Unify duplicate code in xsalsa20-poly1305 and aes128-gcm methods

5 files changed, 229 insertions, 194 deletions

diff --git a/src/methods/CMakeLists.txt b/src/methods/CMakeLists.txt
index 55f41d2..3ef410b 100644
--- a/src/methods/CMakeLists.txt
+++ b/src/methods/CMakeLists.txt
@@ -1,19 +1,26 @@
 set(METHODS null)
+set(METHOD_COMMON FALSE)
 
 if(WITH_METHOD_XSALSA20_POLY1305)
   list(APPEND METHODS xsalsa20_poly1305)
+  set(METHOD_COMMON TRUE)
 endif(WITH_METHOD_XSALSA20_POLY1305)
 
 if(WITH_METHOD_AES128_GCM)
   list(APPEND METHODS aes128_gcm)
+  set(METHOD_COMMON TRUE)
 endif(WITH_METHOD_AES128_GCM)
 
 
-set(METHOD_OBJECTS "")
+set(METHOD_SOURCES "")
 
 foreach(method ${METHODS})
   add_subdirectory(${method})
-  list(APPEND METHOD_OBJECTS $<TARGET_OBJECTS:method_${method}>)
+  list(APPEND METHOD_SOURCES $<TARGET_OBJECTS:method_${method}>)
 endforeach(method)
 
-set(METHOD_OBJECTS "${METHOD_OBJECTS}" PARENT_SCOPE)
+if(METHOD_COMMON)
+  list(APPEND METHOD_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/common.c)
+endif(METHOD_COMMON)
+
+set(METHOD_SOURCES "${METHOD_SOURCES}" PARENT_SCOPE)
diff --git a/src/methods/aes128_gcm/aes128_gcm.c b/src/methods/aes128_gcm/aes128_gcm.c
index 46dba5c..610df7c 100644
--- a/src/methods/aes128_gcm/aes128_gcm.c
+++ b/src/methods/aes128_gcm/aes128_gcm.c
@@ -26,57 +26,21 @@
 
 #include <fastd.h>
 #include <crypto.h>
+#include "../common.h"
 
 
 #define KEYBYTES 16
-#define NONCEBYTES 7
 
 struct fastd_method_session_state {
-	struct timespec valid_till;
-	struct timespec refresh_after;
-
-	uint8_t send_nonce[NONCEBYTES];
-	uint8_t receive_nonce[NONCEBYTES];
-
-	struct timespec receive_last;
-	uint64_t receive_reorder_seen;
+	fastd_method_common_t common;
 
 	fastd_crypto_aes128ctr_state_t *cstate_aes128ctr;
 	fastd_crypto_ghash_state_t *cstate_ghash;
 };
 
 
-static inline void increment_nonce(uint8_t nonce[NONCEBYTES]) {
-	nonce[0] += 2;
-
-	if (nonce[0] == 0 || nonce[0] == 1) {
-		int i;
-		for (i = 1; i < NONCEBYTES; i++) {
-			nonce[i]++;
-			if (nonce[i] != 0)
-				break;
-		}
-	}
-}
-
-static inline bool is_nonce_valid(const uint8_t nonce[NONCEBYTES], const uint8_t old_nonce[NONCEBYTES], int64_t *age) {
-	if ((nonce[0] & 1) != (old_nonce[0] & 1))
-		return false;
-
-	int i;
-	*age = 0;
-
-	for (i = NONCEBYTES-1; i >= 0; i--) {
-		*age *= 256;
-		*age += old_nonce[i]-nonce[i];
-	}
-
-	*age /= 2;
-	return true;
-}
-
 static size_t method_max_packet_size(fastd_context_t *ctx) {
-	return (fastd_max_packet_size(ctx) + NONCEBYTES + sizeof(fastd_block128_t));
+	return (fastd_max_packet_size(ctx) + COMMON_NONCEBYTES + sizeof(fastd_block128_t));
 }
 
