def break_bounded_length_code_with_mcmc_monogram_criteria(
encryption, alphabet, n_list, coefs, log_distributions, steps_constant,
lower_bound, upper_bound, monogram_log_distribution, scrabble):
max_weight = float("-inf")
max_state = [cipher.get_zero_mono_key()]
for length in range(lower_bound, upper_bound + 1):
state = get_max_monogram_state(encryption, monogram_log_distribution,
length, alphabet)[0]
if length > (lower_bound + upper_bound) / 2:
state = break_fixed_length_code_with_mcmc(
encryption, alphabet, state, n_list, coefs, log_distributions,
int(steps_constant * alphabet.length * length *
(2 + log(length))))[0]
words_list = cipher.encrypt_decrypt_text(encryption, state,
alphabet).get_words_list()
weight = sum([word in scrabble
for word in words_list]) / len(words_list)
if weight > max_weight:
max_weight = weight
max_state = state
if max_weight > 0.5:
break
return break_fixed_length_code_with_mcmc(
encryption, alphabet, max_state, n_list, coefs, log_distributions,
int(steps_constant * alphabet.length * len(max_state) *
(10 + log(len(max_state)))))
def get_max_bigram_state(encryption, bigram_log_distribution, key_length,
alphabet):
all_mono_keys = cipher.get_all_mono_keys(alphabet)
codes = {
a: {
b: [cipher.get_zero_mono_key() for i in range(key_length - 1)]
for b in all_mono_keys
}
for a in all_mono_keys
}
values = {
a: {
b: get_bigram_part_weight(encryption, (a, b), 0, key_length,
bigram_log_distribution, alphabet)
for b in all_mono_keys
}
for a in all_mono_keys
}
new_values = {a: {b: 0 for b in all_mono_keys} for a in all_mono_keys}
for r in range(1, key_length):
for i in all_mono_keys:
for j in codes[i]:
max_func = float("-inf")
max_arg = cipher.get_zero_mono_key()
for k in codes[i]:
func = values[i][k] + get_bigram_part_weight(
encryption, (k, j), r, key_length,
bigram_log_distribution, alphabet)
if func > max_func:
max_func = func
max_arg = k
new_values[i][j] = max_func
codes[i][j][r - 1] = max_arg
aux = values
values = new_values
new_values = aux
return get_max_bigram_key_and_weight(values, codes, all_mono_keys)
def get_max_monogram_state_coord(encryption, coordinate,
monogram_log_distribution, key_length,
alphabet):
max_state = cipher.get_zero_mono_key()
max_weight = float("-inf")
for j in cipher.get_all_mono_keys(alphabet):
weight = 0
for i in range(coordinate, len(encryption), key_length):
weight += monogram_log_distribution[cipher.encrypt_decrypt_single(
encryption[i], j, alphabet)]
if weight > max_weight:
max_state = j
max_weight = weight
return max_state, max_weight
def break_bounded_length_code_with_mcmc(encryption, alphabet, n_list, coefs,
distributions, steps, boundary,
monogram_log_distribution):
max_weight = float("-inf")
max_state = [cipher.get_zero_mono_key()]
for length in range(1, boundary + 1):
start = get_max_monogram_state(encryption, monogram_log_distribution,
length, alphabet)[0]
break_attempt = break_fixed_length_code_with_mcmc(
encryption, alphabet, start, n_list, coefs, distributions, steps)
if break_attempt[1] > max_weight:
max_state = break_attempt[0]
max_weight = break_attempt[1]
return max_state, max_weight
def get_max_bigram_key_and_weight(values, codes, all_mono_keys):
max_bigram_weight_value = -float("inf")
max_state = cipher.get_zero_mono_key()
for i in all_mono_keys:
if values[i][i] > max_bigram_weight_value:
max_bigram_weight_value = values[i][i]
max_state = i
bigram_maximizer = []
t = len(codes[max_state][max_state]) - 1
current = max_state
for i in range(len(codes[max_state][max_state])):
current = codes[max_state][current][t]
bigram_maximizer.append(current)
t -= 1
bigram_maximizer.append(max_state)
bigram_maximizer.reverse()
return bigram_maximizer, max_bigram_weight_value