| yuezonghe | 824eb0c | 2024-06-27 02:32:26 -0700 | [diff] [blame] | 1 | =pod |
| 2 | |
| 3 | =head1 NAME |
| 4 | |
| 5 | RAND_bytes, RAND_priv_bytes, RAND_pseudo_bytes - generate random data |
| 6 | |
| 7 | =head1 SYNOPSIS |
| 8 | |
| 9 | #include <openssl/rand.h> |
| 10 | |
| 11 | int RAND_bytes(unsigned char *buf, int num); |
| 12 | int RAND_priv_bytes(unsigned char *buf, int num); |
| 13 | |
| 14 | Deprecated: |
| 15 | |
| 16 | #if OPENSSL_API_COMPAT < 0x10100000L |
| 17 | int RAND_pseudo_bytes(unsigned char *buf, int num); |
| 18 | #endif |
| 19 | |
| 20 | =head1 DESCRIPTION |
| 21 | |
| 22 | RAND_bytes() generates B<num> random bytes using a cryptographically |
| 23 | secure pseudo random generator (CSPRNG) and stores them in B<buf>. |
| 24 | |
| 25 | RAND_priv_bytes() has the same semantics as RAND_bytes(). It is intended to |
| 26 | be used for generating values that should remain private. If using the |
| 27 | default RAND_METHOD, this function uses a separate "private" PRNG |
| 28 | instance so that a compromise of the "public" PRNG instance will not |
| 29 | affect the secrecy of these private values, as described in L<RAND(7)> |
| 30 | and L<RAND_DRBG(7)>. |
| 31 | |
| 32 | =head1 NOTES |
| 33 | |
| 34 | By default, the OpenSSL CSPRNG supports a security level of 256 bits, provided it |
| 35 | was able to seed itself from a trusted entropy source. |
| 36 | On all major platforms supported by OpenSSL (including the Unix-like platforms |
| 37 | and Windows), OpenSSL is configured to automatically seed the CSPRNG on first use |
| 38 | using the operating systems's random generator. |
| 39 | |
| 40 | If the entropy source fails or is not available, the CSPRNG will enter an |
| 41 | error state and refuse to generate random bytes. For that reason, it is important |
| 42 | to always check the error return value of RAND_bytes() and RAND_priv_bytes() and |
| 43 | not take randomness for granted. |
| 44 | |
| 45 | On other platforms, there might not be a trusted entropy source available |
| 46 | or OpenSSL might have been explicitly configured to use different entropy sources. |
| 47 | If you are in doubt about the quality of the entropy source, don't hesitate to ask |
| 48 | your operating system vendor or post a question on GitHub or the openssl-users |
| 49 | mailing list. |
| 50 | |
| 51 | =head1 RETURN VALUES |
| 52 | |
| 53 | RAND_bytes() and RAND_priv_bytes() |
| 54 | return 1 on success, -1 if not supported by the current |
| 55 | RAND method, or 0 on other failure. The error code can be |
| 56 | obtained by L<ERR_get_error(3)>. |
| 57 | |
| 58 | =head1 SEE ALSO |
| 59 | |
| 60 | L<RAND_add(3)>, |
| 61 | L<RAND_bytes(3)>, |
| 62 | L<RAND_priv_bytes(3)>, |
| 63 | L<ERR_get_error(3)>, |
| 64 | L<RAND(7)>, |
| 65 | L<RAND_DRBG(7)> |
| 66 | |
| 67 | =head1 HISTORY |
| 68 | |
| 69 | =over 2 |
| 70 | |
| 71 | =item * |
| 72 | |
| 73 | RAND_pseudo_bytes() was deprecated in OpenSSL 1.1.0; use RAND_bytes() instead. |
| 74 | |
| 75 | =item * |
| 76 | |
| 77 | The RAND_priv_bytes() function was added in OpenSSL 1.1.1. |
| 78 | |
| 79 | =back |
| 80 | |
| 81 | =head1 COPYRIGHT |
| 82 | |
| 83 | Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved. |
| 84 | |
| 85 | Licensed under the OpenSSL license (the "License"). You may not use |
| 86 | this file except in compliance with the License. You can obtain a copy |
| 87 | in the file LICENSE in the source distribution or at |
| 88 | L<https://www.openssl.org/source/license.html>. |
| 89 | |
| 90 | =cut |