Security

--  Simple Security API
--  By Cranium
--[[ How to use the API
    This API is designed to have ease of use in mind, not ultimate security.
    As such, I would rate this on a 3/10 in terms of security, since the'encryption' used
    is super easy to break. The average person would not try to look for the user/pass files,
    but our more seasoned coders would find them in a heartbeat, and with some work, could
    see your password in plain text. Do not use this API as an absolute means of security.

    Functions:
        checkFile()
            ensures that the .user and .pass files are intact. If they are deleted,
            then the login fails.
        saveUser(user)
            Saves the user entered into a file, 'encrypting' it
        savePass(pass)
            Saves the password entered into a file, 'encrypting' it
        loadUser()
            Loads the 'encrypted' user from the file, and returns the unserialized table.
        loadPass()
            loads the 'encrypted' password from the file, and returns the unserialized table.
        register(user, pass)
            Saves the user and pass at the same time. Not super necessary, but can be useful
            when saving space on your code.
        login(user, pass)
            Retrieves the user and password from the files, 'decrypts' it into a table, and
            checks it character by character if it is accurate.
            Returns true if successful, false if not.

]]

function checkFile()
    if not fs.exists(".user") then
        local userFile = fs.open(".user", "w")
        userFile.write("temp_user")
        userFile.close()
    end
    if not fs.exists(".pass") then
        local passFile = fs.open(".pass", "w")
        passFile.write("temp_pass")
        passFile.close()
    end
end

function saveUser(user)
    checkFile()
    local userTab = {}
    for char in string.gmatch(user, ".") do
        table.insert(userTab, char)
    end
    for i = 1, #userTab do
        userTab[i] = (string.byte(userTab[i]) * string.byte(userTab[i])) - 42
    end
    local userFile = fs.open(".user", "w")
    userFile.write(textutils.serialize(userTab))
    userFile.close()
end

function savePass(pass)
    checkFile()
    local passTab = {}
    for char in string.gmatch(pass, ".") do
        table.insert(passTab, char)
    end
    for i = 1, #passTab do
        passTab[i] = (string.byte(passTab[i]) * string.byte(passTab[i])) - 42
    end
    local passFile = fs.open(".pass", "w")
    passFile.write(textutils.serialize(passTab))
    passFile.close()
end

function loadUser()
    checkFile()
    local userFile = fs.open(".user", "r")
    local userTab = textutils.unserialize(userFile.readAll())
    userFile.close()
    return userTab
end

function loadPass()
    checkFile()
    local passFile = fs.open(".pass", "r")
    local passTab = textutils.unserialize(passFile.readAll())
    passFile.close()
    return passTab
end

function register(user, pass)
    saveUser(user)
    savePass(pass)
end

function login(user, pass)
    local savedUser = loadUser()
    local savedPass = loadPass()
    if #user == #savedUser and #pass == #savedPass then
        if savedUser ~= "temp_user" and savedPass ~= "temp_pass" then
            -- convert existing user to a decrypted string
            local userTab = {}
            for char in string.gmatch(user, ".") do
                table.insert(userTab, char)
            end
            for i = 1, #savedUser do
                userTab[i] = string.char((savedUser[i] + 42) / string.byte(userTab[i]))
            end
            local userCheck = table.concat(userTab)
            -- convert existing pass to a decrypted string
            local passTab = {}
            for char in string.gmatch(pass, ".") do
                table.insert(passTab, char)
            end
            for i = 1, #savedPass do
                passTab[i] = string.char((savedPass[i] + 42) / string.byte(passTab[i]))
            end
            local passCheck = table.concat(passTab)
            -- check against entered user/pass
            if user == userCheck and pass == passCheck then
                return true
            end
        end
    end
    return false
end