function approveProxy(address _from, address _spender, uint256 _value,
        uint8 _v,bytes32 _r, bytes32 _s) returns (bool success) {

        uint256 nonce = nonces[_from];
        bytes32 hash = sha3(_from,_spender,_value,nonce);
        if(_from != ecrecover(hash,_v,_r,_s)) throw;
        allowed[_from][_spender] = _value;
        Approval(_from, _spender, _value);
        nonces[_from] = nonce + 1;
        return true;
    }