safe_rpc.md

SafeRpc

The idea behind this is that :rpc is not encrypted.

Setting up TLS just for :rpc is yucky. So maybe there is a safer way than just plain HTTP but not as safe as TLS?

This will not encrypt your cookie, but it will encrypt the arguments!

How to use

Set an Environment variable: System.put_env("RPC_TOKEN", "NjkmlOJ343jkhKJAH")

Or in bash: export RPC_TOKEN=NjkmlOJ343jkhKJAH

---

Now the idea is on one distributed node:

payload = %{hello: ["world", "earth", {42, 9000}]}

secret_list = SafeRpc.encrypt(payload)

:rpc.call(
  :name@host,
  MyMod,
  :my_fun,
  [:saferpc, secret_list]
)

Now on the other node you pattern match :saferpc and decrypt the secret list:

defmodule MyModule do
  def my_fun(:saferpc, secret_list) do
    my_map = SafeRpc.decrypt(secret_list)

    IO.inspect my_map
  end
end

Now you have your data!

This works with any term! 🎉

Example of lib logic and use on a single node

Here is an example of the lib itself and a dry run:

System.put_env("RPC_TOKEN", "Njk##mlOJ(&#$)788Hn!@343jkhKJAH")

defmodule SafeRpc do
  @secret System.get_env("RPC_TOKEN") |> to_charlist
  @secret_length System.get_env("RPC_TOKEN") |> to_charlist |> length

  def encrypt(term) do
    term
    |> :erlang.term_to_binary
    |> :binary.bin_to_list
    |> Enum.with_index
    |> Enum.map(fn {e, i} -> (e + 1) * secret_char(i) end)
  end

  def decrypt(list) do
    list
    |> Enum.with_index
    |> Enum.map(fn {e, i} -> (e - 1) / secret_char(i) |> trunc end)
    |> :binary.list_to_bin
    |> :erlang.binary_to_term
  end

  defp secret_char(i) do
    Enum.at(@secret, rem(i, @secret_length))
  end
end

secret_term_list = SafeRpc.encrypt(%{hello: ["world", 'earth', {42, 9000}]})

IO.inspect secret_term_list

IO.inspect SafeRpc.decrypt(secret_term_list)

# OUTPUT OF PROGRAM

[10296, 12402, 107, 35, 35, 218, 10908, 79, 444, 4200, 3876, 3815, 3924, 4592,
 5995, 56, 56, 72, 440, 3630, 64, 51, 52, 306, 12720, 11984, 11960, 8175, 7474,
 7150, 72, 78, 106, 642, 3570, 3430, 12535, 12636, 8295, 7770, 120, 3724, 1505,
 3564, 41, 55, 2016, 2296, 7704]
%{hello: ["world", 'earth', {42, 9000}]}