Initial implementation of the FHMQV-C handshake

1 files changed, 492 insertions, 13 deletions

diff --git a/src/protocol_ec25519_fhmqvc_xsalsa20_poly1305.c b/src/protocol_ec25519_fhmqvc_xsalsa20_poly1305.c
index 4152601..c729428 100644
--- a/src/protocol_ec25519_fhmqvc_xsalsa20_poly1305.c
+++ b/src/protocol_ec25519_fhmqvc_xsalsa20_poly1305.c
@@ -29,34 +29,165 @@
 
 #include "fastd.h"
 #include "peer.h"
+#include "task.h"
 
 #include <arpa/inet.h>
 
 #include <libuecc/ecc.h>
+#include <crypto_auth_hmacsha256.h>
+#include <crypto_hash_sha256.h>
 #include <crypto_secretbox_xsalsa20poly1305.h>
 
 
-typedef struct _protocol_context {
-	ecc_secret_key_256 secret_key;
-} protocol_context;
+#define NONCEBYTES crypto_secretbox_xsalsa20poly1305_NONCEBYTES
+#define PUBLICKEYBYTES 32
+#define SECRETKEYBYTES 32
+#define HMACBYTES crypto_auth_hmacsha256_BYTES
+#define HASHBYTES crypto_hash_sha256_BYTES
+
+
+#if HASHBYTES != crypto_auth_hmacsha256_KEYBYTES
+#error bug: HASHBYTES != crypto_auth_hmacsha256_KEYBYTES
+#endif
+
+#if HASHBYTES != crypto_secretbox_xsalsa20poly1305_KEYBYTES
+#error bug: HASHBYTES != crypto_secretbox_xsalsa20poly1305_KEYBYTES
+#endif
+
+#if HASHBYTES != SECRETKEYBYTES
+#error bug: HASHBYTES != SECRETKEYBYTES
+#endif
 
-typedef struct _protocol_peer_config {
+
+struct _fastd_protocol_context {
+	ecc_secret_key_256 secret_key;
 	ecc_public_key_256 public_key;
-} protocol_peer_config;
+};
+
+typedef enum _handshake_state {
+	HANDSHAKE_STATE_INIT = 0,
+	HANDSHAKE_STATE_RESPONSE,
+	HANDSHAKE_STATE_FINISH,
+	HANDSHAKE_STATE_ESTABLISHED
+} handshake_state;
+
+struct _fastd_protocol_peer_state {
+	ecc_public_key_256 peer_public_key;
+
+	handshake_state state;
+	ecc_secret_key_256 handshake_secret_key;
+	ecc_public_key_256 handshake_public_key;
+	ecc_public_key_256 peer_handshake_key;
+	ecc_public_key_256 sigma;
+
+	uint8_t shared_handshake_key[HASHBYTES];
+	uint8_t shared_session_key[HASHBYTES];
+	uint8_t send_nonce[NONCEBYTES];
+	uint8_t receive_nonce[NONCEBYTES];
+};
 
-typedef struct _protocol_peer_state {
-} protocol_peer_state;
+typedef enum _handshake_packet_type {
+	HANDSHAKE_PACKET_INIT = 0,
+	HANDSHAKE_PACKET_RESPONSE,
+	HANDSHAKE_PACKET_FINISH
+} handshake_packet_type;
+
+typedef struct __attribute__ ((__packed__)) _protocol_handshake_init_packet {
+	uint8_t noncepad[NONCEBYTES];
+	uint8_t type;
+
+	uint8_t sender_key[PUBLICKEYBYTES];
+	uint8_t receipient_key[PUBLICKEYBYTES];
+	uint8_t handshake_key[PUBLICKEYBYTES];
+} protocol_handshake_init_packet;
+
+typedef struct __attribute__ ((__packed__)) _protocol_handshake_response_finish_packet {
+	uint8_t noncepad[NONCEBYTES];
+	uint8_t type;
+
+	uint8_t sender_key[PUBLICKEYBYTES];
+	uint8_t receipient_key[PUBLICKEYBYTES];
+	uint8_t handshake_key[PUBLICKEYBYTES];
+	uint8_t handshake_key2[PUBLICKEYBYTES];
+	uint8_t t[HMACBYTES];
+} protocol_handshake_response_packet, protocol_handshake_finish_packet;
+
+typedef union _protocol_handshake_packet {
+	struct {
+		uint8_t noncepad[NONCEBYTES];
+		uint8_t type;
+	};
+	protocol_handshake_init_packet init;
+	protocol_handshake_response_packet response;
+	protocol_handshake_finish_packet finish;
+} protocol_handshake_packet;
+
+
+static inline bool read_key(uint8_t key[32], const char *hexkey) {
+	if ((strlen(hexkey) != 64) || (strspn(hexkey, "0123456789abcdefABCDEF") != 64))
+		return false;
+
+	int i;
+	for (i = 0; i < 32; i++)
+		sscanf(&hexkey[2*i], "%02hhx", &key[i]);
 
