prf-plus: Fail after counter has wrapped around

The behavior is undefined if this happens (RFC 7296, section 2.13).
Instead of switching to the non-counter mode, or letting the counter
wrap, this makes it clear that the usage was not as intended.

src/libstrongswan/crypto/prf_plus.c

@@ -20,6 +20,8 @@
 
 typedef struct private_prf_plus_t private_prf_plus_t;
 
+typedef bool (*apply_prf_t)(private_prf_plus_t *this);
+
 /**
  * Private data of an prf_plus_t object.
  *
@@ -42,7 +44,7 @@ struct private_prf_plus_t {
 	chunk_t seed;
 
 	/**
-	 * Octet which will be appended to the seed, 0 if not used
+	 * Octet which will be appended to the seed if a counter is used.
 	 */
 	uint8_t counter;
 
@@ -55,8 +57,41 @@ struct private_prf_plus_t {
 	 * Buffer to store current PRF result.
 	 */
 	chunk_t buffer;
+
+	/**
+	 * The prf application method depending on whether a counter is used.
+	 */
+	apply_prf_t apply_prf;
 };
 
+/**
+ * Apply the PRF using the running counter
+ */
+static bool apply_prf_counter(private_prf_plus_t *this)
+{
+	if (!this->prf->get_bytes(this->prf, this->seed, NULL) ||
+		!this->prf->get_bytes(this->prf, chunk_from_thing(this->counter),
+							  this->buffer.ptr))
+	{
+		return FALSE;
+	}
+	this->counter++;
+	if (!this->counter)
+	{	/* according to RFC 7296, section 2.13, prf+ is undefined once the
+		 * counter wrapped, so let's fail for future calls */
+		this->apply_prf = (void*)return_false;
+	}
+	return TRUE;
+}
+
+/**
+ * Apply the PRF using the running counter
+ */
+static bool apply_prf(private_prf_plus_t *this)
+{
+	return this->prf->get_bytes(this->prf, this->seed, this->buffer.ptr);
+}
+
 METHOD(prf_plus_t, get_bytes, bool,
 	private_prf_plus_t *this, size_t length, uint8_t *buffer)
 {
@@ -70,23 +105,9 @@ METHOD(prf_plus_t, get_bytes, bool,
 			{
 				return FALSE;
 			}
-			if (this->counter)
+			if (!this->apply_prf(this))
 			{
-				if (!this->prf->get_bytes(this->prf, this->seed, NULL) ||
-					!this->prf->get_bytes(this->prf,
-							chunk_from_thing(this->counter), this->buffer.ptr))
-				{
-					return FALSE;
-				}
-				this->counter++;
-			}
-			else
-			{
-				if (!this->prf->get_bytes(this->prf, this->seed,
-										  this->buffer.ptr))
-				{
-					return FALSE;
-				}
+				return FALSE;
 			}
 			this->used = 0;
 		}
@@ -136,28 +157,14 @@ prf_plus_t *prf_plus_create(prf_t *prf, bool counter, chunk_t seed)
 		.prf = prf,
 		.seed = chunk_clone(seed),
 		.buffer = chunk_alloc(prf->get_block_size(prf)),
+		.apply_prf = counter ? apply_prf_counter : apply_prf,
+		.counter = 0x01,
 	);
 
-	if (counter)
+	if (!this->apply_prf(this))
 	{
-		this->counter = 0x01;
-		if (!this->prf->get_bytes(this->prf, this->seed, NULL) ||
-			!this->prf->get_bytes(this->prf, chunk_from_thing(this->counter),
-								  this->buffer.ptr))
-		{
-			destroy(this);
-			return NULL;
-		}
-		this->counter++;
+		destroy(this);
+		return NULL;
 	}
-	else
-	{
-		if (!this->prf->get_bytes(this->prf, this->seed, this->buffer.ptr))
-		{
-			destroy(this);
-			return NULL;
-		}
-	}
-
 	return &this->public;
 }

src/libstrongswan/tests/Makefile.am

@@ -55,6 +55,7 @@ libstrongswan_tests_SOURCES = tests.h tests.c \
   suites/test_printf.c \
   suites/test_rng_tester.c \
   suites/test_mgf1.c \
+  suites/test_prf_plus.c \
   suites/test_ntru.c \
   suites/test_ed25519.c \
   suites/test_ed448.c \

