RAND_DRBG_RESEED(3)

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 can be requested by setting the prediction_resistance flag to 1. Requesting prediction resistance is a relative expensive operation. See NOTES section for more details.

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.

Prediction resistance is supported from OpenSSL 3.0.

COPYRIGHT
Copyright 2017-2019 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>.