[Chromoting] Factor out common code for pin hashing.

remoting/host/pin_hash.h

+// Copyright (c) 2012 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.
+
+#ifndef REMOTING_HOST_PIN_HASH_H_
+#define REMOTING_HOST_PIN_HASH_H_
+
+#include <string>
+
+namespace remoting {
+
+// Hashes a host ID and a PIN.
+// A Me2Me host uses this to hash a shared secret.

[Wez, 2012/05/01 01:02:36]

nit: Suggest "Create a Me2Me shared-secret hash, consisting of the hash method
and the hashed PIN."

[simonmorris, 2012/05/01 01:11:55]

Done.

+std::string MakeHostPinHash(const std::string& host_id, const std::string& pin);
+
+// Extracts the hash function from the given hash, uses it to calculate the
+// hash of the given host ID and PIN, and compares that hash to the given hash.
+// Returns true if the calculated and given hashes are equal.
+bool VerifyHostPinHash(const std::string& hash,
+                       const std::string& host_id,
+                       const std::string& pin);
+
+}  // namespace remoting
+
+#endif  // REMOTING_HOST_PIN_HASH_