src/libstrongswan/tests/suites/test_prf_plus.c

@@ -0,0 +1,161 @@
+/*
+ * Copyright (C) 2019 Tobias Brunner
+ * 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 "test_suite.h"
+
+#include <crypto/prf_plus.h>
+
+static struct {
+	chunk_t key;
+	chunk_t seed;
+	chunk_t iterations[10];
+} counter_data[] = {
+	{ .key = chunk_from_chars(0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,
+							  0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,
+							  0x0b,0x0b,0x0b,0x0b),
+	  .seed = chunk_from_chars(0x48,0x69,0x20,0x54,0x68,0x65,0x72,0x65),
+	  .iterations = {
+		chunk_from_chars(0xb9,0xbd,0xc0),
+		chunk_from_chars(0x89,0x88,0xb4,0xc2,0xb7,0x5a),
+		chunk_from_chars(0xa9,0x3e,0x59,0x6a,0xc8,0x42,0x05),
+		chunk_from_chars(0xfa,0x2d,0xdd,0xe1,0xbf,0x7a,0x25,0x72,
+						 0x06,0x7b,0x00,0xe1,0x4b,0x23,0x77,0x32),
+		chunk_from_chars(0x83,0x05,0x09,0x98,0x1a,0xd2,0xf9,0x4a),
+		chunk_from_chars(0x8c,0x32,0xa4,0x7d,0xaa,0x22,0x55,0xb6),
+		chunk_from_chars(0x60,0xc4,0x36,0x34,0x7a,0xe7,0x56,0xa6,
+						 0xed,0xc0,0x23,0x47,0x7d,0x80),
+		chunk_from_chars(0x95,0x90,0xe6,0x82,0xf6,0x1d,0x9c,0x04,
+						 0xb0,0x6b,0x4a,0xd9,0x71,0xa3,0x4c,0x81,
+						 0x47,0xfa,0x66,0x79),
+		chunk_from_chars(0x2f,0xf1,0x43,0x4b,0x93,0xc7,0x22,0xb3,
+						 0x2e,0x12,0xf4,0x88,0x32,0xeb,0xc1,0x5c,
+						 0xe2,0x36,0x9c,0xe7,0x1f,0xe9,0xb7,0xb8,
+						 0x1e,0x57,0x04,0xc1,0x4d,0x0f,0x52,0x80,
+						 0xa6,0xec,0x62,0x6e,0x99,0x2d,0x7a,0x9f),
+	  },
+	},
+};
+
+START_TEST(test_vectors_counter)
+{
+	prf_plus_t *prf_plus;
+	prf_t *prf;
+	chunk_t *iter = counter_data[_i].iterations, out;
+
+	prf = lib->crypto->create_prf(lib->crypto, PRF_HMAC_SHA2_256);
+	ck_assert(prf->set_key(prf, counter_data[_i].key));
+	prf_plus = prf_plus_create(prf, TRUE, counter_data[_i].seed);
+	while (iter->ptr)
+	{
+		ck_assert(prf_plus->allocate_bytes(prf_plus, iter->len, &out));
+		ck_assert_chunk_eq(*iter, out);
+		chunk_free(&out);
+		iter++;
+	}
+	prf_plus->destroy(prf_plus);
+	prf->destroy(prf);
+}
+END_TEST
+
+START_TEST(test_wrap)
+{
+	prf_plus_t *prf_plus;
+	prf_t *prf;
+	u_char buf[32];
+	int i;
+
+	prf = lib->crypto->create_prf(lib->crypto, PRF_HMAC_SHA2_256);
+	ck_assert(prf->set_key(prf, counter_data[0].key));
+	prf_plus = prf_plus_create(prf, TRUE, counter_data[0].seed);
+	for (i = 1; i < 256; i++)
+	{
+		ck_assert(prf_plus->get_bytes(prf_plus, sizeof(buf), buf));
+	}
+	ck_assert(!prf_plus->get_bytes(prf_plus, sizeof(buf), buf));
+	prf_plus->destroy(prf_plus);
+	prf->destroy(prf);
+}
+END_TEST
+
+static struct {
+	chunk_t key;
+	chunk_t seed;
+	chunk_t iterations[10];
+} classic_data[] = {
+	{ .key = chunk_from_chars(0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,
