git.squeep.com Git - akkoma/blob - lib/pleroma/web/salmon/salmon.ex

   1 defmodule Pleroma.Web.Salmon do
   2   use Bitwise
   3
   4   def decode(salmon) do
   5     {doc, _rest} = :xmerl_scan.string(to_charlist(salmon))
   6
   7     {:xmlObj, :string, data} = :xmerl_xpath.string('string(//me:data[1])', doc)
   8     {:xmlObj, :string, sig} = :xmerl_xpath.string('string(//me:sig[1])', doc)
   9     {:xmlObj, :string, alg} = :xmerl_xpath.string('string(//me:alg[1])', doc)
  10     {:xmlObj, :string, encoding} = :xmerl_xpath.string('string(//me:encoding[1])', doc)
  11     {:xmlObj, :string, type} = :xmerl_xpath.string('string(//me:data[1]/@type)', doc)
  12
  13
  14     {:ok, data} = Base.url_decode64(to_string(data), ignore: :whitespace)
  15     {:ok, sig} = Base.url_decode64(to_string(sig), ignore: :whitespace)
  16     alg = to_string(alg)
  17     encoding = to_string(encoding)
  18     type = to_string(type)
  19
  20     [data, type, encoding, alg, sig]
  21   end
  22
  23   def fetch_magic_key(salmon) do
  24     [data, _, _, _, _] = decode(salmon)
  25     {doc, _rest} = :xmerl_scan.string(to_charlist(data))
  26     {:xmlObj, :string, uri} = :xmerl_xpath.string('string(//author[1]/uri)', doc)
  27
  28     uri = to_string(uri)
  29     base = URI.parse(uri).host
  30
  31     # TODO: Find out if this endpoint is mandated by the standard.
  32     {:ok, response} = HTTPoison.get(base <> "/.well-known/webfinger", ["Accept": "application/xrd+xml"], [params: [resource: uri]])
  33
  34     {doc, _rest} = :xmerl_scan.string(to_charlist(response.body))
  35
  36     {:xmlObj, :string, magickey} = :xmerl_xpath.string('string(//Link[@rel="magic-public-key"]/@href)', doc)
  37     "data:application/magic-public-key," <> magickey = to_string(magickey)
  38
  39     magickey
  40   end
  41
  42   def decode_and_validate(magickey, salmon) do
  43     [data, type, encoding, alg, sig] = decode(salmon)
  44
  45     signed_text = [data, type, encoding, alg]
  46     |> Enum.map(&Base.url_encode64/1)
  47     |> Enum.join(".")
  48
  49     key = decode_key(magickey)
  50
  51     verify = :public_key.verify(signed_text, :sha256, sig, key)
  52
  53     if verify do
  54       {:ok, data}
  55     else
  56       :error
  57     end
  58   end
  59
  60   defp decode_key("RSA." <> magickey) do
  61     make_integer = fn(bin) ->
  62       list = :erlang.binary_to_list(bin)
  63       Enum.reduce(list, 0, fn (el, acc) -> (acc <<< 8) ||| el end)
  64     end
  65
  66     [modulus, exponent] = magickey
  67     |> String.split(".")
  68     |> Enum.map(&Base.url_decode64!/1)
  69     |> Enum.map(make_integer)
  70
  71     {:RSAPublicKey, modulus, exponent}
  72   end
  73 end