X-Git-Url: http://git.meshlink.io/?p=meshlink;a=blobdiff_plain;f=src%2Fsptps.c;h=ed1f67ff95afd11ac1adfd6f6b95edcca72bf7de;hp=ff7c4168e0410b3564ceb32e74fce0da780b4f4a;hb=963c5055505f2fc117cd5efa06eaa02c9b2bf85d;hpb=248d300f1be0d5f2aae39202041699ab2b46c56b

diff --git a/src/sptps.c b/src/sptps.c
index ff7c4168..ed1f67ff 100644
--- a/src/sptps.c
+++ b/src/sptps.c
@@ -1,6 +1,6 @@
 /*
     sptps.c -- Simple Peer-to-Peer Security
-    Copyright (C) 2011 Guus Sliepen <guus@tinc-vpn.org>,
+    Copyright (C) 2014-2017 Guus Sliepen <guus@meshlink.io>
 
     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
@@ -19,11 +19,11 @@
 
 #include "system.h"
 
-#include "cipher.h"
+#include "chacha-poly1305/chacha-poly1305.h"
 #include "crypto.h"
-#include "digest.h"
 #include "ecdh.h"
 #include "ecdsa.h"
+#include "logger.h"
 #include "prf.h"
 #include "sptps.h"
 
@@ -47,85 +47,112 @@
    Make sure ECC operations are fixed time (aka prevent side-channel attacks).
 */
 
+void sptps_log_quiet(sptps_t *s, int s_errno, const char *format, va_list ap) {
+	(void)s;
+	(void)s_errno;
+	(void)format;
+	(void)ap;
+
+	assert(format);
+}
+
+void sptps_log_stderr(sptps_t *s, int s_errno, const char *format, va_list ap) {
+	(void)s;
+	(void)s_errno;
+
+	assert(format);
+
+	vfprintf(stderr, format, ap);
+	fputc('\n', stderr);
+}
+
+void (*sptps_log)(sptps_t *s, int s_errno, const char *format, va_list ap) = sptps_log_quiet;
+
 // Log an error message.
-static bool error(sptps_t *s, int s_errno, const char *msg) {
-	fprintf(stderr, "SPTPS error: %s\n", msg);
+static bool error(sptps_t *s, int s_errno, const char *format, ...) {
+	assert(s_errno);
+	assert(format);
+
+	if(format) {
+		va_list ap;
+		va_start(ap, format);
+		sptps_log(s, s_errno, format, ap);
+		va_end(ap);
+	}
+
 	errno = s_errno;
 	return false;
 }
 
+static void warning(sptps_t *s, const char *format, ...) {
+	assert(format);
+
+	va_list ap;
+	va_start(ap, format);
+	sptps_log(s, 0, format, ap);
+	va_end(ap);
+}
+
 // Send a record (datagram version, accepts all record types, handles encryption and authentication).
-static bool send_record_priv_datagram(sptps_t *s, uint8_t type, const char *data, uint16_t len) {
-	char buffer[len + 23UL];
+static bool send_record_priv_datagram(sptps_t *s, uint8_t type, const void *data, uint16_t len) {
+	char buffer[len + 21UL];
 
 	// Create header with sequence number, length and record type
-	uint32_t seqno = htonl(s->outseqno++);
-	uint16_t netlen = htons(len);
-
-	memcpy(buffer, &netlen, 2);
-	memcpy(buffer + 2, &seqno, 4);
-	buffer[6] = type;
+	uint32_t seqno = s->outseqno++;
+	uint32_t netseqno = ntohl(seqno);
 
-	// Add plaintext (TODO: avoid unnecessary copy)
-	memcpy(buffer + 7, data, len);
+	memcpy(buffer, &netseqno, 4);
+	buffer[4] = type;
+	memcpy(buffer + 5, data, len);
 
 	if(s->outstate) {
 		// If first handshake has finished, encrypt and HMAC
-		cipher_set_counter(&s->outcipher, &seqno, sizeof seqno);
-		if(!cipher_counter_xor(&s->outcipher, buffer + 6, len + 1UL, buffer + 6))
-			return false;
-
-		if(!digest_create(&s->outdigest, buffer, len + 7UL, buffer + 7UL + len))
-			return false;
-
-		return s->send_data(s->handle, buffer + 2, len + 21UL);
+		chacha_poly1305_encrypt(s->outcipher, seqno, buffer + 4, len + 1, buffer + 4, NULL);
+		return s->send_data(s->handle, type, buffer, len + 21UL);
 	} else {
 		// Otherwise send as plaintext
-		return s->send_data(s->handle, buffer + 2, len + 5UL);
+		return s->send_data(s->handle, type, buffer, len + 5UL);
 	}
 }
 // Send a record (private version, accepts all record types, handles encryption and authentication).
-static bool send_record_priv(sptps_t *s, uint8_t type, const char *data, uint16_t len) {
-	if(s->datagram)
+static bool send_record_priv(sptps_t *s, uint8_t type, const void *data, uint16_t len) {
+	if(s->datagram) {
 		return send_record_priv_datagram(s, type, data, len);
+	}
 
