Coursework for CSC 512, Cryptography.

This repository consists of the coursework for my CSC 512 Cryptography class at SDSM&T. It is split into two pieces:

• crypto/
• homework/

The homework/ folder is, unsurprisingly, my homework for the course. The crypto/ folder is my class portfolio of cryptography-related code. It is implemented as a Python module providing a number of different logical submodules.

The crypto library has the following dependencies:

• Python 3.6+
• gmpy2 which has its own dependencies:
  • libgmp3-dev
  • libmpc-dev
  • libmpfr-dev
• numpy
• concurrencytest (optional, but recommended)
• sympy

The dependencies may be installed on Ubuntu as follows:

• Install python3.6 and pip:

  # Add Python3.6 apt repository if using 16.04 LTS
  sudo add-apt-repository ppa:jonathonf/python-3.6  # (only for 16.04 LTS)
  sudo apt update
  # Install Python 3.6
  sudo apt install python3.6
  sudo apt install python3.6-dev
  sudo apt install python3.6-venv
  # Install an up-to-date version of Pip
  wget https://bootstrap.pypa.io/get-pip.py
  sudo python3.6 get-pip.py
  
  # Use Python 3.6 as the default Python3
  sudo ln -s /usr/bin/python3.6 /usr/local/bin/python3
  sudo ln -s /usr/local/bin/pip /usr/local/bin/pip3
  
  # Verify installation
  python --version
  python3 --version
  $(head -1 `which pip` | tail -c +3) --version
  $(head -1 `which pip3` | tail -c +3) --version

• Install gmpy2

  # Install dependencies for pip to compile gmpy2
  sudo apt install libgmp3-dev libmpc-dev libmpfr-dev
  # Might have to use pip3 depending on the output of $(head -1 `which pip` | tail -c +3) --version
  sudo -H pip install --upgrade gmpy2

• Install other Python dependencies:

  sudo -H pip install --upgrade numpy sympy concurrencytest

Example usage may be found in the course homework and in the unit tests. Run pydoc3 -b and navigate to the crypto link to view the crypto library documentation.

The unit tests may be ran by any of the following:

$ python3 runtests.py
$ ./runtests.py
$ python3.6 runtests.py

Note that sometimes the test script hangs while waiting for a lock to release due to the tests being run concurrently. If this happens, send a KeyboardInterrupt and try again.

• Download the repository and create a test.py script to test code in:

  ~ $ git clone https://github.com/Notgnoshi/cryptography.git
  ~ $ cd cryptography
  ~/cryptography/ $ echo '#!/usr/bin/env python3' >> test.py
  ~/cryptography/ $ chmod +x test.py

• Inside test.py the crypto library may be used like so:

  • Running the unit tests with a given number of processes

    #!/usr/bin/env python3
    from crypto.tests import runtests
    # Requires the concurrencytest library installed. Will run in serial otherwise
    runtests(processes=8)

  • Some bitwise utilities

    #!/usr/bin/env python3
    from crypto.utilities import Bitstream, lazy_pad, bits_to_string
    
    # One of many forms a bytestream can take
    bytestream = b'This is a test'
    # Lazily pad the bytestream so that it's length is evenly divisible by 8
    # The pad values will be randomly chosen from the given array
    bytestream = lazy_pad(bytestream, multiple=8, pad_values=b'abcdefghijklmnopqrstuvwxyz')
    # Construct a Bitstream
    bitstream = Bitstream(bytestream)
    
    # Hopefully unchanged
    output = bits_to_string(bitstream)
    print(output)
    # Will be `This is a test` with two random characters appended

  • Some classical ciphers

    #!/usr/bin/env python3
    from crypto.classical import AffineCipher, LfsrCipher
    import numpy
    
    plaintext = 'affine'
    cipher = AffineCipher(9, 2)
    ciphertext = cipher.encrypt(plaintext)
    assert ciphertext == 'cvvwpm'
    
    # Values taken from HW 1 problem 6
    initial_values = numpy.array([1, 0, 1, 0, 0, 1])
    coeffs = numpy.array([1, 1, 0, 1, 1, 0])
    cipher = LfsrCipher(initial_values, coeffs)
    
    ciphertext = cipher.encrypt('zyxwvuts')
    ciphertext = [ord(c) for c in ciphertext]
    expected = [31, 90, 153, 215, 233, 255, 13, 164]
    assert ciphertext == expected