 
@@ -98,18 +62,12 @@ static size_t method_min_decrypt_tail_space(fastd_context_t *ctx UNUSED) {
 
 
 static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, uint8_t *secret, size_t length, bool initiator) {
-	int i;
-
 	if (length < KEYBYTES)
 		exit_bug(ctx, "aes128-gcm: tried to init with short secret");
 
 	fastd_method_session_state_t *session = malloc(sizeof(fastd_method_session_state_t));
 
-	session->valid_till = ctx->now;
-	session->valid_till.tv_sec += ctx->conf->key_valid;
-
-	session->refresh_after = ctx->now;
-	session->refresh_after.tv_sec += ctx->conf->key_refresh - fastd_rand(ctx, 0, ctx->conf->key_refresh_splay);
+	fastd_method_common_init(ctx, &session->common, initiator);
 
 	fastd_block128_t key;
 	memcpy(key.b, secret, sizeof(fastd_block128_t));
@@ -122,39 +80,27 @@ static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, u
 
 	session->cstate_ghash = ctx->conf->crypto_ghash->set_h(ctx, ctx->crypto_ghash, &H);
 
-	session->send_nonce[0] = initiator ? 3 : 2;
-	session->receive_nonce[0] = initiator ? 0 : 1;
-
-	for (i = 1; i < NONCEBYTES; i++) {
-		session->send_nonce[i] = 0;
-		session->receive_nonce[i] = 0;
-	}
-
 	return session;
 }
 
 static bool method_session_is_valid(fastd_context_t *ctx, fastd_method_session_state_t *session) {
-	return (session && timespec_after(&session->valid_till, &ctx->now));
+	return (session && fastd_method_session_common_is_valid(ctx, &session->common));
 }
 
 static bool method_session_is_initiator(fastd_context_t *ctx UNUSED, fastd_method_session_state_t *session) {
-	return (session->send_nonce[0] & 1);
+	return fastd_method_session_common_is_initiator(&session->common);
 }
 
 static bool method_session_want_refresh(fastd_context_t *ctx, fastd_method_session_state_t *session) {
-	return timespec_after(&ctx->now, &session->refresh_after);
+	return fastd_method_session_common_want_refresh(ctx, &session->common);
 }
 
 static void method_session_superseded(fastd_context_t *ctx, fastd_method_session_state_t *session) {
-	struct timespec valid_max = ctx->now;
-	valid_max.tv_sec += ctx->conf->key_valid_old;
-
-	if (timespec_after(&session->valid_till, &valid_max))
-		session->valid_till = valid_max;
+	fastd_method_session_common_superseded(ctx, &session->common);
 }
 
 static void method_session_free(fastd_context_t *ctx, fastd_method_session_state_t *session) {
-	if(session) {
+	if (session) {
 		ctx->conf->crypto_aes128ctr->free_state(ctx, session->cstate_aes128ctr);
 		ctx->conf->crypto_ghash->free_state(ctx, session->cstate_ghash);
 
@@ -177,14 +123,14 @@ static bool method_encrypt(fastd_context_t *ctx, fastd_peer_t *peer UNUSED, fast
 	memset(in.data, 0, sizeof(fastd_block128_t));
 
 	size_t tail_len = alignto(in.len, sizeof(fastd_block128_t))-in.len;
-	*out = fastd_buffer_alloc(ctx, in.len, alignto(NONCEBYTES, 16), sizeof(fastd_block128_t)+tail_len);
+	*out = fastd_buffer_alloc(ctx, in.len, alignto(COMMON_NONCEBYTES, 16), sizeof(fastd_block128_t)+tail_len);
 
 	if (tail_len)
 		memset(in.data+in.len, 0, tail_len);
 
 	fastd_block128_t nonce;
-	memcpy(nonce.b, session->send_nonce, NONCEBYTES);
-	memset(nonce.b+NONCEBYTES, 0, sizeof(fastd_block128_t)-NONCEBYTES-1);
+	memcpy(nonce.b, session->common.send_nonce, COMMON_NONCEBYTES);
+	memset(nonce.b+COMMON_NONCEBYTES, 0, sizeof(fastd_block128_t)-COMMON_NONCEBYTES-1);
 	nonce.b[sizeof(fastd_block128_t)-1] = 1;
 
 	int n_blocks = (in.len+sizeof(fastd_block128_t)-1)/sizeof(fastd_block128_t);
@@ -215,38 +161,30 @@ static bool method_encrypt(fastd_context_t *ctx, fastd_peer_t *peer UNUSED, fast
 
 	fastd_buffer_free(in);
 
