The tpm plugin offers random number generation

The tpm plugin can be used to derive true random numbers from a
TPM 2.0 device. The get_random method must be explicitly enabled
in strongswan.conf with the plugin.tpm.use_rng = yes option.

conf/Makefile.am

@@ -93,6 +93,7 @@ plugins = \
 	plugins/tnc-pdp.opt \
 	plugins/tnccs-11.opt \
 	plugins/tnccs-20.opt \
+	plugins/tpm.opt \
 	plugins/unbound.opt \
 	plugins/updown.opt \
 	plugins/vici.opt \

conf/plugins/tpm.opt

@@ -0,0 +1,2 @@
+charon.plugins.tpm.use_rng = no
+	Whether the TPM should be used as RNG.

src/libtpmtss/plugins/tpm/Makefile.am

@@ -15,6 +15,7 @@ endif
 
 libstrongswan_tpm_la_SOURCES = \
 	tpm_plugin.h tpm_plugin.c \
-	tpm_private_key.h tpm_private_key.c
+	tpm_private_key.h tpm_private_key.c \
+	tpm_rng.h tpm_rng.c
 
 libstrongswan_tpm_la_LDFLAGS = -module -avoid-version

src/libtpmtss/plugins/tpm/tpm_plugin.c

@@ -15,6 +15,7 @@
 
 #include "tpm_plugin.h"
 #include "tpm_private_key.h"
+#include "tpm_rng.h"
 
 #include <library.h>
 
@@ -40,13 +41,32 @@ METHOD(plugin_t, get_name, char*,
 METHOD(plugin_t, get_features, int,
 	private_tpm_plugin_t *this, plugin_feature_t *features[])
 {
-	static plugin_feature_t f[] = {
+	static plugin_feature_t f_rng[] = {
+		PLUGIN_REGISTER(RNG, tpm_rng_create),
+			PLUGIN_PROVIDE(RNG, RNG_STRONG),
+			PLUGIN_PROVIDE(RNG, RNG_TRUE),
+	};
+	static plugin_feature_t f_privkey[] = {
 		PLUGIN_REGISTER(PRIVKEY, tpm_private_key_connect, FALSE),
 			PLUGIN_PROVIDE(PRIVKEY, KEY_ANY),
 	};
+	static plugin_feature_t f[countof(f_rng) + countof(f_privkey)] = {};
+
+	static int count = 0;
+
+	if (!count)
+	{
+		plugin_features_add(f, f_privkey, countof(f_privkey), &count);
+
+		if (lib->settings->get_bool(lib->settings,
+								"%s.plugins.tpm.use_rng", FALSE, lib->ns))
+		{
+			plugin_features_add(f, f_rng, countof(f_rng), &count);
+		}
+	}
 	*features = f;
 
-	return countof(f);
+	return count;
 }
 
 METHOD(plugin_t, destroy, void,

src/libtpmtss/plugins/tpm/tpm_rng.c

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2017 Andreas Steffen
+ * HSR 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.
+ */
+
+#include "tpm_rng.h"
+
+#include <tpm_tss.h>
+#include <utils/debug.h>
+
+typedef struct private_tpm_rng_t private_tpm_rng_t;
+
+/**
+ * Private data of an tpm_rng_t object.
+ */
+struct private_tpm_rng_t {
+
+	/**
+	 * Public interface.
+	 */
+	tpm_rng_t public;
+
+	/**
+	 * Trusted Platform Module
+	 */
+	tpm_tss_t *tpm;
+
+};
+
+METHOD(rng_t, get_bytes, bool,
+	private_tpm_rng_t *this, size_t bytes, uint8_t *buffer)
+{
+	return this->tpm->get_random(this->tpm, bytes, buffer);
+}
+
+METHOD(rng_t, allocate_bytes, bool,
+	private_tpm_rng_t *this, size_t bytes, chunk_t *chunk)
+{
+	*chunk = chunk_alloc(bytes);
+	if (!get_bytes(this, chunk->len, chunk->ptr))
+	{
+		chunk_clear(chunk);
+		return FALSE;
+	}
+	return TRUE;
+}
+
+METHOD(rng_t, destroy, void,
+	private_tpm_rng_t *this)
+{
+	this->tpm->destroy(this->tpm);
+	free(this);
+}
+
+/*
+ * Described in header.
+ */
+tpm_rng_t *tpm_rng_create(rng_quality_t quality)
+{
+	private_tpm_rng_t *this;
+	tpm_tss_t *tpm;
+
+	/* try to find a TPM 2.0 */
+	tpm = tpm_tss_probe(TPM_VERSION_2_0);
+	if (!tpm)
+	{
+		DBG1(DBG_LIB, "no TPM 2.0 found");
+		return NULL;	
+	}
+
+	INIT(this,
+		.public = {
+			.rng = {
+				.get_bytes = _get_bytes,
+				.allocate_bytes = _allocate_bytes,
+				.destroy = _destroy,
+			},
+		},
+		.tpm = tpm,
+	);
+
+	return &this->public;
+}
+

