数据加密（2）

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对称密码技术

对称密码技术的基本特征是加密密钥与解密密钥相同，或者两者之间互相容易推导出来。

典型的对称密码技术主要包括DES、AES、IDEA、Blowfish、RC系列、CAST等。

对称分组密码的安全性主要取决于以下参数：

* 分组长度 * 密钥长度 * 迭代轮数 *密钥扩展算法 * 轮函数

（参数越复杂，密文破译难度越高）

一、DES

DES加密 / 解密过程中，将置换与代换等经典操作相结合。

密钥通常表示为64位的数，但每个第8位均用作奇偶校验，可以忽略，故密钥长度为56位。

密钥可以是任意的56为的数，且可在任意时候改变。

加密过程：

1. 总过程：

a. 对明文分组进行一次初始置换。

b. 对所得结果进行16轮加密操作。

c. 对所得结果进行逆初始置换，获得密文分组。

2. 每轮加密操作：

a. 将64位的数据分为各32位两部分。

b. 将其中一部分与该轮子密钥作为一个复杂函数的输入。

c. 将所得结果与另一部分执行异或操作。

3. 子密钥生成过程：

a. 对初始密钥进行一次置换。

b. 对所得结果进行密钥扩展（循环左移和二次置换）。

c. 生成每轮使用的48位子密钥。

4. 每轮操作的复杂函数：包括8个预先确定的非线性代换（称为 S 盒子），通过它将6位的输入代换为4位的输出。DES的安全性主要依赖于S盒子。

DES的解密过程与加密过程基本相同，不同之处在于使用密钥的次序为逆序。

DES算法最初是针对硬件实现而设计的，没有高效的软件实现造成其运算速度较慢。随着技术进步带来的计算能力的显著提高，DES及后继算法的安全性受到了严峻的挑战。2001年以后，AES开始在美国政府的信息保护中得到广泛应用，并逐步取代DES作为首选的加密算法。至今，AES已成为流行的对称加密算法之一。

