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RAND_DRBG_GENERATE(3)		    OpenSSL		 RAND_DRBG_GENERATE(3)

NAME
       RAND_DRBG_generate, RAND_DRBG_bytes - generate random bytes using the
       given drbg instance

SYNOPSIS
	#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);

DESCRIPTION
       RAND_DRBG_generate() generates outlen random bytes using	the given DRBG
       instance	drbg and stores	them in	the buffer at out.

       Before generating the output, the DRBG instance checks whether the
       maximum number of generate requests (reseed interval) or	the maximum
       timespan	(reseed	time interval) since its last seeding have been
       reached.	 If this is the	case, the DRBG reseeds automatically.
       Additionally, an	immediate reseeding can	be requested by	setting	the
       prediction_resistance flag to 1.	See NOTES section for more details.

       The caller can optionally provide additional data to be used for
       reseeding by passing a pointer adin to a	buffer of length adinlen.
       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 adin to NULL and adinlen to 0;

       RAND_DRBG_bytes() generates outlen random bytes using the given DRBG
       instance	drbg and stores	them in	the buffer at out.  This function is a
       wrapper around the RAND_DRBG_generate() 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).

RETURN VALUES
       RAND_DRBG_generate() and	RAND_DRBG_bytes() return 1 on success, and 0
       on failure.

NOTES
       The reseed interval and reseed time interval of the drbg	are set	to
       reasonable default values, which	in general do not have to be adjusted.
       If necessary, they can be changed using
       RAND_DRBG_set_reseed_interval(3)	and
       RAND_DRBG_set_reseed_time_interval(3), respectively.

       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	[NIST SP 800-90C].  Since the default DRBG
       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 DRBG.

SEE ALSO
       RAND_bytes(3), RAND_DRBG_set_reseed_interval(3),
       RAND_DRBG_set_reseed_time_interval(3), RAND_DRBG(7)

HISTORY
       The RAND_DRBG functions were added in OpenSSL 1.1.1.

COPYRIGHT
       Copyright 2017-2019 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>.

1.1.1d				  2019-09-10		 RAND_DRBG_GENERATE(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | NOTES | SEE ALSO | HISTORY | COPYRIGHT

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