前言
AES加密算法根据密钥长度不同可分为128位，192位和256位，下面主要介绍128位对称AES算法的实现。
AES算法流程
AES加密算法主要步骤有：
轮密钥加：AddRoundKey
字节替代：ByteSub
行移位： ShiftRow
列混肴： MixColumns
步骤详解及实现代码
我们用
明文：0123456789abcdeffedcba9876543210
密钥：0f1571c947d9e8590cb7add6af7f6798
密文：ff0b844a0853bf7c6934ab4364148fb9
来演示。
将待加密/解密的输入转换成4x4矩阵，记为state;
1.字节替代
字节替代作用是将state矩阵的数据替换为S盒中的数据，state矩阵中每个元素的第一位作为S盒的行索引，第二位作为S盒的列索引。将获取到的S盒中的值赋给state矩阵。
例如：state中某一元素为ab，则用S盒中第a行第b列的数据0x62替换0xab。
过字节替代后变为
S盒数据：
逆字节替代就是用逆S盒来替换state矩阵中的数据，替换方法和字节替代一致。
逆S盒数据：
代码：
void subBytes(int a[4][4], int encode){
// encode 为1 代表字节替代，为0代表逆向字节替代
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < 4; ++j) {
int temp = a[i][j];
int row = temp / 16;
int column = temp % 16;
if (encode)
a[i][j] = S_BOX[row][column];
else
a[i][j] = INVERSE_S_BOX[row][column];
}
}
}2.行移位
行移位操作是将矩阵的第k行循环左移k-1位。
经过行移位后变成
逆向行移位就是将矩阵的第k行循环右移k-1位。
代码：
void shiftRows(int a[4][4], int encode){
//encode 为1代表行移位，为0代表逆向行移位
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < i; ++j) {
if (encode) {
int temp = a[i][0];
a[i][0] = a[i][1];
a[i][1] = a[i][2];
a[i][2] = a[i][3];
a[i][3] = temp;
} else{
int temp = a[i][3];
a[i][3] = a[i][2];
a[i][2] = a[i][1];
a[i][1] = a[i][0];
a[i][0] = temp;
}
}
}
}3.列混肴
首先介绍aes算法中的加法和乘法：
对于任意正整数c，都有
例如：
列混淆变换是用一个常数矩阵去乘以矩阵state来得到新的state矩阵：
逆向列混淆使用另一个常数矩阵去乘以矩阵state来得到新的state矩阵：
代码：
void mixColumns(int a[4][4], int encode){
//encode 为1代表列混淆，为0代表逆向列混淆
for (int i = 0; i < 4; ++i) {
int temp0 = a[0][i];
int temp1 = a[1][i];
int temp2 = a[2][i];
int temp3 = a[3][i];
if (encode) {
a[0][i] = aes_multiple(temp0, 2) ^ aes_multiple(temp1, 3) ^ temp2 ^ temp3;
a[1][i] = temp0 ^ (aes_multiple(temp1, 2)) ^ (temp2 ^ aes_multiple(temp2, 2)) ^ temp3;
a[2][i] = temp0 ^ temp1 ^ (aes_multiple(temp2, 2)) ^ (temp3 ^ aes_multiple(temp3, 2));
a[3][i] = temp0 ^ (aes_multiple(temp0, 2)) ^ temp1 ^ temp2 ^ aes_multiple(temp3, 2);
}else{
a[0][i] = aes_multiple(temp0, 14) ^ aes_multiple(temp1, 11) ^ aes_multiple(temp2, 13) ^ aes_multiple(temp3, 9);
a[1][i] = aes_multiple(temp0, 9) ^ aes_multiple(temp1, 14) ^ aes_multiple(temp2, 11) ^ aes_multiple(temp3, 13);
a[2][i] = aes_multiple(temp0, 13) ^ aes_multiple(temp1, 9) ^ aes_multiple(temp2, 14) ^ aes_multiple(temp3, 11);
a[3][i] = aes_multiple(temp0, 11) ^ aes_multiple(temp1, 13) ^ aes_multiple(temp2, 9) ^ aes_multiple(temp3, 14);
}
}
}
//AES乘法计算
int aes_multiple(int a, int le){
int thr = le & 0x8;
int sec = le & 0x4;
int fir = le & 0x2;
int fir_mod = le % 2;
int result = 0;
if (thr){
int b = a;
for (int i = 1; i <=3 ; ++i) {
b = b<<1;
if (b >= 256)
b = b ^ 0x11b;
}
b = b % 256;
result = result ^ b;
}
if (sec){
int b = a;
for (int i = 1; i <=2 ; ++i) {
b = b<<1;
if (b >= 256)
b = b ^ 0x11b;
}
b = b % 256;
