1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157

# coding:utf-8
import math

def encryptionVirginia(plaintext, secret_key):
    '''加密'''
    table = [chr(x) for x in range(ord('a'), ord('z') + 1)]
    tmp = ''
    for x in plaintext:
        if x.lower() in table:
            tmp += x.lower()
    ciphertext = ''

    for index, value in enumerate(tmp):
        t = (table.index(value) + table.index(secret_key[index % len(secret_key)])) % 26
        ciphertext += table[t]
    return ciphertext


def decryptionVirginia(ciphertext, secret_key):
    '''解密'''
    ciphertext = ciphertext.lower()
    table = [chr(x) for x in range(ord('a'), ord('z') + 1)]

    plaintext = ''
    num = 0
    for index, value in enumerate(ciphertext):
        plaintext += table[(table.index(value) - table.index(secret_key[index % len(secret_key)])) % 26]
        num += 1
    return plaintext

class CrackVirginia:
    '''破解'''
    # 字母概率，从a到z
    LETTER_PROBILITY = {
        'a':0.08167, # a
        'b':0.01492, # b
        'c':0.02782, # c
        'd':0.04253, # d
        'e':0.12702, # e
        'f':0.02228, # f
        'g':0.02015, # g
        'h':0.06094, # h
        'i':0.06966, # i
        'j':0.00153, # j
        'k':0.00772, # k
        'l':0.04025, # l
        'm':0.02406, # m
        'n':0.06749, # n
        'o':0.07507, # o
        'p':0.01929, # p
        'q':0.00095, # q
        'r':0.05897, # r
        's':0.06327, # s
        't':0.09056, # t
        'u':0.02758, # u
        'v':0.00978, # v
        'w':0.02360, # w
        'x':0.00150, # x
        'y':0.01974, # y
        'z':0.00074, # z
    }
    def __getSubstring(self, key_length):
        '''分割为子串'''
        num = 0
        while num < key_length:
            yield self.ciphertext[num::key_length].upper()
            num += 1

    def __fangcha(self, average, li):
        '''方差计算'''
        tmp = 0
        for x in li:
            tmp += (x - average) ** 2
        return tmp / len(li)

    def __init__(self, ciphertext):
        self.ciphertext = ciphertext.upper()

    def __IC_calculate(self, string_str):
        '''无偏估计值计算'''
        dict_ = {}
        for x in string_str:
            try:
                dict_[x] += 1
            except KeyError:
                dict_[x] = 1
        tmp = 0
        for value in dict_.values():
            try:
                tmp += ((value * (value-1)) / (len(string_str) * (len(string_str) - 1)))
            except ZeroDivisionError:
                return 1
        return tmp

    def __calculate_Mj(self, text):
        '''拟重合指数法'''
        Mj = 0
        alpha = {}
        for x in text:
            try:
                alpha[x] += 1
            except KeyError:
                alpha[x] = 1
        for key, value in alpha.items():
            Mj += ((self.LETTER_PROBILITY[key.lower()] * value) / len(text))
        return Mj

    def __getKeyLength(self):
        '''破解密钥长度'''
        key_length_ic = {}
        key_length_fangcha = {}
        key_length = 1
        result = {}
        while key_length < len(self.ciphertext):
            substring = []
            for x in self.__getSubstring(key_length):
                substring.append(x)
            key_length += 1
            tmp = []
            for x in substring:
                ic = self.__IC_calculate(x)
                tmp.append(ic)
            if tmp:
                key_length_ic[str(key_length-1)] = math.fabs(sum(tmp) / len(tmp) - 0.065)
                key_length_fangcha[str(key_length-1)] = self.__fangcha(key_length_ic[str(key_length-1)], tmp)
        for key, value in key_length_ic.items():
            result[key] = key_length_fangcha[key] * 4 + value
        key_length = sorted(result.items(), key=lambda a:a[1])[0][0]
        return int(key_length)

    def crack(self):
        '''破解'''
        key_length = self.__getKeyLength()
        num = 0
        key_ic = []
        for x in self.__getSubstring(key_length):
            for t in range(1, 27):
                s = ''.join([chr(((ord(l)+t-65) % 26) + 65) for l in x])
                try:
                    key_ic[num].append(math.fabs(self.__calculate_Mj(s) - 0.065))
                except IndexError:
                    key_ic.append([math.fabs(self.__calculate_Mj(s) - 0.065)])
            num += 1
        key = ''
        for value in key_ic:
            key += chr(ord('z') - value.index(min(value)))
        return key

string = 'CHREEVOAHMAERATBIAXXWTNXBEEOPHBSBQMQEQERBWRVXUOAKXAOSXXWEAHBWGJMMQMNKGRFVGXWTRZXWIAKLXFPSKAUTEMNDCMGTSXMXBTUIADNGMGPSRELXNJELXVRVPRTULHDNQWTWDTYGBPHXTFALJHASVBFXNGLLCHRZBWELEKMSJIKNBHWRJGNMGJSGLXFEYPHAGNRBIEQJTAMRVLCRREMNDGLXRRIMGNSNRWCHRQHAEYEVTAQEBBIPEEWEVKAKOEWADREMXMTBHHCHRTKDNVRZCHRCLQOHPWQAIIWXNRMGWOIIFKEE'
a = CrackVirginia(string)
key = a.crack()
plaintext = decryptionVirginia(string, a.crack())
print('明文为:', plaintext, end='\n\n')
print('加密密钥:', key, end='\n\n')
print('加密后:', string, end='\n\n')
print('破解密钥:', key, end='\n\n')
print('破解明文:', plaintext, end='\n\n')