+	return true;
+}
+
+static inline bool is_nonce_zero(const uint8_t nonce[NONCEBYTES]) {
+	int i;
+	for (i = 0; i < NONCEBYTES; i++) {
+		if (nonce[i] != 0)
+			return false;
+	}
 
-static bool protocol_check_config(fastd_context *ctx, const fastd_config *conf) {
 	return true;
 }
 
+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]) {
+	if ((nonce[0] & 1) != (old_nonce[0] & 1))
+		return false;
+
+	int i;
+	for (i = NONCEBYTES-1; i >= 0; i--) {
+		if (nonce[i] > old_nonce[i])
+			return true;
+		if (nonce[i] < old_nonce[i])
+			return false;
+	}
+
+	return false;
+}
+
 static void protocol_init(fastd_context *ctx) {
+	ctx->protocol_context = malloc(sizeof(fastd_protocol_context));
+
+	if (!ctx->conf->secret)
+		exit_error(ctx, "no secret key configured");
+
+	if (!read_key(ctx->protocol_context->secret_key.s, ctx->conf->secret))
+		exit_error(ctx, "invalid secret key");
+
+	ecc_25519_work work;
+	ecc_25519_scalarmult_base(&work, &ctx->protocol_context->secret_key);
+	ecc_25519_store(&ctx->protocol_context->public_key, &work);
 }
 
 static size_t protocol_max_packet_size(fastd_context *ctx) {
-	return (fastd_max_packet_size(ctx) - crypto_secretbox_xsalsa20poly1305_NONCEBYTES);
+	return (fastd_max_packet_size(ctx) - NONCEBYTES);
 }
 
 static char* protocol_peer_str(const fastd_context *ctx, const fastd_peer *peer) {
@@ -92,11 +223,360 @@ static char* protocol_peer_str(const fastd_context *ctx, const fastd_peer *peer)
 	return NULL;
 }
 
