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RAND_set_rand_method.3
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By modifying the method, alternative implementations such as hardware RNGs may be used. \s-1IMPORTANT:\s0 See the \s-1NOTES\s0 section for important information about how these \s-1RAND\s0 \s-1API\s0 functions are affected by the use of \&\fB\s-1ENGINE\s0\fR \s-1API\s0 calls. .PP Initially, the default \s-1RAND_METHOD\s0 is the OpenSSL internal implementation, as returned by \fIRAND_SSLeay()\fR. .PP \&\fIRAND_set_default_method()\fR makes \fBmeth\fR the method for \s-1PRNG\s0 use. \fB\s-1NB\s0\fR: This is true only whilst no \s-1ENGINE\s0 has been set as a default for \s-1RAND\s0, so this function is no longer recommended. .PP \&\fIRAND_get_default_method()\fR returns a pointer to the current \s-1RAND_METHOD\s0. However, the meaningfulness of this result is dependent on whether the \s-1ENGINE\s0 \&\s-1API\s0 is being used, so this function is no longer recommended. .SH "THE RAND_METHOD STRUCTURE" .IX Header "THE RAND_METHOD STRUCTURE" .Vb 9 \& typedef struct rand_meth_st \& { \& void (*seed)(const void *buf, int num); \& int (*bytes)(unsigned char *buf, int num); \& void (*cleanup)(void); \& void (*add)(const void *buf, int num, int entropy); \& int (*pseudorand)(unsigned char *buf, int num); \& int (*status)(void); \& } RAND_METHOD; .Ve .PP The components point to the implementation of \fIRAND_seed()\fR, \&\fIRAND_bytes()\fR, \fIRAND_cleanup()\fR, \fIRAND_add()\fR, \fIRAND_pseudo_rand()\fR and \fIRAND_status()\fR. Each component may be \s-1NULL\s0 if the function is not implemented. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fIRAND_set_rand_method()\fR returns no value. \fIRAND_get_rand_method()\fR and \&\fIRAND_SSLeay()\fR return pointers to the respective methods. .SH "NOTES" .IX Header "NOTES" As of version 0.9.7, \s-1RAND_METHOD\s0 implementations are grouped together with other algorithmic APIs (eg. \s-1RSA_METHOD\s0, \s-1EVP_CIPHER\s0, etc) in \fB\s-1ENGINE\s0\fR modules. If a default \s-1ENGINE\s0 is specified for \s-1RAND\s0 functionality using an \s-1ENGINE\s0 \s-1API\s0 function, that will override any \s-1RAND\s0 defaults set using the \s-1RAND\s0 \s-1API\s0 (ie. \&\fIRAND_set_rand_method()\fR). For this reason, the \s-1ENGINE\s0 \s-1API\s0 is the recommended way to control default implementations for use in \s-1RAND\s0 and other cryptographic algorithms. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fIrand\fR\|(3), \fIengine\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" \&\fIRAND_set_rand_method()\fR, \fIRAND_get_rand_method()\fR and \fIRAND_SSLeay()\fR are available in all versions of OpenSSL. .PP In the engine version of version 0.9.6, \fIRAND_set_rand_method()\fR was altered to take an \s-1ENGINE\s0 pointer as its argument. As of version 0.9.7, that has been reverted as the \s-1ENGINE\s0 \s-1API\s0 transparently overrides \s-1RAND\s0 defaults if used, otherwise \s-1RAND\s0 \s-1API\s0 functions work as before. \fIRAND_set_rand_engine()\fR was also introduced in version 0.9.7.