1=pod 2 3=head1 NAME 4 5RAND_bytes, RAND_priv_bytes, RAND_bytes_ex, RAND_priv_bytes_ex, 6RAND_pseudo_bytes - generate random data 7 8=head1 SYNOPSIS 9 10 #include <openssl/rand.h> 11 12 int RAND_bytes(unsigned char *buf, int num); 13 int RAND_priv_bytes(unsigned char *buf, int num); 14 15 int RAND_bytes_ex(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num, 16 unsigned int strength); 17 int RAND_priv_bytes_ex(OSSL_LIB_CTX *ctx, unsigned char *buf, size_t num, 18 unsigned int strength); 19 20The following function has been deprecated since OpenSSL 1.1.0, and can be 21hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value, 22see L<openssl_user_macros(7)>: 23 24 int RAND_pseudo_bytes(unsigned char *buf, int num); 25 26=head1 DESCRIPTION 27 28RAND_bytes() generates B<num> random bytes using a cryptographically 29secure pseudo random generator (CSPRNG) and stores them in B<buf>. 30 31RAND_priv_bytes() has the same semantics as RAND_bytes(). It is intended to 32be used for generating values that should remain private. If using the 33default RAND_METHOD, this function uses a separate "private" PRNG 34instance so that a compromise of the "public" PRNG instance will not 35affect the secrecy of these private values, as described in L<RAND(7)> 36and L<EVP_RAND(7)>. 37 38RAND_bytes_ex() and RAND_priv_bytes_ex() are the same as RAND_bytes() and 39RAND_priv_bytes() except that they both take additional I<strength> and 40I<ctx> parameters. The bytes generated will have a security strength of at 41least I<strength> bits. 42The DRBG used for the operation is the public or private DRBG associated with 43the specified I<ctx>. The parameter can be NULL, in which case 44the default library context is used (see L<OSSL_LIB_CTX(3)>. 45If the default RAND_METHOD has been changed then for compatibility reasons the 46RAND_METHOD will be used in preference and the DRBG of the library context 47ignored. 48 49=head1 NOTES 50 51By default, the OpenSSL CSPRNG supports a security level of 256 bits, provided it 52was able to seed itself from a trusted entropy source. 53On all major platforms supported by OpenSSL (including the Unix-like platforms 54and Windows), OpenSSL is configured to automatically seed the CSPRNG on first use 55using the operating systems's random generator. 56 57If the entropy source fails or is not available, the CSPRNG will enter an 58error state and refuse to generate random bytes. For that reason, it is important 59to always check the error return value of RAND_bytes() and RAND_priv_bytes() and 60not take randomness for granted. 61 62On other platforms, there might not be a trusted entropy source available 63or OpenSSL might have been explicitly configured to use different entropy sources. 64If you are in doubt about the quality of the entropy source, don't hesitate to ask 65your operating system vendor or post a question on GitHub or the openssl-users 66mailing list. 67 68=head1 RETURN VALUES 69 70RAND_bytes() and RAND_priv_bytes() 71return 1 on success, -1 if not supported by the current 72RAND method, or 0 on other failure. The error code can be 73obtained by L<ERR_get_error(3)>. 74 75=head1 SEE ALSO 76 77L<RAND_add(3)>, 78L<RAND_bytes(3)>, 79L<RAND_priv_bytes(3)>, 80L<ERR_get_error(3)>, 81L<RAND(7)>, 82L<EVP_RAND(7)> 83 84=head1 HISTORY 85 86=over 2 87 88=item * 89 90RAND_pseudo_bytes() was deprecated in OpenSSL 1.1.0; use RAND_bytes() instead. 91 92=item * 93 94The RAND_priv_bytes() function was added in OpenSSL 1.1.1. 95 96=item * 97 98The RAND_bytes_ex() and RAND_priv_bytes_ex() functions were added in OpenSSL 3.0 99 100=back 101 102=head1 COPYRIGHT 103 104Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved. 105 106Licensed under the Apache License 2.0 (the "License"). You may not use 107this file except in compliance with the License. You can obtain a copy 108in the file LICENSE in the source distribution or at 109L<https://www.openssl.org/source/license.html>. 110 111=cut 112