encrypted-stream

transparent encryption and decryption for file-like objects

Warning

This is a very early release! Some parts of the code are not tested yet, some are in need of improvement. The documetation is incomplete. There may be cryptographically relevant bugs. Things may break without warning!

Say you want to upload a file somewhere, but you’d like to encrypt it beforehand.

To do this, you could encrypt the entire file at once. You’ll need a temporary file to hold the encrypted data, and it needs to be at least as big as your original file. For large files, this would use a lot of extra disk space.

If you don’t want to fit the entire file into your RAM at once, you might also want to use a chunking encryption protocol, and you should probably make sure that your cryptographic system is secure and tamper resistant.

Or, you could just say:

from encrypted_stream import EncryptingReader

with open("source", "rb") as source_file:
    encrypted_file = EncryptingReader(source_file, key)

That’s it! encrypted_file will behave just as if you had created a temporary file and stored the encrypted data inside of it, except that it uses no extra disk space and only about 1 MB of your precious RAM.

There’s also a matching DecryptingWriter that works the same way: Write encrypted data to it, and it writes the decrypted result into the file you give it.

Features

  • built on solid crypto

  • easy-to-use API

  • lightweight: minimal extra storage, fast seek()-ing to arbitrary positions

Not-yet features

  • 100% test coverage (we’re at 99%, so close!!)

  • hard-to-misuse

    • It is currently possible, even if unlikely, to trigger nonce-reuse in the underlying primitive. There is a big warning in the API reference about this, but this doesn’t really go with the definition of “hard-to-misuse”. Sadly, this problem is inherent in the current API (allowing fast seeking while staying lightweight); I am planning to fix it by switching to a misuse-resistant primitive, which will have a couple of other advantages as well. (Disadvantages too, but meh… it needs to be secure first, everything else second.)

Anti-features

  • contains crypto implemented by a non-expert

  • project will be on ice while I’m busy with Life™