DES 加密解密算法的C++实现

 

 

网络与信息安全

Introduction to Network and Security

 

——DES 加密解密算法的C++实现

   

   

 

 

 

 

姓 名:                       

学 号:                       

学 院:                       

 

 

 

2010年10月

 

 

 

 

 

一、        DES算法的实现

1.DES简介

本世纪五十年代以来,密码学研究领域出现了最具代表性的两大成就。其中之一就是1971年美国学者塔奇曼(Tuchman)和麦耶(Meyer)根据信息论创始人香农(Shannon)提出的“多重加密有效性理论”创立的,后于1977年由美国国家标准局颁布的数据加密标准。

DES密码实际上是Lucifer密码的进一步发展。它是一种采用传统加密方法的区组密码。它的算法是对称的,既可用于加密又可用于解密。

美国国家标准局1973年开始研究除国防部外的其它部门的计算机系统的数据加密标准,于1973年5月15日和1974年8月27日先后两次向公众发出了征求加密算法的公告。加密算法要达到的目的通常称为DES密码算法要求主要为以下四点:

提供高质量的数据保护,防止数据未经授权的泄露和未被察觉的修改;具有相当高的复杂性,使得破译的开销超过可能获得的利益,同时又要便于理解和掌握DES密码体制的安全性应该不依赖于算法的保密,其安全性仅以加密密钥的保密为基础实现经济,运行有效,并且适用于多种完全不同的应用。

1977年1月,美国政府颁布:采纳IBM公司设计的方案作为非机密数据的正式数据加密标准(DES枣Data Encryption Standard)。

目前在这里,随着三金工程尤其是金卡工程的启动,DES算法在POS、ATM、磁卡及智能卡(IC卡)、加油站、高速公路收费站等领域被广泛应用,以此来实现关键数据的保密,如信用卡持卡人的PIN的加密传输,IC卡与POS间的双向认证、金融交易数据包的MAC校验等,均用到DES算法。

DES算法的入口参数有三个:Key、Data、Mode。其中Key为8个字节共64位,是DES算法的工作密钥;Data也为8个字节64位,是要被加密或被解密的数据;Mode为DES的工作方式,有两种:加密或解密。

DES算法是这样工作的:如Mode为加密,则用Key 去把数据Data进行加密, 生成Data的密码形式(64位)作为DES的输出结果;如Mode为解密,则用Key去把密码形式的数据Data解密,还原为Data的明码形式(64位)作为DES的输出结果。在通信网络的两端,双方约定一致的Key,在通信的源点用Key对核心数据进行DES加密,然后以密码形式在公共通信网(如电话网)中传输到通信网络的终点,数据到达目的地后,用同样的Key对密码数据进行解密,便再现了明码形式的核心数据。这样,便保证了核心数据(如PIN、MAC等)在公共通信网中传输的安全性和可靠性。

通过定期在通信网络的源端和目的端同时改用新的Key,便能更进一步提高数据的保密性,这正是现在金融交易网络的流行做法。

2.DES算法详述

DES算法把64位的明文输入块变为64位的密文输出块,它所使用的密钥也是64位,其功能是把输入的64位数据块按位重新组合,并把输出分为L0 、R0两部分,每部分各长32位,其置换规则见下表:

58,50,12,34,26,18,10,2,60,52,44,36,28,20,12,4,

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,

即将输入的第58位换到第一位,第50位换到第2位,……,依此类推,最后一位是原来的第7位。 L0、R0则是换位输出后的两部分,L0是输出的左32位,R0 是右32位,例:设置换前的输入值为D1D2D3……D64,则经过初始置换后的结果为:L0=D550……D8;R0=D57D49...D7。

经过26次迭代运算后,得到L16、R16,将此作为输入,进行逆置换,即得到密文输出。逆置换正好是初始置的逆运算,例如,第1位经过初始置换后,处于第40位,而通过逆置换,又将第40位换回到第1位,其逆置换规则如下表所示:

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,

放大换位表

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,

单纯换位表

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,

 

在f(Ri,Ki)算法描述图中,S1,S2...S8为选择函数,其功能是把6bit数据变为4bit数据。下面给出选择函数Si(i=1,2......8)的功能表:

选择函数Si

S1:

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,

S2:

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,

S3:

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,

S4:

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,

S5:

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,

S6:

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,

S7:

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,

S8:

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,

3.子密钥Ki(48bit)的生成算法

初始Key值为64位,但DES算法规定,其中第8、16、......64位是奇偶校验位,不参与DES运算。故Key 实际可用位数便只有56位。即:经过缩小选择换位表1的变换后,Key 的位数由64 位变成了56位,此56位分为C0、D0两部分,各28位,然后分别进行第1次循环左移,得到C1、D1,将C1(28位)、D1(28位)合并得到56位,再经过缩小选择换位2,从而便得到了密钥K0(48位)。依此类推,便可得到K1、K2、......、K15,不过需要注意的是,16次循环左移对应的左移位数要依据下述规则进行:

循环左移位数1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1

以上介绍了DES算法的加密过程。 DES算法的解密过程是一样的,区别仅仅在于第一次迭代时用子密钥K15,第二次K14、……,最后一次用K0,算法本身并没有任何变化。