result = result ^ b;
}
if (fir){
int b = a << 1;
if (b >= 256)
b = b ^ 0x11b;
b = b % 256;
result = result ^ b;
}
if (fir_mod)
result = result ^ a;
return result;
}
4.密钥扩展
密钥扩展将16字节的密钥扩展成11*16字节。设k0k1k2...k15为输入的密钥。密钥扩展流程图如下图：
我们将w[44]存储到w[11][4][4]类型的数组中，密钥扩展代码如下：
void keyExpansion(int key[4][4], int w[11][4][4]){
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < 4; ++j) {
w[0][i][j] = key[j][i];
}
}
for (int i = 1; i < 11; ++i){
for (int j = 0; j < 4; ++j) {
int temp[4];
if (j == 0){
temp[0] = w[i-1][3][1];
temp[1] = w[i-1][3][2];
temp[2] = w[i-1][3][3];
temp[3] = w[i-1][3][0];
for (int k = 0; k < 4; ++k) {
int m = temp[k];
int row = m / 16;
int column = m % 16;
temp[k] = S_BOX[row][column];
if (k == 0){
temp[k] = temp[k] ^ RC[i-1];
}
}
} else{
temp[0] = w[i][j-1][0];
temp[1] = w[i][j-1][1];
temp[2] = w[i][j-1][2];
temp[3] = w[i][j-1][3];
}
for (int l = 0; l < 4; ++l) {
w[i][j][l] = w[i-1][j][l] ^ temp[l];
}
}
}
}5.轮密钥加
轮密钥加操作是将state矩阵与密钥矩阵相加，即
代码：
void addRoundKey(int a[4][4], int k[4][4]){
// 由于用w[11][4][4]表示W[44]导致行列转置，所以在进行异或操作的时候应该是a[i，j] 异或 k[j,i]
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < 4; ++j) {
a[i][j] = a[i][j] ^ k[i][j];
}
}
}总代码
#include <stdio.h>
#include <pbt.h>
#include <ctype.h>
void aes(char*, char*, char*, int);
void aes_detail(int[4][4], int[4][4], int);
void subBytes(int [4][4], int);
void shiftRows(int [4][4], int);
void mixColumns(int [4][4], int);
void addRoundKey(int [4][4], int[4][4]);
int aes_multiple(int, int);
void keyExpansion(int key[4][4], int w[11][4][4]);
int c2i(char );
/**
* S盒
*/
static const int S_BOX[16][16] = { 0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 };
/**
* 逆S盒
*/
static const int INVERSE_S_BOX[16][16] = { 0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb,
0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb,
0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25,
0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92,
0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84,
0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06,
0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b,
0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73,
0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e,
0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b,
0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4,
0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f,
0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef,
0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61,
0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d };
int RC[10] = {0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36};
int main(){
int method = 0;//1表示加密， 0表示解密
