encrypted ids work

README.md

@@ -1,2 +1,5 @@
 # vonbraun
 
+Run:
+
+elixir --erl '-args_file vm.args' -S mix run --no-halt

config/dev.exs

@@ -12,4 +12,6 @@ config :vonbraun,
   nickname: "moonman",
   domain: "vonbraun.discontent.top",
   summary: "I am the famous Fediverse Moon",
-  approve_followers: false
+  approve_followers: false,
+  # MUST be 32
+  id_key: "53F0CB234DA3DB1A43AE32DE4038516B"

lib/vonbraun/control.ex

@@ -0,0 +1,11 @@
+defmodule Vonbraun.Control do
+  def follow(id) when is_binary(id) do
+  end
+
+  def unfollow(id) when is_binary(id) do
+  end
+
+  def post_note(content, public?, to \\ [])
+      when is_binary(content) and is_list(to) and is_boolean(public?) do
+  end
+end

lib/vonbraun/crypto_id.ex

@@ -0,0 +1,63 @@
+defmodule Vonbraun.CryptoID do
+  require Logger
+
+  @spec encrypt(integer()) :: String.t()
+  @spec encrypt(integer(), <<_::128>>) :: String.t()
+  def encrypt(epoch_milliseconds, <<iv::bytes-size(16)>> \\ :crypto.strong_rand_bytes(16))
+      when is_integer(epoch_milliseconds) do
+    key = Application.fetch_env!(:vonbraun, :id_key) |> Base.decode16!()
+
+    encrypted =
+      :crypto.crypto_one_time(:aes_128_ctr, key, iv, <<epoch_milliseconds::64-big>>, true)
+
+    Logger.debug("bytes length of encrypted: #{byte_size(encrypted)}")
+    Base.encode16(iv <> encrypted)
+  end
+
+  def to_milliseconds(<<iv_hex::bytes-size(32), encrypted_payload::bytes-size(16)>>) do
+    key = Application.fetch_env!(:vonbraun, :id_key) |> Base.decode16!()
+
+    with {:iv_decode, {:ok, iv}} <- {:iv_decode, Base.decode16(iv_hex)},
+         {:decode, {:ok, encrypted_bytes}} <- {:decode, Base.decode16(encrypted_payload)},
+         {:decrypt, <<epoch_milliseconds::64>>} <-
+           {:decrypt, :crypto.crypto_one_time(:aes_128_ctr, key, iv, encrypted_bytes, false)} do
+      {:ok, epoch_milliseconds}
+    else
+      {:iv_decode, :error} ->
+        {:error, :iv_decode}
+
+      {:decode, :error} ->
+        {:error, :base16_decode}
+
+      {:decrypt, _} ->
+        {:error, :integer_decrypt}
+    end
+  end
+
+  def encrypt_id(epoch_milliseconds) when is_integer(epoch_milliseconds) do
+    encrypted_milliseconds = encrypt(epoch_milliseconds)
+    instance = Application.fetch_env!(:vonbraun, :domain)
+
+    "https://#{instance}/id/#{encrypted_milliseconds}"
+  end
+
+  def now!() do
+    epoch_milliseconds = System.system_time(:microsecond)
+    id = encrypt_id(epoch_milliseconds)
+
+    {id, epoch_milliseconds}
+  end
+
+  def decrypt_id(id) when is_binary(id) do
+    instance = Application.fetch_env!(:vonbraun, :domain)
+    prefix = "https://#{instance}/id/"
+
+    with {:prefix, ^prefix <> <<payload::bytes-size(48)>>} <- {:prefix, id},
+         {:ms, {:ok, milliseconds}} <- {:ms, to_milliseconds(payload)} do
+      {:ok, milliseconds}
+    else
+      {:prefix, _} -> {:error, :prefix_unmatch}
+      {:ms, {:error, error}} -> {:error, error}
+    end
+  end
+end

vm.args

@@ -0,0 +1,2 @@
+-name vb@falco
+-setcookie cookie