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The RAND_DRBG API was added in PR #5462 and modified by PR #5547. This commit adds the corresponding documention. Reviewed-by: Kurt Roeckx <kurt@roeckx.be> Reviewed-by: Rich Salz <rsalz@openssl.org> (Merged from https://github.com/openssl/openssl/pull/5461)
79 lines
2.8 KiB
Plaintext
79 lines
2.8 KiB
Plaintext
=pod
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=head1 NAME
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RAND
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- the OpenSSL random generator
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=head1 DESCRIPTION
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Random numbers are a vital part of cryptography, they are needed to provide
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unpredictability for tasks like key generation, creating salts, and many more.
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Software-based generators must be seeded with external randomness before they
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can be used as a cryptographically-secure pseudo-random number generator
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(CSPRNG).
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The availability of common hardware with special instructions and
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modern operating systems, which may use items such as interrupt jitter
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and network packet timings, can be reasonable sources of seeding material.
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OpenSSL comes with a default implementation of the RAND API which is based on
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the deterministic random bit generator (DRBG) model as described in
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[NIST SP 800-90A Rev. 1]. The default random generator will initialize
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automatically on first use and will be fully functional without having
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to be initialized ('seeded') explicitly.
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It seeds and reseeds itself automatically using trusted random sources
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provided by the operating system.
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As a normal application developer, you don't have to worry about any details,
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just use L<RAND_bytes(3)> to obtain random data.
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Having said that, there is one important rule to obey: Always check the error
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return value of L<RAND_bytes(3)> and don't take randomness for granted.
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For long-term secrets, you can use L<RAND_priv_bytes(3)> instead.
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This method does not provide 'better' randomness, it uses the same type of CSPRNG.
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The intention behind using a dedicated CSPRNG exclusively for long-term secrets is
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that none of its output should be visible to an attacker (e.g used as salt value),
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in order to reveal as little information as possible about its internal state.
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In the rare case where the default implementation does not satisfy your special
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requirements, there are two options:
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=over 2
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=item *
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Replace the default RAND method by your own RAND method using
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L<RAND_set_rand_method(3)>.
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=item *
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Modify the default settings of the OpenSSL RAND method by modifying the security
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parameters of the underlying DRBG, which is described in detail in L<RAND_DRBG(7)>.
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=back
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Changing the default random generator or its default parameters should be necessary
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only in exceptional cases and is not recommended, unless you have a profound knowledge
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of cryptographic principles and understand the implications of your changes.
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=head1 SEE ALSO
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L<RAND_add(3)>,
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L<RAND_bytes(3)>,
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L<RAND_priv_bytes(3)>,
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L<RAND_get_rand_method(3)>
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L<RAND_set_rand_method(3)>
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L<RAND_OpenSSL(3)>,
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L<RAND_DRBG(7)>,
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=head1 COPYRIGHT
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Copyright 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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