mirror of
https://github.com/openssl/openssl.git
synced 2024-12-15 06:01:37 +08:00
8020d79b40
Reviewed-by: Richard Levitte <levitte@openssl.org> (Merged from https://github.com/openssl/openssl/pull/14512)
83 lines
3.3 KiB
Plaintext
83 lines
3.3 KiB
Plaintext
=pod
|
|
|
|
=head1 NAME
|
|
|
|
RAND
|
|
- the OpenSSL random generator
|
|
|
|
=head1 DESCRIPTION
|
|
|
|
Random numbers are a vital part of cryptography, they are needed to provide
|
|
unpredictability for tasks like key generation, creating salts, and many more.
|
|
Software-based generators must be seeded with external randomness before they
|
|
can be used as a cryptographically-secure pseudo-random number generator
|
|
(CSPRNG).
|
|
The availability of common hardware with special instructions and
|
|
modern operating systems, which may use items such as interrupt jitter
|
|
and network packet timings, can be reasonable sources of seeding material.
|
|
|
|
OpenSSL comes with a default implementation of the RAND API which is based on
|
|
the deterministic random bit generator (DRBG) model as described in
|
|
[NIST SP 800-90A Rev. 1]. The default random generator will initialize
|
|
automatically on first use and will be fully functional without having
|
|
to be initialized ('seeded') explicitly.
|
|
It seeds and reseeds itself automatically using trusted random sources
|
|
provided by the operating system.
|
|
|
|
As a normal application developer, you do not have to worry about any details,
|
|
just use L<RAND_bytes(3)> to obtain random data.
|
|
Having said that, there is one important rule to obey: Always check the error
|
|
return value of L<RAND_bytes(3)> and do not take randomness for granted.
|
|
Although (re-)seeding is automatic, it can fail because no trusted random source
|
|
is available or the trusted source(s) temporarily fail to provide sufficient
|
|
random seed material.
|
|
In this case the CSPRNG enters an error state and ceases to provide output,
|
|
until it is able to recover from the error by reseeding itself.
|
|
For more details on reseeding and error recovery, see L<EVP_RAND(7)>.
|
|
|
|
For values that should remain secret, you can use L<RAND_priv_bytes(3)>
|
|
instead.
|
|
This method does not provide 'better' randomness, it uses the same type of
|
|
CSPRNG.
|
|
The intention behind using a dedicated CSPRNG exclusively for private
|
|
values is that none of its output should be visible to an attacker (e.g.,
|
|
used as salt value), in order to reveal as little information as
|
|
possible about its internal state, and that a compromise of the "public"
|
|
CSPRNG instance will not affect the secrecy of these private values.
|
|
|
|
In the rare case where the default implementation does not satisfy your special
|
|
requirements, the default RAND internals can be replaced by your own
|
|
L<EVP_RAND(3)> objects.
|
|
|
|
Changing the default random generator should be necessary
|
|
only in exceptional cases and is not recommended, unless you have a profound
|
|
knowledge of cryptographic principles and understand the implications of your
|
|
changes.
|
|
|
|
=head1 DEAFULT SETUP
|
|
|
|
The default OpenSSL RAND method is based on the EVP_RAND deterministic random
|
|
bit generator (DRBG) classes.
|
|
A DRBG is a certain type of cryptographically-secure pseudo-random
|
|
number generator (CSPRNG), which is described in [NIST SP 800-90A Rev. 1].
|
|
|
|
|
|
=head1 SEE ALSO
|
|
|
|
L<RAND_bytes(3)>,
|
|
L<RAND_priv_bytes(3)>,
|
|
L<EVP_RAND(3)>,
|
|
L<RAND_get0_primary(3)>,
|
|
L<EVP_RAND(7)>
|
|
|
|
=head1 COPYRIGHT
|
|
|
|
Copyright 2018-2021 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
|
|
L<https://www.openssl.org/source/license.html>.
|
|
|
|
=cut
|