wg-mux-*: add note on --auth-secret purpose

README.rst

@@ -845,15 +845,22 @@ via --ident-\* string (derived from /etc/machine-id by default), and both
 client/server need to use same -s/--auth-secret to create/validate MACs in each
 packet.
 
+Note that all that --auth-secret is used for is literally handing-out sequential
+numbers, and isn't expected to be strong protection against anything, unlike ssh
+auth that should come after that.
+
 wg-mux-\*
 '''''''''
 
 Same thing as ssh-reverse-mux-\* scripts above, but for negotiating WireGuard
 tunnels, with persistent host tunnel IPs tracked via --ident-\* strings with
 simple auth via MACs on UDP packets derived from symmetric -s/--auth-secret.
 
-Host identity, wg port, public keys and tunnel IPs are authenticated,
-but are sent in the clear otherwise.
+Client identity, wg port, public key and tunnel IPs are sent in the clear with
+relatively weak authentication (hmac of -s/--auth-secret string), but wg server
+is also authenticated by pre-shared public key (and --wg-psk, if specified).
+
+Such setup is roughly equivalent to a weak-password-protected public network.
 
 Runs "wg set" commands to update configuration, which need privileges, but can
 be wrapped in sudo or suid/caps stuff via --wg-cmd to avoid root in the rest of

wg-mux-client

@@ -210,18 +210,18 @@ def build_req(secret, ident, wg_key_pk):
 def parse_res(secret, ident, res):
 	if not res: return
 	try:
-		fmt = 'BBHB{}s{}s32s'.format(res[0], {4: 4, 6: 16}[res[1]])
+		fmt = 'BBHB{}s{}s'.format(res[0], {4: 4, 6: 16}[res[1]])
 		( ident_len, ip_len, wg_port, wg_mask, ident_buff,
-			wg_addr, wg_pk, salt, mac ) = struct.unpack(fmt + '8s32s', res)
+			wg_addr, salt, mac ) = struct.unpack(fmt + '8s32s', res)
 		mac_chk = hashlib.blake2s(
 			res[:struct.calcsize(fmt)], key=to_bytes(secret), salt=salt ).digest()
 		if not secrets.compare_digest(mac, mac_chk): raise AuthError('MAC mismatch')
 	except (KeyError, struct.error, AuthError) as err:
 		log.debug('Failed to parse/auth response value: {}', err)
 		return
-	wg_addr, wg_pk = ipaddress.ip_address(wg_addr), b64_encode(wg_pk)
+	wg_addr = ipaddress.ip_address(wg_addr)
 	wg_net = f'{wg_addr}/{wg_mask}'
-	return wg_pk, wg_addr, wg_net, wg_port
+	return wg_addr, wg_net, wg_port
 
 
 async def mux_negotiate(
@@ -266,6 +266,7 @@ def main(args=None, conf=None):
 	group.add_argument('host',
 		help='Host or address (to be resolved via gai) or a host[:port] spec.'
 			' "port" will be used for -m/--mux-port option, if specified here.')
+	group.add_argument('pubkey', help='Base64-encoded WireGuard server public key.')
 	group.add_argument('-m', '--mux-port',
 		default=conf.mux_port, type=int, metavar='port',
 		help='Remote UDP port on which corresponding'
@@ -297,10 +298,6 @@ def main(args=None, conf=None):
 	group = parser.add_argument_group('WireGuard options')
 	group.add_argument('--wg-iface', metavar='iface', default=conf.wg_iface,
 		help='WireGuard interface name to configure. Default: %(default)s')
-	group.add_argument('--wg-pk', metavar='base64-pubkey',
-		help='WireGuard server public key.'
-			' Be sure to specify this if it is important to authenticate server.'
-			' Default is to use one returned by mux-server.')
 	group.add_argument('--wg-port', type=int, metavar='port',
 		help='Remote WireGuard port to use. Default is to use one returned by mux-server.')
 	group.add_argument('--wg-psk', metavar='file',
@@ -371,6 +368,7 @@ def main(args=None, conf=None):
 
 	wg_cmd = opts.wg_cmd.split()
 	wg_addr_net = ipaddress.ip_network(opts.wg_net)
+	wg_pk = opts.pubkey
 