附：算法原理不难，实现起来挺复杂，先马克别人的代码，好好研究下。

#include "pch.h"#include "misc.h"#include "des.h"NAMESPACE_BEGIN(CryptoPP)/* Tables defined in the Data Encryption Standard documents * Three of these tables, the initial permutation, the final * permutation and the expansion operator, are regular enough that * for speed, we hard-code them. They're here for reference only. * Also, the S and P boxes are used by a separate program, gensp.c, * to build the combined SP box, Spbox[]. They're also here just * for reference. */#ifdef notdef/* initial permutation IP */static byte ip[] = { 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 */static byte fp[] = { 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 byte ei[] = { 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};/* The (in)famous S-boxes */static byte sbox[8][64] = { /* 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};/* 32-bit permutation function P used on the output of the S-boxes */static byte p32i[] = { 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};#endif/* permuted choice table (key) */static const byte pc1[] = { 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};/* number left rotations of pc1 */static const byte totrot[] = { 1,2,4,6,8,10,12,14,15,17,19,21,23,25,27,28};/* permuted choice key (table) */static const byte pc2[] = { 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};/* End of DES-defined tables *//* bit 0 is left-most in byte */static const int bytebit[] = { 0200,0100,040,020,010,04,02,01};/* Set key (initialize key schedule array) */DES::DES(const byte *key, CipherDir dir) : k(32){ SecByteBlock buffer(56+56+8); byte *const pc1m=buffer; /* place to modify pc1 into */ byte *const pcr=pc1m+56; /* place to rotate pc1 into */ byte *const ks=pcr+56; register int i,j,l; int m; for (j=0; j<56; j++) { /* convert pc1 to bits of key */ l=pc1[j]-1; /* integer bit location */ m = l & 07; /* find bit */ pc1m[j]=(key[l>>3] & /* find which key byte l is in */ bytebit[m]) /* and which bit of that byte */ ? 1 : 0; /* and store 1-bit result */ } for (i=0; i<16; i++) { /* key chunk for each iteration */ memset(ks,0,8); /* Clear key schedule */ for (j=0; j<56; j++) /* rotate pc1 the right amount */ pcr[j] = pc1m[(l=j+totrot[i])<(j<28? 28 : 56) ? l: l-28]; /* rotate left and right halves independently */ for (j=0; j<48; j++){ /* select bits individually */ /* check bit that goes to ks[j] */ if (pcr[pc2[j]-1]){ /* mask it in if it's there */ l= j % 6; ks[j/6] |= bytebit[l] >> 2; } } /* Now convert to odd/even interleaved form for use in F */ k[2*i] = ((word32)ks[0] << 24) | ((word32)ks[2] << 16) | ((word32)ks[4] << 8) | ((word32)ks[6]); k[2*i+1] = ((word32)ks[1] << 24) | ((word32)ks[3] << 16) | ((word32)ks[5] << 8) | ((word32)ks[7]); } if (dir==DECRYPTION) // reverse key schedule order for (i=0; i<16; i+=2) { std::swap(k[i], k[32-2-i]); std::swap(k[i+1], k[32-1-i]); }}/* End of C code common to both versions *//* C code only in portable version */// Richard Outerbridge's initial permutation algorithm/*inline void IPERM(word32 &left, word32 &right){ word32 work; work = ((left >> 4) ^ right) & 0x0f0f0f0f; right ^= work; left ^= work << 4; work = ((left >> 16) ^ right) & 0xffff; right ^= work; left ^= work << 16; work = ((right >> 2) ^ left) & 0x33333333; left ^= work; right ^= (work << 2); work = ((right >> 8) ^ left) & 0xff00ff; left ^= work; right ^= (work << 8); right = rotl(right, 1); work = (left ^ right) & 0xaaaaaaaa; left ^= work; right ^= work; left = rotl(left, 1);}inline void FPERM(word32 &left, word32 &right){ word32 work; right = rotr(right, 1); work = (left ^ right) & 0xaaaaaaaa; left ^= work; right ^= work; left = rotr(left, 1); work = ((left >> 8) ^ right) & 0xff00ff; right ^= work; left ^= work << 8; work = ((left >> 2) ^ right) & 0x33333333; right ^= work; left ^= work << 2; work = ((right >> 16) ^ left) & 0xffff; left ^= work; right ^= work << 16; work = ((right >> 4) ^ left) & 0x0f0f0f0f; left ^= work; right ^= work << 4;}*/// Wei Dai's modification to Richard Outerbridge's initial permutation // algorithm, this one is faster if you have access to rotate instructions // (like in MSVC)inline void IPERM(word32 &left, word32 &right){ word32 work; right = rotl(right, 4U); work = (left ^ right) & 0xf0f0f0f0; left ^= work; right = rotr(right^work, 20U); work = (left ^ right) & 0xffff0000; left ^= work; right = rotr(right^work, 18U); work = (left ^ right) & 0x33333333; left ^= work; right = rotr(right^work, 6U); work = (left ^ right) & 0x00ff00ff; left ^= work; right = rotl(right^work, 9U); work = (left ^ right) & 0xaaaaaaaa; left = rotl(left^work, 1U); right ^= work;}inline void FPERM(word32 &left, word32 &right){ word32 work; right = rotr(right, 1U); work = (left ^ right) & 0xaaaaaaaa; right ^= work; left = rotr(left^work, 9U); work = (left ^ right) & 0x00ff00ff; right ^= work; left = rotl(left^work, 6U); work = (left ^ right) & 0x33333333; right ^= work; left = rotl(left^work, 18U); work = (left ^ right) & 0xffff0000; right ^= work; left = rotl(left^work, 20U); work = (left ^ right) & 0xf0f0f0f0; right ^= work; left = rotr(left^work, 4U);}// Encrypt or decrypt a block of data in ECB modevoid DES::ProcessBlock(const byte *inBlock, byte * outBlock) const{ word32 l,r,work;#ifdef IS_LITTLE_ENDIAN l = byteReverse(*(word32 *)inBlock); r = byteReverse(*(word32 *)(inBlock+4));#else l = *(word32 *)inBlock; r = *(word32 *)(inBlock+4);#endif IPERM(l,r); const word32 *kptr=k; for (unsigned i=0; i<8; i++) { work = rotr(r, 4U) ^ kptr[4*i+0]; l ^= Spbox[6][(work) & 0x3f] ^ Spbox[4][(work >> 8) & 0x3f] ^ Spbox[2][(work >> 16) & 0x3f] ^ Spbox[0][(work >> 24) & 0x3f]; work = r ^ kptr[4*i+1]; l ^= Spbox[7][(work) & 0x3f] ^ Spbox[5][(work >> 8) & 0x3f] ^ Spbox[3][(work >> 16) & 0x3f] ^ Spbox[1][(work >> 24) & 0x3f]; work = rotr(l, 4U) ^ kptr[4*i+2]; r ^= Spbox[6][(work) & 0x3f] ^ Spbox[4][(work >> 8) & 0x3f] ^ Spbox[2][(work >> 16) & 0x3f] ^ Spbox[0][(work >> 24) & 0x3f]; work = l ^ kptr[4*i+3]; r ^= Spbox[7][(work) & 0x3f] ^ Spbox[5][(work >> 8) & 0x3f] ^ Spbox[3][(work >> 16) & 0x3f] ^ Spbox[1][(work >> 24) & 0x3f]; } FPERM(l,r);#ifdef IS_LITTLE_ENDIAN *(word32 *)outBlock = byteReverse(r); *(word32 *)(outBlock+4) = byteReverse(l);#else *(word32 *)outBlock = r; *(word32 *)(outBlock+4) = l;#endif}void DES_EDE_Encryption::ProcessBlock(byte *inoutBlock) const{ e.ProcessBlock(inoutBlock); d.ProcessBlock(inoutBlock); e.ProcessBlock(inoutBlock);}void DES_EDE_Encryption::ProcessBlock(const byte *inBlock, byte *outBlock) const{ e.ProcessBlock(inBlock, outBlock); d.ProcessBlock(outBlock); e.ProcessBlock(outBlock);}void DES_EDE_Decryption::ProcessBlock(byte *inoutBlock) const{ d.ProcessBlock(inoutBlock); e.ProcessBlock(inoutBlock); d.ProcessBlock(inoutBlock);}void DES_EDE_Decryption::ProcessBlock(const byte *inBlock, byte *outBlock) const{ d.ProcessBlock(inBlock, outBlock); e.ProcessBlock(outBlock); d.ProcessBlock(outBlock);}void TripleDES_Encryption::ProcessBlock(byte *inoutBlock) const{ e1.ProcessBlock(inoutBlock); d.ProcessBlock(inoutBlock); e2.ProcessBlock(inoutBlock);}void TripleDES_Encryption::ProcessBlock(const byte *inBlock, byte *outBlock) const{ e1.ProcessBlock(inBlock, outBlock); d.ProcessBlock(outBlock); e2.ProcessBlock(outBlock);}void TripleDES_Decryption::ProcessBlock(byte *inoutBlock) const{ d1.ProcessBlock(inoutBlock); e.ProcessBlock(inoutBlock); d2.ProcessBlock(inoutBlock);}void TripleDES_Decryption::ProcessBlock(const byte *inBlock, byte *outBlock) const{ d1.ProcessBlock(inBlock, outBlock); e.ProcessBlock(outBlock); d2.ProcessBlock(outBlock);}

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