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原創(chuàng)作品，轉載請注明出自xelz's blog
博客地址：http://mingcn.cnblogs.com/
本文地址：http://mingcn.cnblogs.com/archive/2010/10/31/aes_c.html
快畢業(yè)了，最后一個課程設計，《基于Windows Socket的安全通信》，內容就是基于AES加密的SOCKET通信，貌似挺簡單，不過要用VC++6.0開發(fā)，C++我確實沒有任何代碼經驗，雖然不是強制性，但由于機房里各種糾結，只能用它了（用Java沒有挑戰(zhàn)性，封裝得太好了...也算熟悉下VC++吧）
先搞定AES算法，基本變換包括SubBytes（字節(jié)替代）、ShiftRows（行移位）、MixColumns（列混淆）、AddRoundKey(輪密鑰加）
其算法一般描述為
明文及密鑰的組織排列方式
ByteSubstitution（字節(jié)替代）
非線性的字節(jié)替代，單獨處理每個字節(jié)：
求該字節(jié)在有限域GF(28)上的乘法逆，"0"被映射為自身，即對于α∈GF(28)，求β∈GF(28)，
使得α·β=β·α=1mod(x8+x4+x2+x+1)。
對上一步求得的乘法逆作仿射變換
yi=xi + x(i+4)mod8 + x(i+6)mod8 + x(i+7)mod8 + ci
(其中ci是6310即011000112的第i位），用矩陣表示為
本來打算把求乘法逆和仿射變換算法敲上去，最后還是放棄了...直接打置換表
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | unsigned char sBox[] =
{ /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
0x63,0x7c,0x77,0x7b,0xf2,0x6b,0x6f,0xc5,0x30,0x01,0x67,0x2b,0xfe,0xd7,0xab,0x76, /*0*/
0xca,0x82,0xc9,0x7d,0xfa,0x59,0x47,0xf0,0xad,0xd4,0xa2,0xaf,0x9c,0xa4,0x72,0xc0, /*1*/
0xb7,0xfd,0x93,0x26,0x36,0x3f,0xf7,0xcc,0x34,0xa5,0xe5,0xf1,0x71,0xd8,0x31,0x15, /*2*/
0x04,0xc7,0x23,0xc3,0x18,0x96,0x05,0x9a,0x07,0x12,0x80,0xe2,0xeb,0x27,0xb2,0x75, /*3*/
0x09,0x83,0x2c,0x1a,0x1b,0x6e,0x5a,0xa0,0x52,0x3b,0xd6,0xb3,0x29,0xe3,0x2f,0x84, /*4*/
0x53,0xd1,0x00,0xed,0x20,0xfc,0xb1,0x5b,0x6a,0xcb,0xbe,0x39,0x4a,0x4c,0x58,0xcf, /*5*/
0xd0,0xef,0xaa,0xfb,0x43,0x4d,0x33,0x85,0x45,0xf9,0x02,0x7f,0x50,0x3c,0x9f,0xa8, /*6*/
0x51,0xa3,0x40,0x8f,0x92,0x9d,0x38,0xf5,0xbc,0xb6,0xda,0x21,0x10,0xff,0xf3,0xd2, /*7*/
0xcd,0x0c,0x13,0xec,0x5f,0x97,0x44,0x17,0xc4,0xa7,0x7e,0x3d,0x64,0x5d,0x19,0x73, /*8*/
0x60,0x81,0x4f,0xdc,0x22,0x2a,0x90,0x88,0x46,0xee,0xb8,0x14,0xde,0x5e,0x0b,0xdb, /*9*/
0xe0,0x32,0x3a,0x0a,0x49,0x06,0x24,0x5c,0xc2,0xd3,0xac,0x62,0x91,0x95,0xe4,0x79, /*a*/
0xe7,0xc8,0x37,0x6d,0x8d,0xd5,0x4e,0xa9,0x6c,0x56,0xf4,0xea,0x65,0x7a,0xae,0x08, /*b*/
0xba,0x78,0x25,0x2e,0x1c,0xa6,0xb4,0xc6,0xe8,0xdd,0x74,0x1f,0x4b,0xbd,0x8b,0x8a, /*c*/
0x70,0x3e,0xb5,0x66,0x48,0x03,0xf6,0x0e,0x61,0x35,0x57,0xb9,0x86,0xc1,0x1d,0x9e, /*d*/
0xe1,0xf8,0x98,0x11,0x69,0xd9,0x8e,0x94,0x9b,0x1e,0x87,0xe9,0xce,0x55,0x28,0xdf, /*e*/
0x8c,0xa1,0x89,0x0d,0xbf,0xe6,0x42,0x68,0x41,0x99,0x2d,0x0f,0xb0,0x54,0xbb,0x16 /*f*/
};
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下面是逆置換表，解密時使用
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | unsigned char invsBox[256] =
