密码学课程设计-分组密码-DES

密码学密码学

发布时间 : 2020-02-22 15:02

阅读 :

1 概述
2 算法原理与设计思路
3 关键算法分析
4 运行结果
5 密码安全性分析

1 概述

数据加密标准（DES）的出现是现代密码发展史上的一个非常重要的事件，它是密码学历史上第一个广泛应用于商用数据保密的密码算法，并开创了公开密码算法的先例，极大地促进了密码学的发展。尽管在今天看来，它已经不足以保障数据安全，但是它曾成功地抵抗了几十年的分析攻击，且截至目前，其安全威胁主要来源于穷举攻击。换言之，如果使用诸如三重DES等方式来加长DES的秘钥长度，它仍不失为一个安全的密码系统。因此，DES算法的基本理论和设计思想仍有重要的参考价值。

2 算法原理与设计思路

DES的加密过程可分为置换、F函数和密钥编排三个部分，解密过程与此相似，这里仅介绍DES的加密过程。

2.1 置换分为初始置换和逆初始置换

初始置换和初始逆置换

2.2 F函数包含E盒扩展置换、密钥加、S盒代换和P盒置换

F函数

2.3 密钥编排

密钥编排

3 关键算法分析

main()：函数作为函数的入口和出口
DESenc(mes, key)：函数进行DES的加密入口
DESenc_test(mes, key)：对一组明文进行加密
DESdec(cipher, key)：函数进行DES的解密入口
DESdec_test(cipher, key)：将密文直接输64位2进制
mov_IP(str)：逆IP盒
funcF(str, key)：F函数
box_p(str)：P盒置换
box_s(str)：S盒代换
box_e(str)：e盒扩展
begin_change(str)：初始置换
key_gen(str)：密钥生成
key_change_2(str)：pc-2置换
key_change_1(str)：pc-1置换
xor(str1, str2)：字符串异或
zuoyiwei(str,num)：循环左移
strtobin(str)：字符串转二进制

4 运行结果

完整代码如下所示：

# DES

# 字符串转二进制
def strtobin(str):
    res = ""
    for i in str:
        tmp = bin(ord(i))[2:]
        for i in range(0, 8 - len(tmp)):
            tmp = '0' + tmp
        res += tmp
    return res

# 循环左移
def zuoyiwei(str,num):
    my = str[num:len(str)]
    my = my+str[0:num]
    return my

# 字符串异或
def xor(str1, str2):
    res = ""
    for i in range(0, len(str1)):
        xor_res = int(str1[i], 10)^int(str2[i], 10)
        if xor_res == 1:
            res += '1'
        else:
            res += '0'
    return res

# PC-1盒处理
def key_change_1(str):
    key1_list = [57,49,41,33,25,17,9,1,58,50,42,34,26,18,10,2,59,51,43,35,27,19,11,3,60,52,44,36,63,55,47,39,31,23,15,7,62,54,46,38,30,22,14,6,61,53,45,37,29,21,13,5,28,20,12,4]
    res = ""
    for i in key1_list:
        res += str[i-1]
    return res

# PC-2盒处理
def key_change_2(str):
    key2_list = [14,17,11,24,1,5,3,28,15,6,21,10,23,19,12,4,26,8,16,7,27,20,13,2,41,52,31,37,47,55,30,40,51,45,33,48,44,49,39,56,34,53,46,42,50,36,29,32]
    res = ""
    for i in key2_list:
        res += str[i-1]
    return res

# 生成16个子密钥
def key_gen(str):
    key_list = []
    key_change_res = key_change_1(str)
    key_c = key_change_res[0:28]
    key_d = key_change_res[28:]
    for i in range(1, 17): #共16轮
        if (i == 1) or (i == 2) or (i == 9) or (i == 16):
            key_c = zuoyiwei(key_c, 1)
            key_d = zuoyiwei(key_d, 1)
        else:
            key_c = zuoyiwei(key_c, 2)
            key_d = zuoyiwei(key_d, 2)
        key_yiwei = key_c + key_d
        key_res = key_change_2(key_yiwei)
        key_list.append(key_res)
    return key_list

# IP盒处理
def begin_change(str):
    change_list = [58,50,42,34,26,18,10,2,60,52,44,36,28,20,12,4,62,54,46,38,30,22,14,6,64,56,48,40,32,24,16,8,57,49,41,33,25,17,9,1,59,51,43,35,27,19,11,3,61,53,45,37,29,21,13,5,63,55,47,39,31,23,15,7]
    res = ""
    for i in change_list:
        res += str[i-1]
    return res

# e盒处理
def box_e(str):
    e_list = [32,1,2,3,4,5,4,5,6,7,8,9,8,9,10,11,12,13,12,13,14,15,16,17,16,17,18,19,20,21,20,21,22,23,24,25,24,25,26,27,28,29,28,29,30,31,32,1]
    res = ""
    for i in e_list:
        res += str[i-1]
    return res