二、        加/解密执行过程及结果

1.运行程序

2.加密过程(同时生成密文文档)

3.解密过程(同时生成明文外部文档)

三、          源代码

#include "stdafx.h"

 

#include "DESTest.h"

 

#include "DESTestDlg.h"

 

#include "Encrypt.h"

void CDES::deskey(unsigned char key[8],Mode md)

{

       registerint ii, j, l, m, n;

       unsignedchar pc1m[56],pcr[56];

       unsignedlong kn[32];

 

       for(j = 0; j < 56; j++)

       {

              l= pc1[j];

              m= l & 07;

              pc1m[j] = (key[l >> 3] & bytebit[m])? 1:0;

       }

 

       for(ii = 0; ii < 16; ii++)

       {

              if(md == DECRYPT)

                     m= (15 - ii) << 1;

              else

                     m= ii << 1;

             

              n= m + 1;

              kn[m]= kn[n] = 0L;

 

              for(j = 0; j < 28; j++)

              {

                     l= j + totrot[ii];

 

                     if(l < 28)

                            pcr[j]= pc1m[l];

                     else

                            pcr[j]= pc1m[l - 28];

              }

 

              for(j = 28; j < 56; j++)

              {

                     l= j + totrot[ii];

                    

                     if(l < 56)

                            pcr[j]= pc1m[l];

                     else

                            pcr[j]= pc1m[l - 28];

              }

 

              for(j = 0; j < 24; j++)

              {

                     if(pcr[ pc2[j] ])

                            kn[m]|= bigbyte[j];

 

                     if(pcr[ pc2[j+24] ])

                            kn[n]|= bigbyte[j];

              }

       }

 

   cookey(kn);

 

   return;

}

 

void CDES::cookey(register unsigned long*raw1)

{

       registerunsigned long *cook, *raw0;

       unsignedlong dough[32];

       registerint i;

 

       cook= dough;

      

       for(i = 0; i < 16; i++, raw1++)

       {

              raw0= raw1++;

              *cook= (*raw0 & 0x00fc0000L)<< 6;

              *cook|= (*raw0 & 0x00000fc0L)<< 10;

              *cook|= (*raw1 & 0x00fc0000L)>> 10;

              *cook++|= (*raw1 & 0x00000fc0L)>> 6;

              *cook= (*raw0 & 0x0003f000L) << 12;

              *cook|= (*raw0 & 0x0000003fL) << 16;

              *cook|= (*raw1 & 0x0003f000L) >> 4;

              *cook++|= (*raw1 & 0x0000003fL);

       }

 

   usekey(dough);

 

       return;

}

 

void CDES::usekey(register unsigned long*from)

{

   register unsigned long *to, *endp;

 

   to = KnL, endp = &KnL[32];

 

       while(to < endp)

       {

              *to++= *from++;

       }

      

       return;

}

 

void CDES::scrunch(register unsigned char *outof,register unsigned long *into )

{

       *into= (*outof++ & 0xffL) << 24;

       *into|= (*outof++ & 0xffL) << 16;

       *into|= (*outof++ & 0xffL) << 8;

       *into++|= (*outof++ & 0xffL);

       *into= (*outof++ & 0xffL) << 24;

       *into|= (*outof++ & 0xffL) << 16;

       *into|= (*outof++ & 0xffL) << 8;

       *into|= (*outof & 0xffL);

       return;

}

 

void CDES::unscrun(register unsigned long*outof, register unsigned char *into)

{

       *into++= (*outof >> 24) & 0xffL;

       *into++= (*outof >> 16) & 0xffL;

       *into++= (*outof >> 8) & 0xffL;

       *into++= *outof++ & 0xffL;

       *into++= (*outof >> 24) & 0xffL;

       *into++= (*outof >> 16) & 0xffL;

       *into++= (*outof >> 8) & 0xffL;

       *into= *outof & 0xffL;

 

       return;

}

 

void CDES::desfunc(register unsigned long*block, register unsigned long *keys)

{

       registerunsigned long fval, work, right, leftt;

       registerint round;

 

       leftt= block[0];

       right= block[1];

       work= ((leftt >> 4) ^ right) & 0x0f0f0f0fL;

       right^= work;

       leftt^= (work << 4);

       work= ((leftt >> 16) ^ right) & 0x0000ffffL;

       right^= work;

       leftt^= (work << 16);

       work= ((right >> 2) ^ leftt) & 0x33333333L;

       leftt^= work;

       right^= (work << 2);

       work= ((right >> 8) ^ leftt) & 0x00ff00ffL;

       leftt^= work;

       right^= (work << 8);

       right= ((right << 1) | ((right >> 31) & 1L)) & 0xffffffffL;

       work= (leftt ^ right) & 0xaaaaaaaaL;

       leftt^= work;

       right^= work;

       leftt= ((leftt << 1) | ((leftt >> 31) & 1L)) & 0xffffffffL;

 

       for(round = 0; round < 8; round++)

