def supply_key():
randomise()
while True:
div_key = random.randint(2, len(ropes.ASCII_CHARACTERS))
mod_key = random.randint(2, len(ropes.ASCII_CHARACTERS))
if maths.euclid_gcd(div_key, len(ropes.ASCII_CHARACTERS)) != 1:
return div_key * len(ropes.ASCII_CHARACTERS) + mod_key
def brute_force_affine(ciphertext, key=1):
# brute-force by looping through every possible key
for key in range(key, len(ropes.ASCII_CHARACTERS) ** 2):
div_key = secret_keys(key)[0]
if maths.euclid_gcd(div_key, len(ropes.ASCII_CHARACTERS)) != 1:
continue
decrypt_attempt = decrypt_affine(key, ciphertext)[1]
if is_English(decrypt_attempt):
return key, decrypt_attempt
return None
def secure_keys(div_key, mod_key, mode):
if div_key == 1 and mode == ENCRYPT:
return False, 'The affine cipher becomes incredibly weak when the div_key is set to 1. Choose a different key.'
if mod_key == 0 and mode == ENCRYPT:
return False, 'The affine cipher becomes incredibly weak when the mod_key is set to 0. Choose a different key.'
if div_key < 0 or mod_key < 0 or mod_key > len(ropes.ASCII_CHARACTERS) - 1:
return False, 'The div_key must be greater than 0 and the mod_key must be between 0 and %s.' % (
len(ropes.ASCII_CHARACTERS) - 1)
if maths.euclid_gcd(div_key, len(ropes.ASCII_CHARACTERS)) != 1:
return False, 'The div_key (%s) and the character set size (%s) are not relatively prime. Choose a different key.' % (
div_key, len(ropes.ASCII_CHARACTERS))
return True, 'The key combination does not comprimise the strength of the affine cipher'