content: /*
   * Copyright (C) 2019 The Android Open Source Project
   *
   * 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.android.internal.telephony;
  
  import android.content.Context;
  import android.content.pm.PackageInfo;
  import android.content.pm.PackageManager;
  import android.content.pm.PackageManager.NameNotFoundException;
  import android.content.pm.Signature;
  import android.util.Base64;
  import android.util.Log;
  
  import java.nio.charset.Charset;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.Arrays;
  import java.util.List;
  
  /** Utility class for generating token, i.e., hash of package name and certificate. */
  public class PackageBasedTokenUtil {
      private static final String TAG = "PackageBasedTokenUtil";
      private static final Charset CHARSET_UTF_8 = Charset.forName("UTF-8");
      private static final String HASH_TYPE = "SHA-256";
      private static final int NUM_HASHED_BYTES = 9; // 9 bytes = 72 bits = 12 Base64s
  
      static final int NUM_BASE64_CHARS = 11; // truncate 12 into 11 Base64 chars
  
      /**
       * Generate token and check collision with other packages.
       */
      public static String generateToken(Context context, String packageName) {
          PackageManager packageManager = context.getPackageManager();
          String token = generatePackageBasedToken(packageManager, packageName);
  
          // Check for token confliction
          List<PackageInfo> packages =
                  packageManager.getInstalledPackages(PackageManager.GET_META_DATA);
  
          for (PackageInfo packageInfo : packages) {
              String otherPackageName = packageInfo.packageName;
              if (packageName.equals(otherPackageName)) {
                  continue;
              }
  
              String otherToken = generatePackageBasedToken(packageManager, otherPackageName);
              if (token.equals(otherToken)) {
                  Log.e(TAG, "token collides with other installed app.");
                  token = null;
              }
          }
  
          return token;
      }
  
      private static String generatePackageBasedToken(
              PackageManager packageManager, String packageName) {
          String token = null;
          Signature[] signatures;
  
          try {
              // It is actually a certificate (public key), not a signature.
              signatures = packageManager.getPackageInfo(
                      packageName, PackageManager.GET_SIGNATURES).signatures;
          } catch (NameNotFoundException e) {
              Log.e(TAG, "Failed to find package with package name: " + packageName);
              return token;
          }
  
          if (signatures == null) {
              Log.e(TAG, "The certificates is missing.");
          } else {
              MessageDigest messageDigest;
              try {
                  messageDigest = MessageDigest.getInstance(HASH_TYPE);
              } catch (NoSuchAlgorithmException e) {
                  Log.e(TAG, "NoSuchAlgorithmException" + e);
                  return null;
              }
  
              messageDigest.update(packageName.getBytes(CHARSET_UTF_8));
              String space = " ";
              messageDigest.update(space.getBytes(CHARSET_UTF_8));
              for (int i = 0; i < signatures.length; i++) {
                  messageDigest.update(signatures[i].toCharsString().getBytes(CHARSET_UTF_8));
              }
              byte[] hashSignatures = messageDigest.digest();
              // truncated into NUM_HASHED_BYTES
              hashSignatures = Arrays.copyOf(hashSignatures, NUM_HASHED_BYTES);
              // encode into Base64
              token = Base64.encodeToString(hashSignatures, Base64.NO_PADDING | Base64.NO_WRAP);
              token = token.substring(0, NUM_BASE64_CHARS);
          }
          return token;
      }
  }
  