+							  0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,0x0b,
+							  0x0b,0x0b,0x0b,0x0b),
+	  .seed = chunk_from_chars(0x48,0x69,0x20,0x54,0x68,0x65,0x72,0x65),
+	  .iterations = {
+		chunk_from_chars(0xb0,0x34,0x4c),
+		chunk_from_chars(0x61,0xd8,0xdb,0x38,0x53,0x5c),
+		chunk_from_chars(0xa8,0xaf,0xce,0xaf,0x0b,0xf1,0x2b),
+		chunk_from_chars(0x88,0x1d,0xc2,0x00,0xc9,0x83,0x3d,0xa7,
+						 0x26,0xe9,0x37,0x6c,0x2e,0x32,0xcf,0xf7),
+		chunk_from_chars(0xd0,0x9a,0xe2,0x4b,0x3a,0x83,0xff,0xd4),
+		chunk_from_chars(0xb1,0xef,0xa5,0x94,0x5c,0xc5,0xed,0x85),
+		chunk_from_chars(0xb0,0xb2,0xcc,0x56,0xfc,0xf7,0x5d,0x23,
+						 0xa0,0xa3,0x4c,0xa4,0xdb,0xff,),
+		chunk_from_chars(0xea,0xfd,0xaa,0x6a,0x3b,0xf4,0x11,0x34,
+						 0x24,0xe4,0x50,0x2d,0xf9,0x7a,0x76,0x93,
+						 0x24,0xf6,0x11,0x24),
+		chunk_from_chars(0x24,0x3b,0x99,0x6e,0x7d,0x0f,0x35,0x99,
+						 0x88,0x79,0x73,0x6b,0xdb,0x70,0x65,0x9a,
+						 0x6e,0xfa,0xd2,0x39,0x94,0x10,0xe6,0xce,
+						 0x80,0x45,0x6e,0xb6,0x07,0x07,0x8f,0xe1,
+						 0xc4,0x7c,0x6b,0x5e,0x81,0x65,0x47,0x8a),
+	  },
+	},
+};
+
+START_TEST(test_vectors_classic)
+{
+	prf_plus_t *prf_plus;
+	prf_t *prf;
+	chunk_t *iter = classic_data[_i].iterations, out;
+
+	prf = lib->crypto->create_prf(lib->crypto, PRF_HMAC_SHA2_256);
+	ck_assert(prf->set_key(prf, classic_data[_i].key));
+	prf_plus = prf_plus_create(prf, FALSE, classic_data[_i].seed);
+	while (iter->ptr)
+	{
+		ck_assert(prf_plus->allocate_bytes(prf_plus, iter->len, &out));
+		ck_assert_chunk_eq(*iter, out);
+		chunk_free(&out);
+		iter++;
+	}
+	prf_plus->destroy(prf_plus);
+	prf->destroy(prf);
+}
+END_TEST
+
+Suite *prf_plus_suite_create()
+{
+	Suite *s;
+	TCase *tc;
+
+	s = suite_create("prf_plus");
+
+	tc = tcase_create("counter");
+	tcase_add_loop_test(tc, test_vectors_counter, 0, countof(counter_data));
+	tcase_add_test(tc, test_wrap);
+	suite_add_tcase(s, tc);
+
+	tc = tcase_create("no counter");
+	tcase_add_loop_test(tc, test_vectors_classic, 0, countof(classic_data));
+	suite_add_tcase(s, tc);
+
+	return s;
+}

src/libstrongswan/tests/tests.h

@@ -49,9 +49,9 @@ TEST_SUITE(asn1_parser_suite_create)
 TEST_SUITE(rng_tester_suite_create)
 TEST_SUITE_DEPEND(mgf1_sha1_suite_create, XOF, XOF_MGF1_SHA1)
 TEST_SUITE_DEPEND(mgf1_sha256_suite_create, XOF, XOF_MGF1_SHA256)
+TEST_SUITE_DEPEND(prf_plus_suite_create, PRF, PRF_HMAC_SHA2_256)
 TEST_SUITE_DEPEND(ntru_suite_create, DH, NTRU_112_BIT)
 TEST_SUITE_DEPEND(fetch_http_suite_create, FETCHER, "http://")
 TEST_SUITE_DEPEND(ed25519_suite_create, PRIVKEY_GEN, KEY_ED25519)
 TEST_SUITE_DEPEND(ed448_suite_create, PRIVKEY_GEN, KEY_ED448)
 TEST_SUITE(signature_params_suite_create)
-