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A minimal file host in Python 3 and Flask with encryption at rest, built for use with ShareX.


I'm a big fan of ShareX, an open source screen capture tool. For a long while, I've used imgur as a destination for my captures, but I decided I wanted to be more in control of my data. Hence, this thing.

The name is sort of a play on "one key" per file, as well as the fact that there's no guarantee that any of this works correctly. Don't share state secrets with it. 😉

"your crypto is (probably) bad and you should feel bad"

Sure, I won't deny that I'm not good at this. But I think I've given it a solid shot.

The actual at-rest encryption is backed by Fernet, which is a symmetric key cryptosystem implemented by the cryptography library. This provides a vetted implementation of authenticated encryption, with a small wrapper around the format to provide streaming response capabilities.

Each file stored has a per-file key generated, which is only stored in memory during file creation or access. It's expressed as part of the URL, so maintaining any request logs will sort of defeat the purpose. When a client requests a file, the server transparently decrypts the file and streams it block-by-block using chunked transfer encoding.

I'm not going to pretend to make guarantees about side-channel attacks or anything like that - that's not the point of this. I just wanted a system where if someone gets access to my box, they don't suddenly have every screenshot I've taken or file I've shared.

Additionally, if a truncation or authentication failure occurs halfway through decrypting a streaming response, the server should disconnect the socket, letting the browser know that the file should not be treated as a completed transfer. I haven't tested this thoroughly, however, and some initial research indicates that this may not be a happy story, depending on your WSGI server:


Using Python 3 and virtualenv, make a virtualenv from requirements.txt, then serve using your favorite WSGI server. Make sure to turn off request URL logging.

If you just want to kick the tires, you can run it with the built in Flask server by running: env FLASK_APP=wonkey python -m flask run

server configuration

wonkey supports configuration of several parameters through environment variables:

  • CHUNK_SIZE specifies the encrypted block size used in the Fernet system. This exists to allow streaming transfers, and can be tweaked based on benchmarking that I have not done.
  • UPLOAD_REDIRECT specifies a URL that clients should be redirected to if they attempt to access the root page of the server. By default, they are given a very basic HTML upload form.
  • UPLOAD_SECRET specifies a shared secret for users to upload to the server. If undefined, anyone can upload to the server.
  • CONTENT_DIR specifies the directory for encrypted file storage.

client configuration

for ShareX users:

From the main menu, click Destinations -> Destination settings... to open the destination settings. From there, choose "Custom uploaders" under "Other uploaders".

Enter a name and click add, then configure it like so:

  • Request type: POST
  • Request URL: https://YOUR_DOMAIN_HERE/
  • File form name: file
  • Arguments: secret = YOUR_SECRET_HERE
  • Response type: Redirection URL

for web browser usage:

If you leave UPLOAD_REDIRECT unconfigured, you can navigate to the application in a web browser and get a basic upload form.

for other usage:

  • Send a multipart/form-data POST to the application root (that is, /)
  • Set "file" to the file you'd like to upload
  • Set "secret" to the server's shared UPLOAD_SECRET
  • You'll be redirected to the uploaded file


A minimal file host in Python 3 and Flask with encryption at rest, built for use with ShareX.




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