/*
sptps.c -- Simple Peer-to-Peer Security
- Copyright (C) 2011 Guus Sliepen <guus@tinc-vpn.org>,
+ Copyright (C) 2011-2012 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 "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
return false;
}
+// 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];
+
+ // 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;
+
+ // Add plaintext (TODO: avoid unnecessary copy)
+ memcpy(buffer + 7, 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, type, buffer + 2, len + 21UL);
+ } else {
+ // Otherwise send as plaintext
+ return s->send_data(s->handle, type, buffer + 2, 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)
+ return send_record_priv_datagram(s, type, data, len);
+
char buffer[len + 23UL];
// Create header with sequence number, length and record type
if(!digest_create(&s->outdigest, buffer, len + 7UL, buffer + 7UL + len))
return false;
- return s->send_data(s->handle, buffer + 4, len + 19UL);
+ return s->send_data(s->handle, type, buffer + 4, 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 + 4, len + 3UL);
}
}
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();
s->mykex = realloc(s->mykex, 1 + 32 + keylen);
if(!s->mykex)
return error(s, errno, strerror(errno));
size_t keylen = ECDH_SIZE;
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))
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))
// Ignore version number for now.
// Make a copy of the KEX message, send_sig() and receive_sig() need it
+ if(s->hiskex)
+ abort();
s->hiskex = realloc(s->hiskex, len);
if(!s->hiskex)
return error(s, errno, strerror(errno));
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))
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
return false;
}
- s->outstate = true;
-
return true;
}
// 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 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.
}
}
+// Check datagram for valid HMAC
+bool sptps_verify_datagram(sptps_t *s, const char *data, size_t len) {
+ if(!s->instate || len < 21)
+ return false;
+
+ char buffer[len + 23];
+ uint16_t netlen = htons(len - 21);
+
+ memcpy(buffer, &netlen, 2);
+ memcpy(buffer + 2, data, len);
+
+ return digest_verify(&s->indigest, buffer, len - 14, buffer + len - 14);
+}
+
+// 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) {
+ fprintf(stderr, "Received invalid packet seqno: %d != %d\n", seqno, s->inseqno);
+ return error(s, EIO, "Invalid packet seqno");
+ }
+
+ 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);
+ }
+
+ // 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.
+ if(s->farfuture++ < s->replaywin >> 2) {
+ fprintf(stderr, "Packet is %d seqs in the future, dropped (%u)\n", seqno - s->inseqno, s->farfuture);
+ return false;
+ }
+ // Unless we have seen lots of them, in which case we consider the others lost.
+ fprintf(stderr, "Lost %d packets\n", seqno - s->inseqno);
+ memset(s->late, 0, 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))) {
+ fprintf(stderr, "Received late or replayed packet, seqno %d, last received %d", seqno, s->inseqno);
+ return false;
+ }
+ } 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);
+ s->farfuture = 0;
+ }
+
+ if(seqno > s->inseqno)
+ s->inseqno = seqno + 1;
+
+ uint16_t netlen = htons(len - 21);
+
+ char buffer[len + 23];
+
+ memcpy(buffer, &netlen, 2);
+ memcpy(buffer + 2, data, len);
+
+ memcpy(&seqno, buffer + 2, 4);
+
+ // Check HMAC and decrypt.
+ if(!digest_verify(&s->indigest, buffer, len - 14, buffer + len - 14))
+ return error(s, EIO, "Invalid HMAC");
+
+ cipher_set_counter(&s->incipher, &seqno, sizeof seqno);
+ if(!cipher_counter_xor(&s->incipher, buffer + 6, len - 4, buffer + 6))
+ return false;
+
+ // Append a NULL byte for safety.
+ buffer[len - 14] = 0;
+
+ uint8_t type = buffer[6];
+
+ 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 + 7, len - 21))
+ return false;
+ } else if(type == SPTPS_HANDSHAKE) {
+ if(!receive_handshake(s, buffer + 7, len - 21))
+ return false;
+ } else {
+ return error(s, EIO, "Invalid record 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)
+ return sptps_receive_data_datagram(s, data, len);
+
while(len) {
// First read the 2 length bytes.
if(s->buflen < 6) {
s->buflen += toread;
len -= toread;
data += toread;
-
+
// Exit early if we don't have the full length.
if(s->buflen < 6)
return true;
}
// Start a SPTPS session.
-bool sptps_start(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));
+ }
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 = 4;
+ memset(s->inbuf, 0, 4);
+ }
memcpy(s->label, label, labellen);
s->labellen = labellen;
// Stop a SPTPS session.
bool sptps_stop(sptps_t *s) {
// Clean up any resources.
+ 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;
}
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