{ /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
0x52,0x09,0x6a,0xd5,0x30,0x36,0xa5,0x38,0xbf,0x40,0xa3,0x9e,0x81,0xf3,0xd7,0xfb, /*0*/
0x7c,0xe3,0x39,0x82,0x9b,0x2f,0xff,0x87,0x34,0x8e,0x43,0x44,0xc4,0xde,0xe9,0xcb, /*1*/
0x54,0x7b,0x94,0x32,0xa6,0xc2,0x23,0x3d,0xee,0x4c,0x95,0x0b,0x42,0xfa,0xc3,0x4e, /*2*/
0x08,0x2e,0xa1,0x66,0x28,0xd9,0x24,0xb2,0x76,0x5b,0xa2,0x49,0x6d,0x8b,0xd1,0x25, /*3*/
0x72,0xf8,0xf6,0x64,0x86,0x68,0x98,0x16,0xd4,0xa4,0x5c,0xcc,0x5d,0x65,0xb6,0x92, /*4*/
0x6c,0x70,0x48,0x50,0xfd,0xed,0xb9,0xda,0x5e,0x15,0x46,0x57,0xa7,0x8d,0x9d,0x84, /*5*/
0x90,0xd8,0xab,0x00,0x8c,0xbc,0xd3,0x0a,0xf7,0xe4,0x58,0x05,0xb8,0xb3,0x45,0x06, /*6*/
0xd0,0x2c,0x1e,0x8f,0xca,0x3f,0x0f,0x02,0xc1,0xaf,0xbd,0x03,0x01,0x13,0x8a,0x6b, /*7*/
0x3a,0x91,0x11,0x41,0x4f,0x67,0xdc,0xea,0x97,0xf2,0xcf,0xce,0xf0,0xb4,0xe6,0x73, /*8*/
0x96,0xac,0x74,0x22,0xe7,0xad,0x35,0x85,0xe2,0xf9,0x37,0xe8,0x1c,0x75,0xdf,0x6e, /*9*/
0x47,0xf1,0x1a,0x71,0x1d,0x29,0xc5,0x89,0x6f,0xb7,0x62,0x0e,0xaa,0x18,0xbe,0x1b, /*a*/
0xfc,0x56,0x3e,0x4b,0xc6,0xd2,0x79,0x20,0x9a,0xdb,0xc0,0xfe,0x78,0xcd,0x5a,0xf4, /*b*/
0x1f,0xdd,0xa8,0x33,0x88,0x07,0xc7,0x31,0xb1,0x12,0x10,0x59,0x27,0x80,0xec,0x5f, /*c*/
0x60,0x51,0x7f,0xa9,0x19,0xb5,0x4a,0x0d,0x2d,0xe5,0x7a,0x9f,0x93,0xc9,0x9c,0xef, /*d*/
0xa0,0xe0,0x3b,0x4d,0xae,0x2a,0xf5,0xb0,0xc8,0xeb,0xbb,0x3c,0x83,0x53,0x99,0x61, /*e*/
0x17,0x2b,0x04,0x7e,0xba,0x77,0xd6,0x26,0xe1,0x69,0x14,0x63,0x55,0x21,0x0c,0x7d /*f*/
};
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這里遇到問題了，本來用純c初始化數(shù)組很正常，封裝成類以后發(fā)現(xiàn)不能初始化，不管是聲明、構造函數(shù)都無法初始化，百歌谷度了一通后沒有任何答案，無奈只能在構造函數(shù)中聲明一個局部變量數(shù)組并初始化，然后用memcpy，（成員變量名為Sbox/InvSbox，局部變量名sBox/invsBox）
1 2 3 4 5 6 7 8 9 10 11 | void AES::SubBytes(unsigned char state[][4])
{
int r,c;
for(r=0; r<4; r++)
{
for(c=0; c<4; c++)
{
state[r][c] = Sbox[state[r][c]];
}
}
}
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ShiftRows（行移位變換）
行移位變換完成基于行的循環(huán)位移操作，變換方法：
即行移位變換作用于行上，第0行不變，第1行循環(huán)左移1個字節(jié)，第2行循環(huán)左移2個字節(jié)，第3行循環(huán)左移3個字節(jié)。
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | void AES::ShiftRows(unsigned char state[][4])
{
unsigned char t[4];
int r,c;
for(r=1; r<4; r++)
{
for(c=0; c<4; c++)
{
t[c] = state[r][(c+r)%4];
}
for(c=0; c<4; c++)
{
state[r][c] = t[c];
}
}
}
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MixColumns（列混淆變換）
逐列混合，方法：
b(x) = (03·x3 + 01·x2 + 01·x + 02) · a(x) mod(x4 + 1)
