apt-transport-tor software package provides APT transport for anonymous package downloads via Tor, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install apt-transport-tor
apt-transport-tor is installed in your system.
Make ensure the apt-transport-tor package were installed using the commands given below,
$ sudo dpkg-query -l | grep apt-transport-tor *
You will get with apt-transport-tor package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Administration Utilities |
| Package | apt-transport-tor |
| Version | 0.2.1-1+b1 [s390x], 0.2.1-1 [a |
| Description | APT transport for anonymous package downloads via Tor |
| Sub Section | admin |