keys: Add ChallengeResponseKey header

* Add initial header file for forthcoming challenge response support.
* A ChallengeResponseKey operates by submitting some challenge data and
  getting a deterministic result.
* In the case of the forthcoming YubiKey integration, the master seed is
  submitted as the challenge to the YubiKey hardware and the YubiKey
  returns a HMAC-SHA1 response.

Signed-off-by: Kyle Manna <kyle@kylemanna.com>

src/keys/ChallengeResponseKey.h

@@ -0,0 +1,32 @@
+/*
+*  Copyright (C) 2014 Kyle Manna <kyle@kylemanna.com>
+*
+*  This program is free software: you can redistribute it and/or modify
+*  it under the terms of the GNU General Public License as published by
+*  the Free Software Foundation, either version 2 or (at your option)
+*  version 3 of the License.
+*
+*  This program is distributed in the hope that it will be useful,
+*  but WITHOUT ANY WARRANTY; without even the implied warranty of
+*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*  GNU General Public License for more details.
+*
+*  You should have received a copy of the GNU General Public License
+*  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef KEEPASSX_CHALLENGE_RESPONSE_KEY_H
+#define KEEPASSX_CHALLENGE_RESPONSE_KEY_H
+
+#include <QByteArray>
+
+class ChallengeResponseKey
+{
+public:
+    virtual ~ChallengeResponseKey() {}
+    virtual QByteArray rawKey() const = 0;
+    virtual ChallengeResponseKey* clone() const = 0;
+    virtual bool challenge(const QByteArray& challenge) = 0;
+};
+
+#endif // KEEPASSX_CHALLENGE_RESPONSE_KEY_H