Reticulum/RNS/Link.py

from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives.kdf.hkdf import HKDF
from cryptography.fernet import Fernet
from time import sleep
from .vendor import umsgpack as umsgpack
import threading
import base64
import math
import time
import RNS

import traceback

class LinkCallbacks:
	def __init__(self):
		self.link_established = None
		self.link_closed = None
		self.packet = None
		self.resource_started = None
		self.resource_concluded = None

class Link:
	CURVE = ec.SECP256R1()
	ECPUBSIZE = 91
	BLOCKSIZE = 16
	AES_HMAC_OVERHEAD = 58
	MDU = math.floor((RNS.Reticulum.MDU-AES_HMAC_OVERHEAD)/BLOCKSIZE)*BLOCKSIZE - 1

	# TODO: This should not be hardcoded,
	# but calculated from something like 
	# first-hop RTT latency and distance 
	DEFAULT_TIMEOUT = 15.0
	TIMEOUT_FACTOR = 3
	STALE_GRACE = 2
	KEEPALIVE = 180

	PENDING   = 0x00
	HANDSHAKE = 0x01
	ACTIVE    = 0x02
	STALE     = 0x03
	CLOSED    = 0x04

	TIMEOUT            = 0x01
	INITIATOR_CLOSED   = 0x02
	DESTINATION_CLOSED = 0x03

	ACCEPT_NONE = 0x00
	ACCEPT_APP  = 0x01
	ACCEPT_ALL  = 0x02
	resource_strategies = [ACCEPT_NONE, ACCEPT_APP, ACCEPT_ALL]

	@staticmethod
	def validateRequest(owner, data, packet):
		if len(data) == (Link.ECPUBSIZE):
			try:
				link = Link(owner = owner, peer_pub_bytes = data[:Link.ECPUBSIZE])
				link.setLinkID(packet)
				link.destination = packet.destination
				RNS.log("Validating link request "+RNS.prettyhexrep(link.link_id), RNS.LOG_VERBOSE)
				link.handshake()
				link.attached_interface = packet.receiving_interface
				link.prove()
				link.request_time = time.time()
				RNS.Transport.registerLink(link)
				link.last_inbound = time.time()
				link.start_watchdog()

				# TODO: Why was link_established callback here? Seems weird
				# to call this before RTT packet has been received
				#if self.owner.callbacks.link_established != None:
				#	self.owner.callbacks.link_established(link)
				
				RNS.log("Incoming link request "+str(link)+" accepted", RNS.LOG_VERBOSE)
				return link

			except Exception as e:
				RNS.log("Validating link request failed", RNS.LOG_VERBOSE)
				traceback.print_exc()
				return None

		else:
			RNS.log("Invalid link request payload size, dropping request", RNS.LOG_VERBOSE)
			return None


	def __init__(self, destination=None, owner=None, peer_pub_bytes = None):
		if destination != None and destination.type != RNS.Destination.SINGLE:
			raise TypeError("Links can only be established to the \"single\" destination type")
		self.rtt = None
		self.callbacks = LinkCallbacks()
		self.resource_strategy = Link.ACCEPT_NONE
		self.outgoing_resources = []
		self.incoming_resources = []
		self.last_inbound = 0
		self.last_outbound = 0
		self.tx = 0
		self.rx = 0
		self.txbytes = 0
		self.rxbytes = 0
		self.default_timeout = Link.DEFAULT_TIMEOUT
		self.proof_timeout = self.default_timeout
		self.timeout_factor = Link.TIMEOUT_FACTOR
		self.keepalive = Link.KEEPALIVE
		self.watchdog_lock = False
		self.status = Link.PENDING
		self.type = RNS.Destination.LINK
		self.owner = owner
		self.destination = destination
		self.attached_interface = None
		self.__encryption_disabled = False
		if self.destination == None:
			self.initiator = False
		else:
			self.initiator = True
		
