X-Git-Url: http://git.meshlink.io/?p=meshlink;a=blobdiff_plain;f=src%2Fsptps.c;h=ed1f67ff95afd11ac1adfd6f6b95edcca72bf7de;hp=e03b18a8b12e498182ee16b04deb37f337d90be1;hb=963c5055505f2fc117cd5efa06eaa02c9b2bf85d;hpb=2cfd1205dc9c6e9d42cc569f415afe13f52357ec

diff --git a/src/sptps.c b/src/sptps.c
index e03b18a8..ed1f67ff 100644
--- a/src/sptps.c
+++ b/src/sptps.c
@@ -1,6 +1,6 @@
 /*
     sptps.c -- Simple Peer-to-Peer Security
-    Copyright (C) 2014 Guus Sliepen <guus@meshlink.io>
+    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
@@ -27,8 +27,6 @@
 #include "prf.h"
 #include "sptps.h"
 
-unsigned int sptps_replaywin = 16;
-
 /*
    Nonce MUST be exchanged first (done)
    Signatures MUST be done over both nonces, to guarantee the signature is fresh
@@ -50,17 +48,31 @@ unsigned int sptps_replaywin = 16;
 */
 
 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_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 *format, ...) {
+	assert(s_errno);
+	assert(format);
+
 	if(format) {
 		va_list ap;
 		va_start(ap, format);
@@ -73,6 +85,8 @@ static bool error(sptps_t *s, int s_errno, const char *format, ...) {
 }
 
 static void warning(sptps_t *s, const char *format, ...) {
+	assert(format);
+
 	va_list ap;
 	va_start(ap, format);
 	sptps_log(s, 0, format, ap);
@@ -102,8 +116,9 @@ static bool send_record_priv_datagram(sptps_t *s, uint8_t type, const void *data
 }
 // 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 void *data, uint16_t len) {
-	if(s->datagram)
+	if(s->datagram) {
 		return send_record_priv_datagram(s, type, data, len);
+	}
 
 	char buffer[len + 19UL];
 
@@ -127,13 +142,17 @@ static bool send_record_priv(sptps_t *s, uint8_t type, const void *data, uint16_
 
 // Send an application record.
 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);
 }
@@ -143,11 +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)
+	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;
@@ -156,8 +179,9 @@ static bool send_kex(sptps_t *s) {
 	randomize(s->mykex + 1, 32);
 
 	// Create a new ECDH public key.
-	if(!(s->ecdh = ecdh_generate_public(s->mykex + 1 + 32)))
+	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);
 }
@@ -177,33 +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))
+	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) {
 		s->incipher = chacha_poly1305_init();
 		s->outcipher = chacha_poly1305_init();
-		if(!s->incipher || !s->outcipher)
+
+		if(!s->incipher || !s->outcipher) {
 			return error(s, EINVAL, "Failed to open cipher");
+		}
 	}
 
 	// Allocate memory for key material
 	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);
@@ -211,11 +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 + 77, s->label, s->labellen);
 
 	// Use PRF to generate the key material
-	if(!prf(shared, len, seed, s->labellen + 64 + 13, s->key, keylen))
+	if(!prf(shared, len, seed, s->labellen + 64 + 13, s->key, keylen)) {
 		return error(s, EINVAL, "Failed to generate key material");
+	}
 
 	return true;
 }
@@ -227,15 +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) {
-		if(!chacha_poly1305_set_key(s->incipher, s->key))
+		if(!chacha_poly1305_set_key(s->incipher, s->key)) {
 			return error(s, EINVAL, "Failed to set counter");
+		}
 	} else {
-		if(!chacha_poly1305_set_key(s->incipher, s->key + CHACHA_POLY1305_KEYLEN))
+		if(!chacha_poly1305_set_key(s->incipher, s->key + CHACHA_POLY1305_KEYLEN)) {
 			return error(s, EINVAL, "Failed to set counter");
+		}
 	}
 
 	free(s->key);
@@ -248,17 +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)
+	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);
 
@@ -271,8 +316,9 @@ static bool receive_sig(sptps_t *s, const char *data, uint16_t len) {
 	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];
@@ -283,18 +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))
+	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))
+
+	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);
@@ -303,16 +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) {
-		if(!chacha_poly1305_set_key(s->outcipher, s->key + CHACHA_POLY1305_KEYLEN))
+		if(!chacha_poly1305_set_key(s->outcipher, s->key + CHACHA_POLY1305_KEYLEN)) {
 			return error(s, EINVAL, "Failed to set key");
+		}
 	} else {
-		if(!chacha_poly1305_set_key(s->outcipher, s->key))
+		if(!chacha_poly1305_set_key(s->outcipher, s->key)) {
 			return error(s, EINVAL, "Failed to set key");
+		}
 	}
 
 	return true;
@@ -320,8 +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);
@@ -331,87 +386,127 @@ bool sptps_force_kex(sptps_t *s) {
 static bool receive_handshake(sptps_t *s, const char *data, uint16_t len) {
 	// Only a few states to deal with handshaking.
 	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 %d", s->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 || len < 21)
-		return error(s, EIO, "Received short packet");
+	if(!s->instate) {
+		return error(s, EIO, "SPTPS state not ready to verify this datagram");
+	}
 
