Ошибка проверки сертификата сервера. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none

Я пытаюсь выполнить шаги, описанные на странице Tor Project Debian Repository, чтобы установить последние LTS-пакеты Tor.

Когда я запускаю команду apt update, я получаю следующую ошибку

<omitted unrelated lines>
Err:10 https://deb.torproject.org/torproject.org xenial Release
  server certificate verification failed. CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none
<omitted unrelated lines>
Reading package lists... Done
E: The repository 'https://deb.torproject.org/torproject.org xenial Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Моя версия Ubuntu:

No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.4 LTS
Release:        16.04
Codename:       xenial