-	char buffer[len + 23UL];
+	char buffer[len + 19UL];
 
 	// Create header with sequence number, length and record type
-	uint32_t seqno = htonl(s->outseqno++);
+	uint32_t seqno = s->outseqno++;
 	uint16_t netlen = htons(len);
 
-	memcpy(buffer, &seqno, 4);
-	memcpy(buffer + 4, &netlen, 2);
-	buffer[6] = type;
-
-	// Add plaintext (TODO: avoid unnecessary copy)
-	memcpy(buffer + 7, data, len);
+	memcpy(buffer, &netlen, 2);
+	buffer[2] = type;
+	memcpy(buffer + 3, data, len);
 
 	if(s->outstate) {
 		// If first handshake has finished, encrypt and HMAC
-		if(!cipher_counter_xor(&s->outcipher, buffer + 4, len + 3UL, buffer + 4))
-			return false;
-
-		if(!digest_create(&s->outdigest, buffer, len + 7UL, buffer + 7UL + len))
-			return false;
-
-		return s->send_data(s->handle, buffer + 4, len + 19UL);
+		chacha_poly1305_encrypt(s->outcipher, seqno, buffer + 2, len + 1, buffer + 2, NULL);
+		return s->send_data(s->handle, type, buffer, len + 19UL);
 	} else {
 		// Otherwise send as plaintext
-		return s->send_data(s->handle, buffer + 4, len + 3UL);
+		return s->send_data(s->handle, type, buffer, len + 3UL);
 	}
 }
 
 // Send an application record.
-bool sptps_send_record(sptps_t *s, uint8_t type, const char *data, uint16_t len) {
+bool sptps_send_record(sptps_t *s, uint8_t type, const void *data, uint16_t len) {
+	assert(!len || data);
+
 	// Sanity checks: application cannot send data before handshake is finished,
 	// and only record types 0..127 are allowed.
-	if(!s->outstate)
+	if(!s->outstate) {
 		return error(s, EINVAL, "Handshake phase not finished yet");
+	}
 
-	if(type >= SPTPS_HANDSHAKE)
+	if(type >= SPTPS_HANDSHAKE) {
 		return error(s, EINVAL, "Invalid application record type");
+	}
 
 	return send_record_priv(s, type, data, len);
 }
@@ -135,11 +162,15 @@ static bool send_kex(sptps_t *s) {
 	size_t keylen = ECDH_SIZE;
 
 	// Make room for our KEX message, which we will keep around since send_sig() needs it.
-	if(s->mykex)
-		abort();
+	if(s->mykex) {
+		return false;
+	}
+
 	s->mykex = realloc(s->mykex, 1 + 32 + keylen);
-	if(!s->mykex)
+
+	if(!s->mykex) {
 		return error(s, errno, strerror(errno));
+	}
 
 	// Set version byte to zero.
 	s->mykex[0] = SPTPS_VERSION;
@@ -148,8 +179,9 @@ static bool send_kex(sptps_t *s) {
 	randomize(s->mykex + 1, 32);
 
 	// Create a new ECDH public key.
-	if(!ecdh_generate_public(&s->ecdh, s->mykex + 1 + 32))
-		return false;
+	if(!(s->ecdh = ecdh_generate_public(s->mykex + 1 + 32))) {
+		return error(s, EINVAL, "Failed to generate ECDH public key");
+	}
 
 	return send_record_priv(s, SPTPS_HANDSHAKE, s->mykex, 1 + 32 + keylen);
 }
@@ -157,7 +189,7 @@ static bool send_kex(sptps_t *s) {
 // Send a SIGnature record, containing an ECDSA signature over both KEX records.
 static bool send_sig(sptps_t *s) {
 	size_t keylen = ECDH_SIZE;
-	size_t siglen = ecdsa_size(&s->mykey);
+	size_t siglen = ecdsa_size(s->mykey);
 