+static bool create_peer_state(fastd_context *ctx, fastd_peer *peer) {
+	peer->protocol_state = malloc(sizeof(fastd_protocol_peer_state));
+
+	if (!peer->config->key) {
+		pr_warn(ctx, "no public key configured - ignoring peer %P", peer);
+		return false;
+	}
+
+	if (!read_key(peer->protocol_state->peer_public_key.p, peer->config->key)) {
+		pr_warn(ctx, "invalid public key configured - ignoring peer %P", peer);
+		return false;
+	}
+
+	peer->protocol_state->state = HANDSHAKE_STATE_INIT;
+
+	return true;
+}
+
 static void protocol_init_peer(fastd_context *ctx, fastd_peer *peer) {
 	pr_info(ctx, "Initializing session with %P...", peer);
+
+	if (peer->protocol_state) {
+		pr_warn(ctx, "trying to reinitialize session with %P", peer);
+		return;
+	}
+
+	if (!create_peer_state(ctx, peer))
+		return; /* TODO disable peer */
+
+	fastd_random_bytes(ctx, peer->protocol_state->handshake_secret_key.s, 32, false);
+	ecc_25519_secret_sanitize(&peer->protocol_state->handshake_secret_key, &peer->protocol_state->handshake_secret_key);
+
+	ecc_25519_work work;
+	ecc_25519_scalarmult_base(&work, &peer->protocol_state->handshake_secret_key);
+	ecc_25519_store(&peer->protocol_state->handshake_public_key, &work);
+
+	fastd_buffer buffer = fastd_buffer_alloc(sizeof(protocol_handshake_init_packet), 0, 0);
+	protocol_handshake_init_packet *packet = buffer.data;
+
+	memset(packet->noncepad, 0, NONCEBYTES);
+	packet->type = HANDSHAKE_PACKET_INIT;
+	memcpy(packet->sender_key, ctx->protocol_context->public_key.p, PUBLICKEYBYTES);
+	memcpy(packet->receipient_key, peer->protocol_state->peer_public_key.p, PUBLICKEYBYTES);
+	memcpy(packet->handshake_key, peer->protocol_state->handshake_public_key.p, PUBLICKEYBYTES);
+
+	fastd_task_put_send(ctx, peer, buffer);
+}
+
+static void respond_handshake(fastd_context *ctx, fastd_peer *peer) {
+	pr_info(ctx, "Responding protocol handshake with %P...", peer);
+
+	fastd_random_bytes(ctx, peer->protocol_state->handshake_secret_key.s, 32, false);
+	ecc_25519_secret_sanitize(&peer->protocol_state->handshake_secret_key, &peer->protocol_state->handshake_secret_key);
+
+	ecc_25519_work work;
+	ecc_25519_scalarmult_base(&work, &peer->protocol_state->handshake_secret_key);
+	ecc_25519_store(&peer->protocol_state->handshake_public_key, &work);
+
+	uint8_t hashinput[5*PUBLICKEYBYTES];
+	uint8_t hashbuf[HASHBYTES];
+
+	memcpy(hashinput, peer->protocol_state->handshake_public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+PUBLICKEYBYTES, peer->protocol_state->peer_handshake_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+2*PUBLICKEYBYTES, ctx->protocol_context->public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+3*PUBLICKEYBYTES, peer->protocol_state->peer_public_key.p, PUBLICKEYBYTES);
+
+	crypto_hash_sha256(hashbuf, hashinput, 4*PUBLICKEYBYTES);
+
+	ecc_secret_key_256 d = {{0}}, e = {{0}}, eb, s;
+
+	memcpy(d.s, hashbuf, HASHBYTES/2);
+	memcpy(e.s, hashbuf+HASHBYTES/2, HASHBYTES/2);
+
+	d.s[15] |= 0x80;
+	e.s[15] |= 0x80;
+
+	ecc_25519_secret_mult(&eb, &e, &ctx->protocol_context->secret_key);
+	ecc_25519_secret_add(&s, &eb, &peer->protocol_state->handshake_secret_key);
+
+	ecc_25519_work workX;
+	ecc_25519_load(&work, &peer->protocol_state->peer_public_key);
+	ecc_25519_load(&workX, &peer->protocol_state->peer_handshake_key);
