local getopt = require('getopt')

copyright = ''
author = "Neuromancer"
version = 'v1.0.0'
desc = [[
This script tries to decode Mifare Classic Access bytes
]]
example = 'script run mifare_access -a 7F0F0869'
usage = [[
script run mifare_access -h -a <access bytes>

Arguments:
	-h                   : this help
	-a <access bytes>    : 4 bytes ACCESS CONDITIONS
]]

local DEBUG = true
local bxor = bit32.bxor
local band = bit32.band
local rshift = bit32.rshift

--- 
-- A debug printout-function
local function dbg(args)
    if not DEBUG then return end
    if type(args) == "table" then
		local i = 1
		while args[i] do
			dbg(args[i])
			i = i+1
		end
	else
		print("###", args)
	end	
end	
--- 
-- This is only meant to be used when errors occur
local function oops(err)
	print("ERROR: ",err)
	return nil, err
end
--- 
-- Usage help
local function help()
	print(copyright)
	print(author)	
	print(version)	
	print(desc)
	print('Example usage')
	print(example)
end

local access_condition_sector_trailer = {}
access_condition_sector_trailer[0x0] = {'never','key A','key A','never','key A','key A'}
access_condition_sector_trailer[0x2] = {'never','never','key A','never','key A','never'}
access_condition_sector_trailer[0x4] = {'never','key B','key A|B','never','never','key B'}
access_condition_sector_trailer[0x6] = {'never','never','key A|B','never','never','never'}
access_condition_sector_trailer[0x1] = {'never','key A','key A','key A','key A','key A'}
access_condition_sector_trailer[0x3] = {'never','key B','key A|B','key B','never','key B'}
access_condition_sector_trailer[0x5] = {'never','never','key A|B','key B','never','never'}
access_condition_sector_trailer[0x7] = {'never','never','key A|B','never','never','never'}

local access_condition_data_block = {}
access_condition_data_block[0x0] = {'key A|B','key A|B','key A|B','key A|B'}
access_condition_data_block[0x2] = {'key A|B','never','never','never'}
access_condition_data_block[0x4] = {'key A|B','key B','never','never'}
access_condition_data_block[0x6] = {'key A|B','key B','key B','key A|B'}
access_condition_data_block[0x1] = {'key A|B','never','never','key A|B'}
access_condition_data_block[0x3] = {'key B','key B','never','never'}
access_condition_data_block[0x5] = {'key B','never','never','never'}
access_condition_data_block[0x7] = {'never','never','never','never'}

local function main(args)

	print( string.rep('--',20) )
	print( string.rep('--',20) )	
	print()

	local access = ''
	
	-- Read the parameters
	for o, a in getopt.getopt(args, 'ha:') do
		if o == "h" then return help() end
		if o == "a" then access = a end
	end	
		
	if access == nil then return oops('empty ACCESS CONDITIONS') end
	if #access == 0 then return oops('empty ACCESS CONDITIONS') end
	if #access ~= 8 then return oops("Wrong length. Should be 4 hex bytes ACCESS CONDITIONS (e.g. 7F0F0869)") end
	
	local c2_b = tonumber(string.sub(access, 1, 1), 16)
	local c1_b = tonumber(string.sub(access, 2, 2), 16)
	local c1 = tonumber(string.sub(access, 3, 3), 16)
	local c3_b = tonumber(string.sub(access, 4, 4), 16)
	local c3 = tonumber(string.sub(access, 5, 5), 16)
	local c2 = tonumber(string.sub(access, 6, 6), 16)
	local gpb = string.sub(access, 7, 8)

	if bxor(c1, c1_b) ~= 0xF then print("!!! bitflip in c1") end
	if bxor(c2, c2_b) ~= 0xF then print("!!! bitflip in c2") end
	if bxor(c3, c3_b) ~= 0xF then print("!!! bitflip in c3") end

	local ab = c1 * 256 + c2 * 16 + c3

	for block = 0,3 do
		print("--> block "..block)
		-- mask bits for block
		local abi = band(rshift(ab, block), 0x111)
		-- compress bits
		abi = band(abi + rshift(abi, 3) + rshift(abi, 6),7)
--			print(abi)
		if block == 3 then
			print("     KEYSECXA read: "..access_condition_sector_trailer[abi][1])
			print("    KEYSECXA write: "..access_condition_sector_trailer[abi][2])
			print(" ACCESS COND. read: "..access_condition_sector_trailer[abi][3])
			print("ACCESS COND. write: "..access_condition_sector_trailer[abi][4])
			print("     KEYSECXB read: "..access_condition_sector_trailer[abi][5])
			print("    KEYSECXB write: "..access_condition_sector_trailer[abi][6])
		else
			print("                   read: "..access_condition_data_block[abi][1])
			print("                  write: "..access_condition_data_block[abi][2])
			print("                    inc: "..access_condition_data_block[abi][3])
			print("decr, transfer, restore: "..access_condition_data_block[abi][4])
		end
	end

	print("GPB: "..gpb)
end
main(args)
