1 files changed, 121 insertions, 0 deletions
diff --git a/app/src/main/kotlin/com/pitchedapps/frost/utils/iab/Security.java b/app/src/main/kotlin/com/pitchedapps/frost/utils/iab/Security.java
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+++ b/app/src/main/kotlin/com/pitchedapps/frost/utils/iab/Security.java
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+/* Copyright (c) 2012 Google Inc.
+ *
+ * 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 com.pitchedapps.frost.utils.iab;
+
+import android.text.TextUtils;
+import android.util.Base64;
+import android.util.Log;
+
+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 (TextUtils.isEmpty(signedData) || TextUtils.isEmpty(base64PublicKey) ||
+                TextUtils.isEmpty(signature)) {
+            Log.e(TAG, "Purchase verification failed: missing data.");
+            return false;
+        }
+
+        PublicKey key = Security.generatePublicKey(base64PublicKey);
+        return Security.verify(key, signedData, signature);
+    }
+
+    /**
+     * 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, Base64.DEFAULT);
+            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);
+        }
+    }
+
+    /**
+     * 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) {
+        byte[] signatureBytes;
+        try {
+            signatureBytes = Base64.decode(signature, Base64.DEFAULT);
+        } catch (IllegalArgumentException e) {
+            Log.e(TAG, "Base64 decoding failed.");
+            return false;
+        }
+        try {
+            Signature sig = Signature.getInstance(SIGNATURE_ALGORITHM);
+            sig.initVerify(publicKey);
+            sig.update(signedData.getBytes());
+            if (!sig.verify(signatureBytes)) {
+                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.");
+        }
+        return false;
+    }
+}