Android in-app billing Verification of Receipt in Dot Net(C#)

Question

I have a Android application which provides in-app billing and we have our application server to which android application connects to provide services to the user, on in-app purchase we want to push receipt to the server for verification process.

Now problem is I don't know how to convert Security.java file in dot net(C#) as our server is written in dot net

NOTE: This file comes with android in-app billing same application which provides message signing functions i just need their equivalent in dot net.

More Detail regarding this problem is available at http://social.msdn.microsoft.com/Forums/en-US/netfxbcl/thread/66bb5683-fde6-47ca-92d7-de255cc8655a

Answer 1

Here's a pure C# implementation, from Checking Google Play Signatures on .Net.

Create a console application project to convert the public key into the XML format that RSACryptoServiceProvider expects. Add PEMKeyLoader.cs to the console application project.

using PublicKeyConvert;
using System.Security.Cryptography;

namespace ConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            RSACryptoServiceProvider provider = PEMKeyLoader.CryptoServiceProviderFromPublicKeyInfo(MY_BASE64_PUBLIC_KEY);
            System.Console.WriteLine(provider.ToXmlString(false));
        }

        const string MY_BASE64_PUBLIC_KEY = "Paste your base64 Google public key here.";
    }
}

Running that console application will output (to the console) the XML format that RSACryptoServiceProvider expects.

Now that you have your XML-formatted public key, you can use it verify signatures:

public static bool Verify(string message, string base64Signature, string xmlPublicKey)
{
    // Create the provider and load the KEY
    RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
    provider.FromXmlString(xmlPublicKey);

    // The signature is supposed to be encoded in base64 and the SHA1 checksum
    // of the message is computed against the UTF-8 representation of the message
    byte[] signature = System.Convert.FromBase64String(base64Signature);
    SHA1Managed sha = new SHA1Managed();
    byte[] data = System.Text.Encoding.UTF8.GetBytes(message);

    return provider.VerifyData(data, sha, signature);
}