Add version 4 TypeScript-based FP calculation

assets/js/fingerprint.js

@@ -1,51 +0,0 @@
-/**
- * Fingerprints
- */
-
-// http://stackoverflow.com/a/34842797
-function hashCode(str) {
-  return str.split('').reduce((prevHash, currVal) =>
-    ((prevHash << 5) - prevHash) + currVal.charCodeAt(0), 0) >>> 0;
-}
-
-function createFingerprint() {
-  const prints = [
-    navigator.userAgent,
-    navigator.cpuClass,
-    navigator.oscpu,
-    navigator.platform,
-
-    navigator.browserLanguage,
-    navigator.language,
-    navigator.systemLanguage,
-    navigator.userLanguage,
-
-    screen.availLeft,
-    screen.availTop,
-    screen.availWidth,
-    screen.height,
-    screen.width,
-
-    window.devicePixelRatio,
-    new Date().getTimezoneOffset(),
-  ];
-
-  return hashCode(prints.join(''));
-}
-
-function setFingerprintCookie() {
-  let fingerprint;
-
-  // The prepended 'c' acts as a crude versioning mechanism.
-  try {
-    fingerprint = `c${createFingerprint()}`;
-  }
-  // If fingerprinting fails, use fakeprint "c1836832948" as a last resort.
-  catch {
-    fingerprint = 'c1836832948';
-  }
-
-  document.cookie = `_ses=${fingerprint}; path=/; SameSite=Lax`;
-}
-
-export { setFingerprintCookie };

