.\s0
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBRAND_bytes\fR\|(3),
\&\fBRAND_DRBG_set_reseed_interval\fR\|(3),
\&\fBRAND_DRBG_set_reseed_time_interval\fR\|(3),
\&\s-1\fBRAND_DRBG\s0\fR\|(7)
.SH "HISTORY"
.IX Header "HISTORY"
The \s-1RAND_DRBG\s0 functions were added in OpenSSL 1.1.1.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2017\-2019 The OpenSSL Project Authors. All Rights Reserved.
.PP
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>.