DES算法是一种最通用的对称密钥算法，因为算法本身是公开的，所以其安全性在于密钥的安全性。基于密钥的算法通常有两类：对称算法和公开密钥算法。对称算法的对称性体现在加密密钥能够从解密密钥推算出来，反之亦然。
在大多数对称算法中，加解密的密钥是相同的，DES就是这样。可见，对称密钥算法的加解密密钥都是保密的。而公开密钥算法的加密密钥是公开的，解密密钥是保密的。
DES具体算法如下：
////////////////////////////////////////////////////////////////////////// /* Provided by 朱孟斌, National University Of Technology Email: zmbtsubasa@gmailcom This product is free for use */ ////////////////////////////////////////////////////////////////////////// #ifndef Des_H #define Des_H //! enum bool{false,true}; /*! if bool is not supported,use this or just replace with char and use 1 for true,0 for false; @see enum {ENCRYPT,DECRYPT}; */ enum {ENCRYPT,DECRYPT}; /*@brief 16圈子密钥*/ static bool SubKey[2][16][48];// 16圈子密钥 /*@brief 3次DES标志*/ static bool Is3DES;// 3次DES标志 static char Tmp[256]; static char deskey[16]; typedef bool (*PSubKey)[16][48]; class _declspec(dllexport) Des { public: Des(); ~Des(); //! Type—ENCRYPT:加密,DECRYPT:解密 /*! 输出缓冲区(Out)的长度 >= ((datalen+7)/8)*8,即比datalen大的且是8的倍数的最小正整数 In 可以= Out,此时加/解密后将覆盖输入缓冲区(In)的内容 当keylen>8时系统自动使用3次DES加/解密,否则使用标准DES加/解密超过16字节后只取前16字节 @see bool Des_Go(char *Out,char *In,long datalen,const char *Key,int keylen,bool Type = ENCRYPT); */ bool Des_Go(char *Out,char *In,long datalen,const char *Key,int keylen,bool Type = ENCRYPT); private: /*! @brief 标准DES加/解密 @see static void DES(char Out[8], char In[8], const PSubKey pSubKey, bool Type); */ static void DES(char Out[8], char In[8], const PSubKey pSubKey, bool Type);//标准DES加/解密 /*! @brief 设置密钥 @see static void SetKey(const char* Key, int len); */ static void SetKey(const char* Key, int len);// 设置密钥 /*! @brief 设置子密钥 @see static void SetSubKey(PSubKey pSubKey, const char Key[8]); */ static void SetSubKey(PSubKey pSubKey, const char Key[8]);// 设置子密钥 /*! @brief f 函数 @see static void F_func(bool In[32], const bool Ki[48]); */ static void F_func(bool In[32], const bool Ki[48]);// f 函数 /*! @brief S 盒代替 @see static void S_func(bool Out[32], const bool In[48]); */ static void S_func(bool Out[32], const bool In[48]);// S 盒代替 /*! @brief 变换 @see static void Transform(bool *Out, bool *In, const char *Table, int len); */ static void Transform(bool *Out, bool *In, const char *Table, int len);// 变换 /*! @brief 异或 @see static void Xor(bool *InA, const bool *InB, int len); */ static void Xor(bool *InA, const bool *InB, int len);// 异或 /*! @brief 循环左移 @see static void RotateL(bool *In, int len, int loop); */ static void RotateL(bool *In, int len, int loop);// 循环左移 /*! @brief 字节组转换成位组 @see static void ByteToBit(bool *Out, const char *In, int bits); */ static void ByteToBit(bool *Out, const char *In, int bits);// 字节组转换成位组 /*! @brief 位组转换成字节组 @see static void BitToByte(char *Out, const bool *In, int bits); */ static void BitToByte(char *Out, const bool *In, int bits);// 位组转换成字节组 }; ////////////////////////////////////////////////////////////////////////// ////////////////////////////////////////////////////////////////////////// #endif
DES.cpp文件：
////////////////////////////////////////////////////////////////////////// /* Provided by 朱孟斌, National University Of Technology Email: zmbtsubasa@gmailcom This product is free for use */ ////////////////////////////////////////////////////////////////////////// #include "memoryh" #include "Desh" ////////////////////////////////////////////////////////////////////////// // initial permutation IP const static char IP_Table[64] = { 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 }; // final permutation IP^-1 const static char IPR_Table[64] = { 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 }; // expansion operation matrix static const char E_Table[48] = { 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 }; // 32-bit permutation function P used on the output of the S-boxes const static char P_Table[32] = { 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 }; // permuted choice table (key) const static char PC1_Table[56] = { 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 }; // permuted choice key (table) const static char PC2_Table[48] = { 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 }; // number left rotations of pc1 const static char LOOP_Table[16] = { 1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1 }; // The (in)famous S-boxes const static char S_Box[8][4][16] = { // 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 }; ////////////////////////////////////////////////////////////////////////// // Code starts: ////////////////////////////////////////////////////////////////////////// Des::Des() { } Des::~Des() { } bool Des::Des_Go(char *Out, char *In, long datalen, const char *Key, int keylen, bool Type) { if( !( Out && In && Key && (datalen=(datalen+7)&0xfffffff8) ) ) return false; SetKey(Key, keylen); if( !Is3DES ) { // 1次DES for(long i=0,j=datalen>>3; i<j; ++i,Out+=8,In+=8) DES(Out, In, &SubKey[0], Type); } else{ // 3次DES 加密:加(key0)-解(key1)-加(key0) 解密::解(key0)-加(key1)-解(key0) for(long i=0,j=datalen>>3; i<j; ++i,Out+=8,In+=8) { DES(Out, In, &SubKey[0], Type); DES(Out, Out, &SubKey[1], !Type); DES(Out, Out, &SubKey[0], Type); } } return true; } void Des::SetKey(const char* Key, int len) { memset(deskey, 0, 16); memcpy(deskey, Key, len>16?16:len); SetSubKey(&SubKey[0], &deskey[0]); Is3DES = len>8 ? (SetSubKey(&SubKey[1], &deskey[8]), true) : false; } void Des::DES(char Out[8], char In[8], const PSubKey pSubKey, bool Type) { static bool M[64], tmp[32], *Li=&M[0], *Ri=&M[32]; ByteToBit(M, In, 64); Transform(M, M, IP_Table, 64); if( Type == ENCRYPT ){ for(int i=0; i<16; ++i) { memcpy(tmp, Ri, 32); F_func(Ri, (*pSubKey)[i]); Xor(Ri, Li, 32); memcpy(Li, tmp, 32); } }else{ for(int i=15; i>=0; --i) { memcpy(tmp, Li, 32); F_func(Li, (*pSubKey)[i]); Xor(Li, Ri, 32); memcpy(Ri, tmp, 32); } } Transform(M, M, IPR_Table, 64); BitToByte(Out, M, 64); } void Des::SetSubKey(PSubKey pSubKey, const char Key[8]) { static bool K[64], *KL=&K[0], *KR=&K[28]; ByteToBit(K, Key, 64); Transform(K, K, PC1_Table, 56); for(int i=0; i<16; ++i) { RotateL(KL, 28, LOOP_Table[i]); RotateL(KR, 28, LOOP_Table[i]); Transform((*pSubKey)[i], K, PC2_Table, 48); } } void Des::F_func(bool In[32], const bool Ki[48]) { static bool MR[48]; Transform(MR, In, E_Table, 48); Xor(MR, Ki, 48); S_func(In, MR); Transform(In, In, P_Table, 32); } void Des::S_func(bool Out[32], const bool In[48]) { for(char i=0,j,k; i<8; ++i,In+=6,Out+=4) { j = (In[0]<<1) + In[5]; k = (In[1]<<3) + (In[2]<<2) + (In[3]<<1) + In[4]; ByteToBit(Out, &S_Box[i][j][k], 4); } } void Des::Transform(bool *Out, bool *In, const char *Table, int len) { for(int i=0; i<len; ++i) Tmp[i] = In[ Table[i]-1 ]; memcpy(Out, Tmp, len); } void Des::Xor(bool *InA, const bool *InB, int len) { for(int i=0; i<len; ++i) InA[i] ^= InB[i]; } void Des::RotateL(bool *In, int len, int loop) { memcpy(Tmp, In, loop); memcpy(In, In+loop, len-loop); memcpy(In+len-loop, Tmp, loop); } void Des::ByteToBit(bool *Out, const char *In, int bits) { for(int i=0; i<bits; ++i) Out[i] = (In[i>>3]>>(i&7)) & 1; } void Des::BitToByte(char *Out, const bool *In, int bits) { memset(Out, 0, bits>>3); for(int i=0; i<bits; ++i) Out[i>>3] |= In[i]<<(i&7); } ////////////////////////////////////////////////////////////////////////// // Code ends //////////////////////////////////////////////////////////////////////////
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