 	wg_key = derive_wg_key(
 		pl.Path(conf.key_source_ssh).expanduser(),
@@ -386,14 +384,13 @@ def main(args=None, conf=None):
 		for sig in 'INT TERM'.split():
 			loop.add_signal_handler(getattr(signal, f'SIG{sig}'), muxer.cancel)
 		try:
-			wg_pk, wg_addr, wg_mask, wg_port = loop.run_until_complete(
+			wg_addr, wg_mask, wg_port = loop.run_until_complete(
 				aio_wait_or_cancel(loop, muxer, opts.timeout) )
 		except (asyncio.CancelledError, asyncio.TimeoutError) as err:
 			log.debug('mux_negotiate cancelled: {}', err_fmt(err))
 			return
 
 	if opts.wg_port: wg_port = opts.wg_port
-	if opts.wg_pk: wg_pk = opts.wg_pk
 	if not wg_addr_net and not wg_net:
 		print( 'ERROR: mux-server returned address'
 			' without network, and no --wg-net is specified', file=sys.stderr )

wg-mux-server

@@ -11,7 +11,6 @@ class WGMuxConfig:
 	mux_port = 8739
 	mux_timeout = 5.0
 	wg_iface = 'wg'
-	wg_pk = bytes(32)
 	wg_port = 2200
 	wg_net = '10.215.72.0/24'
 	n_skip = 1 # to reserve e.g. 10.215.72.1/24 for server
@@ -136,11 +135,11 @@ def parse_req(secret, req):
 		return
 	return b64_encode(ident), b64_encode(wg_pk_peer)
 
-def build_res(secret, ident, wg_addr, wg_net, wg_pk, wg_port):
+def build_res(secret, ident, wg_addr, wg_net, wg_port):
 	ident_buff = to_bytes(ident)
 	salt, payload = os.urandom(8), bin_pack(
-		'>BBHBzzz', len(ident_buff), wg_addr.version,
-		wg_port, wg_net.prefixlen, ident_buff, wg_addr.packed, wg_pk )
+		'>BBHBzz', len(ident_buff), wg_addr.version,
+		wg_port, wg_net.prefixlen, ident_buff, wg_addr.packed )
 	mac = hashlib.blake2s(payload, key=to_bytes(secret), salt=salt).digest()
 	return payload + salt + mac
 
@@ -170,8 +169,8 @@ async def mux_listen( loop, secret, ident_db,
 				await responses[ident]
 			peer_info = init_peer(ident, wg_pk_peer, req_addr)
 			if not peer_info: continue
-			wg_addr, wg_net, wg_pk, wg_port = peer_info
-			response = build_res(secret, ident, wg_addr, wg_net, wg_pk, wg_port)
+			wg_addr, wg_net, wg_port = peer_info
+			response = build_res(secret, ident, wg_addr, wg_net, wg_port)
 			responses[ident] = loop.create_task(
 				mux_send(loop, transport, response, req_addr, delays) )
 	finally:
@@ -213,8 +212,6 @@ def main(args=None, conf=None):
 	group = parser.add_argument_group('WireGuard options')
 	group.add_argument('--wg-iface', metavar='iface', default=conf.wg_iface,
 		help='WireGuard interface name to configure. Default: %(default)s')
-	group.add_argument('--wg-pk', metavar='base64-pubkey', default=b64_encode(conf.wg_pk),
-		help='WireGuard server public key. Empty one will be sent, if not specified.')
 	group.add_argument('--wg-port', type=int, metavar='port', default=conf.wg_port,
 		help='WireGuard endpoint port to send to mux-clients. Default: %(default)s')
 	group.add_argument('--wg-psk', metavar='file',
@@ -313,7 +310,7 @@ def main(args=None, conf=None):
 				'peer', wg_pk_peer, 'remove' ], stderr=sp.DEVNULL)
 			sp.run(cmd, check=True)
 		else: log.debug('Config for peer: {}', ' '.join(cmd))
-		return wg_addr, wg_net, b64_decode(opts.wg_pk), opts.wg_port
+		return wg_addr, wg_net, opts.wg_port
 
 	retry_delays = retries_within_timeout(opts.attempts, opts.timeout)
 	with contextlib.closing(asyncio.get_event_loop()) as loop: