Difference between revisions of "Preparation for implementing some cryptographic primitives in Python"
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Revision as of 14:36, 1 September 2017
Later on in the semester we will be implementing some cryptographic primitives in Python. Want to see if you need to do some preparatory work? Here is a good practice task to use as a gauge.
First, set up a virtualenv or conda environment. For conda:
Next install the PETLib package:
Once you have petlib installed and have passed the unit tests, a mini-example you can try is to implement symmetric encryption using AES-GCM. You don't really need knowledge of AES-GCM to do this; it's all about using PETLib effectively.
- Note: don't look at the official documentation for quick_gcm_enc until you're ready to check your work, as it contains the answer as an example. Here is the documentation for quick_gcm_enc that you will need, sans example:
quick_gcm_enc(key, iv, msg, assoc=None, tagl=16)[source] One operation GCM encryption. Args: key (str): the AES symmetric key. Length depends on block cipher choice. iv (str): an Initialization Vector of up to the block size. (Can be shorter.) msg (str): the message encrypt. assoc (str): associated data that will be integrity protected, but not encrypted. tagl (int): the length of the tag, up to the block length.
- Consider these imports:
from os import urandom from petlib.cipher import Cipher
- Note that urandom produces cryptographically strong bytes, which is handy for keys and ivs.
- Use the encoded plaintext rather than the input directly (you can encypt bytes not unicode strings, hence the need for encoding and decoding with UTF8 first).
- The documentation for petlib.cipher is available here.
- Once you've given this a try, you can check your work with the docs by looking at the quick_gcm_enc example
Let me know how it goes.