assets/js/fp.ts

@@ -0,0 +1,210 @@
+/**
+ * FP version 4
+ *
+ * Not reliant on deprecated properties, and potentially
+ * more accurate at what it's supposed to do.
+ */
+
+import store from './utils/store';
+
+const storageKey = 'cached_ses_value';
+
+declare global {
+  interface Keyboard {
+    getLayoutMap: () => Promise<Map<string, string>>
+  }
+
+  interface UserAgentData {
+    brands: [{brand: string, version: string}],
+    mobile: boolean,
+    platform: string,
+  }
+
+  interface Navigator {
+    deviceMemory: number | undefined,
+    keyboard: Keyboard | undefined,
+    userAgentData: UserAgentData | undefined,
+  }
+}
+
+/**
+ * Creates a 53-bit non-cryptographic hash of a string.
+ *
+ * @param str The string to hash.
+ * @param seed The seed to use for hash generation.
+ * @return The resulting hash as a 53-bit number.
+ * @see {@link https://stackoverflow.com/a/52171480}
+ */
+function cyrb53(str: string, seed: number = 0x16fe7b0a): number {
+  let h1 = 0xdeadbeef ^ seed;
+  let h2 = 0x41c6ce57 ^ seed;
+
+  for (let i = 0, ch; i < str.length; i++) {
+    ch = str.charCodeAt(i);
+    h1 = Math.imul(h1 ^ ch, 2654435761);
+    h2 = Math.imul(h2 ^ ch, 1597334677);
+  }
+
+  h1  = Math.imul(h1 ^ h1 >>> 16, 2246822507);
+  h1 ^= Math.imul(h2 ^ h2 >>> 13, 3266489909);
+  h2  = Math.imul(h2 ^ h2 >>> 16, 2246822507);
+  h2 ^= Math.imul(h1 ^ h1 >>> 13, 3266489909);
+
+  return 4294967296 * (2097151 & h2) + (h1 >>> 0);
+}
+
+/**
+ * Get keyboard layout data from the navigator layout map.
+ *
+ * @return String containing layout map entries, or `none` when unavailable
+ */
+async function getKeyboardData(): Promise<string> {
+  if (navigator.keyboard) {
+    const layoutMap = await navigator.keyboard.getLayoutMap();
+
+    return Array.from(layoutMap.entries())
+      .sort()
+      .map(([k, v]) => `${k}${v}`)
+      .join('');
+  }
+
+  return 'none';
+}
+
+/**
+ * Get an approximation of memory available in gigabytes.
+ *
+ * @return String containing device memory data, or `1` when unavailable
+ */
+function getMemoryData(): string {
+  if (navigator.deviceMemory) {
+    return navigator.deviceMemory.toString();
+  }
+
+  return '1';
+}
+
+/**
+ * Get the "brands" of the user agent.
+ *
+ * For Chromium-based browsers this returns additional data like "Edge" or "Chrome"
+ * which may also contain additional data beyond the `userAgent` property.
+ *
+ * @return String containing brand data, or `none` when unavailable
+ */
+function getUserAgentBrands(): string {
+  const data = navigator.userAgentData;
+
+  if (data) {
+    let brands = 'none';
+
+    if (data.brands && data.brands.length > 0) {
+      // NB: Chromium implements GREASE protocol to prevent ossification of
+      // the "Not a brand" string - see https://stackoverflow.com/a/64443187
+      brands = data.brands
+        .filter(e => !e.brand.match(/.*ot.*rand.*/gi))
+        .map(e => `${e.brand}${e.version}`)
+        .sort()
+        .join('');
+    }
+
+    return `${brands}${data.mobile}${data.platform}`;
+  }
+
+  return 'none';
+}
+
+/**
+ * Get the size in rems of the default body font.
+ *
+ * Causes a forced layout. Be sure to cache this value.
+ *
+ * @return String with the rem size
+ */
+function getFontRemSize(): string {
+  const testElement = document.createElement('span');
+  testElement.style.minWidth = '1rem';
+  testElement.style.maxWidth = '1rem';
+  testElement.style.position = 'absolute';
+
+  document.body.appendChild(testElement);
+
+  const width = testElement.clientWidth.toString();
+
+  document.body.removeChild(testElement);
+
+  return width;
+}
+
+/**
+ * Create a semi-unique string from browser attributes.
+ *
+ * @return Hexadecimally encoded 53 bit number padded to 7 bytes.
+ */
+async function createFp(): Promise<string> {
+  const prints: string[] = [
+    navigator.userAgent,
+    navigator.hardwareConcurrency.toString(),
+    navigator.maxTouchPoints.toString(),
+    navigator.language,
+    await getKeyboardData(),
+    getMemoryData(),
+    getUserAgentBrands(),
+    getFontRemSize(),
+
+    screen.height.toString(),
+    screen.width.toString(),
+    screen.colorDepth.toString(),
+    screen.pixelDepth.toString(),
+
+    window.devicePixelRatio.toString(),
+    new Date().getTimezoneOffset().toString(),
+  ];
+
+  return cyrb53(prints.join(''))
+    .toString(16)
+    .padStart(14, '0');
+}
+
+/**
+ * Gets the existing `_ses` value from local storage or cookies.
+ *
+ * @return String `_ses` value or `null`
+ */
+function getSesValue(): string | null {
+  // Try storage
+  const storageValue: string | null = store.get(storageKey);
+  if (storageValue) {
+    return storageValue;
+  }
+
+  // Try cookie
+  const match = document.cookie.match(/_ses=([a-f0-9]+)/);
+  if (match && match[1]) {
+    return match[1];
+  }
+
+  // Not found
+  return null;
+}
+
+/**
+ * Sets the `_ses` cookie.
+ *
+ * If `cached_ses_value` is present in local storage, uses it to set the `_ses` cookie.
+ * Otherwise, if the `_ses` cookie already exists, uses its value instead.
+ * Otherwise, attempts to generate a new value for the `_ses` cookie based on
+ * various browser attributes.
+ * Failing all previous methods, sets the `_ses` cookie to a fallback value.
+ */
+export async function setSesCookie() {
+  let sesValue = getSesValue();
+
+  if (!sesValue || sesValue.charAt(0) !== 'd' || sesValue.length !== 15) {
+    // The prepended 'd' acts as a crude versioning mechanism.
+    sesValue = `d${await createFp()}`;
+    store.set(storageKey, sesValue);
+  }
+
+  document.cookie = `_ses=${sesValue}; path=/; SameSite=Lax`;
+}

