X-Git-Url: http://git.meshlink.io/?a=blobdiff_plain;f=src%2Fsptps.c;h=54c5a55e61bc27ed7eff8aec95803c4d3181842e;hb=158cbe99f972a1613b7d4d95abfe5fe48e019e67;hp=d22390e836a53ee630c42851492a0552c8914f76;hpb=f5dc136cfd7a3a195b75f7174722734e25f30fd9;p=meshlink

diff --git a/src/sptps.c b/src/sptps.c
index d22390e8..54c5a55e 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 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
@@ -21,14 +21,13 @@
 
 #include "cipher.h"
 #include "crypto.h"
-#include "digest.h"
 #include "ecdh.h"
 #include "ecdsa.h"
+#include "logger.h"
 #include "prf.h"
 #include "sptps.h"
 
-char *logfilename;
-#include "utils.c"
+unsigned int sptps_replaywin = 16;
 
 /*
    Nonce MUST be exchanged first (done)
@@ -50,46 +49,99 @@ char *logfilename;
    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 sptps_log_stderr(sptps_t *s, int s_errno, const char *format, va_list ap) {
+	vfprintf(stderr, format, ap);
+	fputc('\n', stderr);
+}
+
+void (*sptps_log)(sptps_t *s, int s_errno, const char *format, va_list ap) = sptps_log_stderr;
+
 // 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, ...) {
+	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, ...) {
+	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 + 21UL];
+
+	// Create header with sequence number, length and record type
+	uint32_t seqno = htonl(s->outseqno++);
+
+	memcpy(buffer, &seqno, 4);
+	buffer[4] = type;
+
+	if(s->outstate) {
+		// If first handshake has finished, encrypt and HMAC
+		if(!cipher_set_counter(s->outcipher, &seqno, sizeof seqno))
+			return error(s, EINVAL, "Failed to set counter");
+
+		if(!cipher_gcm_encrypt_start(s->outcipher, buffer + 4, 1, buffer + 4, NULL))
+			return error(s, EINVAL, "Error encrypting record");
+
+		if(!cipher_gcm_encrypt_finish(s->outcipher, data, len, buffer + 5, NULL))
+			return error(s, EINVAL, "Error encrypting record");
+
+		return s->send_data(s->handle, type, buffer, len + 21UL);
+	} else {
+		// Otherwise send as plaintext
+		memcpy(buffer + 5, data, len);
+		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) {
-	char plaintext[len + 23];
-	char ciphertext[len + 19];
+	if(s->datagram)
+		return send_record_priv_datagram(s, type, data, len);
+
+	char buffer[len + 19UL];
 
 	// Create header with sequence number, length and record type
 	uint32_t seqno = htonl(s->outseqno++);
 	uint16_t netlen = htons(len);
 
-	memcpy(plaintext, &seqno, 4);
-	memcpy(plaintext + 4, &netlen, 2);
-	plaintext[6] = type;
-
-	// Add plaintext (TODO: avoid unnecessary copy)
-	memcpy(plaintext + 7, data, len);
+	memcpy(buffer, &netlen, 2);
+	buffer[2] = type;
 
 	if(s->outstate) {
 		// If first handshake has finished, encrypt and HMAC
-		if(!digest_create(&s->outdigest, plaintext, len + 7, plaintext + 7 + len))
-			return false;
+		if(!cipher_set_counter(s->outcipher, &seqno, 4))
+			return error(s, EINVAL, "Failed to set counter");
 
-		if(!cipher_counter_xor(&s->outcipher, plaintext + 4, sizeof ciphertext, ciphertext))
-			return false;
+		if(!cipher_gcm_encrypt_start(s->outcipher, buffer, 3, buffer, NULL))
+			return error(s, EINVAL, "Error encrypting record");
 
