[unity]Unity3d获取APK签名及公钥的方法

在Unity3d项目中获取APK包签名公钥的方法，核心思想就是通过JNI调用Android提供的方法。不过Unity3d提供了比JNI更上一层的类AndroidJavaObject以及继承它的AndroidJavaClass，帮助开发者省去很多工作。这两种类型的函数及内部原理可以看Unity3d官网，也可以反编译看里面的代码，直接说用法。

首先要获取到当前运行程序的Activity才好继续以后的操作。Unity3d在程序启动时记录下了这个值，可以通过UnityPlayer类的静态字段currentActivity来取得，UnityPlayer是由UnityPlayerActivity这个继承自Activity的类在onCreate时创建并传入当前Activity（详细流程可以通过jd-gui或反编译项目smali查看）。取到Activity以后就可以getPackageManager、getPackageInfo来获取到签名。得到的签名据说保存了公钥以及其他一些信息，这个没有具体深入了解，但是可以从签名获取到公钥是一定可以的，CertificateFactory的generateCertificate、getPublicKey方法取得最终值。下面是完整代码，注释对应java代码：

    private byte[] GetSignature()
    {
        //Player = new UnityPlayer();
        AndroidJavaClass Player = new AndroidJavaClass("com.unity3d.player.UnityPlayer");
        //Activity = Player.currentActivity;
        AndroidJavaObject Activity = Player.GetStatic<AndroidJavaObject>("currentActivity");
        //PackageManager = Activity.getPackageManager();
        AndroidJavaObject PackageManager = Activity.Call<AndroidJavaObject>("getPackageManager");
        //GET_SIGNATURES = PackageManager.GET_SIGNATURES;
        int GET_SIGNATURES = PackageManager.GetStatic<int>("GET_SIGNATURES");
        //PackageInfo = PackageManager.getPackageInfo("com.ztx.uni", PackageManager.GET_SIGNATURES);
        AndroidJavaObject PackageInfo = PackageManager.Call<AndroidJavaObject>("getPackageInfo", "com.ztx.uni", GET_SIGNATURES);
        //Signatures = PackageInfo.signatures;
        AndroidJavaObject[] Signatures = PackageInfo.Get<AndroidJavaObject[]>("signatures");
        //return Signatures[0].toByteArray();
        return (Signatures != null && Signatures.Length > 0) ? Signatures[0].Call<byte[]>("toByteArray") : null;
    }

    private string GetPublicKey()
    {
        byte[] Signatures = GetSignature();

        if (Signatures != null)
        {
            //CCertificateFactory = new CertificateFactory();
            AndroidJavaClass CCertificateFactory = new AndroidJavaClass("java.security.cert.CertificateFactory");
            //OCertFactory = CCertificateFactory.getInstance();
            AndroidJavaObject OCertFactory = CCertificateFactory.CallStatic<AndroidJavaObject>("getInstance", "X.509");
            //OByteArrayInputStream = new ByteArrayInputStream(Signatures);
            AndroidJavaObject OByteArrayInputStream = new AndroidJavaObject("java.io.ByteArrayInputStream", Signatures);
            //OX509Certificate = OCertFactory.generateCertificate(OByteArrayInputStream);
            AndroidJavaObject OX509Certificate = OCertFactory.Call<AndroidJavaObject>("generateCertificate", OByteArrayInputStream);
            //OPublicKey = OX509Certificate.getPublicKey();
            AndroidJavaObject OPublicKey = OX509Certificate.Call<AndroidJavaObject>("getPublicKey");

            string publickey = OPublicKey.Call<string>("toString");
            AndroidJavaObject CString = new AndroidJavaObject("java/lang/String", publickey);
            int start = CString.Call<int>("indexOf", "modulus");
            int end = CString.Call<int>("indexOf", "public");

            if (start >= 0 && end >= 0)
            {
                return CString.Call<string>("substring", start + 8, end - 1);
            }
        }
        
        return null;
    }

在GetPublicKey()中取得的OPublicKey是如下的形式：

OpenSSLRSAPublicKey
{modulus=d6931904dec60b24b1edc762e0d9d8253e3ecd6ceb1de2ff068ca8e8bca8cd6bd3786ea70aa76ce
60ebb0f993559ffd93e77a943e7e83d4b64b8e4fea2d3e656f1e267a81bbfb230b578c20443be4c7218b846f
5211586f038a14e89c2be387f8ebecf8fcac3da1ee330c9ea93d0a7c3dc4af350220d50080732e0809717ee6
a053359e6a694ec2cb3f284a0a466c87a94d83b31093a67372e2f6412c06e6d42f15818dffe0381cc0cd444d
a6cddc3b82458194801b32564134fbfde98c9287748dbf5676a540d8154c8bbca07b9e247553311c46b9af76
fdeeccc8e69e7c8a2d08e782620943f99727d3c04fe72991d99df9bae38a0b2177fa31d5b6afee91f,publicExponent=3}

而我们要的只是其中的256位公钥，所以在函数后面取了modulus和publicExponent之间的值。至此全部工作结束，很简单吧，如果在ndk中做公钥提取也是这个道理，不过要写很多很多代码。。