-	fastd_buffer_pull_head(ctx, out, NONCEBYTES);
-	memcpy(out->data, session->send_nonce, NONCEBYTES);
-	increment_nonce(session->send_nonce);
+	fastd_buffer_pull_head(ctx, out, COMMON_NONCEBYTES);
+	memcpy(out->data, session->common.send_nonce, COMMON_NONCEBYTES);
+	fastd_method_increment_nonce(&session->common);
 
 	return true;
 }
 
 static bool method_decrypt(fastd_context_t *ctx, fastd_peer_t *peer, fastd_method_session_state_t *session, fastd_buffer_t *out, fastd_buffer_t in) {
-	if (in.len < NONCEBYTES+sizeof(fastd_block128_t))
+	if (in.len < COMMON_NONCEBYTES+sizeof(fastd_block128_t))
 		return false;
 
 	if (!method_session_is_valid(ctx, session))
 		return false;
 
 	fastd_block128_t nonce;
-	memcpy(nonce.b, in.data, NONCEBYTES);
-	memset(nonce.b+NONCEBYTES, 0, sizeof(fastd_block128_t)-NONCEBYTES-1);
+	memcpy(nonce.b, in.data, COMMON_NONCEBYTES);
+	memset(nonce.b+COMMON_NONCEBYTES, 0, sizeof(fastd_block128_t)-COMMON_NONCEBYTES-1);
 	nonce.b[sizeof(fastd_block128_t)-1] = 1;
 
 	int64_t age;
-	if (!is_nonce_valid(nonce.b, session->receive_nonce, &age))
+	if (!fastd_method_is_nonce_valid(ctx, &session->common, nonce.b, &age))
 		return false;
 
-	if (age >= 0) {
-		if (timespec_diff(&ctx->now, &session->receive_last) > (int)ctx->conf->reorder_time*1000)
-			return false;
-
-		if (age > ctx->conf->reorder_count)
-			return false;
-	}
-
-	fastd_buffer_push_head(ctx, &in, NONCEBYTES);
+	fastd_buffer_push_head(ctx, &in, COMMON_NONCEBYTES);
 
 	size_t tail_len = alignto(in.len, sizeof(fastd_block128_t))-in.len;
 	*out = fastd_buffer_alloc(ctx, in.len, 0, tail_len);
@@ -277,21 +215,10 @@ static bool method_decrypt(fastd_context_t *ctx, fastd_peer_t *peer, fastd_metho
 
 	fastd_buffer_push_head(ctx, out, sizeof(fastd_block128_t));
 
-	if (age < 0) {
-		session->receive_reorder_seen >>= age;
-		session->receive_reorder_seen |= (1 >> (age+1));
-		memcpy(session->receive_nonce, nonce.b, NONCEBYTES);
-		session->receive_last = ctx->now;
-	}
-	else if (age == 0 || session->receive_reorder_seen & (1 << (age-1))) {
-		pr_debug(ctx, "dropping duplicate packet from %P (age %u)", peer, (unsigned)age);
+	if (!fastd_method_reorder_check(ctx, peer, &session->common, nonce.b, age)) {
 		fastd_buffer_free(*out);
 		*out = fastd_buffer_alloc(ctx, 0, 0, 0);
 	}
-	else {
-		pr_debug2(ctx, "accepting reordered packet from %P (age %u)", peer, (unsigned)age);
-		session->receive_reorder_seen |= (1 << (age-1));
-	}
 
