Remove use of strcpy() and sprintf().
[tinc] / src / sptps.c
index 6668763..712d50e 100644 (file)
@@ -1,6 +1,7 @@
 /*
     sptps.c -- Simple Peer-to-Peer Security
-    Copyright (C) 2011 Guus Sliepen <guus@tinc-vpn.org>,
+    Copyright (C) 2011-2015 Guus Sliepen <guus@tinc-vpn.org>,
+                  2010      Brandon L. Black <blblack@gmail.com>
 
     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
 
 #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"
 
-char *logfilename;
-#include "utils.c"
+unsigned int sptps_replaywin = 16;
 
 /*
    Nonce MUST be exchanged first (done)
@@ -39,7 +39,7 @@ char *logfilename;
 
    Sign all handshake messages up to ECDHE kex with long-term public keys. (done)
 
-   HMACed KEX finished message to prevent downgrade attacks and prove you have the right key material (done by virtue of ECDSA over the whole ECDHE exchange?)
+   HMACed KEX finished message to prevent downgrade attacks and prove you have the right key material (done by virtue of Ed25519 over the whole ECDHE exchange?)
 
    Explicit close message needs to be added.
 
@@ -50,46 +50,84 @@ 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;
 }
 
-// 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 buffer[len + 23UL];
-       //char ciphertext[len + 19];
+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);
+}
 
-       // Create header with sequence number, length and record type
-       uint32_t seqno = htonl(s->outseqno++);
-       uint16_t netlen = htons(len);
+// 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 void *data, uint16_t len) {
+       char buffer[len + 21UL];
 
-       memcpy(buffer, &seqno, 4);
-       memcpy(buffer + 4, &netlen, 2);
-       buffer[6] = type;
+       // Create header with sequence number, length and record 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
-               if(!cipher_counter_xor(&s->outcipher, buffer + 4, len + 3UL, buffer + 4))
-                       return false;
+               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, 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 void *data, uint16_t len) {
+       if(s->datagram)
+               return send_record_priv_datagram(s, type, data, len);
 
-               if(!digest_create(&s->outdigest, buffer, len + 7UL, buffer + 7UL + len))
-                       return false;
+       char buffer[len + 19UL];
 
-               return s->send_data(s->handle, buffer + 4, len + 19UL);
+       // Create header with sequence number, length and record type
+       uint32_t seqno = s->outseqno++;
+       uint16_t netlen = htons(len);
+
+       memcpy(buffer, &netlen, 2);
+       buffer[2] = type;
+       memcpy(buffer + 3, data, len);
+
+       if(s->outstate) {
+               // If first handshake has finished, encrypt and HMAC
+               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 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) {
        // Sanity checks: application cannot send data before handshake is finished,
        // and only record types 0..127 are allowed.
        if(!s->outstate)
@@ -106,6 +144,8 @@ 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));
@@ -117,28 +157,29 @@ 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);
 }
 
-// Send a SIGnature record, containing an ECDSA signature over both KEX records.
+// Send a SIGnature record, containing an Ed25519 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 +189,14 @@ 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 = 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)
@@ -166,7 +204,7 @@ static bool generate_key_material(sptps_t *s, const char *shared, size_t len) {
 
        // Create the HMAC seed, which is "key expansion" + session label + server nonce + client nonce
        char seed[s->labellen + 64 + 13];
-       strcpy(seed, "key expansion");
+       memcpy(seed, "key expansion", 13);
        if(s->initiator) {
                memcpy(seed + 13, s->mykex + 1, 32);
                memcpy(seed + 45, s->hiskex + 1, 32);
@@ -174,11 +212,11 @@ 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 +232,11 @@ 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(!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);
@@ -223,6 +255,8 @@ 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 +269,29 @@ 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 +304,23 @@ 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(!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");
        }
 
-       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 +331,6 @@ 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 +346,274 @@ 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);
        }
 }
 
-// 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) {
-       while(len) {
-               // First read the 2 length bytes.
-               if(s->buflen < 6) {
-                       size_t toread = 6 - s->buflen;
-                       if(toread > len)
-                               toread = len;
-
-                       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)
-                               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);
+static bool sptps_check_seqno(sptps_t *s, uint32_t seqno, bool update_state) {
+       // 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) {
+                               // Prevent packets that jump far ahead of the queue from causing many others to be dropped.
+                               bool farfuture = s->farfuture < s->replaywin >> 2;
+                               if (update_state)
+                                       s->farfuture++;
+                               if(farfuture)
+                                       return update_state ? error(s, EIO, "Packet is %d seqs in the future, dropped (%u)\n", seqno - s->inseqno, s->farfuture) : false;
+
+                               // Unless we have seen lots of them, in which case we consider the others lost.
+                               if(update_state)
+                                       warning(s, "Lost %d packets\n", seqno - s->inseqno);
+                               if (update_state) {
+                                       // 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 update_state ? error(s, EIO, "Received late or replayed packet, seqno %d, last received %d\n", seqno, s->inseqno) : false;
+                       } else if (update_state) {
+                               // 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;
                        }
+               }
 
-                       s->reclen = ntohs(s->reclen);
+               if (update_state) {
+                       // Mark the current packet as not being late.
+                       s->late[(seqno / 8) % s->replaywin] &= ~(1 << seqno % 8);
+                       s->farfuture = 0;
+               }
+       }
 
-                       // 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));
+       if (update_state) {
+               if(seqno >= s->inseqno)
+                       s->inseqno = seqno + 1;
 