 	// Concatenate both KEX messages, plus tag indicating if it is from the connection originator, plus label
 	char msg[(1 + 32 + keylen) * 2 + 1 + s->labellen];
@@ -169,36 +201,42 @@ static bool send_sig(sptps_t *s) {
 	memcpy(msg + 1 + 2 * (33 + keylen), s->label, s->labellen);
 
 	// Sign the result.
-	if(!ecdsa_sign(&s->mykey, msg, sizeof msg, sig))
-		return false;
+	if(!ecdsa_sign(s->mykey, msg, sizeof(msg), sig)) {
+		return error(s, EINVAL, "Failed to sign SIG record");
+	}
 
 	// Send the SIG exchange record.
-	return send_record_priv(s, SPTPS_HANDSHAKE, sig, sizeof sig);
+	return send_record_priv(s, SPTPS_HANDSHAKE, sig, sizeof(sig));
 }
 
 // Generate key material from the shared secret created from the ECDHE key exchange.
 static bool generate_key_material(sptps_t *s, const char *shared, size_t len) {
+	assert(shared);
+	assert(len);
+
 	// Initialise cipher and digest structures if necessary
 	if(!s->outstate) {
-		bool result
-			=  cipher_open_by_name(&s->incipher, "aes-256-ecb")
-			&& cipher_open_by_name(&s->outcipher, "aes-256-ecb")
-			&& digest_open_by_name(&s->indigest, "sha256", 16)
-			&& digest_open_by_name(&s->outdigest, "sha256", 16);
-		if(!result)
-			return false;
+		s->incipher = chacha_poly1305_init();
+		s->outcipher = chacha_poly1305_init();
+
+		if(!s->incipher || !s->outcipher) {
+			return error(s, EINVAL, "Failed to open cipher");
+		}
 	}
 
 	// Allocate memory for key material
-	size_t keylen = digest_keylength(&s->indigest) + digest_keylength(&s->outdigest) + cipher_keylength(&s->incipher) + cipher_keylength(&s->outcipher);
+	size_t keylen = 2 * CHACHA_POLY1305_KEYLEN;
 
 	s->key = realloc(s->key, keylen);
-	if(!s->key)
+
+	if(!s->key) {
 		return error(s, errno, strerror(errno));
+	}
 
 	// Create the HMAC seed, which is "key expansion" + session label + server nonce + client nonce
 	char seed[s->labellen + 64 + 13];
 	strcpy(seed, "key expansion");
+
 	if(s->initiator) {
 		memcpy(seed + 13, s->mykex + 1, 32);
 		memcpy(seed + 45, s->hiskex + 1, 32);
@@ -206,11 +244,13 @@ static bool generate_key_material(sptps_t *s, const char *shared, size_t len) {
 		memcpy(seed + 13, s->hiskex + 1, 32);
 		memcpy(seed + 45, s->mykex + 1, 32);
 	}
-	memcpy(seed + 78, s->label, s->labellen);
+
+	memcpy(seed + 77, s->label, s->labellen);
 
 	// Use PRF to generate the key material
-	if(!prf(shared, len, seed, s->labellen + 64 + 13, s->key, keylen))
-		return false;
+	if(!prf(shared, len, seed, s->labellen + 64 + 13, s->key, keylen)) {
+		return error(s, EINVAL, "Failed to generate key material");
+	}
 
 	return true;
 }
@@ -222,21 +262,20 @@ static bool send_ack(sptps_t *s) {
 
 // Receive an ACKnowledgement record.
 static bool receive_ack(sptps_t *s, const char *data, uint16_t len) {
-	if(len)
+	(void)data;
+
+	if(len) {
 		return error(s, EIO, "Invalid ACK record length");
+	}
 
 	if(s->initiator) {
-		bool result
-			= cipher_set_counter_key(&s->incipher, s->key)
-			&& digest_set_key(&s->indigest, s->key + cipher_keylength(&s->incipher), digest_keylength(&s->indigest));
-		if(!result)
-			return false;
+		if(!chacha_poly1305_set_key(s->incipher, s->key)) {
+			return error(s, EINVAL, "Failed to set counter");
+		}
 	} else {
-		bool result
-			= cipher_set_counter_key(&s->incipher, s->key + cipher_keylength(&s->outcipher) + digest_keylength(&s->outdigest))
-			&& digest_set_key(&s->indigest, s->key + cipher_keylength(&s->outcipher) + digest_keylength(&s->outdigest) + cipher_keylength(&s->incipher), digest_keylength(&s->indigest));
-		if(!result)
-			return false;
+		if(!chacha_poly1305_set_key(s->incipher, s->key + CHACHA_POLY1305_KEYLEN)) {
+			return error(s, EINVAL, "Failed to set counter");
+		}
 	}
 
 	free(s->key);
@@ -249,17 +288,22 @@ static bool receive_ack(sptps_t *s, const char *data, uint16_t len) {
 // Receive a Key EXchange record, respond by sending a SIG record.
 static bool receive_kex(sptps_t *s, const char *data, uint16_t len) {
 	// Verify length of the HELLO record
-	if(len != 1 + 32 + ECDH_SIZE)
+	if(len != 1 + 32 + ECDH_SIZE) {
 		return error(s, EIO, "Invalid KEX record length");
+	}
 
 	// Ignore version number for now.
 
