challenge03.py

#!/usr/bin/env python3
# Single-byte XOR cipher 
from string import ascii_letters
from utils import xor
 
# Adding numerals to the dataset
ascii_alphanumerals = ascii_letters+ "123456890,.;:/'"

# --------------------------------------------------------
# ---------------------- functions -----------------------
# --------------------------------------------------------
def get_score(message: str) -> int:
    '''
    a function that takes input string and using letter 
    frequency it scores it. The closer the score is 
    to 1.00, the more realistic.
    '''
    score = 0
    freq = {'a': 0.0812, 'b': 0.0149, 'c': 0.0271, 'd': 0.0432,
    'e': 0.1202, 'f': 0.0230, 'g': 0.0202, 'h': 0.0592, 'i': 0.0731,
    'j': 0.001, 'k': 0.0069, 'l': 0.0398, 'm': 0.0261, 'n': 0.0695,
    'o': 0.0768, 'p': 0.0182, 'q': 0.0011, 'r': 0.0602, 's': 0.0628,
    't': 0.091, 'u': 0.0288, 'v': 0.0111, 'w': 0.0209, 'x': 0.0017,
    'y': 0.0211, 'z': 0.0007, ' ': .1}
    for c in message:
        score += freq.get(c, 0) #if it is not an alphabet, give it a score of 0
    return score

# --------------------------------------------------------
# ------------------- Problem Solution -------------------
# --------------------------------------------------------
def main():
    ct_hex = '1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736'
    ct_bytes = bytes.fromhex(ct_hex)
    print(ct_bytes)
    highestscore = 0
    # XOR'ing x and y using the python XOR operator
    for c in ascii_alphanumerals:
        #convert the character to an integer to use it in the strxor_c function
        result = xor(ct_bytes, c.encode())
        #decode 'UTF-8' from bytes to string of text
        result = result.decode()
        score = get_score(result)
        if (score > highestscore):
            highestscore = score
            output = 'Character: ' + c + "\nXOR'd output: "+result+'\nscore = '+str(score)
    print(output)

if __name__ == "__main__":
    main()