+
+	ecc_25519_scalarmult(&work, &d, &work);
+	ecc_25519_add(&work, &workX, &work);
+	ecc_25519_scalarmult(&work, &s, &work);
+
+	ecc_25519_store(&peer->protocol_state->sigma, &work);
+
+	memcpy(hashinput+4*PUBLICKEYBYTES, peer->protocol_state->sigma.p, PUBLICKEYBYTES);
+	crypto_hash_sha256(peer->protocol_state->shared_handshake_key, hashinput, 5*PUBLICKEYBYTES);
+
+	memcpy(hashinput, ctx->protocol_context->public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+PUBLICKEYBYTES, peer->protocol_state->handshake_public_key.p, PUBLICKEYBYTES);
+
+	fastd_buffer buffer = fastd_buffer_alloc(sizeof(protocol_handshake_response_packet), 0, 0);
+	protocol_handshake_response_packet *packet = buffer.data;
+
+	memset(packet->noncepad, 0, NONCEBYTES);
+	packet->type = HANDSHAKE_PACKET_RESPONSE;
+	memcpy(packet->sender_key, ctx->protocol_context->public_key.p, PUBLICKEYBYTES);
+	memcpy(packet->receipient_key, peer->protocol_state->peer_public_key.p, PUBLICKEYBYTES);
+	memcpy(packet->handshake_key, peer->protocol_state->peer_handshake_key.p, PUBLICKEYBYTES);
+	memcpy(packet->handshake_key2, peer->protocol_state->handshake_public_key.p, PUBLICKEYBYTES);
+
+	crypto_auth_hmacsha256(packet->t, hashinput, 2*PUBLICKEYBYTES, peer->protocol_state->shared_handshake_key);
+
+	fastd_task_put_send(ctx, peer, buffer);
+
+	peer->protocol_state->state = HANDSHAKE_STATE_RESPONSE;
+}
+
+static void establish(fastd_context *ctx, fastd_peer *peer, bool initiator) {
+	peer->protocol_state->state = HANDSHAKE_STATE_ESTABLISHED;
+
+	int i;
+
+	peer->protocol_state->send_nonce[0] = initiator ? 3 : 2;
+	peer->protocol_state->receive_nonce[0] = initiator ? 0 : 1;
+	for (i = 1; i < NONCEBYTES; i++) {
+		peer->protocol_state->send_nonce[i] = 0;
+		peer->protocol_state->receive_nonce[i] = 0;
+	}
+
+	pr_info(ctx, "Connection with %P established.", peer);
+}
+
+static void finish_handshake(fastd_context *ctx, fastd_peer *peer, uint8_t t[HMACBYTES]) {
+	pr_info(ctx, "Finishing protocol handshake with %P...", peer);
+
+	uint8_t hashinput[5*PUBLICKEYBYTES];
+	uint8_t hashbuf[HASHBYTES];
+
+	memcpy(hashinput, peer->protocol_state->peer_handshake_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+PUBLICKEYBYTES, peer->protocol_state->handshake_public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+2*PUBLICKEYBYTES, peer->protocol_state->peer_public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+3*PUBLICKEYBYTES, ctx->protocol_context->public_key.p, PUBLICKEYBYTES);
+
+	crypto_hash_sha256(hashbuf, hashinput, 4*PUBLICKEYBYTES);
+
+	ecc_secret_key_256 d = {{0}}, e = {{0}}, da, s;
+
+	memcpy(d.s, hashbuf, HASHBYTES/2);
+	memcpy(e.s, hashbuf+HASHBYTES/2, HASHBYTES/2);
+
+	d.s[15] |= 0x80;
+	e.s[15] |= 0x80;
+
+	ecc_25519_secret_mult(&da, &d, &ctx->protocol_context->secret_key);
+	ecc_25519_secret_add(&s, &da, &peer->protocol_state->handshake_secret_key);
+
+	ecc_25519_work work, workY;
+	ecc_25519_load(&work, &peer->protocol_state->peer_public_key);
+	ecc_25519_load(&workY, &peer->protocol_state->peer_handshake_key);
+
+	ecc_25519_scalarmult(&work, &e, &work);
+	ecc_25519_add(&work, &workY, &work);
+	ecc_25519_scalarmult(&work, &s, &work);
+
+	ecc_25519_store(&peer->protocol_state->sigma, &work);
+
