XOR Encryption

local tArgs = {...}
if #tArgs < 2 then
    print("Usage: "..shell.getRunningProgram().." [infile] <outfile> [key]")
    return
end

local infile, outfile, key
if #tArgs == 2 then
    infile, key = unpack(tArgs)
    outfile = infile
else
    infile, outfile, key = unpack(tArgs)
end

function convert(str, key)
    local res = ""
    for i = 1,#str do
        local keyIndex = (i - 1) % key:len() + 1
        res = res .. string.char( bit.bxor( str:sub(i,i):byte(), key:sub(keyIndex,keyIndex):byte() ) )
    end

    return res
end

local h = fs.open(infile, 'rb')

if h == nil then
    error("No such file!")
end

local str = ""
for c in h.read do
    str = str .. string.char(c)
end
h.close()
local converted = convert(str, key)
h = fs.open(outfile, 'wb')
for c in converted:gmatch('.') do
    h.write(c:byte())
end
h.close()