Fix pattern encryption when applying to patterns other than 1:9

We used to skip all the remaining bytes if the size is less than
|crypt_byte_block| blocks.

This interpretation is incorrect. We should only leave the last partial
16-byte block un-encrypted.

Change-Id: I4f09600efa52e2fdf4d0b661dfc418dcb675f9f6

packager/media/base/aes_pattern_cryptor.cc

@@ -51,14 +51,31 @@ bool AesPatternCryptor::CryptInternal(const uint8_t* text,
 
   while (text_size > 0) {
     const size_t crypt_byte_size = crypt_byte_block_ * AES_BLOCK_SIZE;
-    if (NeedEncrypt(text_size, crypt_byte_size)) {
-      if (!cryptor_->Crypt(text, crypt_byte_size, crypt_text))
-        return false;
-    } else {
-      // If there is not enough data, just keep it in clear.
+
+    if (text_size <= crypt_byte_size) {
+      const bool need_encrypt =
+          encryption_mode_ == kSkipIfCryptByteBlockRemaining
+              ? (text_size > crypt_byte_size)
+              : (text_size >= AES_BLOCK_SIZE);
+      if (need_encrypt) {
+        // The partial pattern SHALL be followed with the partial 16-byte block
+        // remains unencrypted.
+        const size_t aligned_crypt_byte_size =
+            text_size / AES_BLOCK_SIZE * AES_BLOCK_SIZE;
+        if (!cryptor_->Crypt(text, aligned_crypt_byte_size, crypt_text))
+          return false;
+        text += aligned_crypt_byte_size;
+        text_size -= aligned_crypt_byte_size;
+        crypt_text += aligned_crypt_byte_size;
+      }
+
+      // The remaining bytes are not encrypted.
       memcpy(crypt_text, text, text_size);
       return true;
     }
+
+    if (!cryptor_->Crypt(text, crypt_byte_size, crypt_text))
+      return false;
     text += crypt_byte_size;
     text_size -= crypt_byte_size;
     crypt_text += crypt_byte_size;
@@ -77,12 +94,5 @@ void AesPatternCryptor::SetIvInternal() {
   CHECK(cryptor_->SetIv(iv()));
 }
 
-bool AesPatternCryptor::NeedEncrypt(size_t input_size,
-                                    size_t target_data_size) {
-  if (encryption_mode_ == kSkipIfCryptByteBlockRemaining)
-    return input_size > target_data_size;
-  return input_size >= target_data_size;
-}
-
 }  // namespace media
 }  // namespace shaka

packager/media/base/aes_pattern_cryptor.h

@@ -19,18 +19,16 @@ class AesPatternCryptor : public AesCryptor {
   /// Enumerator for controling encrytion/decryption mode for the last
   /// encryption/decrytion block(s).
   enum PatternEncryptionMode {
-    /// Use kEncryptIfCryptByteBlockRemaining if the last blocks is exactly the
-    /// same as the number of remaining bytes. IOW
-    /// if (remaining_bytes == encryption_block_bytes)
-    ///   encrypt(remaining_data)
+    /// Use kEncryptIfCryptByteBlockRemaining to encrypt all the full 16-byte
+    /// blocks even if the remaining bytes are less than encryption_block_bytes.
+    /// IOW:
+    /// if (remaining_bytes <= encryption_block_bytes)
+    ///   encrypt(block_aligned_remaining_data)
     kEncryptIfCryptByteBlockRemaining,
-    /// Use kSkipIfCryptByteBlockRemaining to not encrypt/decrypt the last
-    /// clocks if it is exactly the same as the number of remaining bytes.
-    /// if (remaining_bytes > encryption_block_bytes) {
-    ///   // Since this is the last blocks, this is effectively the same
-    ///   // condition as remaining_bytes != encryption_block_bytes.
+    /// Use kSkipIfCryptByteBlockRemaining to not encrypt/decrypt the remaining
+    /// bytes if it is less than or equal to encryption_block_bytes.
+    /// if (remaining_bytes > encryption_block_bytes)
     ///   encrypt().
-    /// }
     /// Use this mode for HLS SAMPLE-AES.
     kSkipIfCryptByteBlockRemaining,
   };
@@ -70,8 +68,6 @@ class AesPatternCryptor : public AesCryptor {
                      size_t* crypt_text_size) override;
   void SetIvInternal() override;
 
-  bool NeedEncrypt(size_t input_size, size_t target_data_size);
-
   uint8_t crypt_byte_block_;
   const uint8_t skip_byte_block_;
   const PatternEncryptionMode encryption_mode_;

packager/media/base/aes_pattern_cryptor_unittest.cc

@@ -103,11 +103,15 @@ const PatternTestCase kPatternTestCases[] = {
     {"", ""},
     // One partial block (not encrypted).
     {"010203", "010203"},
-    // One block (not encrypted).
-    {"01020304050607080910111213141516", "01020304050607080910111213141516"},
-    // One block + partial block (not encrypted).
-    {"010203040506070809101112131415161718",
-     "010203040506070809101112131415161718"},
+    // One block (encrypted).
+    {"01020304050607080910111213141516", "11121314151617181920212223242526"},
+    // One block + partial block.
+    {// One block encrypted.
+     "01020304050607080910111213141516"
+     // Partial block unencrypted.
+     "1718",
+     "11121314151617181920212223242526"
+     "1718"},
     // Two blocks (encrypted) - the mock encryptor adds every byte by 0x10.
     {"0102030405060708091011121314151617181920212223242526272829303132",
      "1112131415161718192021222324252627282930313233343536373839404142"},
@@ -125,13 +129,13 @@ const PatternTestCase kPatternTestCases[] = {
      "4950515253545556575859606162636465666768697071727374757677787980"
      // kSkipByteBlock (1) block not encrypted.
      "81828384858687888990919293949596"
-     // Less than kCryptByteBlock blocks remaining, so not encrypted.
+     // One full block remaining, encrypted.
      "97989900010203040506070809101112",
      "1112131415161718192021222324252627282930313233343536373839404142"
      "33343536373839404142434445464748"
      "5960616263646566676869707172737475767778798081828384858687888990"
      "81828384858687888990919293949596"
-     "97989900010203040506070809101112"},
+     "a7a8a910111213141516171819202122"},
 };
 }  // namespace