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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;
}
}
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