| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | RAND_bytes, RAND_priv_bytes, RAND_bytes_ex, RAND_priv_bytes_ex,
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| 6 | RAND_pseudo_bytes - generate random data
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| 7 |
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| 8 | =head1 SYNOPSIS
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| 9 |
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| 10 | #include <openssl/rand.h>
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| 11 |
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| 12 | int RAND_bytes(unsigned char *buf, int num);
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| 13 | int RAND_priv_bytes(unsigned char *buf, int num);
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| 14 |
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| 15 | int RAND_bytes_ex(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num,
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| 16 | unsigned int strength);
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| 17 | int RAND_priv_bytes_ex(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num,
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| 18 | unsigned int strength);
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| 19 |
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| 20 | The following function has been deprecated since OpenSSL 1.1.0, and can be
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| 21 | hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
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| 22 | see L<openssl_user_macros(7)>:
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| 23 |
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| 24 | int RAND_pseudo_bytes(unsigned char *buf, int num);
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| 25 |
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| 26 | =head1 DESCRIPTION
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| 27 |
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| 28 | RAND_bytes() generates B<num> random bytes using a cryptographically
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| 29 | secure pseudo random generator (CSPRNG) and stores them in B<buf>.
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| 30 |
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| 31 | RAND_priv_bytes() has the same semantics as RAND_bytes(). It is intended to
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| 32 | be used for generating values that should remain private. If using the
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| 33 | default RAND_METHOD, this function uses a separate "private" PRNG
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| 34 | instance so that a compromise of the "public" PRNG instance will not
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| 35 | affect the secrecy of these private values, as described in L<RAND(7)>
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| 36 | and L<EVP_RAND(7)>.
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| 37 |
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| 38 | RAND_bytes_ex() and RAND_priv_bytes_ex() are the same as RAND_bytes() and
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| 39 | RAND_priv_bytes() except that they both take additional I<strength> and
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| 40 | I<ctx> parameters. The bytes generated will have a security strength of at
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| 41 | least I<strength> bits.
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| 42 | The DRBG used for the operation is the public or private DRBG associated with
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| 43 | the specified I<ctx>. The parameter can be NULL, in which case
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| 44 | the default library context is used (see L<OSSL_LIB_CTX(3)>.
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| 45 | If the default RAND_METHOD has been changed then for compatibility reasons the
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| 46 | RAND_METHOD will be used in preference and the DRBG of the library context
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| 47 | ignored.
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| 48 |
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| 49 | =head1 NOTES
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| 50 |
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| 51 | By default, the OpenSSL CSPRNG supports a security level of 256 bits, provided it
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| 52 | was able to seed itself from a trusted entropy source.
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| 53 | On all major platforms supported by OpenSSL (including the Unix-like platforms
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| 54 | and Windows), OpenSSL is configured to automatically seed the CSPRNG on first use
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| 55 | using the operating systems's random generator.
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| 56 |
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| 57 | If the entropy source fails or is not available, the CSPRNG will enter an
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| 58 | error state and refuse to generate random bytes. For that reason, it is important
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| 59 | to always check the error return value of RAND_bytes() and RAND_priv_bytes() and
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| 60 | not take randomness for granted.
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| 61 |
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| 62 | On other platforms, there might not be a trusted entropy source available
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| 63 | or OpenSSL might have been explicitly configured to use different entropy sources.
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| 64 | If you are in doubt about the quality of the entropy source, don't hesitate to ask
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| 65 | your operating system vendor or post a question on GitHub or the openssl-users
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| 66 | mailing list.
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| 67 |
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| 68 | =head1 RETURN VALUES
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| 69 |
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| 70 | RAND_bytes() and RAND_priv_bytes()
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| 71 | return 1 on success, -1 if not supported by the current
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| 72 | RAND method, or 0 on other failure. The error code can be
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| 73 | obtained by L<ERR_get_error(3)>.
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| 74 |
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| 75 | =head1 SEE ALSO
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| 76 |
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| 77 | L<RAND_add(3)>,
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| 78 | L<RAND_bytes(3)>,
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| 79 | L<RAND_priv_bytes(3)>,
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| 80 | L<ERR_get_error(3)>,
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| 81 | L<RAND(7)>,
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| 82 | L<EVP_RAND(7)>
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| 83 |
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| 84 | =head1 HISTORY
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| 85 |
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| 86 | =over 2
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| 87 |
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| 88 | =item *
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| 89 |
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| 90 | RAND_pseudo_bytes() was deprecated in OpenSSL 1.1.0; use RAND_bytes() instead.
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| 91 |
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| 92 | =item *
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| 93 |
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| 94 | The RAND_priv_bytes() function was added in OpenSSL 1.1.1.
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| 95 |
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| 96 | =item *
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| 97 |
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| 98 | The RAND_bytes_ex() and RAND_priv_bytes_ex() functions were added in OpenSSL 3.0
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| 99 |
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| 100 | =back
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| 101 |
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| 102 | =head1 COPYRIGHT
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| 103 |
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| 104 | Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.
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| 105 |
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| 106 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 107 | this file except in compliance with the License. You can obtain a copy
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| 108 | in the file LICENSE in the source distribution or at
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| 109 | L<https://www.openssl.org/source/license.html>.
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| 110 |
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| 111 | =cut
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