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NAME

       RAND_DRBG_reseed, RAND_DRBG_set_reseed_interval, RAND_DRBG_set_reseed_time_interval,
       RAND_DRBG_set_reseed_defaults - reseed a RAND_DRBG instance

SYNOPSIS

        #include <openssl/rand_drbg.h>

        int RAND_DRBG_reseed(RAND_DRBG *drbg,
                             const unsigned char *adin, size_t adinlen,
                             int prediction_resistance);

        int RAND_DRBG_set_reseed_interval(RAND_DRBG *drbg,
                                          unsigned int interval);

        int RAND_DRBG_set_reseed_time_interval(RAND_DRBG *drbg,
                                               time_t interval);

        int RAND_DRBG_set_reseed_defaults(
                                          unsigned int master_reseed_interval,
                                          unsigned int slave_reseed_interval,
                                          time_t master_reseed_time_interval,
                                          time_t slave_reseed_time_interval
                                          );

DESCRIPTION

       RAND_DRBG_reseed() reseeds the given drbg, obtaining entropy input from its entropy source
       and mixing in the specified additional data provided in the buffer adin of length adinlen.
       The additional data can be omitted by setting adin to NULL and adinlen to 0.  An immediate
       reseeding from a live entropy source can be requested by setting the prediction_resistance
       flag to 1.  This feature is not implemented yet, so reseeding with prediction resistance
       requested will always fail.

       RAND_DRBG_set_reseed_interval() sets the reseed interval of the drbg, which is the maximum
       allowed number of generate requests between consecutive reseedings.  If interval > 0, then
       the drbg will reseed automatically whenever the number of generate requests since its last
       seeding exceeds the given reseed interval.  If interval == 0, then this feature is
       disabled.

       RAND_DRBG_set_reseed_time_interval() sets the reseed time interval of the drbg, which is
       the maximum allowed number of seconds between consecutive reseedings.  If interval > 0,
       then the drbg will reseed automatically whenever the elapsed time since its last reseeding
       exceeds the given reseed time interval.  If interval == 0, then this feature is disabled.

       RAND_DRBG_set_reseed_defaults() sets the default values for the reseed interval
       (master_reseed_interval and slave_reseed_interval) and the reseed time interval
       (master_reseed_time_interval and slave_reseed_tme_interval) of DRBG instances.  The
       default values are set independently for master DRBG instances (which don't have a parent)
       and slave DRBG instances (which are chained to a parent DRBG).

RETURN VALUES

       RAND_DRBG_reseed(), RAND_DRBG_set_reseed_interval(), and
       RAND_DRBG_set_reseed_time_interval(), return 1 on success, 0 on failure.

NOTES

       The default OpenSSL random generator is already set up for automatic reseeding, so in
       general it is not necessary to reseed it explicitly, or to modify its reseeding
       thresholds.

       Normally, the entropy input for seeding a DRBG is either obtained from a trusted os
       entropy source or from a parent DRBG instance, which was seeded (directly or indirectly)
       from a trusted os entropy source.  In exceptional cases it is possible to replace the
       reseeding mechanism entirely by providing application defined callbacks using
       RAND_DRBG_set_callbacks().

       The reseeding default values are applied only during creation of a DRBG instance.  To
       ensure that they are applied to the global and thread-local DRBG instances (<master>,
       resp. <public> and <private>), it is necessary to call RAND_DRBG_set_reseed_defaults()
       before creating any thread and before calling any
        cryptographic routines that obtain random data directly or indirectly.

SEE ALSO

       RAND_DRBG_generate(3), RAND_DRBG_bytes(3), RAND_DRBG_set_callbacks(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>.