Decrypt encrypted Teardown files (.tde)

tdedecrypt.lua

#!/usr/bin/env luajit
local argparse = require('argparse')
local parser = argparse("tdedecrypt", "Decrypt encrypted Teardown files")
parser:argument("input", "Input file(s)"):args("*")
parser:option("-o --output", "Output file")
local args = parser:parse()

if args.input[2] and args.output then
	parser:error("cannot use output option with multiple input files")
end

for _, input in pairs(args.input) do
	local infile = io.open(input, 'rb')
	if not infile then
		parser:error("could not open infile")
	end
	local outfile = io.open(args.output or string.gsub(input, '%.tde$', ''), 'wb')
	if not outfile then
		parser:error("could not open outfile")
	end

	-- Derived from https://github.com/lyhyl/TDEDecrypt/blob/master/TDEDecrypt/main.cpp
	local a = '599Cc51887A8cb0C20F9CdE34cf9e0A535E5cAd1C26c7b562596ACC207Ae9A0bfB3E3161f31af5bEf1c2f064b3628174D83BF6E0739D9D6918fD9C2Eba02D5aD\x00'
	local b = '0C3b676fe8d7188Cde022F71632830F36b98b181aD48Fed160006eA59\x00'
	local i = 0
	while true do
		local enc = infile:read(1)
		if not enc then
			break
		end
		enc = string.byte(enc)
		local a2 = bit.band(i, 0x7f)+1
		a2 = string.byte(string.sub(a, a2, a2))
		local b2 = (i%57)+1
		b2 = string.byte(string.sub(b, b2, b2))
		local dec = bit.bxor(bit.bxor(enc, a2), b2)
		dec = string.char(dec)
		outfile:write(dec)
		i = i+1
	end

	infile:close()
	outfile:close()
end