Decode and verify salmons.

lib/pleroma/web/salmon/salmon.ex

@@ -0,0 +1,48 @@
+defmodule Pleroma.Web.Salmon do
+  use Bitwise
+
+  def decode_and_validate(magickey, salmon) do
+    {doc, _rest} = :xmerl_scan.string(to_charlist(salmon))
+
+    {:xmlObj, :string, data} = :xmerl_xpath.string('string(//me:data[1])', doc)
+    {:xmlObj, :string, sig} = :xmerl_xpath.string('string(//me:sig[1])', doc)
+    {:xmlObj, :string, alg} = :xmerl_xpath.string('string(//me:alg[1])', doc)
+    {:xmlObj, :string, encoding} = :xmerl_xpath.string('string(//me:encoding[1])', doc)
+    {:xmlObj, :string, type} = :xmerl_xpath.string('string(//me:data[1]/@type)', doc)
+
+
+    {:ok, data} = Base.url_decode64(to_string(data), ignore: :whitespace)
+    {:ok, sig} = Base.url_decode64(to_string(sig), ignore: :whitespace)
+    alg = to_string(alg)
+    encoding = to_string(encoding)
+    type = to_string(type)
+
+    signed_text = [data, type, encoding, alg]
+    |> Enum.map(&Base.url_encode64/1)
+    |> Enum.join(".")
+
+    key = decode_key(magickey)
+
+    verify = :public_key.verify(signed_text, :sha256, sig, key)
+
+    if verify do
+      {:ok, data}
+    else
+      :error
+    end
+  end
+
+  defp decode_key("RSA." <> magickey) do
+    make_integer = fn(bin) ->
+      list = :erlang.binary_to_list(bin)
+      Enum.reduce(list, 0, fn (el, acc) -> (acc <<< 8) ||| el end)
+    end
+
+    [modulus, exponent] = magickey
+    |> String.split(".")
+    |> Enum.map(&Base.url_decode64!/1)
+    |> Enum.map(make_integer)
+
+    {:RSAPublicKey, modulus, exponent}
+  end
+end