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| from collections import Counter
import numpy as np
from itertools import product
KEYLENGTHNUM = 5
ENGLISH_FREQ = {
'A': 0.08167, 'B': 0.01492, 'C': 0.02782, 'D': 0.04253,
'E': 0.12702, 'F': 0.02228, 'G': 0.02015, 'H': 0.06094,
'I': 0.06966, 'J': 0.00153, 'K': 0.00772, 'L': 0.04025,
'M': 0.02406, 'N': 0.06749, 'O': 0.07507, 'P': 0.01929,
'Q': 0.00095, 'R': 0.05987, 'S': 0.06327, 'T': 0.09056,
'U': 0.02758, 'V': 0.00978, 'W': 0.0236, 'X': 0.0015,
'Y': 0.01974, 'Z': 0.00074
}
def alpha(cipher):
"""提取密文中的字母并统一转换为大写"""
return ''.join([char.upper() for char in cipher if char.isalpha()])
def count_IC(cipher):
"""计算重合指数"""
freq = Counter(cipher)
L = len(cipher)
IC = sum(f * (f - 1) for f in freq.values()) / (L * (L - 1))
return IC
def guess_key_length(cipher, max_len=50):
"""猜测密钥长度"""
best_lengths = []
for key_len in range(1, max_len + 1):
groups = ['' for _ in range(key_len)]
for i, char in enumerate(cipher):
groups[i % key_len] += char
avg_IC = np.mean([count_IC(group) for group in groups])
diff = abs(avg_IC - 0.0667)
best_lengths.append((diff, key_len))
best_lengths.sort()
return [length for _, length in best_lengths]
def frequency_analysis(group, num_candidates=3):
"""频率分析，找到最匹配的位移"""
R_list = []
group_len = len(group)
for shift in range(26):
shifted_freq = Counter(
chr(((ord(char) - ord('A') - shift) % 26) + ord('A')) for char in group
)
R = 0
for char in ENGLISH_FREQ:
Q_i = shifted_freq.get(char, 0) / group_len
R += ENGLISH_FREQ[char] * Q_i
R_list.append((shift, R))
R_list.sort(key=lambda x: -x[1])
return [(chr(shift + ord('A')), R) for shift, R in R_list[:num_candidates]]
def guess_key(cipher, key_len):
"""猜测密钥，按照优先级列出所有可能的密钥"""
groups = [cipher[i::key_len] for i in range(key_len)]
candidates = []
for group in groups:
shifts = frequency_analysis(group, num_candidates=1)
candidates.append(shifts)
keys_with_score = []
for key in product(*candidates):
key_str = ''.join([k[0] for k in key])
total_R = sum(k[1] for k in key)
keys_with_score.append((key_str, total_R))
keys_with_score.sort(key=lambda x: -x[1])
return [key for key, _ in keys_with_score]
def vigenere_decrypt(cipher, key):
"""维吉尼亚解密"""
decrypted = []
key_length = len(key)
key_as_int = [ord(k) - ord('A') for k in key]
index = 0
for char in cipher:
if char.isalpha():
offset = key_as_int[index % key_length]
if char.isupper():
value = (ord(char) - offset - ord('A')) % 26
decrypted.append(chr(value + ord('A')))
else:
value = (ord(char) - offset - ord('a')) % 26
decrypted.append(chr(value + ord('a')))
index += 1
else:
decrypted.append(char)
return ''.join(decrypted)
if __name__ == '__main__':
cipher = """Zs vxb fxcnz evm enare usca tvdcs wgkduhtytero xjwmato xpjb jqjl krth bhzl tk hcbb nvb aolmb. Xhase
jsb bw zcah plm vigmpiwp ib bum gdaet, owe qbewpa jtbvc ijzmbb yqde smbq urilijk iwl nzc ob
ivmceqlg sszcp. Nlb lkzm cw n pmuoi iwl lws hwzm j pbuc. Azh zroubcoqwvnaf bm a ymbh ial woq
liem n kmmiyvrbl. Ibd pvccp gw y pepm xn emb bnmkt ial woq liem n aahkst. Jlq zclekqxv gw rha
lcktrar ob ilrnvkcs wrl hwh pyva e ajvpbsanc. """
alpha_cipher = alpha(cipher)
key_len = guess_key_length(alpha_cipher)[:KEYLENGTHNUM]
print("候选密钥长度:", key_len)
for length in key_len:
keys = guess_key(alpha_cipher, length)
print(f"\n密钥长度 {length} 的可能密钥（按优先级排序）:")
for key in keys:
decrypted_text = vigenere_decrypt(cipher, key)
print(f"密钥: {key}")
print(f"解密结果: {decrypted_text}")
|
