Bank server

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 keys = {}
local logs = {}
local users = {}

local function loadLogs()
    if fs.exists("logs") then
        local file = fs.open("log", "r")
        logs = textutils.unserialize(file.readAll())
        file.close()
    end
end

local function loadUsers()
    if fs.exists("users") then
        local file = fs.open("users", "r")
        users = textutils.unserialize(file.readAll())
        file.close()
    end
end

local function saveUsers()
    local file = fs.open("users", "w")
    file.write(textutils.serialize(users))
    file.close()
end

local function saveLogs()
    local file = fs.open("log", "w")
    file.write(textutils.serialize(logs))
    file.close()
end

local function log(text)
    table.insert(logs, text)
    saveLogs()
    print(text)
end

local function generateKey()
    return {math.random(1, 255), math.random(1, 255), math.random(1, 255), math.random(1, 255), math.random(1, 255)}
end

local function receiveData()
    local event, side, from, id, data
    while true do
        event, side, from, id, data = os.pullEvent("modem_message")
        if from == BANK_CHANNEL then
            if data == "@!)#njsdf)(#84njd)" then -- Renew key
                keys[id] = generateKey()
                modem.transmit(BANK_CHANNEL, BANK_CHANNEL, textutils.serialize(keys[id]));
            elseif keys[id] then
                data = crypt(data, keys[id], true)
                print(data)
                data = textutils.unserialize(data)
                if type(data) == "table" then
                    return id, data
                end
            end
        end
    end
end

local function sendMessage(text, id)
    modem.transmit(BANK_CHANNEL, BANK_CHANNEL, crypt(textutils.serialize({id, text}), myKey))
end

local function main() -- The main function
    getModem()
    loadLogs()
    loadUsers()
    if modem == nil then
        log("No modem attached")
        return
    end

    while true do
        pcall(function()
            local id, data = receiveData()

            if data[1] == "createUser" then
                if data[2] and data[3] then
                    if not users[data[2]:lower()] then
                        users[data[2]:lower()] = {data[3], 0}
                        sendMessage({true}, id)
                        log("Created user '" .. data[2] .. "'")
                    else
                        sendMessage({false, "User exists"}, id)
                    end
                else
                    sendMessage({false, "Username or password empty"})
                end
            end
        end)
    end
end

main()