 	return true;
 }
diff --git a/src/methods/common.c b/src/methods/common.c
new file mode 100644
index 0000000..7c67253
--- /dev/null
+++ b/src/methods/common.c
@@ -0,0 +1,90 @@
+/*
+  Copyright (c) 2012-2013, Matthias Schiffer <mschiffer@universe-factory.net>
+  All rights reserved.
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+
+    1. Redistributions of source code must retain the above copyright notice,
+       this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright notice,
+       this list of conditions and the following disclaimer in the documentation
+       and/or other materials provided with the distribution.
+
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+
+#include "common.h"
+
+
+void fastd_method_common_init(fastd_context_t *ctx, fastd_method_common_t *session, bool initiator) {
+	memset(session, 0, sizeof(*session));
+
+	session->valid_till = ctx->now;
+	session->valid_till.tv_sec += ctx->conf->key_valid;
+
+	session->refresh_after = ctx->now;
+	session->refresh_after.tv_sec += ctx->conf->key_refresh - fastd_rand(ctx, 0, ctx->conf->key_refresh_splay);
+
+	if (initiator) {
+		session->send_nonce[0] = 3;
+	}
+	else {
+		session->send_nonce[0] = 2;
+		session->receive_nonce[0] = 1;
+	}
+}
+
+bool fastd_method_is_nonce_valid(fastd_context_t *ctx, const fastd_method_common_t *session, const uint8_t nonce[COMMON_NONCEBYTES], int64_t *age) {
+	if ((nonce[0] & 1) != (session->receive_nonce[0] & 1))
+		return false;
+
+	int i;
+	*age = 0;
+
+	for (i = COMMON_NONCEBYTES-1; i >= 0; i--) {
+		*age *= 256;
+		*age += session->receive_nonce[i]-nonce[i];
+	}
+
+	*age /= 2;
+
+	if (*age >= 0) {
+		if (timespec_diff(&ctx->now, &session->receive_last) > (int)ctx->conf->reorder_time*1000)
+			return false;
+
+		if (*age > ctx->conf->reorder_count)
+			return false;
+	}
+
+	return true;
+}
+
+bool fastd_method_reorder_check(fastd_context_t *ctx, fastd_peer_t *peer, fastd_method_common_t *session, const uint8_t nonce[COMMON_NONCEBYTES], int64_t age) {
+	if (age < 0) {
+		session->receive_reorder_seen >>= age;
+		session->receive_reorder_seen |= (1 >> (age+1));
+		memcpy(session->receive_nonce, nonce, COMMON_NONCEBYTES);
+		session->receive_last = ctx->now;
+		return true;
+	}
+	else if (age == 0 || session->receive_reorder_seen & (1 << (age-1))) {
+		pr_debug(ctx, "dropping duplicate packet from %P (age %u)", peer, (unsigned)age);
+		return false;
+	}
+	else {
+		pr_debug2(ctx, "accepting reordered packet from %P (age %u)", peer, (unsigned)age);
+		session->receive_reorder_seen |= (1 << (age-1));
+		return true;
+	}
+}
diff --git a/src/methods/common.h b/src/methods/common.h
new file mode 100644
index 0000000..0337265
--- /dev/null
+++ b/src/methods/common.h
@@ -0,0 +1,86 @@
+/*
+  Copyright (c) 2012-2013, Matthias Schiffer <mschiffer@universe-factory.net>
+  All rights reserved.
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+
+    1. Redistributions of source code must retain the above copyright notice,
+       this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright notice,
+       this list of conditions and the following disclaimer in the documentation
+       and/or other materials provided with the distribution.
+
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+
+#ifndef _FASTD_METHODS_COMMON_H_
+#define _FASTD_METHODS_COMMON_H_
+
+#include <fastd.h>
+
+
+#define COMMON_NONCEBYTES 7
+
+
+typedef struct fastd_method_common {
+	struct timespec valid_till;
+	struct timespec refresh_after;
+
+	uint8_t send_nonce[COMMON_NONCEBYTES];
+	uint8_t receive_nonce[COMMON_NONCEBYTES];
+
+	struct timespec receive_last;
+	uint64_t receive_reorder_seen;
+} fastd_method_common_t;
+
+
+void fastd_method_common_init(fastd_context_t *ctx, fastd_method_common_t *session, bool initiator);
+bool fastd_method_is_nonce_valid(fastd_context_t *ctx, const fastd_method_common_t *session, const uint8_t nonce[COMMON_NONCEBYTES], int64_t *age);
+bool fastd_method_reorder_check(fastd_context_t *ctx, fastd_peer_t *peer, fastd_method_common_t *session, const uint8_t nonce[COMMON_NONCEBYTES], int64_t age);
+
+
+static inline bool fastd_method_session_common_is_valid(fastd_context_t *ctx, const fastd_method_common_t *session) {
+	return (timespec_after(&session->valid_till, &ctx->now));
+}
+
+static inline bool fastd_method_session_common_is_initiator(const fastd_method_common_t *session) {
+	return (session->send_nonce[0] & 1);
+}
+
+static inline bool fastd_method_session_common_want_refresh(fastd_context_t *ctx, const fastd_method_common_t *session) {
+	return timespec_after(&ctx->now, &session->refresh_after);
+}
+
+static inline void fastd_method_session_common_superseded(fastd_context_t *ctx, fastd_method_common_t *session) {
+	struct timespec valid_max = ctx->now;
+	valid_max.tv_sec += ctx->conf->key_valid_old;
+
+	if (timespec_after(&session->valid_till, &valid_max))
+		session->valid_till = valid_max;
+}
+
+static inline void fastd_method_increment_nonce(fastd_method_common_t *session) {
+	session->send_nonce[0] += 2;
+
+	if (session->send_nonce[0] == 0 || session->send_nonce[0] == 1) {
+		int i;
+		for (i = 1; i < COMMON_NONCEBYTES; i++) {
+			session->send_nonce[i]++;
+			if (session->send_nonce[i] != 0)
+				break;
+		}
+	}
+}
+
+#endif /* _FASTD_METHODS_COMMON_H_ */
diff --git a/src/methods/xsalsa20_poly1305/xsalsa20_poly1305.c b/src/methods/xsalsa20_poly1305/xsalsa20_poly1305.c
index d891aa5..0a9f2c8 100644
--- a/src/methods/xsalsa20_poly1305/xsalsa20_poly1305.c
+++ b/src/methods/xsalsa20_poly1305/xsalsa20_poly1305.c
@@ -25,58 +25,20 @@
 
