Change AesCbcEncryptor/AesCbcDecryptor kNoPadding behavior

Leave unaligned residual block in clear in stead of rejecting it.

Change-Id: Id5452f32f6147e26ac68d9cddb948e8b4f77d107

packager/media/base/aes_cryptor_unittest.cc

@@ -553,6 +553,9 @@ const CbcTestCase kCbcTestCases[] = {
     {kNoPadding,
      "6bc1bee22e409f96e93d7e117393172a6bc1bee22e409f96e93d7e117393172a",
      "77cde91fe6df9cbc5d0c98f96efd590bbddde439526f100c9545c274d4f7fd3f"},
+    {kNoPadding,
+     "6bc1bee22e409f96e93d7e117393172a6bc1bee22e409f96e93d7e117393172a1234",
+     "77cde91fe6df9cbc5d0c98f96efd590bbddde439526f100c9545c274d4f7fd3f1234"},
     // Pkcs5 padding with zero bytes.
     {kPkcs5Padding, "", "f6a3569dea3cda208eb3d5792942612b"},
     // Cts Padding with zero bytes.

packager/media/base/aes_decryptor.cc

@@ -84,6 +84,7 @@ bool AesCbcDecryptor::CryptInternal(const uint8_t* ciphertext,
 
   std::vector<uint8_t> local_iv(iv());
   const size_t residual_block_size = ciphertext_size % AES_BLOCK_SIZE;
+  const size_t cbc_size = ciphertext_size - residual_block_size;
   if (residual_block_size == 0) {
     AES_cbc_encrypt(ciphertext, plaintext, ciphertext_size, aes_key(),
                     local_iv.data(), AES_DECRYPT);
@@ -101,6 +102,15 @@ bool AesCbcDecryptor::CryptInternal(const uint8_t* ciphertext,
     }
     *plaintext_size -= num_padding_bytes;
     return true;
+  } else if (padding_scheme_ == kNoPadding) {
+    AES_cbc_encrypt(ciphertext, plaintext, cbc_size, aes_key(), local_iv.data(),
+                    AES_DECRYPT);
+    if (chain_across_calls_)
+      set_iv(local_iv);
+
+    // The residual block is not encrypted.
+    memcpy(plaintext + cbc_size, ciphertext + cbc_size, residual_block_size);
+    return true;
   } else if (padding_scheme_ != kCtsPadding) {
     LOG(ERROR) << "Expecting cipher text size to be multiple of "
                << AES_BLOCK_SIZE << ", got " << ciphertext_size;
@@ -116,7 +126,6 @@ bool AesCbcDecryptor::CryptInternal(const uint8_t* ciphertext,
   }
 
   // AES-CBC decrypt everything up to the next-to-last full block.
-  const size_t cbc_size = ciphertext_size - residual_block_size;
   if (cbc_size > AES_BLOCK_SIZE) {
     AES_cbc_encrypt(ciphertext, plaintext, cbc_size - AES_BLOCK_SIZE, aes_key(),
                     local_iv.data(), AES_DECRYPT);

packager/media/base/aes_encryptor.cc

@@ -171,12 +171,6 @@ bool AesCbcEncryptor::CryptInternal(const uint8_t* plaintext,
   DCHECK(aes_key());
 
   const size_t residual_block_size = plaintext_size % AES_BLOCK_SIZE;
-  if (padding_scheme_ == kNoPadding && residual_block_size != 0) {
-    LOG(ERROR) << "Expecting input size to be multiple of " << AES_BLOCK_SIZE
-               << ", got " << plaintext_size;
-    return false;
-  }
-
   const size_t num_padding_bytes = NumPaddingBytes(plaintext_size);
   const size_t required_ciphertext_size = plaintext_size + num_padding_bytes;
   if (*ciphertext_size < required_ciphertext_size) {
@@ -205,6 +199,12 @@ bool AesCbcEncryptor::CryptInternal(const uint8_t* plaintext,
   }
   DCHECK(!chain_across_calls_);
 
+  if (padding_scheme_ == kNoPadding) {
+    // The residual block is left unencrypted.
+    memcpy(ciphertext + cbc_size, plaintext + cbc_size, residual_block_size);
+    return true;
+  }
+
   std::vector<uint8_t> residual_block(plaintext + cbc_size,
                                       plaintext + plaintext_size);
   DCHECK_EQ(residual_block.size(), residual_block_size);

packager/media/base/aes_encryptor.h

@@ -71,8 +71,12 @@ class AesCtrEncryptor : public AesEncryptor {
 };
 
 enum CbcPaddingScheme {
+  // Residual block is left unencrypted.
   kNoPadding,
+  // Residual block is padded with pkcs5 and encrypted.
   kPkcs5Padding,
+  // Residual block and the next-to-last block are encrypted using ciphertext
+  // stealing method.
   kCtsPadding,
 };
 

packager/media/formats/mp4/encrypting_fragmenter.cc

@@ -330,12 +330,7 @@ Status EncryptingFragmenter::EncryptSample(scoped_refptr<MediaSample> sample) {
     traf()->auxiliary_size.sample_info_sizes.push_back(
         sample_encryption_entry.ComputeSize());
   } else {
-    uint64_t encryption_data_size = sample->data_size();
-    // AES-CBC mode requires all encrypted cipher blocks to be 16 bytes. The
-    // partial blocks are left unencrypted.
-    if (protection_scheme_ == FOURCC_cbc1)
-      encryption_data_size -= encryption_data_size % kCencBlockSize;
-    EncryptBytes(data, encryption_data_size);
+    EncryptBytes(data, sample->data_size());
   }
 
   traf()->sample_encryption.sample_encryption_entries.push_back(