In-App purchasing demo

 /* Copyright (c) 2012 Google Inc.
  * Copyright (c) 2015 The Qt Company Ltd.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package org.qtproject.qt.android.purchasing;

 import android.text.TextUtils;
 import android.util.Log;

 import org.json.JSONException;
 import org.json.JSONObject;

 import java.security.InvalidKeyException;
 import java.security.KeyFactory;
 import java.security.NoSuchAlgorithmException;
 import java.security.PublicKey;
 import java.security.Signature;
 import java.security.SignatureException;
 import java.security.spec.InvalidKeySpecException;
 import java.security.spec.X509EncodedKeySpec;

 /**
  * Security-related methods. For a secure implementation, all of this code
  * should be implemented on a server that communicates with the
  * application on the device. For the sake of simplicity and clarity of this
  * example, this code is included here and is executed on the device. If you
  * must verify the purchases on the phone, you should obfuscate this code to
  * make it harder for an attacker to replace the code with stubs that treat all
  * purchases as verified.
  */
 public class Security {
     private static final String TAG = "IABUtil/Security";

     private static final String KEY_FACTORY_ALGORITHM = "RSA";
     private static final String SIGNATURE_ALGORITHM = "SHA1withRSA";

     /**
      * Verifies that the data was signed with the given signature, and returns
      * the verified purchase. The data is in JSON format and signed
      * with a private key. The data also contains the {@link PurchaseState}
      * and product ID of the purchase.
      * @param base64PublicKey the base64-encoded public key to use for verifying.
      * @param signedData the signed JSON string (signed, not encrypted)
      * @param signature the signature for the data, signed with the private key
      */
     public static boolean verifyPurchase(String base64PublicKey, String signedData, String signature) {
         if (signedData == null) {
             Log.e(TAG, "data is null");
             return false;
         }

         boolean verified = false;
         if (!TextUtils.isEmpty(signature)) {
             PublicKey key = Security.generatePublicKey(base64PublicKey);
             verified = Security.verify(key, signedData, signature);
             if (!verified) {
                 Log.w(TAG, "signature does not match data.");
                 return false;
             }
         }
         return true;
     }

     /**
      * Generates a PublicKey instance from a string containing the
      * Base64-encoded public key.
      *
      * @param encodedPublicKey Base64-encoded public key
      * @throws IllegalArgumentException if encodedPublicKey is invalid
      */
     public static PublicKey generatePublicKey(String encodedPublicKey) {
         try {
             byte[] decodedKey = Base64.decode(encodedPublicKey);
             KeyFactory keyFactory = KeyFactory.getInstance(KEY_FACTORY_ALGORITHM);
             return keyFactory.generatePublic(new X509EncodedKeySpec(decodedKey));
         } catch (NoSuchAlgorithmException e) {
             throw new RuntimeException(e);
         } catch (InvalidKeySpecException e) {
             Log.e(TAG, "Invalid key specification.");
             throw new IllegalArgumentException(e);
         } catch (Base64DecoderException e) {
             Log.e(TAG, "Base64 decoding failed.");
             throw new IllegalArgumentException(e);
         }
     }

     /**
      * Verifies that the signature from the server matches the computed
      * signature on the data.  Returns true if the data is correctly signed.
      *
      * @param publicKey public key associated with the developer account
      * @param signedData signed data from server
      * @param signature server signature
      * @return true if the data and signature match
      */
     public static boolean verify(PublicKey publicKey, String signedData, String signature) {
         Signature sig;
         try {
             sig = Signature.getInstance(SIGNATURE_ALGORITHM);
             sig.initVerify(publicKey);
             sig.update(signedData.getBytes());
             if (!sig.verify(Base64.decode(signature))) {
                 Log.e(TAG, "Signature verification failed.");
                 return false;
             }
             return true;
         } catch (NoSuchAlgorithmException e) {
             Log.e(TAG, "NoSuchAlgorithmException.");
         } catch (InvalidKeyException e) {
             Log.e(TAG, "Invalid key specification.");
         } catch (SignatureException e) {
             Log.e(TAG, "Signature exception.");
         } catch (Base64DecoderException e) {
             Log.e(TAG, "Base64 decoding failed.");
         }
         return false;
     }
 }