 
 #include <fastd.h>
+#include "../common.h"
 
 #include <crypto_secretbox_xsalsa20poly1305.h>
 
 
-#define NONCEBYTES 7
-
-
 struct fastd_method_session_state {
-	struct timespec valid_till;
-	struct timespec refresh_after;
+	fastd_method_common_t common;
 
 	uint8_t key[crypto_secretbox_xsalsa20poly1305_KEYBYTES];
-
-	uint8_t send_nonce[NONCEBYTES];
-	uint8_t receive_nonce[NONCEBYTES];
-
-	struct timespec receive_last;
-	uint64_t receive_reorder_seen;
 };
 
 
-static inline void increment_nonce(uint8_t nonce[NONCEBYTES]) {
-	nonce[0] += 2;
-
-	if (nonce[0] == 0 || nonce[0] == 1) {
-		int i;
-		for (i = 1; i < NONCEBYTES; i++) {
-			nonce[i]++;
-			if (nonce[i] != 0)
-				break;
-		}
-	}
-}
-
-static inline bool is_nonce_valid(const uint8_t nonce[NONCEBYTES], const uint8_t old_nonce[NONCEBYTES], int64_t *age) {
-	if ((nonce[0] & 1) != (old_nonce[0] & 1))
-		return false;
-
-	int i;
-	*age = 0;
-
-	for (i = NONCEBYTES-1; i >= 0; i--) {
-		*age *= 256;
-		*age += old_nonce[i]-nonce[i];
-	}
-
-	*age /= 2;
-	return true;
-}
-
 static size_t method_max_packet_size(fastd_context_t *ctx) {
-	return (fastd_max_packet_size(ctx) + NONCEBYTES + crypto_secretbox_xsalsa20poly1305_ZEROBYTES - crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES);
+	return (fastd_max_packet_size(ctx) + COMMON_NONCEBYTES + crypto_secretbox_xsalsa20poly1305_ZEROBYTES - crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES);
 }
 