assets/js/when-ready.ts

@@ -11,7 +11,7 @@ import { setupBurgerMenu }      from './burger';
 import { bindCaptchaLinks }     from './captcha';
 import { setupComments }        from './comment';
 import { setupDupeReports }     from './duplicate_reports';
-import { setFingerprintCookie } from './fingerprint';
+import { setSesCookie }         from './fp';
 import { setupGalleryEditing }  from './galleries';
 import { initImagesClientside } from './imagesclientside';
 import { bindImageTarget }      from './image_expansion';
@@ -44,7 +44,7 @@ whenReady(() => {
   initImagesClientside();
   setupComments();
   setupDupeReports();
-  setFingerprintCookie();
+  setSesCookie();
   setupGalleryEditing();
   bindImageTarget();
   setupEvents();

lib/philomena_web/fingerprint.ex

@@ -0,0 +1,85 @@
+defmodule PhilomenaWeb.Fingerprint do
+  import Plug.Conn
+
+  @type t :: String.t()
+  @name "_ses"
+
+  @doc """
+  Assign the current fingerprint to the conn.
+  """
+  @spec fetch_fingerprint(Plug.Conn.t(), any()) :: Plug.Conn.t()
+  def fetch_fingerprint(conn, _opts) do
+    conn =
+      conn
+      |> fetch_session()
+      |> fetch_cookies()
+
+    # Try to get the fingerprint from the session, then from the cookie.
+    fingerprint = upgrade(get_session(conn, @name), conn.cookies[@name])
+
+    # If the fingerprint is valid, persist to session.
+    case valid_format?(fingerprint) do
+      true ->
+        conn
+        |> put_session(@name, fingerprint)
+        |> assign(:fingerprint, fingerprint)
+
+      false ->
+        assign(conn, :fingerprint, nil)
+    end
+  end
+
+  defp upgrade(<<"c", _::binary>> = session_value, <<"d", _::binary>> = cookie_value) do
+    if valid_format?(cookie_value) do
+      # When both fingerprint values are valid and the session value
+      # is an old version, use the cookie value.
+      cookie_value
+    else
+      # Use the session value.
+      session_value
+    end
+  end
+
+  defp upgrade(session_value, cookie_value) do
+    # Prefer the session value, using the cookie value if it is unavailable.
+    session_value || cookie_value
+  end
+
+  @doc """
+  Determine whether the fingerprint corresponds to a valid format.
+
+  Valid formats start with `c` or `d` (for the version). The `c` format is a legacy format
+  corresponding to an integer-valued hash from the frontend. The `d` format is the current
+  format corresponding to a hex-valued hash from the frontend. By design, it is not
+  possible to infer anything else about these values from the server.
+
+  See assets/js/fp.ts for additional information on the generation of the `d` format.
+
+  ## Examples
+
+      iex> valid_format?("b2502085657")
+      false
+
+      iex> valid_format?("c637334158")
+      true
+
+      iex> valid_format?("d63c4581f8cf58d")
+      true
+
+      iex> valid_format?("5162549b16e8448")
+      false
+
+  """
+  @spec valid_format?(any()) :: boolean()
+  def valid_format?(fingerprint)
+
+  def valid_format?(<<"c", rest::binary>>) when byte_size(rest) <= 12 do
+    match?({_result, ""}, Integer.parse(rest))
+  end
+
+  def valid_format?(<<"d", rest::binary>>) when byte_size(rest) == 14 do
+    match?({:ok, _result}, Base.decode16(rest, case: :lower))
+  end
+
+  def valid_format?(_fingerprint), do: false
+end

lib/philomena_web/plugs/current_ban_plug.ex

@@ -16,9 +16,7 @@ defmodule PhilomenaWeb.CurrentBanPlug do
   @doc false
   @spec call(Conn.t(), any()) :: Conn.t()
   def call(conn, _opts) do
-    conn = Conn.fetch_cookies(conn)
-
-    fingerprint = conn.cookies["_ses"]
+    fingerprint = conn.assigns.fingerprint
     user = conn.assigns.current_user
     ip = conn.remote_ip
 

