Android专项-针对Xposed hook密码框的防护

原理

TextWatcher接口为EditText控件的响应字符输入事件提供了3个方法，这三个方法分别为:

• public void beforeTextChanged(CharSequence s, int start, int count, int after)
• public void onTextChanged(CharSequence s, int start, int before, int count)
• public void afterTextChanged(Editable s)

我们通过自定义一个类，实现该接口，然后重写这三个方法，将输入的字符保存到StringBuilder中，而在EditText实际显示的是*号。这样当你hook住EditText.getText()的时候，获取的密码肯定是多个*,而实际的密码保存在StringBuilder中。

步骤

自定义TextWatcher类

public class EditChangedListener implements TextWatcher {

    private static final String TAG = "EditChangedListener";
    private CharSequence temp;
    private EditText editText;
    private boolean add = false;
    private StringBuilder password = new StringBuilder();
    private int mStart;

    public EditChangedListener(EditText editText) {
        this.editText = editText;
    }

    //after表示这次新加了几个字符,count表示旧的内容中被修改了几个字符，start表示修改的开始位置
    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
// Log.i(TAG, "beforeTextChanged : " + s + ",start = " + start + ",count = " + count + ",after = " + after);


    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        //before 原有内容被修改的数量,count为新增的数量,start为操作位置
        if (s.length() == 0) return;
// Log.i(TAG, "onTextChanged : " + s + ",start = " + start + ",count = " + count + ",before = " + before);

        if (count == 0 && password.length() > start) {
            password.deleteCharAt(start);
            Log.i(TAG, "删除了第" + start + "个字符 : " + s.charAt(start - 1));
            inputStarForEdit(password.length());
            add = false;
            return;
        }

        if (count > 0) {
            add = true;
        }
    }


    @Override
    public void afterTextChanged(Editable s) {

        if (!add || s.length() == 0) return;
        int length = s.length();
        char c = s.charAt(length - 1);

        if (c == '*') return;
        password.append(c);
        inputStarForEdit(length);
    }

    private void inputStarForEdit(int length) {

        editText.getText().clear();

        for (int i = 0; i < length; ++i) {
            editText.getText().append("*");
        }
        Log.i(TAG, "真实的为密码: " + password.toString() + ",伪装的密码为 : " + editText.getText());
    }
}

这里面的代码逻辑，一定要理解，核心在这

设置密码框的响应器为上面的类

 mPasswordView = (EditText) findViewById(R.id.password);

 mPasswordView.addTextChangedListener(new EditChangedListener(mPasswordView));

效果

总结

具体应用到你项目中，可能要考虑的问题比上面的demo要多，但是原理基本差不多，招行银行的策略与上面类似。