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Filename : RAND_set_rand_method.3
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.\" ========================================================================
.\"
.IX Title "RAND_set_rand_method 3"
.TH RAND_set_rand_method 3 "2016-09-22" "1.0.1u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
RAND_set_rand_method, RAND_get_rand_method, RAND_SSLeay \- select RAND method
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/rand.h>
\&
\& void RAND_set_rand_method(const RAND_METHOD *meth);
\&
\& const RAND_METHOD *RAND_get_rand_method(void);
\&
\& 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 API\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 \fBRAND_SSLeay()\fR.
.PP
\&\fBRAND_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
\&\fBRAND_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
API\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 \fBRAND_seed()\fR,
\&\fBRAND_bytes()\fR, \fBRAND_cleanup()\fR, \fBRAND_add()\fR, \fBRAND_pseudo_rand()\fR
and \fBRAND_status()\fR.
Each component may be \s-1NULL\s0 if the function is not implemented.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBRAND_set_rand_method()\fR returns no value. \fBRAND_get_rand_method()\fR and
\&\fBRAND_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, EVP_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 API\s0 function,
that will override any \s-1RAND\s0 defaults set using the \s-1RAND API\s0 (ie.
\&\fBRAND_set_rand_method()\fR). For this reason, the \s-1ENGINE API\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"
\&\fBrand\fR\|(3), \fBengine\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fBRAND_set_rand_method()\fR, \fBRAND_get_rand_method()\fR and \fBRAND_SSLeay()\fR are
available in all versions of OpenSSL.
.PP
In the engine version of version 0.9.6, \fBRAND_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 API\s0 transparently overrides \s-1RAND\s0 defaults if used,
otherwise \s-1RAND API\s0 functions work as before. \fBRAND_set_rand_engine()\fR was also
introduced in version 0.9.7.