【Android 逆向】【攻防世界】easy-apk

apk 安装到手机，随便输入点内容，提示错误

2. apk 拖入到jadx中看看

public class MainActivity extends AppCompatActivity {
    /* JADX INFO: Access modifiers changed from: protected */
    @Override // android.support.v7.app.AppCompatActivity, android.support.v4.app.FragmentActivity, android.support.v4.app.SupportActivity, android.app.Activity
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btn = (Button) findViewById(R.id.button);
        btn.setOnClickListener(new View.OnClickListener() { // from class: com.testjava.jack.pingan1.MainActivity.1
            @Override // android.view.View.OnClickListener
            public void onClick(View view) {
                EditText edit1 = (EditText) MainActivity.this.findViewById(R.id.editText);
                String strIn = edit1.getText().toString();
                Base64New nb = new Base64New();
                String enStr = nb.Base64Encode(strIn.getBytes());
                if (enStr.equals("5rFf7E2K6rqN7Hpiyush7E6S5fJg6rsi5NBf6NGT5rs=")) {
                    Toast.makeText(MainActivity.this, "验证通过!", 1).show();
                } else {
                    Toast.makeText(MainActivity.this, "验证失败!", 1).show();
                }
            }
        });
    }
}

大概意思是，输入经过一个base64加密类加密后和一个字符串对比就ok，看看这个base64类

/* loaded from: classes.dex */
public class Base64New {
    private static final int RANGE = 255;
    private static final char[] Base64ByteToStr = {'v', 'w', 'x', 'r', 's', 't', 'u', 'o', 'p', 'q', '3', '4', '5', '6', '7', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'y', 'z', '0', '1', '2', 'P', 'Q', 'R', 'S', 'T', 'K', 'L', 'M', 'N', 'O', 'Z', 'a', 'b', 'c', 'd', 'U', 'V', 'W', 'X', 'Y', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', '8', '9', '+', '/'};
    private static byte[] StrToBase64Byte = new byte[128];

    public String Base64Encode(byte[] bytes) {
        StringBuilder res = new StringBuilder();
        for (int i = 0; i <= bytes.length - 1; i += 3) {
            byte[] enBytes = new byte[4];
            byte tmp = 0;
            for (int k = 0; k <= 2; k++) {
                if (i + k <= bytes.length - 1) {
                    enBytes[k] = (byte) (((bytes[i + k] & 255) >>> ((k * 2) + 2)) | tmp);
                    tmp = (byte) ((((bytes[i + k] & 255) << (((2 - k) * 2) + 2)) & 255) >>> 2);
                } else {
                    enBytes[k] = tmp;
                    tmp = 64;
                }
            }
            enBytes[3] = tmp;
            for (int k2 = 0; k2 <= 3; k2++) {
                if (enBytes[k2] <= 63) {
                    res.append(Base64ByteToStr[enBytes[k2]]);
                } else {
                    res.append('=');
                }
            }
        }
        return res.toString();
    }
}

大概就是用了一个新的字典表。扣出来vwxrstuopq34567ABCDEFGHIJyz012PQRSTKLMNOZabcdUVWXYefghijklmn89+/丢到CyberChef里试试，直接出答案 05397c42f9b6da593a3644162d36eb01

填入flag中报错干，需要价格flag 变成 flag{05397c42f9b6da593a3644162d36eb01}