Bank client

local BANK_CHANNEL = 1329


local function convert(chars,dist,inv)
    local charInt = string.byte(chars);
    for i=1,dist do
        if(inv)then charInt = charInt - 1; else charInt = charInt + 1; end
        if(charInt<32)then
            if(inv)then charInt = 126; else charInt = 126; end
        elseif(charInt>126)then
            if(inv)then charInt = 32; else charInt = 32; end
        end
    end
    return string.char(charInt);
end

local function crypt(str,k,inv)
    local enc= "";
    for i=1,#str do
        if(#str-k[5] >= i or not inv)then
            for inc=0,3 do
                if(i%4 == inc)then
                    enc = enc .. convert(string.sub(str,i,i),k[inc+1],inv);
                    break;
                end
            end
        end
    end
    if(not inv)then
        for i=1,k[5] do
            enc = enc .. string.char(math.random(32,126));
        end
    end
    return enc;
end

local modem

local function getModem()
    for i,v in pairs(peripheral.getNames()) do
        if peripheral.getType(v) == "modem" then
            modem = peripheral.wrap(v)
            modem.open(BANK_CHANNEL)
            break
        end
    end
end

local myKey

local function sendMessage(text)
    text = textutils.serialize(text)
    print(text)
    modem.transmit(BANK_CHANNEL, os.getComputerID(), crypt(text, myKey))
end

local function receiveMessage()
    local event, side, from, id, text
    repeat
        event, side, from, id, text = os.pullEvent("modem_message")
        text = textutils.unserialize(crypt(text, myKey, true))
    until from == BANK_CHANNEL and id == BANK_CHANNEL and type(text) == "table" and text[1] == os.getComputerID()
    return text[2]
end

function createUser(user, pass)
    sendMessage({"createUser", user, pass})
    local tab = receiveMessage()
    if tab[1] == false then
        return false, tab[2]
    else
        return true
    end
end

local function loadKey()
    if fs.exists(".bankkey") then
        local file = fs.open(".bankkey", "r")
        myKey = textutils.unserialize(file.readAll())
        file.close()
    else
        modem.transmit(BANK_CHANNEL, os.getComputerID(), "@!)#njsdf)(#84njd)")
        local event, side, from, id, text
        repeat
            event, side, from, id, text = os.pullEvent("modem_message")
        until from == BANK_CHANNEL and id == BANK_CHANNEL
        myKey = textutils.unserialize(text)
        local file = fs.open(".bankkey", "w")
        file.write(textutils.serialize(myKey))
        file.close()
    end
end

function load()
    getModem()
    if not modem then
        error("No modem attached", 0)
    end
    loadKey()
end