function _checkSigned(bytes32 _hash, uint _nonce, uint8 _v, bytes32 _r, bytes32 _s) internal returns (bool) {
        address recovered = ecrecover(_hash, _v, _r, _s);

        if (tenant != recovered) {
            Error(_nonce, 3);
            return false;
        }
        if (nonceUsed[_nonce]) {
            Error(_nonce, 4);
            return false;
        }
        nonceUsed[_nonce] = true; 
        return true;
    }