mirror of https://github.com/openssl/openssl.git
112 lines
3.7 KiB
Plaintext
112 lines
3.7 KiB
Plaintext
=pod
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=head1 NAME
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RAND_bytes, RAND_priv_bytes, RAND_bytes_ex, RAND_priv_bytes_ex,
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RAND_pseudo_bytes - generate random data
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=head1 SYNOPSIS
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#include <openssl/rand.h>
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int RAND_bytes(unsigned char *buf, int num);
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int RAND_priv_bytes(unsigned char *buf, int num);
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int RAND_bytes_ex(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num,
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unsigned int strength);
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int RAND_priv_bytes_ex(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num,
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unsigned int strength);
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The following function has been deprecated since OpenSSL 1.1.0, and can be
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hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
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see L<openssl_user_macros(7)>:
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int RAND_pseudo_bytes(unsigned char *buf, int num);
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=head1 DESCRIPTION
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RAND_bytes() generates B<num> random bytes using a cryptographically
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secure pseudo random generator (CSPRNG) and stores them in B<buf>.
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RAND_priv_bytes() has the same semantics as RAND_bytes(). It is intended to
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be used for generating values that should remain private. If using the
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default RAND_METHOD, this function uses a separate "private" PRNG
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instance so that a compromise of the "public" PRNG instance will not
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affect the secrecy of these private values, as described in L<RAND(7)>
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and L<EVP_RAND(7)>.
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RAND_bytes_ex() and RAND_priv_bytes_ex() are the same as RAND_bytes() and
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RAND_priv_bytes() except that they both take additional I<strength> and
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I<ctx> parameters. The bytes generated will have a security strength of at
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least I<strength> bits.
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The DRBG used for the operation is the public or private DRBG associated with
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the specified I<ctx>. The parameter can be NULL, in which case
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the default library context is used (see L<OSSL_LIB_CTX(3)>.
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If the default RAND_METHOD has been changed then for compatibility reasons the
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RAND_METHOD will be used in preference and the DRBG of the library context
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ignored.
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=head1 NOTES
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By default, the OpenSSL CSPRNG supports a security level of 256 bits, provided it
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was able to seed itself from a trusted entropy source.
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On all major platforms supported by OpenSSL (including the Unix-like platforms
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and Windows), OpenSSL is configured to automatically seed the CSPRNG on first use
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using the operating systems's random generator.
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If the entropy source fails or is not available, the CSPRNG will enter an
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error state and refuse to generate random bytes. For that reason, it is important
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to always check the error return value of RAND_bytes() and RAND_priv_bytes() and
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not take randomness for granted.
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On other platforms, there might not be a trusted entropy source available
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or OpenSSL might have been explicitly configured to use different entropy sources.
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If you are in doubt about the quality of the entropy source, don't hesitate to ask
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your operating system vendor or post a question on GitHub or the openssl-users
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mailing list.
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=head1 RETURN VALUES
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RAND_bytes() and RAND_priv_bytes()
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return 1 on success, -1 if not supported by the current
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RAND method, or 0 on other failure. The error code can be
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obtained by L<ERR_get_error(3)>.
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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<ERR_get_error(3)>,
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L<RAND(7)>,
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L<EVP_RAND(7)>
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=head1 HISTORY
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=over 2
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=item *
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RAND_pseudo_bytes() was deprecated in OpenSSL 1.1.0; use RAND_bytes() instead.
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=item *
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The RAND_priv_bytes() function was added in OpenSSL 1.1.1.
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=item *
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The RAND_bytes_ex() and RAND_priv_bytes_ex() functions were added in OpenSSL 3.0
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=back
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=head1 COPYRIGHT
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Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (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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