       {

              work= (right << 28) | (right >> 4);

              work^= *keys++;

              fval= SP7[work & 0x3fL];

              fval|= SP5[(work >> 8) & 0x3fL];

              fval|= SP3[(work >> 16) & 0x3fL];

              fval|= SP1[(work >> 24) & 0x3fL];

              work= right ^ *keys++;

              fval|= SP8[work & 0x3fL];

              fval|= SP6[(work >> 8) & 0x3fL];

              fval|= SP4[(work >> 16) & 0x3fL];

              fval|= SP2[(work >> 24) & 0x3fL];

              leftt^= fval;

              work= (leftt << 28) | (leftt >> 4);

              work^= *keys++;

              fval= SP7[work & 0x3fL];

              fval|= SP5[(work >> 8) & 0x3fL];

              fval|= SP3[(work >> 16) & 0x3fL];

              fval|= SP1[(work >> 24) & 0x3fL];

              work= leftt ^ *keys++;

              fval|= SP8[work & 0x3fL];

              fval|= SP6[(work >> 8) & 0x3fL];

              fval|= SP4[(work >> 16) & 0x3fL];

              fval|= SP2[(work >> 24) & 0x3fL];

              right^= fval;

       }

 

       right= (right << 31) | (right >> 1);

       work= (leftt ^ right) & 0xaaaaaaaaL;

       leftt^= work;

       right^= work;

       leftt= (leftt << 31) | ( leftt >> 1);

       work= ((leftt >> 8) ^ right) & 0x00ff00ffL;

       right^= work;

       leftt^= (work << 8);

       work= ((leftt >> 2) ^ right) & 0x33333333L;

       right^= work;

       leftt^= (work << 2);

       work= ((right >> 16) ^ leftt) & 0x0000ffffL;

       leftt^= work;

       right^= (work << 16);

       work= ((right >> 4) ^ leftt) & 0x0f0f0f0fL;

       leftt^= work;

       right^= (work << 4);

       *block++= right;

       *block= leftt;

 

       return;

};

 

unsigned char CDES::Df_Key[24] =

{

0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd,0xef,

0xfe, 0xdc, 0xba, 0x98, 0x76, 0x54, 0x32,0x10,

0x89, 0xab, 0xcd, 0xef, 0x01, 0x23, 0x45,0x67

};

 

unsigned short CDES::bytebit[8] =

{

0200, 0100, 040, 020, 010, 04, 02, 01

};

 

unsigned long CDES::bigbyte[24] =

{

0x800000L, 0x400000L, 0x200000L, 0x100000L,

0x80000L, 0x40000L, 0x20000L, 0x10000L,

0x8000L, 0x4000L,0x2000L, 0x1000L,

0x800L, 0x400L,0x200L, 0x100L,

0x80L, 0x40L,0x20L, 0x10L,

0x8L,0x4L, 0x2L, 0x1L

};

 

unsigned char CDES::pc1[56] =

{

56, 48, 40, 32, 24, 16, 8, 0, 57, 49, 41,33, 25, 17,

9, 1, 58, 50, 42, 34, 26, 18, 10, 2, 59,51, 43, 35,

62, 54, 46, 38, 30, 22, 14, 6, 61, 53, 45,37, 29, 21,

13, 5, 60, 52, 44, 36, 28, 20, 12, 4, 27,19, 11, 3

};

 

unsigned char CDES::totrot[16] =

{

1, 2, 4, 6, 8, 10, 12, 14, 15, 17, 19, 21,23, 25, 27, 28

};

 

unsigned char CDES::pc2[48] =

{

13, 16, 10, 23, 0, 4, 2, 27, 14, 5, 20, 9,

22, 18, 11, 3, 25, 7, 15, 6, 26, 19, 12, 1,

40, 51, 30, 36, 46, 54, 29, 39, 50, 44, 32,47,

43, 48, 38, 55, 33, 52, 45, 41, 49, 35, 28,31

};

 

unsigned long CDES::SP1[64] =

{

0x01010400L, 0x00000000L,0x00010000L, 0x01010404L,

0x01010004L, 0x00010404L, 0x00000004L,0x00010000L,

0x00000400L, 0x01010400L, 0x01010404L, 0x00000400L,

0x01000404L, 0x01010004L, 0x01000000L, 0x00000004L,

0x00000404L, 0x01000400L, 0x01000400L, 0x00010400L,

0x00010400L, 0x01010000L, 0x01010000L, 0x01000404L,

0x00010004L, 0x01000004L, 0x01000004L, 0x00010004L,

0x00000000L,0x00000404L, 0x00010404L, 0x01000000L,

0x00010000L, 0x01010404L, 0x00000004L,0x01010000L,

0x01010400L, 0x01000000L, 0x01000000L, 0x00000400L,

0x01010004L, 0x00010000L, 0x00010400L, 0x01000004L,

0x00000400L, 0x00000004L,0x01000404L, 0x00010404L,

0x01010404L, 0x00010004L, 0x01010000L, 0x01000404L,

0x01000004L, 0x00000404L, 0x00010404L, 0x01010400L,

0x00000404L, 0x01000400L, 0x01000400L, 0x00000000L,

0x00010004L, 0x00010400L, 0x00000000L,0x01010004L

};

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