# s盒处理
def box_s(str):
    j = 0
    s_list = [[14,4,13,1,2,15,11,8,3,10,6,12,5,9,0,7,0,15,7,4,14,2,13,1,10,6,12,11,9,5,3,8,4,1,14,8,13,6,2,11,15,12,9,7,3,10,5,0,15,12,8,2,4,9,1,7,5,11,3,14,10,0,6,13],
              [15,1,8,14,6,11,3,4,9,7,2,13,12,0,5,10,3,13,4,7,15,2,8,14,12,0,1,10,6,9,11,5,0,14,7,11,10,4,13,1,5,8,12,6,9,3,2,15,13,8,10,1,3,15,4,2,11,6,7,12,0,5,14,9],
              [10,0,9,14,6,3,15,5,1,13,12,7,11,4,2,8,13,7,0,9,3,4,6,10,2,8,5,14,12,11,15,1,13,6,4,9,8,15,3,0,11,1,2,12,5,10,14,7,1,10,13,0,6,9,8,7,4,15,14,3,11,5,2,12],
              [7,13,14,3,0,6,9,10,1,2,8,5,11,12,4,15,13,8,11,5,6,15,0,3,4,7,2,12,1,10,14,9,10,6,9,0,12,11,7,13,15,1,3,14,5,2,8,4,3,15,0,6,10,1,13,8,9,4,5,11,12,7,2,14],
              [2,12,4,1,7,10,11,6,8,5,3,15,13,0,14,9,14,11,2,12,4,7,13,1,5,0,15,10,3,9,8,6,4,2,1,11,10,13,7,8,15,9,12,5,6,3,0,14,11,8,12,7,1,14,2,13,6,15,0,9,10,4,5,3],
              [12,1,10,15,9,2,6,8,0,13,3,4,14,7,5,11,10,15,4,2,7,12,9,5,6,1,13,14,0,11,3,8,9,14,15,5,2,8,12,3,7,0,4,10,1,13,11,6,4,3,2,12,9,5,15,10,11,14,1,7,6,0,8,13],
              [4,11,2,14,15,0,8,13,3,12,9,7,5,10,6,1,13,0,11,7,4,9,1,10,14,3,5,12,2,15,8,6,1,4,11,13,12,3,7,14,10,15,6,8,0,5,9,2,6,11,13,8,1,4,10,7,9,5,0,15,14,2,3,12],
              [13,2,8,4,6,15,11,1,10,9,3,14,5,0,12,7,1,15,13,8,10,3,7,4,12,5,6,11,0,14,9,2,7,11,4,1,9,12,14,2,0,6,10,13,15,3,5,8,2,1,14,7,4,10,8,13,15,12,9,0,3,5,6,11]
              ]
    res = ""
    for i in range(0, len(str), 6):
        begin_s = str[i:i + 6]
        row = int(begin_s[0] + begin_s[5], 2)
        col = int(begin_s[1:5], 2)
        num = bin(s_list[j][row * 16 + col])[2:]
        for padd in range(0, 4 - len(num)):
            num = "0" + num
        res += num
        j = j + 1
    return res

# p盒处理
def box_p(str):
    res = ""
    p_list = [16,7,20,21,29,12,28,17,1,15,23,26,5,18,31,10,2,8,24,14,32,27,3,9,19,13,30,6,22,11,4,25]
    for i in p_list:
        res += str[i - 1]
    return res

# F函数
def funcF(str, key):
    str_e_res = box_e(str)
    xor_res = xor(str_e_res, key)
    str_s_res = box_s(xor_res)
    str_p_res = box_p(str_s_res)
    return str_p_res

# 逆IP盒
def mov_IP(str):
    res = ""
    ip_list = [40,8,48,16,56,24,64,32,39,7,47,15,55,23,63,31,38,6,46,14,54,22,62,30,37,5,45,13,53,21,61,29,36,4,44,12,52,20,60,28,35,3,43,11,51,19,59,27,34,2,42,10,50,18,58,26,33,1,41,9,49,17,57,25]
    for i in ip_list:
        res += str[i-1]
    return res

# 针对一组的加密程序
def DESenc_test(mes, key):
    mes_bin = strtobin(mes)
    mes_IP = begin_change(mes_bin)
    key_bin = strtobin(key)
    key_list = key_gen(key_bin)
    mes_left = mes_IP[0:32]
    mes_right = mes_IP[32:]
    for i in range(0, 15):
        mes_tmp = mes_right
        right_f_res = funcF(mes_right, key_list[i])
        mes_right = xor(right_f_res, mes_left)
        mes_left = mes_tmp
    fin_right = mes_right
    fin_left = xor(funcF(mes_right, key_list[15]), mes_left)
    fin = fin_left + fin_right
    fin = mov_IP(fin)
    return fin

# 针对一组的解密程序
def DESdec_test(cipher, key):  #密文直接输64位2进制
    key_bin = strtobin(key)
    key_list = key_gen(key_bin)
    cipher = begin_change(cipher)
    i = 15
    cipher_left = cipher[0:32]
    cipher_right = cipher[32:]
    while i > 0:
        cipher_tmp = cipher_right
        cipher_right = xor(cipher_left, funcF(cipher_right, key_list[i]))
        cipher_left = cipher_tmp
        i = i - 1
    fin_left = xor(cipher_left, funcF(cipher_right, key_list[0]))
    fin_right = cipher_right
    fin = fin_left + fin_right
    fin = mov_IP(fin)
    my_plain = ""
    for j in range(0, len(fin), 8):
        my_plain += chr(int(fin[j:j + 8], 2))
    return my_plain

# DES加密
def DESenc(mes, key):
    res = ""
    i = 0
    while mes[i:i+8] != "":
        res += DESenc_test(mes[i:i+8], key)
        i = i + 8
    return res

# DES解密
def DESdec(cipher, key):
    res = ""
    i = 0
    while cipher[i:i + 64] != "":
        res += DESdec_test(cipher[i:i + 64], key)
        i = i + 64
    return res

def main():
    plaintext = ''
    key = ''
    ciphertext = ''
    userInput = ''
    print("加密请按D,解密请按E:")
    userInput = input()
    if userInput == 'D':
        print("请输入明文：")
        plaintext = input()
        print("请输入密钥：")
        key = input()
        ciphertext = DESenc(plaintext, key)
        print("密文是：")
        print(ciphertext)
    else:
        print("请输入密文：")
        ciphertext = input()
        print("请输入密钥：")
        key = input()
        plaintext = DESdec(ciphertext, key)
        print("明文是：")
        print(plaintext)

if __name__ == '__main__':
    main()