lib/philomena_web/plugs/filter_banned_users_plug.ex

@@ -37,9 +37,7 @@ defmodule PhilomenaWeb.FilterBannedUsersPlug do
   defp maybe_halt_no_fingerprint(%{method: "GET"} = conn), do: conn
 
   defp maybe_halt_no_fingerprint(conn) do
-    conn = Conn.fetch_cookies(conn)
-
-    case conn.cookies["_ses"] do
+    case conn.assigns.fingerprint do
       nil ->
         PhilomenaWeb.NotAuthorizedPlug.call(conn)
 

lib/philomena_web/router.ex

@@ -2,6 +2,7 @@ defmodule PhilomenaWeb.Router do
   use PhilomenaWeb, :router
 
   import PhilomenaWeb.UserAuth
+  import PhilomenaWeb.Fingerprint
 
   pipeline :browser do
     plug :accepts, ["html"]
@@ -9,6 +10,7 @@ defmodule PhilomenaWeb.Router do
     plug :fetch_flash
     plug :protect_from_forgery
     plug :put_secure_browser_headers
+    plug :fetch_fingerprint
     plug :fetch_current_user
     plug PhilomenaWeb.ContentSecurityPolicyPlug
     plug PhilomenaWeb.CurrentFilterPlug

lib/philomena_web/user_auth.ex

@@ -211,9 +211,8 @@ defmodule PhilomenaWeb.UserAuth do
 
   defp update_usages(conn, user) do
     now = DateTime.utc_now() |> DateTime.truncate(:second)
-    conn = fetch_cookies(conn)
 
     UserIpUpdater.cast(user.id, conn.remote_ip, now)
-    UserFingerprintUpdater.cast(user.id, conn.cookies["_ses"], now)
+    UserFingerprintUpdater.cast(user.id, conn.assigns.fingerprint, now)
   end
 end

lib/philomena_web/user_fingerprint_updater.ex

@@ -3,6 +3,8 @@ defmodule PhilomenaWeb.UserFingerprintUpdater do
   alias Philomena.Repo
   import Ecto.Query
 
+  alias PhilomenaWeb.Fingerprint
+
   def child_spec([]) do
     %{
       id: PhilomenaWeb.UserFingerprintUpdater,
@@ -14,14 +16,13 @@ defmodule PhilomenaWeb.UserFingerprintUpdater do
     {:ok, spawn_link(&init/0)}
   end
 
-  def cast(user_id, <<"c", _rest::binary>> = fingerprint, updated_at)
-      when byte_size(fingerprint) <= 12 do
-    pid = Process.whereis(:fingerprint_updater)
-    if pid, do: send(pid, {user_id, fingerprint, updated_at})
+  def cast(user_id, fingerprint, updated_at) do
+    if Fingerprint.valid_format?(fingerprint) do
+      pid = Process.whereis(:fingerprint_updater)
+      if pid, do: send(pid, {user_id, fingerprint, updated_at})
+    end
   end
 
-  def cast(_user_id, _fingerprint, _updated_at), do: nil
-
   defp init do
     Process.register(self(), :fingerprint_updater)
     run()

test/philomena_web/user_auth_test.exs

@@ -9,6 +9,7 @@ defmodule PhilomenaWeb.UserAuthTest do
     conn =
       conn
       |> Map.replace!(:secret_key_base, PhilomenaWeb.Endpoint.config(:secret_key_base))
+      |> assign(:fingerprint, "d015c342859dde3")
       |> init_test_session(%{})
 
     %{user: user_fixture(), conn: conn}

test/support/conn_case.ex

@@ -41,9 +41,11 @@ defmodule PhilomenaWeb.ConnCase do
     |> Philomena.Filters.change_filter()
     |> Philomena.Repo.insert!()
 
+    fingerprint = to_string(:io_lib.format(~c"d~14.16.0b", [:rand.uniform(2 ** 53)]))
+
     conn =
       Phoenix.ConnTest.build_conn()
-      |> Phoenix.ConnTest.put_req_cookie("_ses", Integer.to_string(System.unique_integer()))
+      |> Phoenix.ConnTest.put_req_cookie("_ses", fingerprint)
 
     {:ok, conn: conn}
   end