src/libtpmtss/plugins/tpm/tpm_rng.h

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2017 Andreas Steffen
+ * HSR 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 tpm_rng tpm_rng
+ * @{ @ingroup tpm
+ */
+
+#ifndef TPM_RNG_H_
+#define TPM_RNG_H_
+
+typedef struct tpm_rng_t tpm_rng_t;
+
+#include <library.h>
+
+/**
+ * rng_t implementation via TSS 2.0
+ */
+struct tpm_rng_t {
+
+	/**
+	 * Implements rng_t.
+	 */
+	rng_t rng;
+};
+
+/**
+ * Creates a tpm_rng_t instance.
+ *
+ * @param quality	required quality of randomness
+ * @return			created tpm_rng_t
+ */
+tpm_rng_t *tpm_rng_create(rng_quality_t quality);
+
+#endif /** TPM_RNG_H_ @} */

src/libtpmtss/tpm_tss.h

@@ -134,6 +134,15 @@ struct tpm_tss_t {
 				 signature_scheme_t scheme, chunk_t data, chunk_t pin,
 				 chunk_t *signature);
 
+	/**
+	 * Get random bytes from the TPM
+	 *
+	 * @param bytes			number of random bytes requested
+	 * @param buffer		buffer where the random bytes are written into
+	 * @return				TRUE if random bytes could be delivered
+	 */
+	bool (*get_random)(tpm_tss_t *this, size_t bytes, uint8_t *buffer);
+
 	/**
 	 * Destroy a tpm_tss_t.
 	 */

src/libtpmtss/tpm_tss_trousers.c

@@ -589,6 +589,12 @@ METHOD(tpm_tss_t, sign, bool,
 	return FALSE;
 }
 
+METHOD(tpm_tss_t, get_random, bool,
+	private_tpm_tss_trousers_t *this, size_t bytes, uint8_t *buffer)
+{
+	return FALSE;
+}
+
 METHOD(tpm_tss_t, destroy, void,
 	private_tpm_tss_trousers_t *this)
 {
@@ -632,6 +638,7 @@ tpm_tss_t *tpm_tss_trousers_create()
 				.extend_pcr = _extend_pcr,
 				.quote = _quote,
 				.sign = _sign,
+				.get_random = _get_random,
 				.destroy = _destroy,
 			},
 			.load_aik = _load_aik,

src/libtpmtss/tpm_tss_tss2.c

@@ -829,6 +829,32 @@ METHOD(tpm_tss_t, sign, bool,
 	return TRUE;
 }
 
+METHOD(tpm_tss_t, get_random, bool,
+	private_tpm_tss_tss2_t *this, size_t bytes, uint8_t *buffer)
+{
+	size_t len, random_len= sizeof(TPM2B_DIGEST)-2;
+	TPM2B_DIGEST random = { { random_len, } };
+	uint8_t *pos = buffer;
+	uint32_t rval;
+
+	while (bytes > 0)
+	{
+		len = min(bytes, random_len);
+
+		rval = Tss2_Sys_GetRandom(this->sys_context, NULL, len, &random, NULL);
+		if (rval != TSS2_RC_SUCCESS)
+		{
+			DBG1(DBG_PTS,"%s Tss2_Sys_GetRandom failed: 0x%06x", LABEL, rval);
+			return FALSE;
+	    }
+		memcpy(pos, random.t.buffer, random.t.size);
+		pos   += random.t.size;
+		bytes -= random.t.size;
+	}
+
+	return TRUE;
+}
+
 METHOD(tpm_tss_t, destroy, void,
 	private_tpm_tss_tss2_t *this)
 {
@@ -854,6 +880,7 @@ tpm_tss_t *tpm_tss_tss2_create()
 			.extend_pcr = _extend_pcr,
 			.quote = _quote,
 			.sign = _sign,
+			.get_random = _get_random,
 			.destroy = _destroy,
 		},
 	);