/*
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
if(!digest_create(&s->outdigest, buffer, len + 7UL, buffer + 7UL + len))
return false;
- return s->send_data(s->handle, buffer + 2, len + 21UL);
+ return s->send_data(s->handle, type, buffer + 2, 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 + 2, len + 5UL);
}
}
// Send a record (private version, accepts all record types, handles encryption and authentication).
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;
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))
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;
+ 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 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;
+ // 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)
- fprintf(stderr, "Missed %d packets\n", seqno - s->inseqno);
-
- s->inseqno = seqno + 1;
+ s->inseqno = seqno + 1;
uint16_t netlen = htons(len - 21);
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)
s->buflen += toread;
len -= toread;
data += toread;
-
+
// Exit early if we don't have the full length.
if(s->buflen < 6)
return true;
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)
// 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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