-		return s->send_data(s->handle, ciphertext, len + 19);
+		if(!cipher_gcm_encrypt_finish(s->outcipher, data, len, buffer + 3, NULL))
+			return error(s, EINVAL, "Error encrypting record");
+
+		return s->send_data(s->handle, type, buffer, len + 19UL);
 	} else {
 		// Otherwise send as plaintext
-		return s->send_data(s->handle, plaintext + 4, len + 3);
+		memcpy(buffer + 3, data, len);
+		return s->send_data(s->handle, type, buffer, len + 3UL);
 	}
 }
 
 // Send an application record.
-bool 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 char *data, uint16_t len) {
 	// Sanity checks: application cannot send data before handshake is finished,
 	// and only record types 0..127 are allowed.
 	if(!s->outstate)
@@ -106,6 +158,8 @@ 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)
+		return false;
 	s->mykex = realloc(s->mykex, 1 + 32 + keylen);
 	if(!s->mykex)
 		return error(s, errno, strerror(errno));
@@ -117,8 +171,8 @@ 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);
 }
@@ -126,19 +180,20 @@ 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
-	char msg[(1 + 32 + keylen) * 2 + 1];
+	// 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];
 	char sig[siglen];
 
 	msg[0] = s->initiator;
 	memcpy(msg + 1, s->mykex, 1 + 32 + keylen);
-	memcpy(msg + 2 + 32 + keylen, s->hiskex, 1 + 32 + keylen);
+	memcpy(msg + 1 + 33 + keylen, s->hiskex, 1 + 32 + keylen);
+	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);
@@ -148,17 +203,14 @@ static bool send_sig(sptps_t *s) {
 static bool generate_key_material(sptps_t *s, const char *shared, size_t 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 = cipher_open_by_name("aes-256-gcm");
+		s->outcipher = cipher_open_by_name("aes-256-gcm");
+		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 = cipher_keylength(s->incipher) + cipher_keylength(s->outcipher);
 
 	s->key = realloc(s->key, keylen);
 	if(!s->key)
@@ -174,11 +226,11 @@ 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;
+		return error(s, EINVAL, "Failed to generate key material");
 
 	return true;
 }
@@ -194,17 +246,11 @@ static bool receive_ack(sptps_t *s, const char *data, uint16_t 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(!cipher_set_counter_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(!cipher_set_counter_key(s->incipher, s->key + cipher_keylength(s->outcipher)))
+			return error(s, EINVAL, "Failed to set counter");
 	}
 
 	free(s->key);
@@ -223,6 +269,8 @@ static bool receive_kex(sptps_t *s, const char *data, uint16_t len) {
 	// Ignore version number for now.
 
 	// Make a copy of the KEX message, send_sig() and receive_sig() need it
+	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)
 		return error(s, errno, strerror(errno));
@@ -235,27 +283,29 @@ 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)
 		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];
+	char msg[(1 + 32 + keylen) * 2 + 1 + s->labellen];
 
 	msg[0] = !s->initiator;
 	memcpy(msg + 1, s->hiskex, 1 + 32 + keylen);
-	memcpy(msg + 2 + 32 + keylen, s->mykex, 1 + 32 + keylen);
+	memcpy(msg + 1 + 33 + keylen, s->mykex, 1 + 32 + keylen);
+	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))
@@ -268,31 +318,23 @@ static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
 	s->hiskex = NULL;
 
 	// Send cipher change record
-	if(!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(!cipher_set_counter_key(s->outcipher, s->key + cipher_keylength(s->incipher)))
+			return error(s, EINVAL, "Failed to set counter");
 	} 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(!cipher_set_counter_key(s->outcipher, s->key))
+			return error(s, EINVAL, "Failed to set counter");
 	}
 
-	s->outstate = true;
-
 	return true;
 }
 
 // Force another Key EXchange (for testing purposes).
-bool force_kex(sptps_t *s) {
+bool sptps_force_kex(sptps_t *s) {
 	if(!s->outstate || s->state != SPTPS_SECONDARY_KEX)
 		return error(s, EINVAL, "Cannot force KEX in current state");
 
