Author: Leslie Horace
Purpose: Dynamically finding hill cipher encryption/decryption key pairs 
Version: 1.0

Hill Cipher KeyPair Generator

Included files

• hillcipher_main.c
  • Functions for creating encryption key and computing decryption key
• hillcipher_main.h
  • Header file to use functions from "hillcipher_main.c"
• hillcipher_main.c
  • simple main to demonstrate hill cipher key pair generation
• Makefile
  • compiling program and cleaning out files

Compiling the program

make

gcc ./hillcipher_main.c ./hillcipher_keypair.c -o < outfile>

Cleaning compiled files

make clean

Running the program

usage: < outfile> <enc_key filename> <dec_key filename>

output files are written in binary, use (.bin) extension

About the program

1. Creates a random square key matrix of order n, where n is in range [2, 9]
   • The matrix is filled with random codes [0,26] for language [A-Z]
   • Keeping the order small for demoing purposes
2. Computes the modular inverse by performing elementary row operations
   • Row Multiplication
   • Row swap
   • Row addition
3. All computations are reduced (mod 26) for language [A-Z]
   • [MODULUS] macro in "hillcipher_key.c" can be modified as needed
4. Generates new encryption keys until finding one that is invertible (mod 26)
5. Upon finding valid keypair, each key is written to the specified filenames
6. The keys can be read back in for use and/or display to the console