 	// Make a copy of the KEX message, send_sig() and receive_sig() need it
-	if(s->hiskex)
-		abort();
+	if(s->hiskex) {
+		return error(s, EINVAL, "Received a second KEX message before first has been processed");
+	}
+
 	s->hiskex = realloc(s->hiskex, len);
-	if(!s->hiskex)
+
+	if(!s->hiskex) {
 		return error(s, errno, strerror(errno));
+	}
 
 	memcpy(s->hiskex, data, len);
 
@@ -269,11 +313,12 @@ static bool receive_kex(sptps_t *s, const char *data, uint16_t len) {
 // Receive a SIGnature record, verify it, if it passed, compute the shared secret and calculate the session keys.
 static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
 	size_t keylen = ECDH_SIZE;
-	size_t siglen = ecdsa_size(&s->hiskey);
+	size_t siglen = ecdsa_size(s->hiskey);
 
 	// Verify length of KEX record.
-	if(len != siglen)
+	if(len != siglen) {
 		return error(s, EIO, "Invalid KEX record length");
+	}
 
 	// Concatenate both KEX messages, plus tag indicating if it is from the connection originator
 	char msg[(1 + 32 + keylen) * 2 + 1 + s->labellen];
@@ -284,17 +329,23 @@ static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
 	memcpy(msg + 1 + 2 * (33 + keylen), s->label, s->labellen);
 
 	// Verify signature.
-	if(!ecdsa_verify(&s->hiskey, msg, sizeof msg, data))
-		return false;
+	if(!ecdsa_verify(s->hiskey, msg, sizeof(msg), data)) {
+		return error(s, EIO, "Failed to verify SIG record");
+	}
 
 	// Compute shared secret.
 	char shared[ECDH_SHARED_SIZE];
-	if(!ecdh_compute_shared(&s->ecdh, s->hiskex + 1 + 32, shared))
-		return false;
+
+	if(!ecdh_compute_shared(s->ecdh, s->hiskex + 1 + 32, shared)) {
+		return error(s, EINVAL, "Failed to compute ECDH shared secret");
+	}
+
+	s->ecdh = NULL;
 
 	// Generate key material from shared secret.
-	if(!generate_key_material(s, shared, sizeof shared))
+	if(!generate_key_material(s, shared, sizeof(shared))) {
 		return false;
+	}
 
 	free(s->mykex);
 	free(s->hiskex);
@@ -303,22 +354,19 @@ static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
 	s->hiskex = NULL;
 
 	// Send cipher change record
-	if(s->outstate && !send_ack(s))
+	if(s->outstate && !send_ack(s)) {
 		return false;
+	}
 
 	// TODO: only set new keys after ACK has been set/received
 	if(s->initiator) {
-		bool result
-			= cipher_set_counter_key(&s->outcipher, s->key + cipher_keylength(&s->incipher) + digest_keylength(&s->indigest))
-			&& digest_set_key(&s->outdigest, s->key + cipher_keylength(&s->incipher) + digest_keylength(&s->indigest) + cipher_keylength(&s->outcipher), digest_keylength(&s->outdigest));
-		if(!result)
-			return false;
+		if(!chacha_poly1305_set_key(s->outcipher, s->key + CHACHA_POLY1305_KEYLEN)) {
+			return error(s, EINVAL, "Failed to set key");
+		}
 	} else {
-		bool result
-			=  cipher_set_counter_key(&s->outcipher, s->key)
-			&& digest_set_key(&s->outdigest, s->key + cipher_keylength(&s->outcipher), digest_keylength(&s->outdigest));
-		if(!result)
-			return false;
+		if(!chacha_poly1305_set_key(s->outcipher, s->key)) {
+			return error(s, EINVAL, "Failed to set key");
+		}
 	}
 
 	return true;
@@ -326,8 +374,9 @@ static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
 
