authclient.lua

local chan = 15432

local k = require("k")
local secret = "secretword"
local mod = peripheral.wrap("back")

local trusted = {
    ["16714"] = true
}

mod.open(chan)

while true do
    local e, p1, p2, p3, p4, p5 = os.pullEvent()
    if e == "modem_message" and p2 == chan and type(p4) == "string" and p4:sub(1, 10) == "authchall:" and p5 and p5 < 5 then
        local computerID, epoch = p4:match("authchall:(%d+):(%d+)")
        if computerID and trusted[tostring(computerID)] then
            local response = "authresp:" .. k.sha256(p4 .. ":" .. secret .. ":" .. tostring(p5))
            mod.transmit(chan, chan, response)
            print("fulfilled challenge")
        else
            print("invalid challenge")
        end
    end
end