.\"	$OpenBSD: BN_rand.3,v 1.6 2016/12/10 21:13:25 schwarze Exp $
.\"	OpenSSL 05ea606a May 20 20:52:46 2016 -0400
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.Dd $Mdocdate: December 10 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_new 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.