Проверка валидности покупки в Google Play

#java #android #android_studio #google_play

После покупки получаем JSON

        {
          "packageName":"*****",
          "productId":"test2",
          "purchaseTime":1449140071159,
          "purchaseState":0,
          "developerPayload":"subs:*****",
          "purchaseToken":"*******",
          "autoRenewing":false
        }


Стандартно можем проверить его на андроид устройстве на валидность (т.е. не подделка
ли покупка).
Данным методом:

        public boolean isValid(TransactionDetails transactionDetails);


используется библиотека https://github.com/anjlab/android-inapp-billing-v3

А необходимо проверять валидность покупки на стороне нашего сервера. т.е. отправить
туда полученный JSON и уже там проверить на валидность.. Как это можно реализовать?
Серверная часть пишется на c#

UP#1
Все работает..
один момент при отправке Сигнатуры его надо Энкодить

       URLEncoder.encode(_base64Signature, "UTF-8")

    

Ответы

Ответ 1

Когда приходит результат покупки, то в поле inapp_signed_data у Intent'а  будет сигнатура.

Теперь вам нужен RSA. Для C# вам надо его сгенерировать из публичного ключа из вашей
консоли разработчика в GP:

const string MY_BASE64_PUBLIC_KEY = "Ваш base64 Google публичный ключ";
RSACryptoServiceProvider provider = PEMKeyLoader.CryptoServiceProviderFromPublicKeyInfo(MY_BASE64_PUBLIC_KEY);
string xmlPublicKey = provider.ToXmlString(false);


Вот класс для этого:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Security.Cryptography;
using System.IO;

namespace PublicKeyConvert
{
    public class PEMKeyLoader
    {

        // encoded OID sequence for  PKCS #1 rsaEncryption szOID_RSA_RSA = "1.2.840.113549.1.1.1"
        static byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86,
0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };

        private static bool CompareBytearrays(byte[] a, byte[] b)
        {
            if (a.Length != b.Length)
                return false;
            int i = 0;
            foreach (byte c in a)
            {
                if (c != b[i])
                    return false;
                i++;
            }
            return true;
        }

        public static RSACryptoServiceProvider CryptoServiceProviderFromPublicKeyInfo(byte[]
x509key)
        {
            byte[] seq = new byte[15];
            int x509size;

            if (x509key == null || x509key.Length == 0)
                return null;

            x509size = x509key.Length;

            // ---------  Set up stream to read the asn.1 encoded SubjectPublicKeyInfo
blob  ------
            MemoryStream mem = new MemoryStream(x509key);
            BinaryReader binr = new BinaryReader(mem);    //wrap Memory Stream with
BinaryReader for easy reading
            byte bt = 0;
            ushort twobytes = 0;

            try
            {
                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130) //data read as little endian order (actual
data order for Sequence is 30 81)
                    binr.ReadByte();    //advance 1 byte
                else if (twobytes == 0x8230)
                    binr.ReadInt16();   //advance 2 bytes
                else
                    return null;

                seq = binr.ReadBytes(15);       //read the Sequence OID
                if (!CompareBytearrays(seq, SeqOID))    //make sure Sequence for
OID is correct
                    return null;

                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8103) //data read as little endian order (actual
data order for Bit String is 03 81)
                    binr.ReadByte();    //advance 1 byte
                else if (twobytes == 0x8203)
                    binr.ReadInt16();   //advance 2 bytes
                else
                    return null;

                bt = binr.ReadByte();
                if (bt != 0x00)     //expect null byte next
                    return null;

                twobytes = binr.ReadUInt16();
                if (twobytes == 0x8130) //data read as little endian order (actual
data order for Sequence is 30 81)
                    binr.ReadByte();    //advance 1 byte
                else if (twobytes == 0x8230)
                    binr.ReadInt16();   //advance 2 bytes
                else
                    return null;

                twobytes = binr.ReadUInt16();
                byte lowbyte = 0x00;
                byte highbyte = 0x00;

                if (twobytes == 0x8102) //data read as little endian order (actual
data order for Integer is 02 81)
                    lowbyte = binr.ReadByte();  // read next bytes which is bytes
in modulus
                else if (twobytes == 0x8202)
                {
                    highbyte = binr.ReadByte(); //advance 2 bytes
                    lowbyte = binr.ReadByte();
                }
                else
                    return null;
                byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };   //reverse byte
order since asn.1 key uses big endian order
                int modsize = BitConverter.ToInt32(modint, 0);

                int firstbyte = binr.PeekChar();
                if (firstbyte == 0x00)
                {   //if first byte (highest order) of modulus is zero, don't include it
                    binr.ReadByte();    //skip this null byte
                    modsize -= 1;   //reduce modulus buffer size by 1
                }

                byte[] modulus = binr.ReadBytes(modsize);   //read the modulus bytes

                if (binr.ReadByte() != 0x02)            //expect an Integer for the
exponent data
                    return null;
                int expbytes = (int)binr.ReadByte();        // should only need one
byte for actual exponent data (for all useful values)
                byte[] exponent = binr.ReadBytes(expbytes);


                // ------- create RSACryptoServiceProvider instance and initialize
with public key -----
                RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
                RSAParameters RSAKeyInfo = new RSAParameters();
                RSAKeyInfo.Modulus = modulus;
                RSAKeyInfo.Exponent = exponent;
                RSA.ImportParameters(RSAKeyInfo);

                return RSA;
            }
            finally
            {
                binr.Close();
            }
        }

        public static RSACryptoServiceProvider CryptoServiceProviderFromPublicKeyInfo(String
base64EncodedKey)
        {
            try
            {
                //see if the file is a valid Base64 encoded cert
                return CryptoServiceProviderFromPublicKeyInfo(Convert.FromBase64String(base64EncodedKey));
            }
            catch (System.FormatException)
            {
            }

            return null;
        }

        public static byte[] X509KeyFromFile(String filename)
        {
            byte[] x509key;

            if (String.IsNullOrWhiteSpace(filename) || !File.Exists(filename))
                return null;

            StreamReader sr = File.OpenText(filename);
            String filestr = sr.ReadToEnd();
            sr.Close();
            StringBuilder sb = new StringBuilder(filestr);
            sb.Replace("-----BEGIN PUBLIC KEY-----", "");  //remove headers/footers,
if present
            sb.Replace("-----END PUBLIC KEY-----", "");

            try
            {   
                //see if the file is a valid Base64 encoded cert
                x509key = Convert.FromBase64String(sb.ToString());
            }
            catch (System.FormatException)
            {       
                //if not a b64-encoded publiccert, assume it's binary
                Stream stream = new FileStream(filename, FileMode.Open);
                int datalen = (int)stream.Length;
                x509key = new byte[datalen];
                stream.Read(x509key, 0, datalen);
                stream.Close();
            }

            return x509key;
        }

    }
}


Теперь можно проверять подпись сообщения:

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);
}


message - это ваш JSON.