@@ -303,7 +345,6 @@ bool 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.
@@ -319,130 +360,253 @@ static bool receive_handshake(sptps_t *s, const char *data, uint16_t len) {
 			// If we already sent our secondary public ECDH key, we expect the peer to send his.
 			if(!receive_sig(s, data, len))
 				return false;
-			// s->state = SPTPS_ACK;
-			s->state = SPTPS_ACK;
+			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 error(s, EIO, "Invalid session state %d", s->state);
+	}
+}
+
+// Check datagram for valid HMAC
+bool sptps_verify_datagram(sptps_t *s, const char *data, size_t len) {
+	if(!s->instate || len < 21)
+		return error(s, EIO, "Received short packet");
+
+	// TODO: just decrypt without updating the replay window
+
+	return true;
+}
+
+// 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");
+
+	uint32_t seqno;
+	memcpy(&seqno, data, 4);
+	seqno = ntohl(seqno);
+
+	if(!s->instate) {
+		if(seqno != s->inseqno)
+			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)
+			return error(s, EIO, "Application record received before handshake finished");
+
+		return receive_handshake(s, data + 5, len - 5);
 	}
+
+	// Decrypt
+
+	char buffer[len];
+
+	if(!cipher_set_counter(s->incipher, data, sizeof seqno))
+		return error(s, EINVAL, "Failed to set counter");
+	size_t outlen;
+
+	if(!cipher_gcm_decrypt(s->incipher, data + 4, len - 4, buffer, &outlen))
+		return error(s, EIO, "Failed to decrypt and verify packet");
+
+	// 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(int i = s->inseqno; i < seqno; i++)
+					s->late[(i / 8) % s->replaywin] |= 1 << i % 8;
+			}
+		}
+
+		// Mark the current packet as not being late.
+		s->late[(seqno / 8) % s->replaywin] &= ~(1 << seqno % 8);
+	}
+
+	if(seqno >= s->inseqno)
+		s->inseqno = seqno + 1;
+
+	if(!s->inseqno)
+		s->received = 0;
+	else
+		s->received++;
+
+	// Append a NULL byte for safety.
+	buffer[len - 20] = 0;
+
+	uint8_t type = buffer[0];
+
+	if(type < SPTPS_HANDSHAKE) {
+		if(!s->instate)
+			return error(s, EIO, "Application record received before handshake finished");
+		if(!s->receive_record(s->handle, type, buffer + 1, len - 21))
+			abort();
+	} else if(type == SPTPS_HANDSHAKE) {
+		if(!receive_handshake(s, buffer + 1, len - 21))
+			abort();
+	} else {
+		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 receive_data(sptps_t *s, const char *data, size_t len) {
+bool sptps_receive_data(sptps_t *s, const char *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);
+
 	while(len) {
 		// First read the 2 length bytes.
-		if(s->buflen < 6) {
-			size_t toread = 6 - s->buflen;
+		if(s->buflen < 2) {
+			size_t toread = 2 - s->buflen;
 			if(toread > len)
 				toread = len;
 
-			if(s->instate) {
-				if(!cipher_counter_xor(&s->incipher, data, toread, s->inbuf + s->buflen))
-					return false;
-			} else {
-				memcpy(s->inbuf + s->buflen, data, toread);
-			}
+			memcpy(s->inbuf + s->buflen, data, toread);
 
 			s->buflen += toread;
 			len -= toread;
 			data += toread;
 
 			// Exit early if we don't have the full length.
-			if(s->buflen < 6)
+			if(s->buflen < 2)
 				return true;
 
+			// Update sequence number.
+
+			uint32_t seqno = htonl(s->inseqno++);
+
+			// Decrypt the length bytes
+
+			if(s->instate) {
+				if(!cipher_set_counter(s->incipher, &seqno, 4))
+					return error(s, EINVAL, "Failed to set counter");
+
+				if(!cipher_gcm_decrypt_start(s->incipher, s->inbuf, 2, &s->reclen, NULL))
+					return error(s, EINVAL, "Failed to decrypt record");
+			} else {
+				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.
-			uint16_t reclen;
-			memcpy(&reclen, s->inbuf + 4, 2);
-			reclen = htons(reclen);
-			s->inbuf = realloc(s->inbuf, reclen + 23UL);
+			s->inbuf = realloc(s->inbuf, s->reclen + 19UL);
 			if(!s->inbuf)
 				return error(s, errno, strerror(errno));
 
