.\"	$OpenBSD: BN_rand.3,v 1.18 2021/11/30 18:34:35 tb Exp $
.\" full merge up to: OpenSSL 05ea606a May 20 20:52:46 2016 -0400
.\" selective merge up to: OpenSSL df75c2bf Dec 9 01:02:36 2018 +0100
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.Dd $Mdocdate: November 30 2021 $
.Dt BN_RAND 3
.Os
.Sh NAME
.Nm BN_rand ,
.Nm BN_rand_range ,
.Nm BN_pseudo_rand ,
.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_rand_range
.Fa "BIGNUM *rnd"
.Fa "const 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
.Dv BN_RAND_TOP_ANY ,
the most significant bit of the random number can be zero.
If
.Fa top
is
.Dv BN_RAND_TOP_ONE ,
the most significant bit is set to 1, and if
.Fa top
is
.Dv BN_RAND_TOP_TWO ,
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
.Dv BN_RAND_BOTTOM_ODD ,
the number will be odd;
if it is
.Dv BN_RAND_BOTTOM_ANY ,
it can be odd or even.
The value of
.Fa bits
must be zero or greater.
If
.Fa bits
is +1 then
.Fa top
cannot be
.Dv BN_RAND_TOP_TWO .
.Pp
.Fn BN_rand_range
generates a cryptographically strong pseudo-random number
.Fa rnd
in the range 0 <=
.Fa rnd No < Fa range .
.Pp
.Fn BN_pseudo_rand
is a deprecated alias for
.Fn BN_rand ,
and
.Fn BN_pseudo_rand_range
for
.Fn BN_rand_range .
.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_new 3
.Sh HISTORY
.Fn BN_rand
first appeared in SSLeay 0.5.1 and has been available since
.Ox 2.4 .
.Pp
The
.Fa top
== -1 case and the function
.Fn BN_rand_range
first appeared in OpenSSL 0.9.6a and have been available since
.Ox 3.0 .