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124 .\" ========================================================================
126 .IX Title "RAND_set_rand_method 3"
127 .TH RAND_set_rand_method 3 "2015-01-15" "1.0.1l" "OpenSSL"
128 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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133 RAND_set_rand_method, RAND_get_rand_method, RAND_SSLeay \- select RAND method
135 .IX Header "SYNOPSIS"
137 \& #include <openssl/rand.h>
139 \& void RAND_set_rand_method(const RAND_METHOD *meth);
141 \& const RAND_METHOD *RAND_get_rand_method(void);
143 \& RAND_METHOD *RAND_SSLeay(void);
146 .IX Header "DESCRIPTION"
147 A \fB\s-1RAND_METHOD\s0\fR specifies the functions that OpenSSL uses for random number
148 generation. By modifying the method, alternative implementations such as
149 hardware RNGs may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for important
150 information about how these \s-1RAND\s0 \s-1API\s0 functions are affected by the use of
151 \&\fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
153 Initially, the default \s-1RAND_METHOD\s0 is the OpenSSL internal implementation, as
154 returned by \fIRAND_SSLeay()\fR.
156 \&\fIRAND_set_default_method()\fR makes \fBmeth\fR the method for \s-1PRNG\s0 use. \fB\s-1NB\s0\fR: This is
157 true only whilst no \s-1ENGINE\s0 has been set as a default for \s-1RAND\s0, so this function
158 is no longer recommended.
160 \&\fIRAND_get_default_method()\fR returns a pointer to the current \s-1RAND_METHOD\s0.
161 However, the meaningfulness of this result is dependent on whether the \s-1ENGINE\s0
162 \&\s-1API\s0 is being used, so this function is no longer recommended.
163 .SH "THE RAND_METHOD STRUCTURE"
164 .IX Header "THE RAND_METHOD STRUCTURE"
166 \& typedef struct rand_meth_st
168 \& void (*seed)(const void *buf, int num);
169 \& int (*bytes)(unsigned char *buf, int num);
170 \& void (*cleanup)(void);
171 \& void (*add)(const void *buf, int num, int entropy);
172 \& int (*pseudorand)(unsigned char *buf, int num);
173 \& int (*status)(void);
177 The components point to the implementation of \fIRAND_seed()\fR,
178 \&\fIRAND_bytes()\fR, \fIRAND_cleanup()\fR, \fIRAND_add()\fR, \fIRAND_pseudo_rand()\fR
179 and \fIRAND_status()\fR.
180 Each component may be \s-1NULL\s0 if the function is not implemented.
182 .IX Header "RETURN VALUES"
183 \&\fIRAND_set_rand_method()\fR returns no value. \fIRAND_get_rand_method()\fR and
184 \&\fIRAND_SSLeay()\fR return pointers to the respective methods.
187 As of version 0.9.7, \s-1RAND_METHOD\s0 implementations are grouped together with other
188 algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a
189 default \s-1ENGINE\s0 is specified for \s-1RAND\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function,
190 that will override any \s-1RAND\s0 defaults set using the \s-1RAND\s0 \s-1API\s0 (ie.
191 \&\fIRAND_set_rand_method()\fR). For this reason, the \s-1ENGINE\s0 \s-1API\s0 is the recommended way
192 to control default implementations for use in \s-1RAND\s0 and other cryptographic
195 .IX Header "SEE ALSO"
196 \&\fIrand\fR\|(3), \fIengine\fR\|(3)
199 \&\fIRAND_set_rand_method()\fR, \fIRAND_get_rand_method()\fR and \fIRAND_SSLeay()\fR are
200 available in all versions of OpenSSL.
202 In the engine version of version 0.9.6, \fIRAND_set_rand_method()\fR was altered to
203 take an \s-1ENGINE\s0 pointer as its argument. As of version 0.9.7, that has been
204 reverted as the \s-1ENGINE\s0 \s-1API\s0 transparently overrides \s-1RAND\s0 defaults if used,
205 otherwise \s-1RAND\s0 \s-1API\s0 functions work as before. \fIRAND_set_rand_engine()\fR was also
206 introduced in version 0.9.7.