Modify fake encryptor/decrytor to avoid streaming.

A conversation with experts gave a recommendation to not use
streaming ciphers - instead, accumulate data and do encyption/decryption
at the end (in place).

Bug: b:153649905
Change-Id: I1a146fcf571089c648a75c4d4cbd1b75a6900ff0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2363392Reviewed-by: Zach Trudo <zatrudo@google.com>
Commit-Queue: Leonid Baraz <lbaraz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799281}

chrome/browser/policy/messaging_layer/encryption/fake_decryption.cc

@@ -24,21 +24,22 @@ class MockRecordHandle : public DecryptorBase::Handle {
 
   void AddToRecord(base::StringPiece data,
                    base::OnceCallback<void(Status)> cb) override {
-    // Decrypt data by XORing every byte with the bytes of symmetric key and add
-    // to the record.
-    record_.reserve(record_.size() + data.size());
-    size_t key_i = 0;
-    for (const auto& data_byte : data) {
-      record_.push_back(data_byte ^ symmetric_key_[key_i++]);
-      if (key_i >= symmetric_key_.size()) {
-        key_i = 0;
-      }
-    }
+    // Add piece of data to the record.
+    record_.append(data.data(), data.size());
     std::move(cb).Run(Status::StatusOK());
   }
 
   void CloseRecord(
       base::OnceCallback<void(StatusOr<base::StringPiece>)> cb) override {
+    // Decrypt data in place by XORing every byte with the bytes of symmetric
+    // key.
+    size_t key_i = 0;
+    for (auto& record_byte : record_) {
+      record_byte ^= symmetric_key_[key_i++];
+      if (key_i >= symmetric_key_.size()) {
+        key_i = 0;
+      }
+    }
     std::move(cb).Run(record_);
     delete this;
   }

chrome/browser/policy/messaging_layer/encryption/fake_encryption.cc

@@ -28,21 +28,23 @@ class MockRecordHandle : public EncryptorBase::Handle {
 
   void AddToRecord(base::StringPiece data,
                    base::OnceCallback<void(Status)> cb) override {
-    // Encrypt new data by XORing every byte with the symmetric key and add to
-    // the encrypted record.
-    record_.reserve(record_.size() + data.size());
-    size_t key_i = 0;
-    for (const auto& data_byte : data) {
-      record_.push_back(data_byte ^ symmetric_key_[key_i++]);
-      if (key_i >= symmetric_key_.size()) {
-        key_i = 0;
-      }
-    }
+    // Append new data to the record.
+    record_.append(data.data(), data.size());
     std::move(cb).Run(Status::StatusOK());
   }
 
   void CloseRecord(
       base::OnceCallback<void(StatusOr<EncryptedRecord>)> cb) override {
+    // Encrypt all collected data in place by XORing every byte with the
+    // symmetric key.
+    size_t key_i = 0;
+    for (auto& record_byte : record_) {
+      record_byte ^= symmetric_key_[key_i++];
+      if (key_i >= symmetric_key_.size()) {
+        key_i = 0;
+      }
+    }
+    // Encrypt the symmetric key.
     encryptor()->EncryptKey(
         symmetric_key_,
         base::BindOnce(