Alice and Bob information sharing code challenge

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

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

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)

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

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

Python Example

>>> from alice_and_bob.key_share import main as code
>>> code(p=2, g=3)  # only one possibility as primes very small
Shared secret key: 1
>>> code(61, 53)
Shared secret key: 34
>>> code(61, 53)
Shared secret key: 37
>>> code(61, 53)
Shared secret key: 9
>>> code(61, 53)
Shared secret key: 11