pub fn random_vec(len: usize) -> Vec<u8> {
        let mut buf = vec![0; len];
        Self::random(&mut buf);
        buf
    }
// create a random vector with size len
create a random vector with size len
create a random vector with size len
pub fn random_vec(len: usize) -> Vec<u8> {
        let mut buf = vec![0; len];
        Self::random(&mut buf);
        buf
    }
pub fn random_vec ( len : usize ) -> Vec < u8 > { let mut buf = vec ! [ 0 len ] ; Self :: random ( & mut buf ) ; buf }
create a random vector with size len
create a random vector with size len
len
usize