1=pod 2 3=head1 NAME 4 5RAND_DRBG_generate, 6RAND_DRBG_bytes 7- generate random bytes using the given drbg instance 8 9=head1 SYNOPSIS 10 11 #include <openssl/rand_drbg.h> 12 13 int RAND_DRBG_generate(RAND_DRBG *drbg, 14 unsigned char *out, size_t outlen, 15 int prediction_resistance, 16 const unsigned char *adin, size_t adinlen); 17 18 int RAND_DRBG_bytes(RAND_DRBG *drbg, 19 unsigned char *out, size_t outlen); 20 21 22=head1 DESCRIPTION 23 24RAND_DRBG_generate() generates B<outlen> random bytes using the given 25DRBG instance B<drbg> and stores them in the buffer at B<out>. 26 27Before generating the output, the DRBG instance checks whether the maximum 28number of generate requests (I<reseed interval>) or the maximum timespan 29(I<reseed time interval>) since its last seeding have been reached. 30If this is the case, the DRBG reseeds automatically. 31Additionally, an immediate reseeding can be requested by setting the 32B<prediction_resistance> flag to 1. See NOTES section for more details. 33 34The caller can optionally provide additional data to be used for reseeding 35by passing a pointer B<adin> to a buffer of length B<adinlen>. 36This additional data is mixed into the internal state of the random 37generator but does not contribute to the entropy count. 38The additional data can be omitted by setting B<adin> to NULL and 39B<adinlen> to 0; 40 41RAND_DRBG_bytes() generates B<outlen> random bytes using the given 42DRBG instance B<drbg> and stores them in the buffer at B<out>. 43This function is a wrapper around the RAND_DRBG_generate() call, 44which collects some additional data from low entropy sources 45(e.g., a high resolution timer) and calls 46RAND_DRBG_generate(drbg, out, outlen, 0, adin, adinlen). 47 48 49=head1 RETURN VALUES 50 51RAND_DRBG_generate() and RAND_DRBG_bytes() return 1 on success, 52and 0 on failure. 53 54=head1 NOTES 55 56The I<reseed interval> and I<reseed time interval> of the B<drbg> are set to 57reasonable default values, which in general do not have to be adjusted. 58If necessary, they can be changed using L<RAND_DRBG_set_reseed_interval(3)> 59and L<RAND_DRBG_set_reseed_time_interval(3)>, respectively. 60 61A request for prediction resistance can only be satisfied by pulling fresh 62entropy from one of the approved entropy sources listed in section 5.5.2 of 63[NIST SP 800-90C]. 64Since the default DRBG implementation does not have access to such an approved 65entropy source, a request for prediction resistance will always fail. 66In other words, prediction resistance is currently not supported yet by the DRBG. 67 68=head1 SEE ALSO 69 70L<RAND_bytes(3)>, 71L<RAND_DRBG_set_reseed_interval(3)>, 72L<RAND_DRBG_set_reseed_time_interval(3)>, 73L<RAND_DRBG(7)> 74 75=head1 HISTORY 76 77The RAND_DRBG functions were added in OpenSSL 1.1.1. 78 79=head1 COPYRIGHT 80 81Copyright 2017-2019 The OpenSSL Project Authors. All Rights Reserved. 82 83Licensed under the OpenSSL license (the "License"). You may not use 84this file except in compliance with the License. You can obtain a copy 85in the file LICENSE in the source distribution or at 86L<https://www.openssl.org/source/license.html>. 87 88=cut 89