//待加密/解密文件存放路径
char * source_path = "G:\\aes2.txt";
// 加密/解密后文件存放路径
char *des_path = "G:\\aes3.txt";
// 32位16进制密钥
char * password = "0f1571c947d9e8590cb7add6af7f6798";
aes(source_path, des_path, password, method);
printf("success!!!!!!!!!!");
}
void aes(char* source_path, char* des_path, char* password, int method){
//将密钥转换成4*4数组
int p[4][4];
for (int m = 0; m < 4; ++m) {
for (int i = 0; i < 4; ++i) {
int indx = 4 * i + m;
p[i][m] = 16 * c2i(password[indx]) + c2i(password[indx + 1]);
}
}
FILE *file = fopen(source_path, "r"); //获取文件的指针
fseek(file, 0, SEEK_END); //移动文件的指针到文件结尾
int len = ftell(file); //获取文件的长度
rewind(file); //将文件指针移动回文件开始
// 如果文件长度不是128位（16字节）的整数倍，则补齐
int size = len;
if (len % 16 != 0) {
size = (len / 16 + 1) * 16;
}
unsigned char content[size];
//读取文件内容赋值给content
fread(content, 1, len, file);
for (int j = len; j < size; ++j) {
content[j] = 0;
}
fclose(file);
//存储结果
unsigned char encry[size];
//将文件转换成16字节的int型数组加密、解密
for (int i = 0; i < size / 16; ++i) {
int content_to_int[4][4];
for (int j = 0; j < 4; ++j) {
for (int k = 0; k < 4; ++k) {
content_to_int[j][k] = content[j * 4 + k + 16 * i];
}
}
aes_detail(content_to_int, p, method);
for (int j = 0; j < 4; ++j) {
for (int k = 0; k < 4; ++k) {
encry[j * 4 + k + 16 * i] = content_to_int[j][k];
}
}
}
FILE *file1 = fopen(des_path, "w");
fwrite(encry, size, 1, file1);
fflush(file1);
fclose(file1);
}
void aes_detail(int content[4][4], int password[4][4], int encode){
int p[11][4][4];
keyExpansion(password, p);
if (encode) {
addRoundKey(content, p[0]);
for (int i = 1; i <= 10; ++i) {
subBytes(content, encode);
shiftRows(content, encode);
if (i != 10) {
mixColumns(content, encode);
}
addRoundKey(content, p[i]);
}
}else {
addRoundKey(content, p[10]);
for (int i = 9; i >= 0; --i) {
shiftRows(content, encode);
subBytes(content, encode);
addRoundKey(content, p[i]);
if (i != 0) {
mixColumns(content, encode);
}
}
}
}
void subBytes(int a[4][4], int encode){
// encode 为1 代表字节替代，为0代表逆向字节替代
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < 4; ++j) {
int temp = a[i][j];
int row = temp / 16;
int column = temp % 16;
if (encode)
a[i][j] = S_BOX[row][column];
else
a[i][j] = INVERSE_S_BOX[row][column];
}
}
}
void shiftRows(int a[4][4], int encode){
//encode 为1代表行移位，为0代表逆向行移位
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < i; ++j) {
if (encode) {
int temp = a[i][0];
a[i][0] = a[i][1];
a[i][1] = a[i][2];
a[i][2] = a[i][3];
a[i][3] = temp;
} else{
int temp = a[i][3];
a[i][3] = a[i][2];
a[i][2] = a[i][1];
a[i][1] = a[i][0];
a[i][0] = temp;
}
}
}
}
void mixColumns(int a[4][4], int encode){
//encode 为1代表列混淆，为0代表逆向列混淆
for (int i = 0; i < 4; ++i) {
int temp0 = a[0][i];
int temp1 = a[1][i];
int temp2 = a[2][i];