		self.prv = ec.generate_private_key(Link.CURVE, default_backend())
		self.pub = self.prv.public_key()
		self.pub_bytes = self.pub.public_bytes(
			encoding=serialization.Encoding.DER,
			format=serialization.PublicFormat.SubjectPublicKeyInfo
		)

		if peer_pub_bytes == None:
			self.peer_pub = None
			self.peer_pub_bytes = None
		else:
			self.loadPeer(peer_pub_bytes)

		if (self.initiator):
			self.request_data = self.pub_bytes
			self.packet = RNS.Packet(destination, self.request_data, packet_type=RNS.Packet.LINKREQUEST)
			self.packet.pack()
			self.setLinkID(self.packet)
			RNS.Transport.registerLink(self)
			self.request_time = time.time()
			self.start_watchdog()
			self.packet.send()
			RNS.log("Link request "+RNS.prettyhexrep(self.link_id)+" sent to "+str(self.destination), RNS.LOG_VERBOSE)


	def loadPeer(self, peer_pub_bytes):
		self.peer_pub_bytes = peer_pub_bytes
		self.peer_pub = serialization.load_der_public_key(peer_pub_bytes, backend=default_backend())
		if not hasattr(self.peer_pub, "curve"):
			self.peer_pub.curve = Link.CURVE

	def setLinkID(self, packet):
		self.link_id = packet.getTruncatedHash()
		self.hash = self.link_id

	def handshake(self):
		self.status = Link.HANDSHAKE
		self.shared_key = self.prv.exchange(ec.ECDH(), self.peer_pub)
		self.derived_key = HKDF(
			algorithm=hashes.SHA256(),
			length=32,
			salt=self.getSalt(),
			info=self.getContext(),
			backend=default_backend()
		).derive(self.shared_key)

	def prove(self):
		signed_data = self.link_id+self.pub_bytes
		signature = self.owner.identity.sign(signed_data)

		proof_data = self.pub_bytes+signature
		proof = RNS.Packet(self, proof_data, packet_type=RNS.Packet.PROOF, context=RNS.Packet.LRPROOF)
		proof.send()

	def prove_packet(self, packet):
		signature = self.sign(packet.packet_hash)
		# TODO: Hardcoded as explicit proof for now
		# if RNS.Reticulum.should_use_implicit_proof():
		# 	proof_data = signature
		# else:
		# 	proof_data = packet.packet_hash + signature
		proof_data = packet.packet_hash + signature

		proof = RNS.Packet(self, proof_data, RNS.Packet.PROOF)
		proof.send()

	def validateProof(self, packet):
		if self.initiator:
			peer_pub_bytes = packet.data[:Link.ECPUBSIZE]
			signed_data = self.link_id+peer_pub_bytes
			signature = packet.data[Link.ECPUBSIZE:RNS.Identity.KEYSIZE//8+Link.ECPUBSIZE]

			if self.destination.identity.validate(signature, signed_data):
				self.loadPeer(peer_pub_bytes)
				self.handshake()
				self.rtt = time.time() - self.request_time
				self.attached_interface = packet.receiving_interface
				RNS.Transport.activateLink(self)
				RNS.log("Link "+str(self)+" established with "+str(self.destination)+", RTT is "+str(self.rtt), RNS.LOG_VERBOSE)
				rtt_data = umsgpack.packb(self.rtt)
				rtt_packet = RNS.Packet(self, rtt_data, context=RNS.Packet.LRRTT)
				RNS.log("Sending RTT packet", RNS.LOG_EXTREME);
				rtt_packet.send()

				self.status = Link.ACTIVE
				if self.callbacks.link_established != None:
					thread = threading.Thread(target=self.callbacks.link_established, args=(self,))
					thread.setDaemon(True)
					thread.start()
			else:
				RNS.log("Invalid link proof signature received by "+str(self), RNS.LOG_VERBOSE)
				# TODO: should we really do this, or just wait
				# for a valid one? Needs analysis.
				self.teardown()