 // Force another Key EXchange (for testing purposes).
 bool sptps_force_kex(sptps_t *s) {
-	if(!s->outstate || s->state != SPTPS_SECONDARY_KEX)
+	if(!s->outstate || s->state != SPTPS_SECONDARY_KEX) {
 		return error(s, EINVAL, "Cannot force KEX in current state");
+	}
 
 	s->state = SPTPS_KEX;
 	return send_kex(s);
@@ -336,50 +385,89 @@ bool sptps_force_kex(sptps_t *s) {
 // Receive a handshake record.
 static bool receive_handshake(sptps_t *s, const char *data, uint16_t len) {
 	// Only a few states to deal with handshaking.
-	fprintf(stderr, "Received handshake message, current state %d\n", s->state);
 	switch(s->state) {
-		case SPTPS_SECONDARY_KEX:
-			// We receive a secondary KEX request, first respond by sending our own.
-			if(!send_kex(s))
-				return false;
-		case SPTPS_KEX:
-			// We have sent our KEX request, we expect our peer to sent one as well.
-			if(!receive_kex(s, data, len))
-				return false;
-			s->state = SPTPS_SIG;
-			return true;
-		case SPTPS_SIG:
-			// If we already sent our secondary public ECDH key, we expect the peer to send his.
-			if(!receive_sig(s, data, len))
+	case SPTPS_SECONDARY_KEX:
+
+		// We receive a secondary KEX request, first respond by sending our own.
+		if(!send_kex(s)) {
+			return false;
+		}
+
+	// fallthrough
+	case SPTPS_KEX:
+
+		// We have sent our KEX request, we expect our peer to sent one as well.
+		if(!receive_kex(s, data, len)) {
+			return false;
+		}
+
+		s->state = SPTPS_SIG;
+		return true;
+
+	case SPTPS_SIG:
+
+		// If we already sent our secondary public ECDH key, we expect the peer to send his.
+		if(!receive_sig(s, data, len)) {
+			return false;
+		}
+
+		if(s->outstate) {
+			s->state = SPTPS_ACK;
+		} else {
+			s->outstate = true;
+
+			if(!receive_ack(s, NULL, 0)) {
 				return false;
-			if(s->outstate)
-				s->state = SPTPS_ACK;
-			else {
-				s->outstate = true;
-				if(!receive_ack(s, NULL, 0))
-					return false;
-				s->receive_record(s->handle, SPTPS_HANDSHAKE, NULL, 0);
-				s->state = SPTPS_SECONDARY_KEX;
 			}
 
-			return true;
-		case SPTPS_ACK:
-			// We expect a handshake message to indicate transition to the new keys.
-			if(!receive_ack(s, data, len))
-				return false;
 			s->receive_record(s->handle, SPTPS_HANDSHAKE, NULL, 0);
 			s->state = SPTPS_SECONDARY_KEX;
-			return true;
-		// TODO: split ACK into a VERify and ACK?
-		default:
-			return error(s, EIO, "Invalid session state");
+		}
+
+		return true;
+
+	case SPTPS_ACK:
+
+		// We expect a handshake message to indicate transition to the new keys.
+		if(!receive_ack(s, data, len)) {
+			return false;
+		}
+
+		s->receive_record(s->handle, SPTPS_HANDSHAKE, NULL, 0);
+		s->state = SPTPS_SECONDARY_KEX;
+		return true;
+
+	// TODO: split ACK into a VERify and ACK?
+	default:
+		return error(s, EIO, "Invalid session state %d", s->state);
+	}
+}
+
+// Check datagram for valid HMAC
+bool sptps_verify_datagram(sptps_t *s, const void *data, size_t len) {
+	if(!s->instate) {
+		return error(s, EIO, "SPTPS state not ready to verify this datagram");
 	}
+
+	if(len < 21) {
+		return error(s, EIO, "Received short packet in sptps_verify_datagram");
+	}
+
+	uint32_t seqno;
+	memcpy(&seqno, data, 4);
+	seqno = ntohl(seqno);
+	// TODO: check whether seqno makes sense, to avoid CPU intensive decrypt
+
+	return chacha_poly1305_verify(s->incipher, seqno, (const char *)data + 4, len - 4);
 }
 
