COSC312 Lab week 10—Homomorphic encryption

• The objective for this lab is for you to experiment with the open source SEAL library from Microsoft, that implements homomorphic encryption.

It's a busy time of semester, so this lab exercise is intended to involve less time and effort than some past lab exercises to reach instructive evaluation results and programming exercises.

Setting up your software environment

• Start the Docker application (i.e., Docker Desktop)
• Clone the public Git repository https://altitude.otago.ac.nz/cosc412/homomorphic-encryption-using-seal into a working copy directory of your choice.

Having said the working directory is your choice, actually, if you're working on the Owheo CS Lab computers, you probably should create your directory under c:\windows\temp\ (Powershell or cmd.exe) or /c/windows/temp/ (Git Bash) to avoid permissions problems regarding Docker's ability to open your files.

• Start Visual Studio Code and open your working copy directory (as a directory). Because I have the Visual Studio Code command line tools instealled, I can do this by opening a shell, cding into my working directory, and then running code . to open Visual Studio Code on that directory (this should work on the Owheo Lab computers too). I see something akin to:
• You should be prompted in the bottom right of the VSCode with the choice to "Reopen in Container", and you should click that button.
• If you consult your Docker Desktop application after a while you should see something like:
  which indicates that VSCode has successfully started your development container.
• Eventually you should see a terminal window pane in VSCode that finishes with "Done. Press any key to close the terminal."

Testing PySEAL

• Within VSCode open the file homomorphic-test-1.py in an editor window.
• On VSCode's left button pannel focus the "Run and Debug" section and click "Run and Debug". Choose "Python file" from the drop-down list that appears. (Or you can just run python3 homomorphic-test-1.py from the terminal pane of VSCode.)
• You should see a terminal pane in which the Python script is run, and you should see the results of an addition and a multiplication result.

FYI: Building PySEAL

• This is not part of the lab exercise in that the Git repository distributes a pre-built instance of the SEAL library (i.e., that's what the seal.cpython-311-x86_64-linux-gnu.so file is).
• If you do want to rebuild the library for yourself, e.g., to run on a different Python version and/or a different operating system, the README.md file links out to the instructions on the repository from which PySEAL was downloaded, and by which the compiled library included in the Git repository was built.

Exercises

Task (recommended) Examine the flow of the Python code, and read the code comments.

Task (recommended) Change the size of the scale factor. Observe how the noise changes for different values of scale.

Task (recommended) Change the code to perform operations in a loop with a selectable iteration count. Show if/how errors accumulate for repeated operations.

Task (optional) Benchmark the speed of homomorphic encryption compared to equivalent native Python arithmetic. This is likely best done by timing a high iteration count of a loop that runs the same operations directly or using homomorphic encryption. Keep in mind that this is a very rough performance comparison, though, since you are performing the computation within a Docker container that by default does not have full access to all of the CPU cores on your computer.

Cleaning up

• Run the Visual Studio Code command to reopen the file locally (from the command pallete, "Dev Containers: Reopen Folder Locally").
• In Docker Desktop's GUI or otherwise, delete the container and any (Docker) images associated with that container.
• Quit Docker Desktop and ensure that any menubar (macOS) or system tray (Windows) items have gone. (Otherwise these Docker items can be used to access a menu from which to request Docker to shut down.)