	def rtt_packet(self, packet):
		try:
			# TODO: This is crude, we should use the delta
			# to model a more representative per-bit round
			# trip time, and use that to set a sensible RTT
			# expectancy for the link. This will have to do
			# for now though.
			measured_rtt = time.time() - self.request_time
			plaintext = self.decrypt(packet.data)
			rtt = umsgpack.unpackb(plaintext)
			self.rtt = max(measured_rtt, rtt)
			self.status = Link.ACTIVE
			
			if self.owner.callbacks.link_established != None:
					self.owner.callbacks.link_established(self)
		except Exception as e:
			RNS.log("Error occurred while processing RTT packet, tearing down link", RNS.LOG_ERROR)
			traceback.print_exc()
			self.teardown()

	def getSalt(self):
		return self.link_id

	def getContext(self):
		return None

	def teardown(self):
		if self.status != Link.PENDING and self.status != Link.CLOSED:
			teardown_packet = RNS.Packet(self, self.link_id, context=RNS.Packet.LINKCLOSE)
			teardown_packet.send()
		self.status = Link.CLOSED
		if self.initiator:
			self.teardown_reason = Link.INITIATOR_CLOSED
		else:
			self.teardown_reason = Link.DESTINATION_CLOSED
		self.link_closed()

	def teardown_packet(self, packet):
		try:
			plaintext = self.decrypt(packet.data)
			if plaintext == self.link_id:
				self.status = Link.CLOSED
				if self.initiator:
					self.teardown_reason = Link.DESTINATION_CLOSED
				else:
					self.teardown_reason = Link.INITIATOR_CLOSED
				self.link_closed()
		except Exception as e:
			pass

	def link_closed(self):
		for resource in self.incoming_resources:
			resource.cancel()
		for resource in self.outgoing_resources:
			resource.cancel()
			
		self.prv = None
		self.pub = None
		self.pub_bytes = None
		self.shared_key = None
		self.derived_key = None

		if self.callbacks.link_closed != None:
			self.callbacks.link_closed(self)

	def start_watchdog(self):
		thread = threading.Thread(target=self.__watchdog_job)
		thread.setDaemon(True)
		thread.start()

	def __watchdog_job(self):
		while not self.status == Link.CLOSED:
			while (self.watchdog_lock):
				sleep(max(self.rtt, 0.025))

			if not self.status == Link.CLOSED:
				# Link was initiated, but no response
				# from destination yet
				if self.status == Link.PENDING:
					next_check = self.request_time + self.proof_timeout
					sleep_time = next_check - time.time()
					if time.time() >= self.request_time + self.proof_timeout:
						RNS.log("Link establishment timed out", RNS.LOG_VERBOSE)
						self.status = Link.CLOSED
						self.teardown_reason = Link.TIMEOUT
						self.link_closed()
						sleep_time = 0.001

				elif self.status == Link.HANDSHAKE:
					next_check = self.request_time + self.proof_timeout
					sleep_time = next_check - time.time()
					if time.time() >= self.request_time + self.proof_timeout:
						RNS.log("Timeout waiting for RTT packet from link initiator", RNS.LOG_DEBUG)
						self.status = Link.CLOSED
						self.teardown_reason = Link.TIMEOUT
						self.link_closed()
						sleep_time = 0.001

				elif self.status == Link.ACTIVE:
					if time.time() >= self.last_inbound + self.keepalive:
						sleep_time = self.rtt * self.timeout_factor + Link.STALE_GRACE
						self.status = Link.STALE
						if self.initiator:
							self.send_keepalive()
					else:
						sleep_time = (self.last_inbound + self.keepalive) - time.time()

				elif self.status == Link.STALE:
					sleep_time = 0.001
					self.status = Link.CLOSED
					self.teardown_reason = Link.TIMEOUT
					self.link_closed()


				if sleep_time == 0:
					RNS.log("Warning! Link watchdog sleep time of 0!", RNS.LOG_ERROR)
				if sleep_time == None or sleep_time < 0:
					RNS.log("Timing error! Tearing down link "+str(self)+" now.", RNS.LOG_ERROR)
					self.teardown()

