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【题目】

1） 实现仿射密码，具体要求：

A. 实现仿射密码加密过程，由用户输入密钥，可以对任意输入的明文进行加密；

B. 根据用户输入的加密密钥，自动生成解密密钥，并能对加密密文进行解密；

C. 实现仿射密码破解程序（穷举），能对任意输入的密文进行解密

【实现代码】

# -*- coding: utf-8 -*-"""Created on Sun Dec 17 20:03:09 2017仿射密码加密， 解密， 破解@author: HP"""from string import ascii_lowercase as lowercasefrom string import ascii_uppercase as uppercasefrequencyTable = [4, 19, 14, 0, 13, 8, 17, 18, 7, 3, \                  11, 2, 20, 12, 15, 24, 22, 6, 1, 21, \                  10, 23, 9, 16, 25]# 删除预留的标点#文本过滤def text_filter (text):    text = text.lower()    result = ""    for i in range(len(text)):        if lowercase.find(text[i]) != -1:            result += text[i]    return result    #加密部分def encryption(plaintext, k1, k2):    plaintext = text_filter(plaintext)    result = ""    for i in range(len(plaintext)):        index = lowercase.find(plaintext[i])        c_index = (k1*index+k2)%26        result += uppercase[c_index]    return result#解密部分def get_inverse(a, b):     """    #求a关于模b的逆元    """    if(a==1 and b==0):        x = 1        y = 0        return x, y    else:        xx, yy = get_inverse(b, a%b)        x = yy        y = xx - a//b*yy        return x, ydef Decryption(k1, k2, ciphertext):    k3 = get_inverse(k1, 26)[0]    result = ""    for i in range(len(ciphertext)):        index = uppercase.find(ciphertext[i])        p_index = k3*(index- k2)%26        result += lowercase[p_index]    return result    #破解部分def get_frequencyTable(ciphertext):     """    返回一个列表；    取得密文的字母频率表, 按字母出现频率从大到小排列， 值为字母对应的索引    """    #取得字母频率字典    count = {}    for i in range(len(ciphertext)):        count[ciphertext[i]] = count[ciphertext[i]] + 1 if ciphertext[i] in count else 1    #把字典转换为列表， 并且对其排序， 最终得到返回值    items = count.items()    items_list = [[item[1], item[0]]for item in items]    items_list1 = sorted(items_list, reverse = True)    chara_list = [item[1] for item in items_list1]    return list(map(lambda x: uppercase.index(x),chara_list))    # 根据a，b，c，d获取密钥K1def get_k1(a, b, c, d):    i = 0    while True:        k1 = ( float(a - d - 26 * i) / float(b - c) )        if k1 < -26 or k1 > 26:            return None        if isinstance(k1, int):            return k1        i = i + 1        def get_abcd(list1, list2):    list3 = list(map(lambda x, y: [x, y], list1, list2))    result = []    for i in range(len(list3)):        for j in range(i+1, len(list3)):            result.append(list3[i]+list3[j])    return result    def crack():    list1 = ['u','v','w']    list2 = ['x','y','z']    list22 = list(list2)    result = []    count = 0    while count<6:        for item in get_abcd(list1, list22):            k1 = get_k1(*item)            if k1 is None or gcd(k1, 26) != 1:                break            k2 = int(d - c * k1) % 26            result.append( decryption(Cs, t, k3) )        if(count%2==1):            first = list2.pop(0)            list2.append(first)            list22 = list(list2)        else:            list22[1], list22[2] = list22[2], list22[1]        count += 1            if __name__ == '__main__':    ciphertext = input("enter the ciphertext: ")    print(Decryption(7, 3, ciphertext))

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