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   1 # Pleroma: A lightweight social networking server
   2 # Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
   3 # SPDX-License-Identifier: AGPL-3.0-only
   4
   5 # https://tools.ietf.org/html/draft-cavage-http-signatures-08
   6 defmodule Pleroma.Web.HTTPSignatures do
   7   alias Pleroma.User
   8   alias Pleroma.Web.ActivityPub.ActivityPub
   9   alias Pleroma.Web.ActivityPub.Utils
  10
  11   require Logger
  12
  13   def split_signature(sig) do
  14     default = %{"headers" => "date"}
  15
  16     sig =
  17       sig
  18       |> String.trim()
  19       |> String.split(",")
  20       |> Enum.reduce(default, fn part, acc ->
  21         [key | rest] = String.split(part, "=")
  22         value = Enum.join(rest, "=")
  23         Map.put(acc, key, String.trim(value, "\""))
  24       end)
  25
  26     Map.put(sig, "headers", String.split(sig["headers"], ~r/\s/))
  27   end
  28
  29   def validate(headers, signature, public_key) do
  30     sigstring = build_signing_string(headers, signature["headers"])
  31     Logger.debug("Signature: #{signature["signature"]}")
  32     Logger.debug("Sigstring: #{sigstring}")
  33     {:ok, sig} = Base.decode64(signature["signature"])
  34     :public_key.verify(sigstring, :sha256, sig, public_key)
  35   end
  36
  37   def validate_conn(conn) do
  38     # TODO: How to get the right key and see if it is actually valid for that request.
  39     # For now, fetch the key for the actor.
  40     with actor_id <- Utils.get_ap_id(conn.params["actor"]),
  41          {:ok, public_key} <- User.get_public_key_for_ap_id(actor_id) do
  42       if validate_conn(conn, public_key) do
  43         true
  44       else
  45         Logger.debug("Could not validate, re-fetching user and trying one more time")
  46         # Fetch user anew and try one more time
  47         with actor_id <- Utils.get_ap_id(conn.params["actor"]),
  48              {:ok, _user} <- ActivityPub.make_user_from_ap_id(actor_id),
  49              {:ok, public_key} <- User.get_public_key_for_ap_id(actor_id) do
  50           validate_conn(conn, public_key)
  51         end
  52       end
  53     else
  54       _e ->
  55         Logger.debug("Could not public key!")
  56         false
  57     end
  58   end
  59
  60   def validate_conn(conn, public_key) do
  61     headers = Enum.into(conn.req_headers, %{})
  62     signature = split_signature(headers["signature"])
  63     validate(headers, signature, public_key)
  64   end
  65
  66   def build_signing_string(headers, used_headers) do
  67     used_headers
  68     |> Enum.map(fn header -> "#{header}: #{headers[header]}" end)
  69     |> Enum.join("\n")
  70   end
  71
  72   def sign(user, headers) do
  73     with {:ok, %{info: %{keys: keys}}} <- Pleroma.Web.WebFinger.ensure_keys_present(user),
  74          {:ok, private_key, _} = Pleroma.Web.Salmon.keys_from_pem(keys) do
  75       sigstring = build_signing_string(headers, Map.keys(headers))
  76
  77       signature =
  78         :public_key.sign(sigstring, :sha256, private_key)
  79         |> Base.encode64()
  80
  81       [
  82         keyId: user.ap_id <> "#main-key",
  83         algorithm: "rsa-sha256",
  84         headers: Map.keys(headers) |> Enum.join(" "),
  85         signature: signature
  86       ]
  87       |> Enum.map(fn {k, v} -> "#{k}=\"#{v}\"" end)
  88       |> Enum.join(",")
  89     end
  90   end
  91 end