diff --git a/pyproject.toml b/pyproject.toml
index 532a6bfe6..e275f9cf8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -85,7 +85,6 @@ dependencies = [
   "pypdf==3.9.*",
   "python-bidi==0.4.*",  # Support for Arabic in reportlab
   "python-dateutil==2.8.*",
-  "python-u2flib-server==4.*",
   "pytz",
   "pytz-deprecation-shim==0.1.*",
   "pyuca",
diff --git a/src/pretix/base/models/auth.py b/src/pretix/base/models/auth.py
index a9c0fa909..c7c63b1d5 100644
--- a/src/pretix/base/models/auth.py
+++ b/src/pretix/base/models/auth.py
@@ -53,13 +53,11 @@ from django.utils.timezone import now
 from django.utils.translation import gettext_lazy as _
 from django_otp.models import Device
 from django_scopes import scopes_disabled
-from u2flib_server.utils import (
-    pub_key_from_der, websafe_decode, websafe_encode,
-)
 
 from pretix.base.i18n import language
 from pretix.helpers.urls import build_absolute_uri
 
+from ...helpers.u2f import pub_key_from_der, websafe_decode, websafe_encode
 from .base import LoggingMixin
 
 
diff --git a/src/pretix/helpers/u2f.py b/src/pretix/helpers/u2f.py
new file mode 100644
index 000000000..f2626639f
--- /dev/null
+++ b/src/pretix/helpers/u2f.py
@@ -0,0 +1,76 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+
+# Backwards compatibility for old U2F key material, with code taken from
+#
+# https://github.com/Yubico/python-u2flib-server/blob/python-u2flib-server-4.0.1/u2flib_server/utils.py
+#
+# Copyright (c) 2013 Yubico AB
+# All rights reserved.
+#
+#   Redistribution and use in source and binary forms, with or
+#   without modification, are permitted provided that the following
+#   conditions are met:
+#
+#    1. Redistributions of source code must retain the above copyright
+#       notice, this list of conditions and the following disclaimer.
+#    2. Redistributions in binary form must reproduce the above
+#       copyright notice, this list of conditions and the following
+#       disclaimer in the documentation and/or other materials provided
+#       with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+from base64 import urlsafe_b64decode, urlsafe_b64encode
+
+from cryptography.hazmat.backends import default_backend
+from cryptography.hazmat.primitives.serialization import load_der_public_key
+
+PUB_KEY_DER_PREFIX = b'\x30\x59\x30\x13\x06\x07\x2a\x86\x48\xce\x3d\x02\x01' \
+                     b'\x06\x08\x2a\x86\x48\xce\x3d\x03\x01\x07\x03\x42\x00'
+
+
+def pub_key_from_der(der):
+    return load_der_public_key(PUB_KEY_DER_PREFIX + der, default_backend())
+
+
+def websafe_decode(data):
+    if isinstance(data, str):
+        data = data.encode('ascii')
+    data += b'=' * (-len(data) % 4)
+    return urlsafe_b64decode(data)
+
+
+def websafe_encode(data):
+    if isinstance(data, str):
+        data = data.encode('ascii')
+    return urlsafe_b64encode(data).replace(b'=', b'').decode('ascii')