合同可以假装吗？

Question

如果合约B中的方法只能由合约A调用，合约A是否可以伪装？

代码如下：

pragma solidity ^0.4.23;

contract A {

    address public owner;
    B public b;

    function A(address _owner) {
        owner = _owner;
        b = B(msg.sender);
    }

    function callB() public view returns(string _greeting)  {
        require(msg.sender == owner);
        return b.onlyForA();
    }

}

contract B {

    A public a;

    function B() {
        a = new A(msg.sender);
    }

    // only contract A can call this function
    function onlyForA() public view returns(string _greeting) {
        require(msg.sender == address(a));
        return "Hello A!";
    }

}

如果攻击者知道合同a的地址，他可以假装合同A然后调用合同B的“onlyForA”方法吗？