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-ap

Answer 1

My solution based on BouncyCastle C# nuget.

Replace the message, signature and key with your one and test it. No need for java to get the Modulus or Exponent.

[TestMethod]
public void ValidadeMessageTest()
{
    //Base64-encoded RSA public key obtained from Google PlayStore, for the app. Go to DevelomentTools->Service & APIs
    var GooglePlayPK = "";

    bool validateReceipt(String message,String  messageSignature)
    {
        const String SIGNATURE_ALGORITHM = "SHA1";

        var rsaParameters = new RSAParameters();
        byte[] publicKeyBytes = Convert.FromBase64String(GooglePlayPK);
        AsymmetricKeyParameter asymmetricKeyParameter = PublicKeyFactory.CreateKey(publicKeyBytes);
        RsaKeyParameters rsaKeyParameters = (RsaKeyParameters)asymmetricKeyParameter;
        rsaParameters.Modulus = rsaKeyParameters.Modulus.ToByteArrayUnsigned();
        rsaParameters.Exponent = rsaKeyParameters.Exponent.ToByteArrayUnsigned();

        using (var rsa = new RSACryptoServiceProvider())
        {
            var encoder = new ASCIIEncoding();
            byte[] bytesToVerify = encoder.GetBytes(message);
            byte[] signedBytes = Convert.FromBase64String(messageSignature);

                rsa.ImportParameters(rsaParameters);
                return  rsa.VerifyData(bytesToVerify, CryptoConfig.MapNameToOID(SIGNATURE_ALGORITHM), signedBytes);                   
        }        
    }
    //test your receipt
    Assert.IsTrue(validateReceipt(, ));
}