 // Receive incoming data, datagram version.
-static bool sptps_receive_data_datagram(sptps_t *s, const char *data, size_t len) {
-	if(len < (s->instate ? 21 : 5))
-		return error(s, EIO, "Received short packet");
+static bool sptps_receive_data_datagram(sptps_t *s, const void *vdata, size_t len) {
+	const char *data = vdata;
+
+	if(len < (s->instate ? 21 : 5)) {
+		return error(s, EIO, "Received short packet in sptps_receive_data_datagram");
+	}
 
 	uint32_t seqno;
 	memcpy(&seqno, data, 4);
@@ -387,177 +475,253 @@ static bool sptps_receive_data_datagram(sptps_t *s, const char *data, size_t len
 
 	if(!s->instate) {
 		if(seqno != s->inseqno) {
-			fprintf(stderr, "Received invalid packet seqno: %d != %d\n", seqno, s->inseqno);
-			return error(s, EIO, "Invalid packet seqno");
+			return error(s, EIO, "Invalid packet seqno: %d != %d", seqno, s->inseqno);
 		}
 
 		s->inseqno = seqno + 1;
 
 		uint8_t type = data[4];
 
-		if(type != SPTPS_HANDSHAKE)
+		if(type != SPTPS_HANDSHAKE) {
 			return error(s, EIO, "Application record received before handshake finished");
+		}
 
 		return receive_handshake(s, data + 5, len - 5);
 	}
 
-	if(seqno < s->inseqno) {
-		fprintf(stderr, "Received late or replayed packet: %d < %d\n", seqno, s->inseqno);
-		return true;
-	}
+	// Decrypt
 
-	if(seqno > s->inseqno)
-		fprintf(stderr, "Missed %d packets\n", seqno - s->inseqno);
+	if(len > s->decrypted_buffer_len) {
+		s->decrypted_buffer_len *= 2;
+		char *new_buffer = realloc(s->decrypted_buffer, s->decrypted_buffer_len);
+
+		if(!new_buffer) {
+			return error(s, errno, strerror(errno));
+		}
 
-	s->inseqno = seqno + 1;
+		s->decrypted_buffer = new_buffer;
+	}
 
-	uint16_t netlen = htons(len - 21);
+	size_t outlen;
 
-	char buffer[len + 23];
+	if(!chacha_poly1305_decrypt(s->incipher, seqno, data + 4, len - 4, s->decrypted_buffer, &outlen)) {
+		return error(s, EIO, "Failed to decrypt and verify packet");
+	}
 
-	memcpy(buffer, &netlen, 2);
-	memcpy(buffer + 2, data, len);
+	// Replay protection using a sliding window of configurable size.
+	// s->inseqno is expected sequence number
+	// seqno is received sequence number
+	// s->late[] is a circular buffer, a 1 bit means a packet has not been received yet
+	// The circular buffer contains bits for sequence numbers from s->inseqno - s->replaywin * 8 to (but excluding) s->inseqno.
+	if(s->replaywin) {
+		if(seqno != s->inseqno) {
+			if(seqno >= s->inseqno + s->replaywin * 8) {
+				// TODO: Prevent packets that jump far ahead of the queue from causing many others to be dropped.
+				warning(s, "Lost %d packets\n", seqno - s->inseqno);
+				// Mark all packets in the replay window as being late.
+				memset(s->late, 255, s->replaywin);
+			} else if(seqno < s->inseqno) {
+				// If the sequence number is farther in the past than the bitmap goes, or if the packet was already received, drop it.
+				if((s->inseqno >= s->replaywin * 8 && seqno < s->inseqno - s->replaywin * 8) || !(s->late[(seqno / 8) % s->replaywin] & (1 << seqno % 8))) {
+					return error(s, EIO, "Received late or replayed packet, seqno %d, last received %d\n", seqno, s->inseqno);
+				}
+			} else {
+				// We missed some packets. Mark them in the bitmap as being late.
+				for(uint32_t i = s->inseqno; i < seqno; i++) {
+					s->late[(i / 8) % s->replaywin] |= 1 << i % 8;
+				}
+			}
+		}
 
-	memcpy(&seqno, buffer + 2, 4);
+		// Mark the current packet as not being late.
+		s->late[(seqno / 8) % s->replaywin] &= ~(1 << seqno % 8);
+	}
 
-	// Check HMAC and decrypt.
-	if(!digest_verify(&s->indigest, buffer, len - 14, buffer + len - 14))
-		return error(s, EIO, "Invalid HMAC");
+	if(seqno >= s->inseqno) {
+		s->inseqno = seqno + 1;
+	}
 
-	cipher_set_counter(&s->incipher, &seqno, sizeof seqno);
-	if(!cipher_counter_xor(&s->incipher, buffer + 6, len - 4, buffer + 6))
-		return false;
+	if(!s->inseqno) {
+		s->received = 0;
+	} else {
+		s->received++;
+	}
 