-			// Add sequence number.
-			uint32_t seqno = htonl(s->inseqno++);
-			memcpy(s->inbuf, &seqno, 4);
-
 			// Exit early if we have no more data to process.
 			if(!len)
 				return true;
 		}
 
 		// Read up to the end of the record.
-		uint16_t reclen;
-		memcpy(&reclen, s->inbuf + 4, 2);
-		reclen = htons(reclen);
-		size_t toread = reclen + (s->instate ? 23UL : 7UL) - s->buflen;
+		size_t toread = s->reclen + (s->instate ? 19UL : 3UL) - s->buflen;
 		if(toread > len)
 			toread = len;
 
-		if(s->instate) {
-			if(!cipher_counter_xor(&s->incipher, data, toread, s->inbuf + s->buflen))
-				return false;
-		} else {
-			memcpy(s->inbuf + s->buflen, data, toread);
-		}
-
+		memcpy(s->inbuf + s->buflen, data, toread);
 		s->buflen += toread;
 		len -= toread;
 		data += toread;
 
 		// If we don't have a whole record, exit.
-		if(s->buflen < reclen + (s->instate ? 23UL : 7UL))
+		if(s->buflen < s->reclen + (s->instate ? 19UL : 3UL))
 			return true;
 
-		// Check HMAC.
-		if(s->instate)
-			if(!digest_verify(&s->indigest, s->inbuf, reclen + 7UL, s->inbuf + reclen + 7UL))
-				error(s, EIO, "Invalid HMAC");
+		// Check HMAC and decrypt.
+		if(s->instate) {
+			if(!cipher_gcm_decrypt_finish(s->incipher, 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 + 3UL] = 0;
 
-		uint8_t type = s->inbuf[6];
+		uint8_t type = s->inbuf[2];
 
-		// Handle record.
 		if(type < SPTPS_HANDSHAKE) {
 			if(!s->instate)
 				return error(s, EIO, "Application record received before handshake finished");
-			if(!s->receive_record(s->handle, type, s->inbuf + 7, 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, 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 start_sptps(sptps_t *s, void *handle, bool initiator, 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) {
 	// Initialise struct sptps
 	memset(s, 0, sizeof *s);
 
 	s->handle = handle;
 	s->initiator = initiator;
+	s->datagram = datagram;
 	s->mykey = mykey;
 	s->hiskey = hiskey;
+	s->replaywin = sptps_replaywin;
+	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)
 		return error(s, errno, strerror(errno));
 
-	s->inbuf = malloc(7);
-	if(!s->inbuf)
-		return error(s, errno, strerror(errno));
-	s->buflen = 4;
-	memset(s->inbuf, 0, 4);
+	if(!datagram) {
+		s->inbuf = malloc(7);
+		if(!s->inbuf)
+			return error(s, errno, strerror(errno));
+		s->buflen = 0;
+	}
 
 	memcpy(s->label, label, labellen);
 	s->labellen = labellen;
@@ -456,13 +620,19 @@ bool start_sptps(sptps_t *s, void *handle, bool initiator, ecdsa_t mykey, ecdsa_
 }
 
 // Stop a SPTPS session.
-bool stop_sptps(sptps_t *s) {
+bool sptps_stop(sptps_t *s) {
 	// Clean up any resources.
-	ecdh_free(&s->ecdh);
+	cipher_close(s->incipher);
+	cipher_close(s->outcipher);
+	digest_close(s->indigest);
+	digest_close(s->outdigest);
+	ecdh_free(s->ecdh);
 	free(s->inbuf);
 	free(s->mykex);
 	free(s->hiskex);
 	free(s->key);
 	free(s->label);
+	free(s->late);
+	memset(s, 0, sizeof *s);
 	return true;
 }