local ecc = require("ecc")

string.toHex = function(str)
    return str:gsub(".", function(ch) return string.format("%02x", ch:byte()) end)
end
string.fromHex = function(hex)
    return hex:gsub("%x%x", function(d) return string.char(tonumber(d, 16)) end)
end

local keypair = {}
if fs.exists("/.id_dh.json") then
    local fp = io.open("/.id_dh.json", "r")
    local d = textutils.unserializeJSON(fp:read())
    keypair.sk = string.fromHex(d.secret)
    keypair.pk = string.fromHex(d.public)
    fp:close()
else
    printError("no identity found, generating...")
    local sk, pk = ecc.keypair(ecc.random.random())
    io.open("/.id_dh.json", "w"):write(textutils.serializeJSON({
        secret = string.toHex(sk),
        public = string.toHex(pk)
    })):close()
    keypair.sk = string.char(table.unpack(sk))
    keypair.pk = string.char(table.unpack(pk))
end

print("pubkey: "..string.toHex(keypair.pk))

local running = true

local known_hosts = {}

parallel.waitForAll(function() while running do -- dh:discover sender
    rednet.broadcast(keypair.pk, "dh:discover")
    os.sleep(10)
end end,
function() while running do -- dh:discover handler
    local id, pk, proto = rednet.receive("dh:discover")
    if proto == "dh:discover" then
        print("DH discover from "..id.." with key "..pk)
        local nonce = string.toHex(ecc.random.random())
        local key = ecc.exchange(keypair.sk, pk)
        known_hosts[id] = {
            id = id,
            pk = pk,
            sk = key,
            verified = false,
            nonce = nonce,
            t = os.clock()
        }
        known_hosts[pk] = known_hosts[id]
        rednet.send(id, {
            pk = keypair.pk,
            msg = ecc.encrypt(nonce, key)
        }, "dh:pair")
    end
end end,
function() while running do -- dh:pair handler
    local id, msg, proto = rednet.receive("dh:pair")
    if proto == "dh:pair" then
        local key = ecc.exchange(keypair.sk, msg.pk)
        known_hosts[id] = {
            id = id,
            pk = msg.pk,
            sk = key,
            verified = false,
            nonce = ecc.decrypt(msg.msg, msg.msg)
        }
    end
end end)