int temp3 = a[3][i];
if (encode) {
a[0][i] = aes_multiple(temp0, 2) ^ aes_multiple(temp1, 3) ^ temp2 ^ temp3;
a[1][i] = temp0 ^ (aes_multiple(temp1, 2)) ^ (temp2 ^ aes_multiple(temp2, 2)) ^ temp3;
a[2][i] = temp0 ^ temp1 ^ (aes_multiple(temp2, 2)) ^ (temp3 ^ aes_multiple(temp3, 2));
a[3][i] = temp0 ^ (aes_multiple(temp0, 2)) ^ temp1 ^ temp2 ^ aes_multiple(temp3, 2);
}else{
a[0][i] = aes_multiple(temp0, 14) ^ aes_multiple(temp1, 11) ^ aes_multiple(temp2, 13) ^ aes_multiple(temp3, 9);
a[1][i] = aes_multiple(temp0, 9) ^ aes_multiple(temp1, 14) ^ aes_multiple(temp2, 11) ^ aes_multiple(temp3, 13);
a[2][i] = aes_multiple(temp0, 13) ^ aes_multiple(temp1, 9) ^ aes_multiple(temp2, 14) ^ aes_multiple(temp3, 11);
a[3][i] = aes_multiple(temp0, 11) ^ aes_multiple(temp1, 13) ^ aes_multiple(temp2, 9) ^ aes_multiple(temp3, 14);
}
}
}
void addRoundKey(int a[4][4], int k[4][4]){
// 由于用w[11][4][4]表示W[44]导致行列转置，所以在进行异或操作的时候应该是a[i，j] 异或 k[j,i]
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < 4; ++j) {
a[i][j] = a[i][j] ^ k[j][i];
}
}
}
//AES乘法计算
int aes_multiple(int a, int le){
int thr = le & 0x8;
int sec = le & 0x4;
int fir = le & 0x2;
int fir_mod = le % 2;
int result = 0;
if (thr){
int b = a;
for (int i = 1; i <=3 ; ++i) {
b = b<<1;
if (b >= 256)
b = b ^ 0x11b;
}
b = b % 256;
result = result ^ b;
}
if (sec){
int b = a;
for (int i = 1; i <=2 ; ++i) {
b = b<<1;
if (b >= 256)
b = b ^ 0x11b;
}
b = b % 256;
result = result ^ b;
}
if (fir){
int b = a << 1;
if (b >= 256)
b = b ^ 0x11b;
b = b % 256;
result = result ^ b;
}
if (fir_mod)
result = result ^ a;
return result;
}
void keyExpansion(int key[4][4], int w[11][4][4]){
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < 4; ++j) {
w[0][i][j] = key[j][i];
}
}
for (int i = 1; i < 11; ++i){
for (int j = 0; j < 4; ++j) {
int temp[4];
if (j == 0){
temp[0] = w[i-1][3][1];
temp[1] = w[i-1][3][2];
temp[2] = w[i-1][3][3];
temp[3] = w[i-1][3][0];
for (int k = 0; k < 4; ++k) {
int m = temp[k];
int row = m / 16;
int column = m % 16;
temp[k] = S_BOX[row][column];
if (k == 0){
temp[k] = temp[k] ^ RC[i-1];
}
}
} else{
temp[0] = w[i][j-1][0];
temp[1] = w[i][j-1][1];
temp[2] = w[i][j-1][2];
temp[3] = w[i][j-1][3];
}
for (int l = 0; l < 4; ++l) {
w[i][j][l] = w[i-1][j][l] ^ temp[l];
}
}
}
}
//将字符转换为数值
int c2i(char ch) {
// 如果是数字，则用数字的ASCII码减去48, 如果ch = '2' ,则 '2' - 48 = 2
if(isdigit(ch))
return ch - 48;
// 如果是字母，但不是A~F,a~f则返回
if( ch < 'A' || (ch > 'F' && ch < 'a') || ch > 'z' )
return -1;
// 如果是大写字母，则用数字的ASCII码减去55, 如果ch = 'A' ,则 'A' - 55 = 10
// 如果是小写字母，则用数字的ASCII码减去87, 如果ch = 'a' ,则 'a' - 87 = 10
if(isalpha(ch))
return isupper(ch) ? ch - 55 : ch - 87;
return -1;
}
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