+	memcpy(hashinput+4*PUBLICKEYBYTES, peer->protocol_state->sigma.p, PUBLICKEYBYTES);
+	crypto_hash_sha256(peer->protocol_state->shared_handshake_key, hashinput, 5*PUBLICKEYBYTES);
+
+	memcpy(hashinput, peer->protocol_state->peer_public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+PUBLICKEYBYTES, peer->protocol_state->peer_handshake_key.p, PUBLICKEYBYTES);
+
+	if(crypto_auth_hmacsha256_verify(t, hashinput, 2*PUBLICKEYBYTES, peer->protocol_state->shared_handshake_key) != 0) {
+		pr_warn(ctx, "received invalid protocol handshake response from %P", peer);
+		return;
+	}
+
+	memcpy(hashinput, ctx->protocol_context->public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+PUBLICKEYBYTES, peer->protocol_state->handshake_public_key.p, PUBLICKEYBYTES);
+
+	fastd_buffer buffer = fastd_buffer_alloc(sizeof(protocol_handshake_finish_packet), 0, 0);
+	protocol_handshake_finish_packet *packet = buffer.data;
+
+	memset(packet->noncepad, 0, NONCEBYTES);
+	packet->type = HANDSHAKE_PACKET_FINISH;
+	memcpy(packet->sender_key, ctx->protocol_context->public_key.p, PUBLICKEYBYTES);
+	memcpy(packet->receipient_key, peer->protocol_state->peer_public_key.p, PUBLICKEYBYTES);
+	memcpy(packet->handshake_key, peer->protocol_state->peer_handshake_key.p, PUBLICKEYBYTES);
+	memcpy(packet->handshake_key2, peer->protocol_state->handshake_public_key.p, PUBLICKEYBYTES);
+
+	crypto_auth_hmacsha256(packet->t, hashinput, 2*PUBLICKEYBYTES, peer->protocol_state->shared_handshake_key);
+
+	fastd_task_put_send(ctx, peer, buffer);
+
+	memcpy(hashinput, peer->protocol_state->handshake_public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+PUBLICKEYBYTES, peer->protocol_state->peer_handshake_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+2*PUBLICKEYBYTES, ctx->protocol_context->public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+3*PUBLICKEYBYTES, peer->protocol_state->peer_public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+4*PUBLICKEYBYTES, peer->protocol_state->sigma.p, PUBLICKEYBYTES);
+	crypto_hash_sha256(peer->protocol_state->shared_session_key, hashinput, 5*PUBLICKEYBYTES);
+
+	establish(ctx, peer, true);
+}
+
+static void handle_finish_handshake(fastd_context *ctx, fastd_peer *peer, uint8_t t[HMACBYTES]) {
+	uint8_t hashinput[5*PUBLICKEYBYTES];
+
+	memcpy(hashinput, peer->protocol_state->peer_public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+PUBLICKEYBYTES, peer->protocol_state->peer_handshake_key.p, PUBLICKEYBYTES);
+
+	if(crypto_auth_hmacsha256_verify(t, hashinput, 2*PUBLICKEYBYTES, peer->protocol_state->shared_handshake_key) != 0) {
+		pr_warn(ctx, "received invalid protocol handshake finish from %P", peer);
+		return;
+	}
+
+	memcpy(hashinput, peer->protocol_state->peer_handshake_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+PUBLICKEYBYTES, peer->protocol_state->handshake_public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+2*PUBLICKEYBYTES, peer->protocol_state->peer_public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+3*PUBLICKEYBYTES, ctx->protocol_context->public_key.p, PUBLICKEYBYTES);
+	memcpy(hashinput+4*PUBLICKEYBYTES, peer->protocol_state->sigma.p, PUBLICKEYBYTES);
+	crypto_hash_sha256(peer->protocol_state->shared_session_key, hashinput, 5*PUBLICKEYBYTES);
+
+	establish(ctx, peer, false);
 }
 
