1. Introduction¶

2. Alice and Bob information sharing code challenge¶

Diffie-Hellman coding challenge for secret information exchange using public/private keys

2.1. Background¶

Alice and Bob use the Diffie-Hellman key exchange algorithm to share secret information. Alice and Bob start with prime numbers, pick private keys, generate and share public keys, finally they then generate a shared secret key.

Your code module should take in two prime numbers, p and g and output the value of p and g, the private key a for Alice and b for Bob. Finally your program should print out the Shared Secret key for Alice and Bob.

If your implementation is correct, the Shared Secret keys should match.

Note: This challenge requires you to perform calculations on large numbers. Further information can be found at https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange

2.2. Code requirements¶

Ensure that your code is clean and uses good practice (e.g. error handling) and is commented well.
Ensure that your code can work cross platform and across different versions of Python.
Feel free to add as many bells and whistles as you so desired (e.g. Unit Tests)

2.3. Running the code¶

git clone https://github.com/Liam-Deacon/alice_and_bob
cd alice_and_bob
python3 -m alice_and_bob.key_share --help

2.3.1. CLI Example¶

$ python3 -m alice_and_bob.key_share -p 61 -g 53
Shared secret key: 60

It is also possible to specify the number of bits used for the generated private keys:

$ python3 -m alice_and_bob.key_share -p 88937 -g 104729  --bits=2048
Shared secret key: 39885

2.3.2. Python Example¶

>>> from alice_and_bob.key_share import PrivateKey, diffie_hellman, main as code

# Lets try using PrivateKey class and diffie_helman function to generate public and private keys from 2 primes
>>> PrivateKey.DEFAULT_BITS = 8  # Should be using at least 2048 bits in real life scenario
>>> diffie_helman(p=2, g=3)  # the primes used in Diffie-Hellman algorithm should be much larger
Keys(public_key_pair=(1, 1), private_key_a=16353971836403060303, private_key_b=9351112014020560943)

# output from diffie_hellman() function is a namedtuple, i.e.
>>> keys = diffie_hellman(p=16353971836403060303, g=9351112014020560943)
>>> keys[0]  # return public keys
(3313824243486361299, 5114973081711194950)
>>> keys[1] != keys[2]  # compare private keys
True

# finally the shared secret key is printed by using the main/code function, which wraps diffie_helman()
>>> code(p=2, g=3)  # only one possibility as primes very small
Shared secret key: 1
>>> code(61, 53)
Shared secret key: 37
>>> code(61, 53)
Shared secret key: 9
>>> code(61, 53)
Shared secret key: 11

2.4. Bells & Whistles 🔔¶

Unit tests 🧪
High code coverage (see shields above) 🔦
Repo badges! 📛
GitHub Actions for CI pipeline ⚙️
- Checks against Python 3.5, 3.6, 3.7 & 3.8 for testing
- Repeats checks on Windows, Mac OS and Linux
- Builds (example) documentation using Sphinx and deploys to https://liam-deacon.github.io/alice_and_bob/
Published as python package to https://PyPI.org 📦
Example command line script provided (see CLI example above) 📜

2.5. TODO¶

Future improvements could be:

Add linter checks to CI pipeline (PEP8, style, docstrings, code compexity, type checks, etc.)
Add web UI and dockerise
Use GitHub Actions to auto increment and deploy PyPI releases on successful PR completion into master branch
Better documentation (devs will complain it is insufficient regardless - its what we do ;-))