def restore_key(cyphertext, key_len):
key = ''
blocks = processing.get_blocks(text=cyphertext, size=key_len)
columns = processing.get_columns(blocks)
frequencies = _get_letter_frequencies(text=cyphertext)
for column in columns:
key += _find_key_letter(text=column, lf=frequencies)
return key
def _decypher(cyphertext, key):
letters = string.ascii_uppercase
shifts = [letters.index(letter) for letter in key]
blocks = processing.get_blocks(text=cyphertext, size=len(key))
cols = processing.get_columns(blocks)
decyphered_blocks = processing.to_blocks(
[fa.shift(col, shift) for col, shift in zip(cols, shifts)])
decyphered = ''.join(decyphered_blocks)
return decyphered
def find_key_length(cyphertext, max_key_len):
min_diff = maxsize
key_len = 0
for candidate_length in range(1, max_key_len + 1):
groups = processing.get_blocks(text=cyphertext, size=candidate_length)
columns = processing.get_columns(groups)
ics = [_ic(letter_counts=fa.get_letter_counts(text=column)) for column in columns]
delta_bar_ic = sum(ics) / len(ics)
if EN_IC-delta_bar_ic < min_diff:
min_diff = EN_IC-delta_bar_ic
key_len = candidate_length
print('KEY_LENGTH: ' + str(candidate_length) + '\n')
print('IC by column: '+str(ics))
print('delta bar IC: '+str(delta_bar_ic)+'\n')
return key_len