cryptopals/cryptlib.py

import base64

CHARACTER_FREQ = {
    'a': 0.0651738, 'b': 0.0124248, 'c': 0.0217339, 'd': 0.0349835, 'e': 0.1041442, 'f': 0.0197881, 'g': 0.0158610,
    'h': 0.0492888, 'i': 0.0558094, 'j': 0.0009033, 'k': 0.0050529, 'l': 0.0331490, 'm': 0.0202124, 'n': 0.0564513,
    'o': 0.0596302, 'p': 0.0137645, 'q': 0.0008606, 'r': 0.0497563, 's': 0.0515760, 't': 0.0729357, 'u': 0.0225134,
    'v': 0.0082903, 'w': 0.0171272, 'x': 0.0013692, 'y': 0.0145984, 'z': 0.0007836, ' ': 0.1918182
}


# this function takes a string representing hex, converts to bytes, and re-encodes to base64
def hex_to_base64(hex_string):
    byte_array = bytearray.fromhex(hex_string)
    base64_value = base64.b64encode(byte_array)
    return base64_value

# this function takes two hex strings, converts them to bytes, and xor's them
def byte_xor(hs1, hs2):
    byte_array1 = int(hs1,16)
    byte_array2 = int(hs2,16)
    return byte_array1 ^ byte_array2

# this function will take a hex string and xor it against a single byte
def single_byte_xor(hexstring,key_candidate):
    byte_array = bytes.fromhex(hexstring)
    results = b''
    for char in byte_array:
        results += bytes([char ^ key_candidate])
    return results

def score_english_lang(byte_string):
    score = 0

    for byte in byte_string:
        letter = chr(byte).lower()
        score += CHARACTER_FREQ.get(letter, 0)
    return score

# this function takes a string and xor's it with a repeating key
def repeating_xor(string):
    byte_array = string.encode()
    cipher_bytes = b'' 
    key_counter = 0

    for char in byte_array:
        match key_counter:
            case 1:
                key = ord("C")
            case 2:
                key = ord("E")
            case _:
                key = ord("I")

        cipher_bytes += bytes([char ^ key])
        key_counter += 1
        if key_counter > 2:
            key_counter = 0
    return cipher_bytes.hex()