 	// Append a NULL byte for safety.
-	buffer[len - 14] = 0;
+	s->decrypted_buffer[len - 20] = 0;
 
-	uint8_t type = buffer[6];
+	uint8_t type = s->decrypted_buffer[0];
 
 	if(type < SPTPS_HANDSHAKE) {
-		if(!s->instate)
+		if(!s->instate) {
 			return error(s, EIO, "Application record received before handshake finished");
-		if(!s->receive_record(s->handle, type, buffer + 7, len - 21))
-			return false;
+		}
+
+		if(!s->receive_record(s->handle, type, s->decrypted_buffer + 1, len - 21)) {
+			abort();
+		}
+	} else if(type == SPTPS_HANDSHAKE) {
+		if(!receive_handshake(s, s->decrypted_buffer + 1, len - 21)) {
+			abort();
+		}
 	} else {
-		return error(s, EIO, "Invalid record type");
+		return error(s, EIO, "Invalid record type %d", type);
 	}
 
 	return true;
 }
+
 // Receive incoming data. Check if it contains a complete record, if so, handle it.
-bool sptps_receive_data(sptps_t *s, const char *data, size_t len) {
-	if(s->datagram)
+bool sptps_receive_data(sptps_t *s, const void *data, size_t len) {
+	if(!s->state) {
+		return error(s, EIO, "Invalid session state zero");
+	}
+
+	if(s->datagram) {
 		return sptps_receive_data_datagram(s, data, len);
+	}
+
+	const char *ptr = data;
 
 	while(len) {
 		// First read the 2 length bytes.
-		if(s->buflen < 6) {
-			size_t toread = 6 - s->buflen;
-			if(toread > len)
+		if(s->buflen < 2) {
+			size_t toread = 2 - s->buflen;
+
+			if(toread > len) {
 				toread = len;
+			}
 
-			memcpy(s->inbuf + s->buflen, data, toread);
+			memcpy(s->inbuf + s->buflen, ptr, toread);
 
 			s->buflen += toread;
 			len -= toread;
-			data += toread;
-		
+			ptr += toread;
+
 			// Exit early if we don't have the full length.
-			if(s->buflen < 6)
+			if(s->buflen < 2) {
 				return true;
-
-			// Decrypt the length bytes
-
-			if(s->instate) {
-				if(!cipher_counter_xor(&s->incipher, s->inbuf + 4, 2, &s->reclen))
-					return false;
-			} else {
-				memcpy(&s->reclen, s->inbuf + 4, 2);
 			}
 
+			// Get the length bytes
+
+			memcpy(&s->reclen, s->inbuf, 2);
 			s->reclen = ntohs(s->reclen);
 
 			// If we have the length bytes, ensure our buffer can hold the whole request.
-			s->inbuf = realloc(s->inbuf, s->reclen + 23UL);
-			if(!s->inbuf)
-				return error(s, errno, strerror(errno));
+			s->inbuf = realloc(s->inbuf, s->reclen + 19UL);
 
-			// Add sequence number.
-			uint32_t seqno = htonl(s->inseqno++);
-			memcpy(s->inbuf, &seqno, 4);
+			if(!s->inbuf) {
+				return error(s, errno, strerror(errno));
+			}
 
 			// Exit early if we have no more data to process.
-			if(!len)
+			if(!len) {
 				return true;
+			}
 		}
 
 		// Read up to the end of the record.
-		size_t toread = s->reclen + (s->instate ? 23UL : 7UL) - s->buflen;
-		if(toread > len)
+		size_t toread = s->reclen + (s->instate ? 19UL : 3UL) - s->buflen;
+
+		if(toread > len) {
 			toread = len;
+		}
 
-		memcpy(s->inbuf + s->buflen, data, toread);
+		memcpy(s->inbuf + s->buflen, ptr, toread);
 		s->buflen += toread;
 		len -= toread;
-		data += toread;
+		ptr += toread;
 
 		// If we don't have a whole record, exit.
-		if(s->buflen < s->reclen + (s->instate ? 23UL : 7UL))
+		if(s->buflen < s->reclen + (s->instate ? 19UL : 3UL)) {
 			return true;
+		}
+
+		// Update sequence number.
+
+		uint32_t seqno = s->inseqno++;
 