矩陣表示形式：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 | void AES::MixColumns(unsigned char state[][4])
{
unsigned char t[4];
int r,c;
for(c=0; c< 4; c++)
{
for(r=0; r<4; r++)
{
t[r] = state[r][c];
}
for(r=0; r<4; r++)
{
state[r][c] = FFmul(0x02, t[r])
^ FFmul(0x03, t[(r+1)%4])
^ FFmul(0x01, t[(r+2)%4])
^ FFmul(0x01, t[(r+3)%4]);
}
}
}
unsigned char AES::FFmul(unsigned char a, unsigned char b)
{
unsigned char bw[4];
unsigned char res=0;
int i;
bw[0] = b;
for(i=1; i<4; i++)
{
bw[i] = bw[i-1]<<1;
if(bw[i-1]&0x80)
{
bw[i]^=0x1b;
}
}
for(i=0; i<4; i++)
{
if((a>>i)&0x01)
{
res ^= bw[i];
}
}
return res;
}
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其中FFmul為有限域GF(28)上的乘法，標準算法應該是循環(huán)8次（b與a的每一位相乘，結果相加），但這里只用到最低2位，解密時用到的逆列混淆也只用了低4位，所以在這里高4位的運算是多余的，只計算低4位。
AddRoundKey（輪密鑰加變換）
簡單來說就是逐字節(jié)相加，有限域GF(28)上的加法是模2加法，即異或
1 2 3 4 5 6 7 8 9 10 11 | void AES::AddRoundKey(unsigned char state[][4], unsigned char k[][4])
{
int r,c;
for(c=0; c<4; c++)
{
for(r=0; r<4; r++)
{
state[r][c] ^= k[r][c];
}
}
}
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KeyExpansion（密鑰擴展）
將輸入的密鑰擴展為11組128位密鑰組，其中第0組為輸入密鑰本身
其后第n組第i列 為 第n-1組第i列 與 第n組第i-1列之和（模2加法，1<= i <=3）
對于每一組 第一列即i=0，有特殊的處理
將前一列即第n-1組第3列的4個字節(jié)循環(huán)左移1個字節(jié)，
并對每個字節(jié)進行字節(jié)替代變換SubBytes
將第一行（即第一個字節(jié)）與輪常量rc[n]相加
最后再與前一組該列相加
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | void AES::KeyExpansion(unsigned char* key, unsigned char w[][4][4])
{
int i,j,r,c;
unsigned char rc[] = {0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36};
for(r=0; r<4; r++)
{
for(c=0; c<4; c++)
{
w[0][r][c] = key[r+c*4];
}
}
for(i=1; i<=10; i++)
{
for(j=0; j<4; j++)
{
unsigned char t[4];
for(r=0; r<4; r++)
{
t[r] = j ? w[i][r][j-1] : w[i-1][r][3];
}
if(j == 0)
{
unsigned char temp = t[0];
for(r=0; r<3; r++)
{
t[r] = Sbox[t[(r+1)%4]];
}
t[3] = Sbox[temp];
t[0] ^= rc[i-1];
}
for(r=0; r<4; r++)
{
w[i][r][j] = w[i-1][r][j] ^ t[r];
}
}
}
}
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解密的基本運算
AES解密算法與加密不同，基本運算中除了AddRoundKey（輪密鑰加）不變外，其余的都需要進行逆變換，即
InvSubBytes（逆字節(jié)替代）、InvShiftRows（逆行移位）、InvMixColumns（逆列混淆）
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 | void AES::InvSubBytes(unsigned char state[][4])
{
int r,c;
for(r=0; r<4; r++)
{
for(c=0; c<4; c++)
{
state[r][c] = InvSbox[state[r][c]];
}
}
}
void AES::InvShiftRows(unsigned char state[][4])
{
unsigned char t[4];
int r,c;
for(r=1; r<4; r++)
{
for(c=0; c<4; c++)
{
