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 com.google.android.exoplayer2.upstream.crypto;
  
  import static com.google.common.truth.Truth.assertThat;
  import static java.lang.Math.min;
  
  import androidx.test.ext.junit.runners.AndroidJUnit4;
  import com.google.android.exoplayer2.testutil.TestUtil;
  import com.google.android.exoplayer2.util.Util;
  import java.util.Random;
  import javax.crypto.Cipher;
  import org.junit.After;
  import org.junit.Before;
  import org.junit.Test;
  import org.junit.runner.RunWith;
  
  /** Unit tests for {@link AesFlushingCipher}. */
  @RunWith(AndroidJUnit4.class)
  public class AesFlushingCipherTest {
  
    private static final int DATA_LENGTH = 65536;
    private static final byte[] KEY = Util.getUtf8Bytes("testKey:12345678");
    private static final long NONCE = 0;
    private static final long START_OFFSET = 11;
    private static final long RANDOM_SEED = 0x12345678;
  
    private AesFlushingCipher encryptCipher;
    private AesFlushingCipher decryptCipher;
  
    @Before
    public void setUp() {
      encryptCipher = new AesFlushingCipher(Cipher.ENCRYPT_MODE, KEY, NONCE, START_OFFSET);
      decryptCipher = new AesFlushingCipher(Cipher.DECRYPT_MODE, KEY, NONCE, START_OFFSET);
    }
  
    @After
    public void tearDown() {
      encryptCipher = null;
      decryptCipher = null;
    }
  
    private static long getMaxUnchangedBytesAllowedPostEncryption(long length) {
      // Assuming that not more than 10% of the resultant bytes should be identical.
      // The value of 10% is arbitrary, ciphers standards do not name a value.
      return length / 10;
    }
  
    // Count the number of bytes that do not match.
    private static int getDifferingByteCount(byte[] data1, byte[] data2, int startOffset) {
      int count = 0;
      for (int i = startOffset; i < data1.length; i++) {
        if (data1[i] != data2[i]) {
          count++;
        }
      }
      return count;
    }
  
    // Count the number of bytes that do not match.
    private static int getDifferingByteCount(byte[] data1, byte[] data2) {
      return getDifferingByteCount(data1, data2, 0);
    }
  
    // Test a single encrypt and decrypt call.
    @Test
    public void single() {
      byte[] reference = TestUtil.buildTestData(DATA_LENGTH);
      byte[] data = reference.clone();
  
      encryptCipher.updateInPlace(data, 0, data.length);
      int unchangedByteCount = data.length - getDifferingByteCount(reference, data);
      assertThat(unchangedByteCount <= getMaxUnchangedBytesAllowedPostEncryption(data.length))
          .isTrue();
  
      decryptCipher.updateInPlace(data, 0, data.length);
      int differingByteCount = getDifferingByteCount(reference, data);
      assertThat(differingByteCount).isEqualTo(0);
    }
  
    // Test several encrypt and decrypt calls, each aligned on a 16 byte block size.
    @Test
    public void aligned() {
      byte[] reference = TestUtil.buildTestData(DATA_LENGTH);
      byte[] data = reference.clone();
      Random random = new Random(RANDOM_SEED);
  
      int offset = 0;
      while (offset < data.length) {
        int bytes = (1 + random.nextInt(50)) * 16;
        bytes = min(bytes, data.length - offset);
        assertThat(bytes % 16).isEqualTo(0);
        encryptCipher.updateInPlace(data, offset, bytes);
        offset += bytes;
      }
  
      int unchangedByteCount = data.length - getDifferingByteCount(reference, data);
      assertThat(unchangedByteCount <= getMaxUnchangedBytesAllowedPostEncryption(data.length))
          .isTrue();
  
      offset = 0;
      while (offset < data.length) {
        int bytes = (1 + random.nextInt(50)) * 16;
        bytes = min(bytes, data.length - offset);
        assertThat(bytes % 16).isEqualTo(0);
        decryptCipher.updateInPlace(data, offset, bytes);
        offset += bytes;
      }
  
      int differingByteCount = getDifferingByteCount(reference, data);
      assertThat(differingByteCount).isEqualTo(0);
    }
  
    // Test several encrypt and decrypt calls, not aligned on block boundary.
    @Test
    public void unAligned() {
      byte[] reference = TestUtil.buildTestData(DATA_LENGTH);
      byte[] data = reference.clone();
      Random random = new Random(RANDOM_SEED);
  
      // Encrypt
      int offset = 0;
      while (offset < data.length) {
        int bytes = 1 + random.nextInt(4095);
        bytes = min(bytes, data.length - offset);
        encryptCipher.updateInPlace(data, offset, bytes);
        offset += bytes;
      }
  
      int unchangedByteCount = data.length - getDifferingByteCount(reference, data);
      assertThat(unchangedByteCount <= getMaxUnchangedBytesAllowedPostEncryption(data.length))
          .isTrue();
  
      offset = 0;
      while (offset < data.length) {
        int bytes = 1 + random.nextInt(4095);
        bytes = min(bytes, data.length - offset);
        decryptCipher.updateInPlace(data, offset, bytes);
        offset += bytes;
      }
  
      int differingByteCount = getDifferingByteCount(reference, data);
      assertThat(differingByteCount).isEqualTo(0);
    }
  
    // Test decryption starting from the middle of an encrypted block.
    @Test
    public void midJoin() {
      byte[] reference = TestUtil.buildTestData(DATA_LENGTH);
      byte[] data = reference.clone();
      Random random = new Random(RANDOM_SEED);
  
      // Encrypt
      int offset = 0;
      while (offset < data.length) {
        int bytes = 1 + random.nextInt(4095);
        bytes = min(bytes, data.length - offset);
        encryptCipher.updateInPlace(data, offset, bytes);
        offset += bytes;
      }
  
      // Verify
      int unchangedByteCount = data.length - getDifferingByteCount(reference, data);
      assertThat(unchangedByteCount <= getMaxUnchangedBytesAllowedPostEncryption(data.length))
          .isTrue();
  
      // Setup decryption from random location
      offset = random.nextInt(4096);
      decryptCipher = new AesFlushingCipher(Cipher.DECRYPT_MODE, KEY, NONCE, offset + START_OFFSET);
      int remainingLength = data.length - offset;
      int originalOffset = offset;
  
      // Decrypt
      while (remainingLength > 0) {
        int bytes = 1 + random.nextInt(4095);
        bytes = min(bytes, remainingLength);
        decryptCipher.updateInPlace(data, offset, bytes);
        offset += bytes;
        remainingLength -= bytes;
      }
  
      // Verify
      int differingByteCount = getDifferingByteCount(reference, data, originalOffset);
      assertThat(differingByteCount).isEqualTo(0);
    }
  }
  