				sleep(sleep_time)


	def send_keepalive(self):
		keepalive_packet = RNS.Packet(self, bytes([0xFF]), context=RNS.Packet.KEEPALIVE)
		keepalive_packet.send()

	def receive(self, packet):
		self.watchdog_lock = True
		if not self.status == Link.CLOSED and not (self.initiator and packet.context == RNS.Packet.KEEPALIVE and packet.data == bytes([0xFF])):
			if packet.receiving_interface != self.attached_interface:
				RNS.log("Link-associated packet received on unexpected interface! Someone might be trying to manipulate your communication!", RNS.LOG_ERROR)
			else:
				self.last_inbound = time.time()
				self.rx += 1
				self.rxbytes += len(packet.data)
				if self.status == Link.STALE:
					self.status = Link.ACTIVE

				if packet.packet_type == RNS.Packet.DATA:
					if packet.context == RNS.Packet.NONE:
						plaintext = self.decrypt(packet.data)
						if self.callbacks.packet != None:
							thread = threading.Thread(target=self.callbacks.packet, args=(plaintext, packet))
							thread.setDaemon(True)
							thread.start()
						
						if self.destination.proof_strategy == RNS.Destination.PROVE_ALL:
							packet.prove()

						elif self.destination.proof_strategy == RNS.Destination.PROVE_APP:
							if self.destination.callbacks.proof_requested:
								self.destination.callbacks.proof_requested(packet)

					elif packet.context == RNS.Packet.LRRTT:
						if not self.initiator:
							self.rtt_packet(packet)

					elif packet.context == RNS.Packet.LINKCLOSE:
						self.teardown_packet(packet)

					elif packet.context == RNS.Packet.RESOURCE_ADV:
						packet.plaintext = self.decrypt(packet.data)
						if self.resource_strategy == Link.ACCEPT_NONE:
							pass
						elif self.resource_strategy == Link.ACCEPT_APP:
							if self.callbacks.resource != None:
								thread = threading.Thread(target=self.callbacks.resource, args=(packet))
								thread.setDaemon(True)
								thread.start()
						elif self.resource_strategy == Link.ACCEPT_ALL:
							RNS.Resource.accept(packet, self.callbacks.resource_concluded)

					elif packet.context == RNS.Packet.RESOURCE_REQ:
						plaintext = self.decrypt(packet.data)
						if ord(plaintext[:1]) == RNS.Resource.HASHMAP_IS_EXHAUSTED:
							resource_hash = plaintext[1+RNS.Resource.MAPHASH_LEN:RNS.Identity.HASHLENGTH//8+1+RNS.Resource.MAPHASH_LEN]
						else:
							resource_hash = plaintext[1:RNS.Identity.HASHLENGTH//8+1]
						for resource in self.outgoing_resources:
							if resource.hash == resource_hash:
								resource.request(plaintext)

					elif packet.context == RNS.Packet.RESOURCE_HMU:
						plaintext = self.decrypt(packet.data)
						resource_hash = plaintext[:RNS.Identity.HASHLENGTH//8]
						for resource in self.incoming_resources:
							if resource_hash == resource.hash:
								resource.hashmap_update_packet(plaintext)

					elif packet.context == RNS.Packet.RESOURCE_ICL:
						plaintext = self.decrypt(packet.data)
						resource_hash = plaintext[:RNS.Identity.HASHLENGTH//8]
						for resource in self.incoming_resources:
							if resource_hash == resource.hash:
								resource.cancel()

					elif packet.context == RNS.Packet.KEEPALIVE:
						if not self.initiator and packet.data == bytes([0xFF]):
							keepalive_packet = RNS.Packet(self, bytes([0xFE]), context=RNS.Packet.KEEPALIVE)
							keepalive_packet.send()


