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.\" Wed Feb 19 16:42:57 2003
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.\" ======================================================================
.\"
.IX Title "RAND_set_rand_method 3"
.TH RAND_set_rand_method 3 "0.9.7a" "2003-02-19" "OpenSSL"
.UC
.SH "NAME"
RAND_set_rand_method, RAND_get_rand_method, RAND_SSLeay \- select \s-1RAND\s0 method
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rand.h>
.Ve
.Vb 1
\& void RAND_set_rand_method(const RAND_METHOD *meth);
.Ve
.Vb 1
\& const RAND_METHOD *RAND_get_rand_method(void);
.Ve
.Vb 1
\& RAND_METHOD *RAND_SSLeay(void);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
A \fB\s-1RAND_METHOD\s0\fR specifies the functions that OpenSSL uses for random number
generation. 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 dependant 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
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"
rand(3), engine(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.
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