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)