=head1 DESCRIPTION
BN_rand() generates a cryptographically strong pseudo-random number of
-B<bits> bits in length and stores it in B<rnd>. If B<top> is -1, the
+B<bits> in length and stores it in B<rnd>.
+If B<bits> is less than zero, or too small to
+accomodate the requirements specified by the B<top> and B<bottom>
+parameters, an error is returned.
+If B<top> is -1, the
most significant bit of the random number can be zero. If B<top> is 0,
it is set to 1, and if B<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 2*B<bits> length. If B<bottom> is true, the
-number will be odd.
+number will be odd. The value of B<bits> must be zero or greater. If B<bits> is
+1 then B<top> cannot also be 1.
BN_pseudo_rand() does the same, but pseudo-random numbers generated by
this function are not necessarily unpredictable. They can be used for
protocols, but usually not for key generation etc.
BN_rand_range() generates a cryptographically strong pseudo-random
-number B<rnd> in the range 0 <lt>= B<rnd> E<lt> B<range>.
+number B<rnd> in the range 0 E<lt>= B<rnd> E<lt> B<range>.
BN_pseudo_rand_range() does the same, but is based on BN_pseudo_rand(),
and hence numbers generated by it are not necessarily unpredictable.