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129.\" ========================================================================
130.\"
131.IX Title "RAND_set_rand_method 3"
aac4ff6f 132.TH RAND_set_rand_method 3 "2008-09-06" "0.9.8h" "OpenSSL"
984263bc 133.SH "NAME"
74dab6c2 134RAND_set_rand_method, RAND_get_rand_method, RAND_SSLeay \- select RAND method
984263bc 135.SH "SYNOPSIS"
8b0cefbb 136.IX Header "SYNOPSIS"
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137.Vb 1
138\& #include <openssl/rand.h>
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139.Ve
140.PP
141.Vb 1
984263bc 142\& void RAND_set_rand_method(const RAND_METHOD *meth);
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143.Ve
144.PP
145.Vb 1
984263bc 146\& const RAND_METHOD *RAND_get_rand_method(void);
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147.Ve
148.PP
149.Vb 1
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150\& RAND_METHOD *RAND_SSLeay(void);
151.Ve
152.SH "DESCRIPTION"
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153.IX Header "DESCRIPTION"
154A \fB\s-1RAND_METHOD\s0\fR specifies the functions that OpenSSL uses for random number
984263bc 155generation. By modifying the method, alternative implementations such as
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156hardware RNGs may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for important
157information about how these \s-1RAND\s0 \s-1API\s0 functions are affected by the use of
158\&\fB\s-1ENGINE\s0\fR \s-1API\s0 calls.
984263bc 159.PP
8b0cefbb 160Initially, the default \s-1RAND_METHOD\s0 is the OpenSSL internal implementation, as
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161returned by \fIRAND_SSLeay()\fR.
162.PP
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163\&\fIRAND_set_default_method()\fR makes \fBmeth\fR the method for \s-1PRNG\s0 use. \fB\s-1NB\s0\fR: This is
164true only whilst no \s-1ENGINE\s0 has been set as a default for \s-1RAND\s0, so this function
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165is no longer recommended.
166.PP
8b0cefbb 167\&\fIRAND_get_default_method()\fR returns a pointer to the current \s-1RAND_METHOD\s0.
aac4ff6f 168However, the meaningfulness of this result is dependent on whether the \s-1ENGINE\s0
8b0cefbb 169\&\s-1API\s0 is being used, so this function is no longer recommended.
984263bc 170.SH "THE RAND_METHOD STRUCTURE"
8b0cefbb 171.IX Header "THE RAND_METHOD STRUCTURE"
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172.Vb 9
173\& typedef struct rand_meth_st
174\& {
175\& void (*seed)(const void *buf, int num);
176\& int (*bytes)(unsigned char *buf, int num);
177\& void (*cleanup)(void);
178\& void (*add)(const void *buf, int num, int entropy);
179\& int (*pseudorand)(unsigned char *buf, int num);
180\& int (*status)(void);
181\& } RAND_METHOD;
182.Ve
8b0cefbb 183.PP
984263bc 184The components point to the implementation of \fIRAND_seed()\fR,
8b0cefbb 185\&\fIRAND_bytes()\fR, \fIRAND_cleanup()\fR, \fIRAND_add()\fR, \fIRAND_pseudo_rand()\fR
984263bc 186and \fIRAND_status()\fR.
8b0cefbb 187Each component may be \s-1NULL\s0 if the function is not implemented.
984263bc 188.SH "RETURN VALUES"
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189.IX Header "RETURN VALUES"
190\&\fIRAND_set_rand_method()\fR returns no value. \fIRAND_get_rand_method()\fR and
191\&\fIRAND_SSLeay()\fR return pointers to the respective methods.
984263bc 192.SH "NOTES"
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193.IX Header "NOTES"
194As of version 0.9.7, \s-1RAND_METHOD\s0 implementations are grouped together with other
195algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a
196default \s-1ENGINE\s0 is specified for \s-1RAND\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function,
197that will override any \s-1RAND\s0 defaults set using the \s-1RAND\s0 \s-1API\s0 (ie.
198\&\fIRAND_set_rand_method()\fR). For this reason, the \s-1ENGINE\s0 \s-1API\s0 is the recommended way
199to control default implementations for use in \s-1RAND\s0 and other cryptographic
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200algorithms.
201.SH "SEE ALSO"
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202.IX Header "SEE ALSO"
203\&\fIrand\fR\|(3), \fIengine\fR\|(3)
984263bc 204.SH "HISTORY"
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205.IX Header "HISTORY"
206\&\fIRAND_set_rand_method()\fR, \fIRAND_get_rand_method()\fR and \fIRAND_SSLeay()\fR are
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207available in all versions of OpenSSL.
208.PP
209In the engine version of version 0.9.6, \fIRAND_set_rand_method()\fR was altered to
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210take an \s-1ENGINE\s0 pointer as its argument. As of version 0.9.7, that has been
211reverted as the \s-1ENGINE\s0 \s-1API\s0 transparently overrides \s-1RAND\s0 defaults if used,
212otherwise \s-1RAND\s0 \s-1API\s0 functions work as before. \fIRAND_set_rand_engine()\fR was also
984263bc 213introduced in version 0.9.7.