Add nonce generator interface

Nonce generators (nonce_gen_t) can be used to get or allocate nonces.

Users can request nonce generators from the crypto factory while nonce
plugins register/remove themselves to/from the crypto factory.

src/libstrongswan/crypto/nonce_gen.h

@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2012 Adrian-Ken Rueegsegger
+ * Hochschule fuer Technik Rapperswil
+ *
+ * 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 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * 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.
+ */
+
+/**
+ * @defgroup nonce_gen nonce_gen
+ * @{ @ingroup crypto
+ */
+
+#ifndef NONCE_GEN_H_
+#define NONCE_GEN_H_
+
+typedef struct nonce_gen_t nonce_gen_t;
+
+#include <library.h>
+
+/**
+ * Generic interface for nonce generators.
+ */
+struct nonce_gen_t {
+
+	/**
+	 * Generates a nonce and writes it into the buffer.
+	 *
+	 * @param size		size of nonce in bytes
+	 * @param buffer	pointer where the generated nonce will be written
+	 */
+	void (*get_nonce) (nonce_gen_t *this, size_t size, u_int8_t *buffer);
+
+	/**
+	 * Generates a nonce and allocates space for it.
+	 *
+	 * @param size		size of nonce in bytes
+	 * @param chunk		chunk which will hold the generated nonce
+	 */
+	void (*allocate_nonce) (nonce_gen_t *this, size_t size, chunk_t *chunk);
+
+	/**
+	 * Destroys a nonce generator object.
+	 */
+	void (*destroy) (nonce_gen_t *this);
+};
+
+#endif /** NONCE_GEN_H_ @}*/