django-encrypted-filefield 0.1.3

Why This Exists

It’s increasingly common to use products like S3 to host static files, but sometimes those static files aren’t exactly meant for public eyes. You might push some bit of personal information into S3 and then anyone with the URL will be able to see it.

Sure, the URL may be really hard to guess, but I’m not a fan of “security through obscurity” so I wrote this to encrypt stuff I push to S3. Now, only encrypted blobs are available publicly, but internally, behind a MyPermissionRequiredMixin, the images and documents are loaded magically and transparently.

How’s It Work?

EncryptedFileField is a thin wrapper around Django’s native FileField that transparently encrypts whatever the user has uploaded and passes off the now encrypted data to whatever storage engine you’ve specified. It also overrides the .url value to return a reference to your own view, which does the decryption for you on the way back to the user.

So where you may have once had this:

# my_app/models.py

class MyModel(models.Model):

    name = models.CharField(max_length=128)
    attachment = models.FileField(upload_to="attachments")
    image = models.ImageField(
        upload_to="images",
        width_field="image_width",
        height_field="image_height"
    )
    image_width = models.PositiveIntegerField()
    image_height = models.PositiveIntegerField()

All you have to do is change the file fields and you’ve got encrypted files

# my_app/models.py

from django_encrypted_filefield.fields import (
    EncryptedFileField,
    EncryptedImageField
)

class MyModel(models.Model):

    name = models.CharField(max_length=128)
    attachment = EncryptedFileField(upload_to="attachments")
    image = EncryptedImageField(
        upload_to="images",
        width_field="image_width",
        height_field="image_height"
    )
    image_width = models.PositiveIntegerField()
    image_height = models.PositiveIntegerField()


# my_app/views.py

from django.contrib.auth.mixins import AuthMixin
from django_encrypted_filefield.views import FetchView


class MyPermissionRequiredMixin(AuthMixin)
    """
    Your own rules live here
    """
    pass


class MyFetchView(MyPermissionRequiredMixin, FetchView):
    pass

# my_app/urls.py

from django_encrypted_filefield.constants import FETCH_URL_NAME
from myapp.views import MyFetchView

urlpatterns = [
    # ...
    url(
        r"^my-fetch-url/(?P<path>.+)",  # up to you, but path is required
        MyFetchView.as_view(),          # your view, your permissions
        name=FETCH_URL_NAME
    ),
    # ...
]

How Do I Configure It?

Configuration of the package requires setting three values in either the environment (recommended) or in your settings.py. These values are:

• DEFF_SALT: The salt value use for generating the synchronous encryption

• DEFF_PASSWORD: The password value for the same thing

• DEFF_FETCH_URL_NAME: The named URL you intend to use to download the files as they’re decrypted on-the-fly.

Outside of that, follow the above and you should be good to go.

How Do I Run the Tests?

As this project depends on the setting of three environment variables, you have to set these for the tests. Also, the tests are expecting these values, so don’t change them:

$ DEFF_SALT="salt" DEFF_PASSWORD="password" DEFF_FETCH_URL_NAME="fetch" ./manage.py test

Is There a Demo?

There is! Just check out the code and run the mini django app in the demo directory:

$ git clone git@github.com:danielquinn/django-encrypted-filefield.git
$ cd django-encrypted-filefield/demo
$ export DEFF_SALT="salt"
$ export DEFF_PASSWORD="password"
$ export DEFF_FETCH_URL_NAME="fetch"
$ ./manage migrate
$ ./manage.py runserver

…then open http://localhost:8000 and submit two files via the form. In this case we’re using Django’s default_storage, but the same logic should apply to all storage engines.

Stuff That Doesn’t Work

Since the file changes just before it’s saved, you can’t apply a validator that acts on the contents of the file. For example, if you’ve got a validator that uses mime-magic to determine the file type, it will always return text/plain which, unless that’s what you’re checking for, will break your validation. To make things more interesting, Django appears to apply validation on field values on every save, not just when the field has changed, so even if the validator were to work on the first run, whenever you would update the object in the admin, your validator will barf in this case.

What’s the Status of the Project?

Stable. I’m actively using it in a production environment now and have been for some time without issue. This isn’t a guarantee that it’ll work for everyone in every case of course, but it’s enough for me to use that word :-)