-	// TODO: just decrypt without updating the replay window
+	if(len < 21) {
+		return error(s, EIO, "Received short packet in sptps_verify_datagram");
+	}
 
-	return true;
+	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 void *vdata, size_t len) {
 	const char *data = vdata;
 
-	if(len < (s->instate ? 21 : 5))
-		return error(s, EIO, "Received short packet");
+	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);
 	seqno = ntohl(seqno);
 
 	if(!s->instate) {
-		if(seqno != s->inseqno)
+		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)
+		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(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->decrypted_buffer = new_buffer;
+	}
 
 	size_t outlen;
 
-	if(!chacha_poly1305_decrypt(s->incipher, seqno, data + 4, len - 4, buffer, &outlen))
+	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");
+	}
 
 	// Replay protection using a sliding window of configurable size.
 	// s->inseqno is expected sequence number
@@ -425,14 +520,16 @@ static bool sptps_receive_data_datagram(sptps_t *s, const void *vdata, size_t le
 				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) {
+			} 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)))
+				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++)
+				for(uint32_t i = s->inseqno; i < seqno; i++) {
 					s->late[(i / 8) % s->replaywin] |= 1 << i % 8;
+				}
 			}
 		}
 
@@ -440,27 +537,33 @@ static bool sptps_receive_data_datagram(sptps_t *s, const void *vdata, size_t le
 		s->late[(seqno / 8) % s->replaywin] &= ~(1 << seqno % 8);
 	}
 
-	if(seqno >= s->inseqno)
+	if(seqno >= s->inseqno) {
 		s->inseqno = seqno + 1;
+	}
 
-	if(!s->inseqno)
+	if(!s->inseqno) {
 		s->received = 0;
-	else
+	} else {
 		s->received++;
+	}
 
 	// Append a NULL byte for safety.
-	buffer[len - 20] = 0;
+	s->decrypted_buffer[len - 20] = 0;
 
-	uint8_t type = buffer[0];
+	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 + 1, len - 21))
+		}
+
+		if(!s->receive_record(s->handle, type, s->decrypted_buffer + 1, len - 21)) {
 			abort();
+		}
 	} else if(type == SPTPS_HANDSHAKE) {
-		if(!receive_handshake(s, buffer + 1, len - 21))
+		if(!receive_handshake(s, s->decrypted_buffer + 1, len - 21)) {
 			abort();
+		}
 	} else {
 		return error(s, EIO, "Invalid record type %d", type);
 	}
@@ -470,28 +573,35 @@ static bool sptps_receive_data_datagram(sptps_t *s, const void *vdata, size_t le
 
 // Receive incoming data. Check if it contains a complete record, if so, handle it.
 bool sptps_receive_data(sptps_t *s, const void *data, size_t len) {
-	if(!s->state)
+	if(!s->state) {
 		return error(s, EIO, "Invalid session state zero");
+	}
 
-	if(s->datagram)
+	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 < 2) {
 			size_t toread = 2 - s->buflen;
-			if(toread > len)
+
+			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 < 2)
+			if(s->buflen < 2) {
 				return true;
+			}
 
 			// Get the length bytes
 
@@ -500,27 +610,33 @@ bool sptps_receive_data(sptps_t *s, const void *data, size_t len) {
 
 			// If we have the length bytes, ensure our buffer can hold the whole request.
 			s->inbuf = realloc(s->inbuf, s->reclen + 19UL);
-			if(!s->inbuf)
+
+			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 ? 19UL : 3UL) - s->buflen;
-		if(toread > len)
+
+		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 ? 19UL : 3UL))
+		if(s->buflen < s->reclen + (s->instate ? 19UL : 3UL)) {
 			return true;
+		}
 
 		// Update sequence number.
 
@@ -528,8 +644,9 @@ bool sptps_receive_data(sptps_t *s, const void *data, size_t len) {
 
 		// Check HMAC and decrypt.
 		if(s->instate) {
-			if(!chacha_poly1305_decrypt(s->incipher, seqno, s->inbuf + 2UL, s->reclen + 17UL, s->inbuf + 2UL, NULL))
+			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.
@@ -538,13 +655,17 @@ bool sptps_receive_data(sptps_t *s, const void *data, size_t len) {
 		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 + 3, 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 + 3, s->reclen))
+			if(!receive_handshake(s, s->inbuf + 3, s->reclen)) {
 				return false;
+			}
 		} else {
 			return error(s, EIO, "Invalid record type %d", type);
 		}
@@ -557,30 +678,49 @@ bool sptps_receive_data(sptps_t *s, const void *data, size_t len) {
 
 // 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) {
+	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 = sptps_replaywin;
+	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)
+
+		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 = 0;
 	}
 
@@ -607,6 +747,8 @@ bool sptps_stop(sptps_t *s) {
 	free(s->key);
 	free(s->label);
 	free(s->late);
-	memset(s, 0, sizeof *s);
+	memset(s->decrypted_buffer, 0, s->decrypted_buffer_len);
+	free(s->decrypted_buffer);
+	memset(s, 0, sizeof(*s));
 	return true;
 }