tweakable-block-cipher

Tweakable Block Cipher

Overview

This folder contains the code for a Tweakable Block Cipher (TBC) which operates in a Tweaked Authentication Encryption (TAE) mode.

The developed cipher is simply a block cipher where each block has a tweak associated with it. The tweak is a value composed by a nounce and some length-encoded information. These tweaks are useful for detecting repetitions or removals of blocks in the ciphertext. Having a nounce guarantees that even blocks that occupy the same position in other ciphertexts will be different and, therefore, cause a decryption failure.

It is interesting to note that by having a tweak we can also rely on using a cipher like AES in ECB mode for each block individually. This is, generally, not a recommended mode, but in this case it is all safe.

Modules

• ruped_tweakable.py which contains the implementation of the TBC ¹;
• utils.py which contains some utility functions for XORing byte strings.

Running

First, make sure you have the required dependencies installed:

pip install -r requirements.txt

Then, you can run the main.py script to test the TBC:

python main.py

Logs will be printed to the console, showing both the encryption and decryption process, as well as block removal detection.

References

• https://people.eecs.berkeley.edu/~daw/papers/tweak-crypto02.pdf
• https://cryptography.io/en/latest/hazmat/primitives/symmetric-encryption/#cryptography.hazmat.primitives.ciphers.modes.ECB

Footnotes

1. Named after me, Rui, and Pedro, a colleague of mine at the University of Minho. (Rui + Pedro = Ruped). ↩