Add base::UnguessableToken

base/nonce.cc

Index: base/nonce.cc
diff --git a/base/nonce.cc b/base/nonce.cc
new file mode 100644
index 0000000000000000000000000000000000000000..cf43a4d635e09161384ac41d6ce7390d7650828f
--- /dev/null
+++ b/base/nonce.cc
@@ -0,0 +1,44 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/nonce.h"
+
+#include "base/format_macros.h"
+#include "base/rand_util.h"
+#include "base/strings/stringprintf.h"
+
+namespace base {
+
+// If base::Nonce is no longer 128 bits, the IPC serialization logic and Mojo
+// StructTraits should be updated to match the size of the struct.
+static_assert(sizeof(Nonce) == 2 * sizeof(uint64_t),
+              "base::Nonce should be of size 2 * sizeof(uint64_t).");
+
+Nonce::Nonce() : high_(0), low_(0) {}
+
+Nonce::Nonce(uint64_t high, uint64_t low) : high_(high), low_(low) {}
+
+std::string Nonce::ToString() const {
+  return base::StringPrintf("(%" PRIu64 ":%" PRIu64 ")", high_, low_);
+}
+
+// static
+Nonce Nonce::Generate() {
+  Nonce nonce;
+  // Use base::RandBytes instead of crypto::RandBytes, because crypto calls the
+  // base version directly, and to prevent the dependency from base/ to crypto/.
+  base::RandBytes(&nonce, sizeof(nonce));
+  return nonce;
+}
+
+// static
+Nonce Nonce::Deserialize(uint64_t high, uint64_t low) {
+  // Make sure we are not trying to deserialize an empty nonce.
+  // Sending an empty nonce accross processes likely means that

[watk, 2016/09/15 18:46:10]

across

[tguilbert, 2016/09/15 22:57:39]

Done.

+  // Nonce::Generate() was never called, which points to a security hole.
+  CHECK((high | low));

[danakj, 2016/09/15 18:06:36]

DCHECK?

[tguilbert, 2016/09/15 22:57:39]

I think this CHECK is important. There is no case where deserializing a zeroed
out NonceToken is a valid scenario. The IPC ParamTraits and Mojo StructTraits
are now checking to see if high/low are both 0, and return false instead of
calling Deserialize, which means we shouldn't run into this CHECK.

If someone planned on creating an intentional empty NonceToken, NonceToken() is
the way to go.

+  return Nonce(high, low);
+}
+
+}  // namespace base