*
     * @param key
     *            The key material to use in hashing.
     */
    public HMACT64 ( byte[] key ) {
        super("HMACT64");
        int length = Math.min(key.length, BLOCK_LENGTH);
        for ( int i = 0; i < length; i++ ) {
            this.ipad[ i ] = (byte) ( key[ i ] ^ IPAD );
            this.opad[ i ] = (byte) ( key[ i ] ^ OPAD );
        }