.\"	$OpenBSD: BN_rand.3,v 1.5 2016/11/21 09:56:35 schwarze Exp $
.\"	OpenSSL 05ea606a May 20 20:52:46 2016 -0400
.\"
.\" This file was written by Ulf Moeller <ulf@openssl.org>.
.\" Copyright (c) 2000, 2001, 2002, 2013, 2015 The OpenSSL Project.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\"
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in
.\"    the documentation and/or other materials provided with the
.\"    distribution.
.\"
.\" 3. All advertising materials mentioning features or use of this
.\"    software must display the following acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
.\"
.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
.\"    endorse or promote products derived from this software without
.\"    prior written permission. For written permission, please contact
.\"    openssl-core@openssl.org.
.\"
.\" 5. Products derived from this software may not be called "OpenSSL"
.\"    nor may "OpenSSL" appear in their names without prior written
.\"    permission of the OpenSSL Project.
.\"
.\" 6. Redistributions of any form whatsoever must retain the following
.\"    acknowledgment:
.\"    "This product includes software developed by the OpenSSL Project
.\"    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
.\" OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: November 21 2016 $
.Dt BN_RAND 3
.Os
.Sh NAME
.Nm BN_rand ,
.Nm BN_pseudo_rand ,
.Nm BN_rand_range ,
.Nm BN_pseudo_rand_range
.Nd generate pseudo-random number
.Sh SYNOPSIS
.In openssl/bn.h
.Ft int
.Fo BN_rand
.Fa "BIGNUM *rnd"
.Fa "int bits"
.Fa "int top"
.Fa "int bottom"
.Fc
.Ft int
.Fo BN_pseudo_rand
.Fa "BIGNUM *rnd"
.Fa "int bits"
.Fa "int top"
.Fa "int bottom"
.Fc
.Ft int
.Fo BN_rand_range
.Fa "BIGNUM *rnd"
.Fa "BIGNUM *range"
.Fc
.Ft int
.Fo BN_pseudo_rand_range
.Fa "BIGNUM *rnd"
.Fa "BIGNUM *range"
.Fc
.Sh DESCRIPTION
.Fn BN_rand
generates a cryptographically strong pseudo-random number of
.Fa bits
in length and stores it in
.Fa rnd .
If
.Fa top
is -1, the most significant bit of the random number can be zero.
If
.Fa top
is 0, it is set to 1, and if
.Fa top
is 1, the two most significant bits of the number will be set to 1, so
that the product of two such random numbers will always have
.Pf 2* Fa bits
length.
If
.Fa bottom
is true, the number will be odd.
The value of
.Fa bits
must be zero or greater.
If
.Fa bits
is +1 then
.Fa top
cannot also be 1.
.Pp
.Fn BN_pseudo_rand
does the same, but pseudo-random numbers generated by this function are
not necessarily unpredictable.
They can be used for non-cryptographic purposes and for certain purposes
in cryptographic protocols, but usually not for key generation etc.
.Pp
.Fn BN_rand_range
generates a cryptographically strong pseudo-random number
.Fa rnd
in the range 0 <=
.Fa rnd No < Fa range .
.Fn BN_pseudo_rand_range
does the same, but is based on
.Fn BN_pseudo_rand ,
and hence numbers generated by it are not necessarily unpredictable.
.Sh RETURN VALUES
The functions return 1 on success, 0 on error.
The error codes can be obtained by
.Xr ERR_get_error 3 .
.Sh SEE ALSO
.Xr bn 3 ,
.Xr ERR_get_error 3 ,
.Xr RAND_add 3 ,
.Xr RAND_bytes 3
.Sh HISTORY
.Fn BN_rand
is available in all versions of SSLeay and OpenSSL.
.Fn BN_pseudo_rand
was added in OpenSSL 0.9.5.
The
.Fa top
== -1 case and the function
.Fn BN_rand_range
were added in OpenSSL 0.9.6a.
.Fn BN_pseudo_rand_range
was added in OpenSSL 0.9.6c.