t[c] = state[r][(c-r+4)%4];
}
for(c=0; c<4; c++)
{
state[r][c] = t[c];
}
}
}
void AES::InvMixColumns(unsigned char state[][4])
{
unsigned char t[4];
int r,c;
for(c=0; c< 4; c++)
{
for(r=0; r<4; r++)
{
t[r] = state[r][c];
}
for(r=0; r<4; r++)
{
state[r][c] = FFmul(0x0e, t[r])
^ FFmul(0x0b, t[(r+1)%4])
^ FFmul(0x0d, t[(r+2)%4])
^ FFmul(0x09, t[(r+3)%4]);
}
}
}
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加密過程
先將輸入的明文按列序組合成4*4的矩陣，直接與第0組密鑰（即輸入的密鑰）相加（異或），作為輪加密的輸入
然后循環(huán)10次進行SubBytes、ShiftRows、MixColumns、AddRoundKey運算，最后恢復原序列
需要注意的是最后一輪并不進行MixColumns（列混淆變換）
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | unsigned char* AES::Cipher(unsigned char* input)
{
unsigned char state[4][4];
int i,r,c;
for(r=0; r<4; r++)
{
for(c=0; c<4 ;c++)
{
state[r][c] = input[c*4+r];
}
}
AddRoundKey(state,w[0]);
for(i=1; i<=10; i++)
{
SubBytes(state);
ShiftRows(state);
if(i!=10)MixColumns(state);
AddRoundKey(state,w[i]);
}
for(r=0; r<4; r++)
{
for(c=0; c<4 ;c++)
{
input[c*4+r] = state[r][c];
}
}
return input;
}
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解密過程
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 | unsigned char* AES::InvCipher(unsigned char* input)
{
unsigned char state[4][4];
int i,r,c;
for(r=0; r<4; r++)
{
for(c=0; c<4 ;c++)
{
state[r][c] = input[c*4+r];
}
}
AddRoundKey(state, w[10]);
for(i=9; i>=0; i--)
{
InvShiftRows(state);
InvSubBytes(state);
AddRoundKey(state, w[i]);
if(i)InvMixColumns(state);
}
for(r=0; r<4; r++)
{
for(c=0; c<4 ;c++)
{
input[c*4+r] = state[r][c];
}
}
return input;
}
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對外部數(shù)據(jù)的加密/解密
至此已經實現(xiàn)了AES加密與解密的原型，在使用的時候一般處理的是字符串等，而不是直接傳入128位的數(shù)據(jù)，所以要封裝一下對外部數(shù)據(jù)的加解密處理
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | void* AES::Cipher(void* input, int length)
{
unsigned char* in = (unsigned char*) input;
int i;
if(!length)
{
while(*(in+length++));
in = (unsigned char*) input;
}
for(i=0; i<length; i+=16)
{
Cipher(in+i);
}
return input;
}
void* AES::InvCipher(void* input, int length)
{
unsigned char* in = (unsigned char*) input;
int i;
for(i=0; i<length; i+=16)
{
InvCipher(in+i);
}
return input;
}
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加密時默認參數(shù)length=0,為要加密的數(shù)據(jù)長度，如果使用默認值，則作為字符串處理，以'\0'為結尾計算長度
加密時傳進的指針要預留夠16整數(shù)倍字節(jié)的空間，因為加密操作直接修改原數(shù)據(jù)，不足128位可能造成內存溢出
最后附上源代碼 Source_AES_Cipher
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