rust lioness error handling?

gistfile1.txt

extern crate crypto;

use std::error::Error;
use std::fmt;
use crypto::mac::Mac;
use crypto::blake2b::Blake2b;


const LIONESS_KEY_SIZE: u32 = 208;

#[derive(Debug)]
enum LionessError {
    BlockSizeError()
}

impl fmt::Display for LionessError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "LionessError is here!")
    }
}

impl Error for LionessError {
    fn description(&self) -> &str {
        "I'm a Lioness error."
    }

    fn cause(&self) -> Option<&Error> {
        match *self {
            LionessError::BlockSizeError(ref err) => Some(err),
        }
    }
}

pub struct LionessCipher {}

impl LionessCipher {
    pub fn new(key: &[u32; 208], blockSize: u32) -> Result<&LionessCipher, LionessError> {
	if blockSize <= LIONESS_KEY_SIZE {
            return Err(LionessError::BlockSizeError)
        }
        return Ok(&LionessCipher {})
    }
}

// xor function taken from:
// https://github.com/DaGenix/rust-crypto/blob/master/src/scrypt.rs
fn xor(x: &[u8], y: &[u8], output: &mut [u8]) {
    for ((out, &x_i), &y_i) in output.iter_mut().zip(x.iter()).zip(y.iter()) {
        *out = x_i ^ y_i;
    }
}

#[cfg(test)]
mod tests {
    fn it_works() {
    }
}