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89 lines
3.0 KiB
Plaintext
89 lines
3.0 KiB
Plaintext
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=pod
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=head1 NAME
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RAND_DRBG_generate,
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RAND_DRBG_bytes
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- generate random bytes using the given drbg instance
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=head1 SYNOPSIS
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#include <openssl/rand_drbg.h>
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int RAND_DRBG_generate(RAND_DRBG *drbg,
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unsigned char *out, size_t outlen,
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int prediction_resistance,
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const unsigned char *adin, size_t adinlen);
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int RAND_DRBG_bytes(RAND_DRBG *drbg,
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unsigned char *out, size_t outlen);
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=head1 DESCRIPTION
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RAND_DRBG_generate() generates B<outlen> random bytes using the given
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DRBG instance B<drbg> and stores them in the buffer at B<out>.
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Before generating the output, the DRBG instance checks whether the maximum
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number of generate requests (I<reseed interval>) or the maximum timespan
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(I<reseed time interval>) since its last seeding have been reached.
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If this is the case, the DRBG reseeds automatically.
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Additionally, an immediate reseeding can be requested by setting the
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B<prediction_resistance> flag to 1. See NOTES section for more details.
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The caller can optionally provide additional data to be used for reseeding
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by passing a pointer B<adin> to a buffer of length B<adinlen>.
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This additional data is mixed into the internal state of the random
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generator but does not contribute to the entropy count.
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The additional data can be omitted by setting B<adin> to NULL and
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B<adinlen> to 0;
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RAND_DRBG_bytes() generates B<outlen> random bytes using the given
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DRBG instance B<drbg> and stores them in the buffer at B<out>.
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This function is a wrapper around the RAND_DRBG_generate() call,
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which collects some additional data from low entropy sources
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(e.g., a high resolution timer) and calls
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RAND_DRBG_generate(drbg, out, outlen, 0, adin, adinlen).
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=head1 RETURN VALUES
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RAND_DRBG_generate() and RAND_DRBG_bytes() return 1 on success,
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and 0 on failure.
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=head1 NOTES
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The I<reseed interval> and I<reseed time interval> of the B<drbg> are set to
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reasonable default values, which in general do not have to be adjusted.
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If necessary, they can be changed using L<RAND_DRBG_set_reseed_interval(3)>
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and L<RAND_DRBG_set_reseed_time_interval(3)>, respectively.
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A request for prediction resistance can only be satisfied by pulling fresh
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entropy from one of the approved entropy sources listed in section 5.5.2 of
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[NIST SP 800-90C].
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Since the default DRBG implementation does not have access to such an approved
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entropy source, a request for prediction resistance will always fail.
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In other words, prediction resistance is currently not supported yet by the DRBG.
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=head1 HISTORY
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The RAND_DRBG functions were added in OpenSSL 1.1.1.
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=head1 SEE ALSO
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L<RAND_bytes(3)>,
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L<RAND_DRBG_set_reseed_interval(3)>,
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L<RAND_DRBG_set_reseed_time_interval(3)>,
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L<RAND_DRBG(7)>
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=head1 COPYRIGHT
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Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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