					# TODO: find the most efficient way to allow multiple
					# transfers at the same time, sending resource hash on
					# each packet is a huge overhead. Probably some kind
					# of hash -> sequence map
					elif packet.context == RNS.Packet.RESOURCE:
						for resource in self.incoming_resources:
							resource.receive_part(packet)

				elif packet.packet_type == RNS.Packet.PROOF:
					if packet.context == RNS.Packet.RESOURCE_PRF:
						resource_hash = packet.data[0:RNS.Identity.HASHLENGTH//8]
						for resource in self.outgoing_resources:
							if resource_hash == resource.hash:
								resource.validateProof(packet.data)

		self.watchdog_lock = False


	def encrypt(self, plaintext):
		if self.__encryption_disabled:
			return plaintext
		try:
			fernet = Fernet(base64.urlsafe_b64encode(self.derived_key))
			ciphertext = base64.urlsafe_b64decode(fernet.encrypt(plaintext))
			return ciphertext
		except Exception as e:
			RNS.log("Encryption on link "+str(self)+" failed. The contained exception was: "+str(e), RNS.LOG_ERROR)


	def decrypt(self, ciphertext):
		if self.__encryption_disabled:
			return ciphertext
		try:
			fernet = Fernet(base64.urlsafe_b64encode(self.derived_key))
			plaintext = fernet.decrypt(base64.urlsafe_b64encode(ciphertext))
			return plaintext
		except Exception as e:
			RNS.log("Decryption failed on link "+str(self)+". The contained exception was: "+str(e), RNS.LOG_ERROR)
			traceback.print_exc()

	def sign(self, message):
		return self.prv.sign(message, ec.ECDSA(hashes.SHA256()))

	def validate(self, signature, message):
		try:
			self.peer_pub.verify(signature, message, ec.ECDSA(hashes.SHA256()))
			return True
		except Exception as e:
			return False

	def link_established_callback(self, callback):
		self.callbacks.link_established = callback

	def link_closed_callback(self, callback):
		self.callbacks.link_closed = callback

	def packet_callback(self, callback):
		self.callbacks.packet = callback

	# Called when an incoming resource transfer is started
	def resource_started_callback(self, callback):
		self.callbacks.resource_started = callback

	# Called when a resource transfer is concluded
	def resource_concluded_callback(self, callback):
		self.callbacks.resource_concluded = callback

	def resource_concluded(self, resource):
		if resource in self.incoming_resources:
			self.incoming_resources.remove(resource)
		if resource in self.outgoing_resources:
			self.outgoing_resources.remove(resource)

	def set_resource_strategy(self, resource_strategy):
		if not resource_strategy in Link.resource_strategies:
			raise TypeError("Unsupported resource strategy")
		else:
			self.resource_strategy = resource_strategy

	def register_outgoing_resource(self, resource):
		self.outgoing_resources.append(resource)

	def register_incoming_resource(self, resource):
		self.incoming_resources.append(resource)

	def cancel_outgoing_resource(self, resource):
		if resource in self.outgoing_resources:
			self.outgoing_resources.remove(resource)
		else:
			RNS.log("Attempt to cancel a non-existing outgoing resource", RNS.LOG_ERROR)

	def cancel_incoming_resource(self, resource):
		if resource in self.incoming_resources:
			self.incoming_resources.remove(resource)
		else:
			RNS.log("Attempt to cancel a non-existing incoming resource", RNS.LOG_ERROR)

	def ready_for_new_resource(self):
		if len(self.outgoing_resources) > 0:
			return False
		else:
			return True

	def disableEncryption(self):
		if (RNS.Reticulum.should_allow_unencrypted()):
			RNS.log("The link "+str(self)+" was downgraded to an encryptionless link", RNS.LOG_NOTICE)
			self.__encryption_disabled = True
		else:
			RNS.log("Attempt to disable encryption on link, but encryptionless links are not allowed by config.", RNS.LOG_CRITICAL)
			RNS.log("Shutting down Reticulum now!", RNS.LOG_CRITICAL)
			RNS.panic()

	def encryption_disabled(self):
		return self.__encryption_disabled

	def __str__(self):
		return RNS.prettyhexrep(self.link_id)