zapret-obfs: ippxor

lua/zapret-obfs.lua

@@ -0,0 +1,148 @@
+-- test case : --in-range=a --out-range=a --lua-desync=wgobfs:secret=mycoolpassword
+-- encrypt standard wireguard messages - initiation, response, cookie - and change udp packet size
+-- do not encrypt data messages and keepalives
+-- wgobfs adds maximum of 30+padmax bytes to udp size
+-- reduce MTU of wireguard interface to avoid ip fragmentation !
+-- without knowing the secret encrypted packets should be crypto strong white noise with no signature
+-- arg : secret - shared secret. any string. must be the same on both peers
+-- arg : padmin - min random garbage bytes. 0 by default
+-- arg : padmax - max random garbage bytes. 16 by default
+-- NOTE : this function does not depend on zapret-lib.lua and should not be run under orchestrator (uses direct instance_cutoff)
+function wgobfs(ctx, desync)
+	local padmin = desync.arg.padmin and tonumber(desync.arg.padmin) or 0
+	local padmax = desync.arg.padmax and tonumber(desync.arg.padmax) or 16
+	local function genkey()
+		-- cache key in a global var bound to instance name
+		local key_cache_name = desync.func_instance.."_key"
+		local key = _G[key_cache_name]
+		if not key then
+			key = hkdf("sha256", "wgobfs_salt", desync.arg.secret, nil, 16)
+			_G[key_cache_name] = key
+		end
+		return key
+	end
+	local function maybe_encrypted_payload(payload)
+		for k,plsize in pairs({2+12+16+148, 2+12+16+92, 2+12+16+64}) do
+			if #payload>=(plsize+padmin) and #payload<=(plsize+padmax) then
+				return true
+			end
+		end
+		return false
+	end
+	local function wg_payload_from_size(payload)
+		if #payload==148 then return "wireguard_initiation"
+		elseif #payload==92 then return "wireguard_response"
+		elseif #payload==64 then return "wireguard_cookie"
+		else return nil
+		end
+	end
+
+	if not desync.dis.udp then
+		instance_cutoff(ctx)
+		return
+	end
+	if not desync.arg.secret or #desync.arg.secret==0 then
+		error("wgobfs: secret required")
+	end
+	if padmin>padmax then
+		error("wgobfs: padmin>padmax")
+	end
+	if (desync.l7payload=="wireguard_initiation" or desync.l7payload=="wireguard_response" or desync.l7payload=="wireguard_cookie") and #desync.dis.payload<65506 then
+		DLOG("wgobfs: encrypting '"..desync.l7payload.."'. size "..#desync.dis.payload)
+		local key = genkey()
+		-- in aes-gcm every message require it's own crypto secure random iv
+		-- encrypting more than one message with the same iv is considered catastrophic failure
+		-- iv must be sent with encrypted message
+		local iv = bcryptorandom(12)
+		local encrypted, atag = aes_gcm(true, key, iv, bu16(#desync.dis.payload)..desync.dis.payload..brandom(math.random(padmin,padmax)), nil)
+		desync.dis.payload = iv..atag..encrypted
+		return VERDICT_MODIFY
+	end
+
+	if desync.l7payload=="unknown" and maybe_encrypted_payload(desync.dis.payload) then
+		local key = genkey()
+		local iv = string.sub(desync.dis.payload,1,12)
+		local atag = string.sub(desync.dis.payload,13,28)
+		local decrypted, atag2 = aes_gcm(false, key, iv, string.sub(desync.dis.payload,29))
+		if atag==atag2 then
+			local plen = u16(decrypted)
+			if plen>(#decrypted-2) then
+				DLOG("wgobfs: bad decrypted payload data")
+			else
+				desync.dis.payload = string.sub(decrypted, 3, 3+plen-1)
+				if b_debug then DLOG("wgobfs: decrypted '"..(wg_payload_from_size(desync.dis.payload) or "unknown").."' message. size "..plen) end
+				return VERDICT_MODIFY
+			end
+		else
+			DLOG("wgobfs: decrypt auth tag mismatch")
+		end
+	end
+end
+
+-- test case :
+--  endpoint1:
+--   --filter-icmp=0,8,128,129 --filter-ipp=193,198,209,250 --filter-tcp=* --filter-udp=* --in-range=a --lua-desync=ippxor:xor=192:dataxor=0xABCD
+--   nft add rule inet ztest pre meta mark and 0x40000000 == 0 meta l4proto {193, 198, 209, 250} queue num 200 bypass
+--   nft add rule inet ztest post meta mark and 0x40000000 == 0 tcp dport "{5001}" queue num 200 bypass
+--   nft add rule inet ztest post meta mark and 0x40000000 == 0 udp dport "{5001}" queue num 200 bypass
+--   iperf -i 1 -c endpoint2
+--  endpoint2:
+--   --filter-icmp=0,8,128,129 --filter-ipp=193,198,209,250 --filter-tcp=* --filter-udp=* --in-range=a --lua-desync=ippxor:xor=192:dataxor=0xABCD --server
+--   nft add rule inet ztest pre meta mark and 0x40000000 == 0 meta l4proto {193, 198, 209, 250} queue num 200 bypass
+--   nft add rule inet ztest post meta mark and 0x40000000 == 0 tcp sport "{5001}" queue num 200 bypass
+--   nft add rule inet ztest post meta mark and 0x40000000 == 0 udp sport "{5001}" queue num 200 bypass
+--   iperf -s
+-- xor ip protocol number and optionally xor tcp,udp,icmp payload with supplied blob pattern
+-- arg : ippxor - value to xor ip protocol number
+-- arg : dataxor - blob to xor tcp, udp or icmp payload
+function ippxor(ctx, desync)
+	local dataxor
+	local function dxor(dis)
+		if dataxor and dis.payload and #dis.payload>0 and (dis.tcp or dis.udp or dis.icmp) then
+			dis.payload = bxor(dis.payload, pattern(dataxor,1,#dis.payload))
+			return true
+		end
+		return false
+	end
+
+	if not desync.arg.ippxor then
+		error("ippxor: ippxor value required")
+	end
+	local ippxor = tonumber(desync.arg.ippxor)
+	if ippxor<0 or ippxor>0xFF then
+		error("ippxor: invalid ippxor value. should be 0..255")
+	end
+	if desync.arg.dataxor then
+		dataxor = blob(desync,desync.arg.dataxor)
+		if #dataxor==0 then
+			error("ippxor: empty dataxor value")
+		end
+	end
+
+	local l3_from = ip_proto_l3(desync.dis)
+	local l3_to = bitxor(l3_from, ippxor)
+
+	local bdxor = dxor(desync.dis)
+	if bdxor then
+		DLOG("ippxor: dataxor out")
+	end
+	fix_ip_proto(desync.dis, l3_to)
+
+	local raw_ip = reconstruct_dissect(desync.dis, {ip6_preserve_next=true})
+
+	local dis = dissect(raw_ip)
+	if not dis.ip and not dis.ip6 then
+		DLOG_ERR("ippxor: could not rebuild packet")
+		return
+	end
+
+	if not bdxor then
+		if dxor(dis) then
+			DLOG("ippxor: dataxor in")
+		end
+	end
+
+	desync.dis = dis
+	DLOG("ippxor: "..l3_from.." => "..l3_to)
+	return VERDICT_MODIFY + VERDICT_PRESERVE_NEXT
+end