 static size_t method_min_encrypt_head_space(fastd_context_t *ctx UNUSED) {
@@ -84,7 +46,7 @@ static size_t method_min_encrypt_head_space(fastd_context_t *ctx UNUSED) {
 }
 
 static size_t method_min_decrypt_head_space(fastd_context_t *ctx UNUSED) {
-	return (crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES - NONCEBYTES);
+	return (crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES - COMMON_NONCEBYTES);
 }
 
 static size_t method_min_tail_space(fastd_context_t *ctx UNUSED) {
@@ -92,50 +54,32 @@ static size_t method_min_tail_space(fastd_context_t *ctx UNUSED) {
 }
 
 static fastd_method_session_state_t* method_session_init(fastd_context_t *ctx, uint8_t *secret, size_t length, bool initiator) {
-	int i;
-
 	if (length < crypto_secretbox_xsalsa20poly1305_KEYBYTES)
 		exit_bug(ctx, "xsalsa20-poly1305: tried to init with short secret");
 
 	fastd_method_session_state_t *session = malloc(sizeof(fastd_method_session_state_t));
 
-	session->valid_till = ctx->now;
-	session->valid_till.tv_sec += ctx->conf->key_valid;
-
-	session->refresh_after = ctx->now;
-	session->refresh_after.tv_sec += ctx->conf->key_refresh - fastd_rand(ctx, 0, ctx->conf->key_refresh_splay);
+	fastd_method_common_init(ctx, &session->common, initiator);
 
 	memcpy(session->key, secret, crypto_secretbox_xsalsa20poly1305_KEYBYTES);
 
-	session->send_nonce[0] = initiator ? 3 : 2;
-	session->receive_nonce[0] = initiator ? 0 : 1;
-
-	for (i = 1; i < NONCEBYTES; i++) {
-		session->send_nonce[i] = 0;
-		session->receive_nonce[i] = 0;
-	}
-
 	return session;
 }
 
 static bool method_session_is_valid(fastd_context_t *ctx, fastd_method_session_state_t *session) {
-	return (session && timespec_after(&session->valid_till, &ctx->now));
+	return (session && fastd_method_session_common_is_valid(ctx, &session->common));
 }
 
 static bool method_session_is_initiator(fastd_context_t *ctx UNUSED, fastd_method_session_state_t *session) {
-	return (session->send_nonce[0] & 1);
+	return fastd_method_session_common_is_initiator(&session->common);
 }
 
 static bool method_session_want_refresh(fastd_context_t *ctx, fastd_method_session_state_t *session) {
-	return timespec_after(&ctx->now, &session->refresh_after);
+	return fastd_method_session_common_want_refresh(ctx, &session->common);
 }
 
 static void method_session_superseded(fastd_context_t *ctx, fastd_method_session_state_t *session) {
-	struct timespec valid_max = ctx->now;
-	valid_max.tv_sec += ctx->conf->key_valid_old;
-
-	if (timespec_after(&session->valid_till, &valid_max))
-		session->valid_till = valid_max;
+	fastd_method_session_common_superseded(ctx, &session->common);
 }
 
 static void method_session_free(fastd_context_t *ctx UNUSED, fastd_method_session_state_t *session) {
@@ -152,45 +96,37 @@ static bool method_encrypt(fastd_context_t *ctx, fastd_peer_t *peer UNUSED, fast
 	*out = fastd_buffer_alloc(ctx, in.len, 0, 0);
 
 	uint8_t nonce[crypto_secretbox_xsalsa20poly1305_NONCEBYTES];
-	memcpy(nonce, session->send_nonce, NONCEBYTES);
-	memset(nonce+NONCEBYTES, 0, crypto_secretbox_xsalsa20poly1305_NONCEBYTES-NONCEBYTES);
+	memcpy(nonce, session->common.send_nonce, COMMON_NONCEBYTES);
+	memset(nonce+COMMON_NONCEBYTES, 0, crypto_secretbox_xsalsa20poly1305_NONCEBYTES-COMMON_NONCEBYTES);
 
 	crypto_secretbox_xsalsa20poly1305(out->data, in.data, in.len, nonce, session->key);
 
 	fastd_buffer_free(in);
 