 		// Check HMAC and decrypt.
 		if(s->instate) {
-			if(!digest_verify(&s->indigest, s->inbuf, s->reclen + 7UL, s->inbuf + s->reclen + 7UL))
-				return error(s, EIO, "Invalid HMAC");
-
-			if(!cipher_counter_xor(&s->incipher, s->inbuf + 6UL, s->reclen + 1UL, s->inbuf + 6UL))
-				return false;
+			if(!chacha_poly1305_decrypt(s->incipher, seqno, s->inbuf + 2UL, s->reclen + 17UL, s->inbuf + 2UL, NULL)) {
+				return error(s, EINVAL, "Failed to decrypt and verify record");
+			}
 		}
 
 		// Append a NULL byte for safety.
-		s->inbuf[s->reclen + 7UL] = 0;
+		s->inbuf[s->reclen + 3UL] = 0;
 
-		uint8_t type = s->inbuf[6];
+		uint8_t type = s->inbuf[2];
 
 		if(type < SPTPS_HANDSHAKE) {
-			if(!s->instate)
+			if(!s->instate) {
 				return error(s, EIO, "Application record received before handshake finished");
-			if(!s->receive_record(s->handle, type, s->inbuf + 7, s->reclen))
+			}
+
+			if(!s->receive_record(s->handle, type, s->inbuf + 3, s->reclen)) {
 				return false;
+			}
 		} else if(type == SPTPS_HANDSHAKE) {
-			if(!receive_handshake(s, s->inbuf + 7, s->reclen))
+			if(!receive_handshake(s, s->inbuf + 3, s->reclen)) {
 				return false;
+			}
 		} else {
-			return error(s, EIO, "Invalid record type");
+			return error(s, EIO, "Invalid record type %d", type);
 		}
 
-		s->buflen = 4;
+		s->buflen = 0;
 	}
 
 	return true;
 }
 
 // Start a SPTPS session.
-bool sptps_start(sptps_t *s, void *handle, bool initiator, bool datagram, ecdsa_t mykey, ecdsa_t hiskey, const char *label, size_t labellen, send_data_t send_data, receive_record_t receive_record) {
+bool sptps_start(sptps_t *s, void *handle, bool initiator, bool datagram, ecdsa_t *mykey, ecdsa_t *hiskey, const char *label, size_t labellen, send_data_t send_data, receive_record_t receive_record) {
+	if(!s || !mykey || !hiskey || !label || !labellen || !send_data || !receive_record) {
+		return error(s, EINVAL, "Invalid argument to sptps_start()");
+	}
+
 	// Initialise struct sptps
-	memset(s, 0, sizeof *s);
+	memset(s, 0, sizeof(*s));
 
 	s->handle = handle;
 	s->initiator = initiator;
 	s->datagram = datagram;
 	s->mykey = mykey;
 	s->hiskey = hiskey;
+	s->replaywin = 32;
+	s->decrypted_buffer_len = 1024;
+	s->decrypted_buffer = malloc(s->decrypted_buffer_len);
+
+	if(!s->decrypted_buffer) {
+		return error(s, errno, strerror(errno));
+	}
+
+	if(s->replaywin) {
+		s->late = malloc(s->replaywin);
+
+		if(!s->late) {
+			return error(s, errno, strerror(errno));
+		}
+
+		memset(s->late, 0, s->replaywin);
+	}
 
 	s->label = malloc(labellen);
-	if(!s->label)
+
+	if(!s->label) {
 		return error(s, errno, strerror(errno));
+	}
 
 	if(!datagram) {
 		s->inbuf = malloc(7);
-		if(!s->inbuf)
+
+		if(!s->inbuf) {
 			return error(s, errno, strerror(errno));
-		s->buflen = 4;
-		memset(s->inbuf, 0, 4);
+		}
+
+		s->buflen = 0;
 	}
 
 	memcpy(s->label, label, labellen);
@@ -574,16 +738,17 @@ bool sptps_start(sptps_t *s, void *handle, bool initiator, bool datagram, ecdsa_
 // Stop a SPTPS session.
 bool sptps_stop(sptps_t *s) {
 	// Clean up any resources.
-	ecdh_free(&s->ecdh);
+	chacha_poly1305_exit(s->incipher);
+	chacha_poly1305_exit(s->outcipher);
+	ecdh_free(s->ecdh);
 	free(s->inbuf);
-	s->inbuf = NULL;
 	free(s->mykex);
-	s->mykex = NULL;
 	free(s->hiskex);
-	s->hiskex = NULL;
 	free(s->key);
-	s->key = NULL;
 	free(s->label);
-	s->label = NULL;
+	free(s->late);
+	memset(s->decrypted_buffer, 0, s->decrypted_buffer_len);
+	free(s->decrypted_buffer);
+	memset(s, 0, sizeof(*s));
 	return true;
 }