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135 .\" ========================================================================
136 .\"
137 .IX Title "RAND_set_rand_method 3"
138 .TH RAND_set_rand_method 3 "2009-07-19" "1.0.1n" "OpenSSL"
139 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
140 .\" way too many mistakes in technical documents.
141 .if n .ad l
142 .nh
143 .SH "NAME"
144 RAND_set_rand_method, RAND_get_rand_method, RAND_SSLeay \- select RAND method
145 .SH "LIBRARY"
146 libcrypto, -lcrypto
147 .SH "SYNOPSIS"
148 .IX Header "SYNOPSIS"
149 .Vb 1
150 \& #include <openssl/rand.h>
151 \&
152 \& void RAND_set_rand_method(const RAND_METHOD *meth);
153 \&
154 \& const RAND_METHOD *RAND_get_rand_method(void);
155 \&
156 \& RAND_METHOD *RAND_SSLeay(void);
157 .Ve
158 .SH "DESCRIPTION"
159 .IX Header "DESCRIPTION"
160 A \fB\s-1RAND_METHOD\s0\fR specifies the functions that OpenSSL uses for random number
161 generation. By modifying the method, alternative implementations such as
162 hardware RNGs may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for important
163 information about how these \s-1RAND API\s0 functions are affected by the use of
164 \&\fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
165 .PP
166 Initially, the default \s-1RAND_METHOD\s0 is the OpenSSL internal implementation, as
167 returned by \fIRAND_SSLeay()\fR.
168 .PP
169 \&\fIRAND_set_default_method()\fR makes \fBmeth\fR the method for \s-1PRNG\s0 use. \fB\s-1NB\s0\fR: This is
170 true only whilst no \s-1ENGINE\s0 has been set as a default for \s-1RAND,\s0 so this function
171 is no longer recommended.
172 .PP
173 \&\fIRAND_get_default_method()\fR returns a pointer to the current \s-1RAND_METHOD.\s0
174 However, the meaningfulness of this result is dependent on whether the \s-1ENGINE
175 API\s0 is being used, so this function is no longer recommended.
176 .SH "THE RAND_METHOD STRUCTURE"
177 .IX Header "THE RAND_METHOD STRUCTURE"
178 .Vb 9
179 \& typedef struct rand_meth_st
180 \& {
181 \& void (*seed)(const void *buf, int num);
182 \& int (*bytes)(unsigned char *buf, int num);
183 \& void (*cleanup)(void);
184 \& void (*add)(const void *buf, int num, int entropy);
185 \& int (*pseudorand)(unsigned char *buf, int num);
186 \& int (*status)(void);
187 \& } RAND_METHOD;
188 .Ve
189 .PP
190 The components point to the implementation of \fIRAND_seed()\fR,
191 \&\fIRAND_bytes()\fR, \fIRAND_cleanup()\fR, \fIRAND_add()\fR, \fIRAND_pseudo_rand()\fR
192 and \fIRAND_status()\fR.
193 Each component may be \s-1NULL\s0 if the function is not implemented.
194 .SH "RETURN VALUES"
195 .IX Header "RETURN VALUES"
196 \&\fIRAND_set_rand_method()\fR returns no value. \fIRAND_get_rand_method()\fR and
197 \&\fIRAND_SSLeay()\fR return pointers to the respective methods.
198 .SH "NOTES"
199 .IX Header "NOTES"
200 As of version 0.9.7, \s-1RAND_METHOD\s0 implementations are grouped together with other
201 algorithmic APIs (eg. \s-1RSA_METHOD, EVP_CIPHER,\s0 etc) in \fB\s-1ENGINE\s0\fR modules. If a
202 default \s-1ENGINE\s0 is specified for \s-1RAND\s0 functionality using an \s-1ENGINE API\s0 function,
203 that will override any \s-1RAND\s0 defaults set using the \s-1RAND API \s0(ie.
204 \&\fIRAND_set_rand_method()\fR). For this reason, the \s-1ENGINE API\s0 is the recommended way
205 to control default implementations for use in \s-1RAND\s0 and other cryptographic
206 algorithms.
207 .SH "SEE ALSO"
208 .IX Header "SEE ALSO"
209 \&\fIopenssl_rand\fR\|(3), \fIengine\fR\|(3)
210 .SH "HISTORY"
211 .IX Header "HISTORY"
212 \&\fIRAND_set_rand_method()\fR, \fIRAND_get_rand_method()\fR and \fIRAND_SSLeay()\fR are
213 available in all versions of OpenSSL.
214 .PP
215 In the engine version of version 0.9.6, \fIRAND_set_rand_method()\fR was altered to
216 take an \s-1ENGINE\s0 pointer as its argument. As of version 0.9.7, that has been
217 reverted as the \s-1ENGINE API\s0 transparently overrides \s-1RAND\s0 defaults if used,
218 otherwise \s-1RAND API\s0 functions work as before. \fIRAND_set_rand_engine()\fR was also
219 introduced in version 0.9.7.