密码学课程设计二之手撸DES加解密程序

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字数统计: 1,991阅读时长: 11 min

 2017/12/24  Share

前记

因为手撸的目的是了解DES加解密全过程，所以并没有追求效率，当时写的时候也很快就写完了，后面如果有时间会改进效率，毕竟测试了一下……加密7000单词的作文需要2秒……实在是太差了，毕竟菜鸡= =

简单说一下原理

密钥编排

1.首先输入64bit密钥
2.将64bit密钥经过PC-1盒变成56bit
3.将56bit分为C0和D0，分别28bit
4.将C0，D0分别循环移位，得到C1，D1
5.将C1，D1拼接，经过PC-2盒变成48bit子密钥key1
6.重复步骤4
7.生成16组子密钥
这里真实加密只用到56bit，后面会有文章借助一道DES题目细致讲解这个密钥编排

F函数

1.将输入的32bit的R经过E盒生成48bit
2.将该48bit值与子密钥异或
3.将异或后的值经过S盒置换，又变回32bit
4.将值经过P盒置换
5.将32bit值与L进行异或得到下一个R

加密程序

1.输入64bit明文
2.经过IP盒置换打乱生成str
3.将str分为L0和R0，分别32bit
4.以下重复15次：
5.将Ri经过F函数处理，再与Li异或，然后将值赋给R(i+1)
6.将Ri赋值给L(i+1)
7.最后一轮，直接将Ri赋给R(i+1),再将Ri经过F函数处理，再与Li异或，然后将值赋给L(i+1)
8.将L和R合并后经过逆IP盒，得到密文C

解密程序

加密程序的逆，就不赘述了，直接看下面的代码吧

DES加解密程序各个函数

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] #因为列表是1-64，而数组是0-63，所以减一
    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

就是上面e盒，异或，s盒，p盒的调用

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

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