-	fastd_buffer_push_head(ctx, out, crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES-NONCEBYTES);
-	memcpy(out->data, session->send_nonce, NONCEBYTES);
+	fastd_buffer_push_head(ctx, out, crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES-COMMON_NONCEBYTES);
+	memcpy(out->data, session->common.send_nonce, COMMON_NONCEBYTES);
 
-	increment_nonce(session->send_nonce);
+	fastd_method_increment_nonce(&session->common);
 
 	return true;
 }
 
 static bool method_decrypt(fastd_context_t *ctx, fastd_peer_t *peer, fastd_method_session_state_t *session, fastd_buffer_t *out, fastd_buffer_t in) {
-	if (in.len < NONCEBYTES)
+	if (in.len < COMMON_NONCEBYTES)
 		return false;
 
 	if (!method_session_is_valid(ctx, session))
 		return false;
 
 	uint8_t nonce[crypto_secretbox_xsalsa20poly1305_NONCEBYTES];
-	memcpy(nonce, in.data, NONCEBYTES);
-	memset(nonce+NONCEBYTES, 0, crypto_secretbox_xsalsa20poly1305_NONCEBYTES-NONCEBYTES);
+	memcpy(nonce, in.data, COMMON_NONCEBYTES);
+	memset(nonce+COMMON_NONCEBYTES, 0, crypto_secretbox_xsalsa20poly1305_NONCEBYTES-COMMON_NONCEBYTES);
 
 	int64_t age;
-	if (!is_nonce_valid(nonce, session->receive_nonce, &age))
+	if (!fastd_method_is_nonce_valid(ctx, &session->common, nonce, &age))
 		return false;
 
-	if (age >= 0) {
-		if (timespec_diff(&ctx->now, &session->receive_last) > (int)ctx->conf->reorder_time*1000)
-			return false;
-
-		if (age > ctx->conf->reorder_count)
-			return false;
-	}
-
-	fastd_buffer_pull_head(ctx, &in, crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES-NONCEBYTES);
+	fastd_buffer_pull_head(ctx, &in, crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES-COMMON_NONCEBYTES);
 	memset(in.data, 0, crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES);
 
 	*out = fastd_buffer_alloc(ctx, in.len, 0, 0);
@@ -199,28 +135,17 @@ static bool method_decrypt(fastd_context_t *ctx, fastd_peer_t *peer, fastd_metho
 		fastd_buffer_free(*out);
 
 		/* restore input buffer */
-		fastd_buffer_push_head(ctx, &in, crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES-NONCEBYTES);
-		memcpy(in.data, nonce, NONCEBYTES);
+		fastd_buffer_push_head(ctx, &in, crypto_secretbox_xsalsa20poly1305_BOXZEROBYTES-COMMON_NONCEBYTES);
+		memcpy(in.data, nonce, COMMON_NONCEBYTES);
 		return false;
 	}
 
 	fastd_buffer_free(in);
 
-	if (age < 0) {
-		session->receive_reorder_seen >>= age;
-		session->receive_reorder_seen |= (1 >> (age+1));
-		memcpy(session->receive_nonce, nonce, NONCEBYTES);
-		session->receive_last = ctx->now;
-	}
-	else if (age == 0 || session->receive_reorder_seen & (1 << (age-1))) {
-		pr_debug(ctx, "dropping duplicate packet from %P (age %u)", peer, (unsigned)age);
+	if (!fastd_method_reorder_check(ctx, peer, &session->common, nonce, age)) {
 		fastd_buffer_free(*out);
 		*out = fastd_buffer_alloc(ctx, crypto_secretbox_xsalsa20poly1305_ZEROBYTES, 0, 0);
 	}
-	else {
-		pr_debug2(ctx, "accepting reordered packet from %P (age %u)", peer, (unsigned)age);
-		session->receive_reorder_seen |= (1 << (age-1));
-	}
 
 	fastd_buffer_push_head(ctx, out, crypto_secretbox_xsalsa20poly1305_ZEROBYTES);