 static void protocol_handle_recv(fastd_context *ctx, fastd_peer *peer, fastd_buffer buffer) {
+	if (buffer.len < NONCEBYTES)
+		goto end;
+
+	/* protocol handshake */
+	if (is_nonce_zero(buffer.data)) {
+		if (buffer.len < NONCEBYTES+1) {
+			pr_debug(ctx, "received short protocol handshake from %P", peer);
+			goto end;
+		}
+
+		protocol_handshake_packet *packet = buffer.data;
+
+		if (!peer->config) {
+			pr_debug(ctx, "received protocol handshake from temporary peer %P", peer);
+			goto end;
+		}
+
+		if (!peer->protocol_state) {
+			if (!create_peer_state(ctx, peer))
+				goto end; /* TODO disable peer */
+		}
+
+		switch (packet->type) {
+		case HANDSHAKE_PACKET_INIT:
+			if (buffer.len < sizeof(protocol_handshake_init_packet)) {
+				pr_debug(ctx, "received short protocol handshake init from %P", peer);
+				goto end;
+			}
+
+			if (memcmp(ctx->protocol_context->public_key.p, packet->init.receipient_key, PUBLICKEYBYTES) != 0) {
+				pr_debug(ctx, "received protocol handshake init with wrong receipient key from %P", peer);
+				goto end;
+			}
+
+			if (memcmp(peer->protocol_state->peer_public_key.p, packet->init.sender_key, PUBLICKEYBYTES) != 0) {
+				pr_debug(ctx, "received protocol handshake init with wrong sender key from %P", peer);
+				goto end;
+			}
+
+			if (peer->protocol_state->state != HANDSHAKE_STATE_INIT) {
+				pr_debug(ctx, "received unexpected protocol handshake init from %P", peer);
+				goto end;
+			}
+
+			pr_debug(ctx, "received protocol handshake init from %P", peer);
+			memcpy(peer->protocol_state->peer_handshake_key.p, packet->init.handshake_key, PUBLICKEYBYTES);
+
+			fastd_peer_set_established(ctx, peer);
+			respond_handshake(ctx, peer);
+
+			break;
+
+		case HANDSHAKE_PACKET_RESPONSE:
+			if (buffer.len < sizeof(protocol_handshake_response_packet)) {
+				pr_debug(ctx, "received short protocol handshake response from %P", peer);
+				goto end;
+			}
+
+			if (memcmp(ctx->protocol_context->public_key.p, packet->response.receipient_key, PUBLICKEYBYTES) != 0) {
+				pr_debug(ctx, "received protocol handshake response with wrong receipient key from %P", peer);
+				goto end;
+			}
+
+			if (memcmp(peer->protocol_state->peer_public_key.p, packet->response.sender_key, PUBLICKEYBYTES) != 0) {
+				pr_debug(ctx, "received protocol handshake response with wrong sender key from %P", peer);
+				goto end;
+			}
+
+			if (memcmp(peer->protocol_state->handshake_public_key.p, packet->response.handshake_key, PUBLICKEYBYTES) != 0) {
+				pr_debug(ctx, "received protocol handshake response with unexpected handshake key from %P", peer);
+				goto end;
+			}
+
+			if (peer->protocol_state->state != HANDSHAKE_STATE_INIT) {
+				pr_debug(ctx, "received unexpected protocol handshake response from %P", peer);
+				goto end;
+			}
+
+
+			pr_debug(ctx, "received protocol handshake response from %P", peer);
+			memcpy(peer->protocol_state->peer_handshake_key.p, packet->response.handshake_key2, PUBLICKEYBYTES);
+
+			finish_handshake(ctx, peer, packet->response.t);
+
+			break;
+
+		case HANDSHAKE_PACKET_FINISH:
+			if (buffer.len < sizeof(protocol_handshake_finish_packet)) {
+				pr_debug(ctx, "received short protocol handshake finish from %P", peer);
+				goto end;
+			}
+
+			if (memcmp(ctx->protocol_context->public_key.p, packet->finish.receipient_key, PUBLICKEYBYTES) != 0) {
+				pr_debug(ctx, "received protocol handshake finish with wrong receipient key from %P", peer);
+				goto end;
+			}
+
+			if (memcmp(peer->protocol_state->peer_public_key.p, packet->finish.sender_key, PUBLICKEYBYTES) != 0) {
+				pr_debug(ctx, "received protocol handshake finish with wrong sender key from %P", peer);
+				goto end;
+			}
+
+			if (memcmp(peer->protocol_state->handshake_public_key.p, packet->finish.handshake_key, PUBLICKEYBYTES) != 0) {
+				pr_debug(ctx, "received protocol handshake finish with unexpected handshake key from %P", peer);
+				goto end;
+			}
+
+			if (memcmp(peer->protocol_state->peer_handshake_key.p, packet->finish.handshake_key2, PUBLICKEYBYTES) != 0) {
+				pr_debug(ctx, "received protocol handshake finish with unexpected peer handshake key from %P", peer);
+				goto end;
+			}
+
+			if (peer->protocol_state->state != HANDSHAKE_STATE_RESPONSE) {
+				pr_debug(ctx, "received unexpected protocol handshake finish from %P", peer);
+				goto end;
+			}
+
+
+			pr_debug(ctx, "received protocol handshake finish from %P", peer);
+
+			handle_finish_handshake(ctx, peer, packet->finish.t);
+
+			break;
+		}
+	}
+	else {
+		if (!peer->protocol_state || peer->protocol_state->state != HANDSHAKE_STATE_ESTABLISHED) {
+			pr_debug(ctx, "received unexpected non-handshake packet from %P", peer);
+			goto end;
+		}
+	}
+
+ end:
 	fastd_buffer_free(buffer);
 }
 
@@ -104,15 +584,14 @@ static void protocol_send(fastd_context *ctx, fastd_peer *peer, fastd_buffer buf
 	fastd_buffer_free(buffer);
 }
 
-static void protocol_free_peer_private(fastd_context *ctx, fastd_peer *peer) {
+static void protocol_free_peer_state(fastd_context *ctx, fastd_peer *peer) {
+	free(peer->protocol_state);
 }
 
 
 const fastd_protocol fastd_protocol_ec25519_fhmqvc_xsalsa20_poly1305 = {
 	.name = "ec25519-fhmqvc-xsalsa20-poly1305",
 
-	.check_config = protocol_check_config,
-
 	.init = protocol_init,
 
 	.max_packet_size = protocol_max_packet_size,
@@ -123,5 +602,5 @@ const fastd_protocol fastd_protocol_ec25519_fhmqvc_xsalsa20_poly1305 = {
 	.handle_recv = protocol_handle_recv,
 	.send = protocol_send,
 
-	.free_peer_private = protocol_free_peer_private,
+	.free_peer_state = protocol_free_peer_state,
 };