content: /*
   * Copyright (C) 2016 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 android.util;
  
  import android.annotation.NonNull;
  import android.annotation.Nullable;
  import android.content.pm.Signature;
  
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.security.MessageDigest;
  import java.security.NoSuchAlgorithmException;
  import java.util.Arrays;
  
  /**
   * Helper functions applicable to packages.
   * @hide
   */
  public final class PackageUtils {
  
      private PackageUtils() {
          /* hide constructor */
      }
  
      /**
       * Computes the SHA256 digests of a list of signatures. Items in the
       * resulting array of hashes correspond to the signatures in the
       * input array.
       * @param signatures The signatures.
       * @return The digest array.
       */
      public static @NonNull String[] computeSignaturesSha256Digests(
              @NonNull Signature[] signatures) {
          final int signatureCount = signatures.length;
          final String[] digests = new String[signatureCount];
          for (int i = 0; i < signatureCount; i++) {
              digests[i] = computeSha256Digest(signatures[i].toByteArray());
          }
          return digests;
      }
      /**
       * Computes a SHA256 digest of the signatures' SHA256 digests. First,
       * individual hashes for each signature is derived in a hexademical
       * form, then these strings are sorted based the natural ordering, and
       * finally a hash is derived from these strings' bytes.
       * @param signatures The signatures.
       * @return The digest.
       */
      public static @NonNull String computeSignaturesSha256Digest(
              @NonNull Signature[] signatures) {
          // Shortcut for optimization - most apps singed by a single cert
          if (signatures.length == 1) {
              return computeSha256Digest(signatures[0].toByteArray());
          }
  
          // Make sure these are sorted to handle reversed certificates
          final String[] sha256Digests = computeSignaturesSha256Digests(signatures);
          return computeSignaturesSha256Digest(sha256Digests);
      }
  
      /**
       * Computes a SHA256 digest in of the signatures SHA256 digests. First,
       * the strings are sorted based the natural ordering, and then a hash is
       * derived from these strings' bytes.
       * @param sha256Digests Signature SHA256 hashes in hexademical form.
       * @return The digest.
       */
      public static @NonNull String computeSignaturesSha256Digest(
              @NonNull String[] sha256Digests) {
          // Shortcut for optimization - most apps singed by a single cert
          if (sha256Digests.length == 1) {
              return sha256Digests[0];
          }
  
          // Make sure these are sorted to handle reversed certificates
          Arrays.sort(sha256Digests);
  
          final ByteArrayOutputStream bytes = new ByteArrayOutputStream();
          for (String sha256Digest : sha256Digests) {
              try {
                  bytes.write(sha256Digest.getBytes());
              } catch (IOException e) {
                  /* ignore - can't happen */
              }
          }
          return computeSha256Digest(bytes.toByteArray());
      }
  
      /**
       * Computes the SHA256 digest of some data.
       * @param data The data.
       * @return The digest or null if an error occurs.
       */
      public static @Nullable byte[] computeSha256DigestBytes(@NonNull byte[] data) {
          MessageDigest messageDigest;
          try {
              messageDigest = MessageDigest.getInstance("SHA256");
          } catch (NoSuchAlgorithmException e) {
              /* can't happen */
              return null;
          }
  
          messageDigest.update(data);
  
          return messageDigest.digest();
      }
  
      /**
       * Computes the SHA256 digest of some data.
       * @param data The data.
       * @return The digest or null if an error occurs.
       */
      public static @Nullable String computeSha256Digest(@NonNull byte[] data) {
          return ByteStringUtils.toHexString(computeSha256DigestBytes(data));
      }
  }
  