-                       // Add sequence number.
-                       uint32_t seqno = htonl(s->inseqno++);
-                       memcpy(s->inbuf, &seqno, 4);
+               if(!s->inseqno)
+                       s->received = 0;
+               else
+                       s->received++;
+       }
 
-                       // Exit early if we have no more data to process.
-                       if(!len)
-                               return true;
-               }
+       return true;
+}
+
+// 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");
 
-               // Read up to the end of the record.
-               size_t toread = s->reclen + (s->instate ? 23UL : 7UL) - s->buflen;
+       uint32_t seqno;
+       memcpy(&seqno, data, 4);
+       seqno = ntohl(seqno);
+       if (!sptps_check_seqno(s, seqno, false))
+               return false;
+
+       char buffer[len];
+       size_t outlen;
+       return chacha_poly1305_decrypt(s->incipher, seqno, data + 4, len - 4, buffer, &outlen);
+}
+
+// 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);
+       data += 4; len -= 4;
+
+       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++); len--;
+
+               if(type != SPTPS_HANDSHAKE)
+                       return error(s, EIO, "Application record received before handshake finished");
+
+               return receive_handshake(s, data, len);
+       }
+
+       // Decrypt
+
+       char buffer[len];
+       size_t outlen;
+       if(!chacha_poly1305_decrypt(s->incipher, seqno, data, len, buffer, &outlen))
+               return error(s, EIO, "Failed to decrypt and verify packet");
+
+       if(!sptps_check_seqno(s, seqno, true))
+               return false;
+
+       // Append a NULL byte for safety.
+       buffer[outlen] = 0;
+
+       data = buffer;
+       len = outlen;
+
+       uint8_t type = *(data++); len--;
+
+       if(type < SPTPS_HANDSHAKE) {
+               if(!s->instate)
+                       return error(s, EIO, "Application record received before handshake finished");
+               if(!s->receive_record(s->handle, type, data, len))
+                       return false;
+       } else if(type == SPTPS_HANDSHAKE) {
+               if(!receive_handshake(s, data, len))
+                       return false;
+       } 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.
+size_t sptps_receive_data(sptps_t *s, const void *data, size_t len) {
+       size_t total_read = 0;
+
+       if(!s->state)
+               return error(s, EIO, "Invalid session state zero");
+
+       if(s->datagram)
+               return sptps_receive_data_datagram(s, data, len) ? len : false;
+
+       // First read the 2 length bytes.
+       if(s->buflen < 2) {
+               size_t toread = 2 - s->buflen;
                if(toread > len)
                        toread = len;
 
                memcpy(s->inbuf + s->buflen, data, toread);
+
+               total_read += toread;
                s->buflen += toread;
                len -= toread;
                data += toread;
 
-               // If we don't have a whole record, exit.
-               if(s->buflen < s->reclen + (s->instate ? 23UL : 7UL))
-                       return true;
+               // Exit early if we don't have the full length.
+               if(s->buflen < 2)
+                       return total_read;
 
-               // 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");
+               // Get the length bytes
 
-                       if(!cipher_counter_xor(&s->incipher, s->inbuf + 6UL, s->reclen + 1UL, s->inbuf + 6UL))
-                               return false;
-               }
+               memcpy(&s->reclen, s->inbuf, 2);
+               s->reclen = ntohs(s->reclen);
 
-               // Append a NULL byte for safety.
-               s->inbuf[s->reclen + 7UL] = 0;
+               // 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)
+                       return error(s, errno, strerror(errno));
 
-               uint8_t type = s->inbuf[6];
+               // Exit early if we have no more data to process.
+               if(!len)
+                       return total_read;
+       }
 
-               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, s->reclen))
-                               return false;
-               } else if(type == SPTPS_HANDSHAKE) {
-                       if(!receive_handshake(s, s->inbuf + 7, s->reclen))
-                               return false;
-               } else {
-                       return error(s, EIO, "Invalid record type");
-               }
+       // Read up to the end of the record.
+       size_t toread = s->reclen + (s->instate ? 19UL : 3UL) - s->buflen;
+       if(toread > len)
+               toread = len;
+
+       memcpy(s->inbuf + s->buflen, data, toread);
+       total_read += toread;
+       s->buflen += toread;
+       len -= toread;
+       data += toread;
+
+       // If we don't have a whole record, exit.
+       if(s->buflen < s->reclen + (s->instate ? 19UL : 3UL))
+               return total_read;
+
+       // Update sequence number.
+
+       uint32_t seqno = s->inseqno++;
 
-               s->buflen = 4;
+       // Check HMAC and decrypt.
+       if(s->instate) {
+               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");
        }
 
-       return true;
+       // Append a NULL byte for safety.
+       s->inbuf[s->reclen + 3UL] = 0;
+
+       uint8_t type = s->inbuf[2];
+
+       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 + 3, s->reclen))
+                       return false;
+       } else if(type == SPTPS_HANDSHAKE) {
+               if(!receive_handshake(s, s->inbuf + 3, s->reclen))
+                       return false;
+       } else {
+               return error(s, EIO, "Invalid record type %d", type);
+       }
+
+       s->buflen = 0;
+
+       return total_read;
 }
 
 // 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 void *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 +627,17 @@ 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);
+       chacha_poly1305_exit(s->incipher);
+       chacha_poly1305_exit(s->outcipher);
+       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;
 }