Network tools for ComputerCraft (not recommended).

network-tools.lua

--[[
    This is a small api to make wireless messages somewhat secure.
    It is not recommended to use this in production as this is just awful. Use something strong.

    However, this may be worth a look to understand what kind of steps could be used to secure a system. 
]]
local tools = {}

---Gets a "random" number in hex format.
---@return string salt The number as string in hex format.
function tools.salt()
    -- Using djb2
    local salt = 9551
    for i=1,100 do
        salt = (salt/math.random())%696969
    end
    return string.format("%x", math.floor((salt*100)%898989))
end

tools.END = "EOF;;;"
tools.ANF = ":=:{"
---Xor encryption/decryption. Salt will be put on each end and seperated with escape chars.
---@param plaintext string The message to encrypt
---@param key string The key to encrypt the message. Ideally should be as long as the message for max strength.
---@param bDecode boolean whenever the message should be encrypted or decrypted.
---@return unknown
function tools.xor(plaintext, key, bDecode)
    -- Salt
    if not bDecode then
        plaintext = 
        tools.salt()..tools.salt()..tools.salt()..tools.salt()..
        tools.ANF..plaintext..tools.END
        ..tools.salt()..tools.salt()..tools.salt()..tools.salt()
    end
    -- Setup key/message
    key = string.rep(key, math.ceil(#plaintext / #key))
    ciphertext = ""
    --Xor
    local cursor = 1
    for i=1, #plaintext do
        ciphertext = ciphertext .. string.char( bit32.bxor(plaintext:byte(i), key:byte(i)) )
    end
    --Cut salt out if decrypting.
    if bDecode then
        local _,nAnf = ciphertext:find(tools.ANF)
        if nAnf then
            ciphertext = ciphertext:sub(nAnf+1)
        end
        local nEnd,_ = ciphertext:find(tools.END)
        if nEnd then
            ciphertext = ciphertext:sub(1,nEnd-1)
        end
       
    end

    return ciphertext
end

tools.chunkSize = 16
---Xor encryption but with multible layers, as long as the key is longer than the message.
---@param msg string The message to encrypt.
---@param key string The key. should be as long as possible for max strength, as this will create more layers.
---@param bDecrypt boolean whenever the message should be decrypted or not.
---@return string result The encrypted/decrypted message.
function tools.multiXor(msg, key, bDecrypt)
    local keys = {}
    for i=1,#key,tools.chunkSize do
        table.insert(keys, string.sub(key, i, i+tools.chunkSize-1))
    end

    local nStart,nEnd,nSkip = 1,#keys,1
    if bDecrypt then nStart,nEnd,nSkip = #keys,1,-1 end

    for i=nStart,nEnd,nSkip do
        msg = tools.xor(msg, keys[i], bDecrypt)
    end

    return msg
end

---TOTP. By giving a token and the current time (os.time()), a number representing a port will be returned.
---@param sToken string The secret token.
---@param nTime number os.time()
---@return number port
function tools.totp(sToken, nTime)
    sToken = '@'..sToken..';'
    nTime = math.floor(nTime*10)

    -- djb2 algorithm
    local port = 5381
    for i=1, #sToken do
        port = bit32.bxor(bit32.lshift(port, 5), port) + string.byte(sToken, i)
    end
    
    port = ((port%65535)^nTime)%65535
    return port
end

tools.type = {
    UPGRADE =   0x006900,
    PING =      0x133700,
    BODY =      0x007777,
    CLOSE =     0x010101,
}
function tools.newPackage(nToID, nType, tData)
    return {
        -- Header
        fromID = os.getComputerID(),
        toID = nToID or (-1),
        type = nType or (-1),
        -- Body
        body = tData or {tools.salt(),tools.salt(),tools.salt()},
        -- Salt (To fuck with others)
        ["."..tools.salt()] = tools.salt(),
        ["@"..tools.salt()] = tools.salt(),
        ["."..tools.salt()] = tools.salt(),
        ["@"..tools.salt()] = tools.salt(),
        ["."..tools.salt()] = tools.salt(),
        ["@"..tools.salt()] = tools.salt(),
    }
end

return tools