http://www./archives/585.html 2012 AES(Advanced Encryption Standard,高级加密标准) 又叫Rijndael加密法,用来替代DES算法。常见AES加密模式有ECB、CBC、CFB、OFB和CTR等五种, CFB、OFB都带反馈,做流加密用的多,CBC和CTR、ECB多用于独立block加密,由于ECB算法有点小缺点(相同输入,相同输出,容易明文攻击),所以CBC和CTR这两种加解密方式用的较多,也是很多标准规范要求的实现算法,下面看一下这两种算法原理。
AES跟Rijndael相比有点小区别,就是使用固定块(block size)为128bits(16字节)(原Rijndael块大小更灵活),密钥长度支持128、192或256位。
一、AES CBC加解密原理CBC加解密原理如下图所示(图片来源维基百科,参考文末地址): CBC加密原理:明文跟向量异或,再用KEY进行加密,结果作为下个BLOCK的初始化向量。解密原理:使用密钥先对密文解密,解密后再同初始向量异或得到明文。 CBC需要对明文块大小进行Padding(补位),由于前后加密的相关性,只能实施串行化动作,无法并行运算。另外,CBC需要参量:密钥和初始化向量。 二、AES CTR加解密原理
CTR加密原理:用密钥对输入的计数器加密,然后同明文异或得到密文。解密原理:用密钥对输入计数器加密,然后同密文异或得到明文。 CTR不需要Padding,而且采用了流密钥方式加解密,适合于并行运算,CTR涉及参量:Nounce随机数、Counter计数器和密钥。Nounce随机数和Counter计数器整体可看作计数器,因为只要算法约定好,就可以回避掉串行化运算。 三、AES CBC和CTR加解密实例下文实例使用了第三方开源源码,官方网址:http://www.gladman./, 本文测试源码来源:http://gladman./oldsite/AES/index.php,测试时,如下源码文件需加入工程:aes_modes.c、aescrypt.c、aeskey.c、aestab.c。 测试源码如下: #include <iostream> #include <string> #include <time.h> #include "aes/aes.h" typedef unsigned char uint8; typedef char int8; typedef unsigned short uint16; typedef short int16; typedef unsigned int uint32; typedef int int32; typedef unsigned __int64 uint64; typedef __int64 int64; /****************************** For _LINUX typedef long long int64; typedef unsigned long long uint64; ******************************/ using namespace std; //same as function rfc3686_inc void ctr_inc(unsigned char ctr_buf[16]) { if(!(++(ctr_buf[15]))) if(!(++(ctr_buf[14]))) if(!(++(ctr_buf[13]))) ++(ctr_buf[12]); } //same as function rfc3686_init //4Bytes nounce+8Bytes iv+4Bytes counter void ctr_init( unsigned char nonce[4], unsigned char iv[8], unsigned char ctr_buf[16]) { memcpy(ctr_buf, nonce, 4); memcpy(ctr_buf + 4, iv, 8); memset(ctr_buf + 12, 0, 4); ctr_inc(ctr_buf); } void print_hex(uint8* buf, uint64 len) { //Print results: for(int i=0;i<len;i++) { printf("%02X",buf[i]); if(15 == i%16) printf("\n"); } printf("\n"); } void main() { uint8 key[] = {0x10,0xa5,0x88,0x69,0xd7,0x4b,0xe5,0xa3,0x74,0xcf, 0x86,0x7c,0xfb,0x47,0x38,0x59};//AES::DEFAULT_KEYLENGTH uint8 buf[16];//tmp buffer uint8 msg[] = "HelloWorld!23456"; uint64 fsize=strlen((char*)msg);//message size uint8* DataBuf=new uint8[1024];//Data Buffer //AES with CBC printf("AES with CBC\n"); //Copy data memset(DataBuf,0,1024); strcpy((char*)DataBuf,(char*)msg); uint8* pDataBuf = DataBuf;//tmp pointer uint8 iv1[] = {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00}; uint64 iEncryptTimes = fsize/16+1; uint8 iPaddings = 16-fsize%16;//Padding size uint64 newlen = fsize+iPaddings;//New length //memcpy(DataBuf,iv,16);//Save iv memset(pDataBuf+fsize, iPaddings,iPaddings);//Padding printf("input =\n"); print_hex(DataBuf,newlen); aes_encrypt_ctx en_ctx[1];//Init encrypt //Encrypt for(uint64 i=0;i<iEncryptTimes;i++) { aes_encrypt_key128(key,en_ctx); aes_cbc_encrypt(pDataBuf,buf,16,iv1,en_ctx);//iv has been changed, ctx has been changed!!! memcpy(pDataBuf,buf,16); pDataBuf += 16; } printf("encrypt =\n"); print_hex(DataBuf,newlen); //Decrypt pDataBuf = DataBuf; uint8 iv2[] = {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00}; uint8 buf3[256]={'\0'}; aes_decrypt_ctx de_ctx[1]; aes_decrypt_key128(key,de_ctx); aes_cbc_decrypt(pDataBuf,buf3,newlen,iv2,de_ctx); printf("decrypt =\n"); print_hex(buf3,newlen); //================================ printf("AES with CTR\n"); //Copy data memset(DataBuf,0,1024); strcpy((char*)DataBuf,(char*)msg); pDataBuf = DataBuf;//tmp pointer uint8 iv3[] = {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00}; iEncryptTimes = fsize/16; uint8 iRemain = fsize%16; uint8 ctr_buf[AES_BLOCK_SIZE]; //Save iv(as ctrl buffer) //memcpy(DataBuf,iv,16); printf("input =\n"); print_hex(DataBuf,fsize); //Init encrypt //aes_encrypt_ctx en_ctx[1]; //Encrypt for(i=0;i<iEncryptTimes;i++) { aes_encrypt_key128(key,en_ctx); ctr_init(iv3,iv3+4,ctr_buf);//we set iv as the nouce aes_ctr_encrypt(pDataBuf,buf,16,ctr_buf,ctr_inc,en_ctx);//iv has been changed, ctx has been changed!!! memcpy(pDataBuf,buf,16); pDataBuf += 16; } if(iRemain!=0) {//last times pDataBuf += i*16; aes_encrypt_key128(key,en_ctx); ctr_init(iv3,iv3+4,ctr_buf);//we set iv as the nouce aes_ctr_encrypt(pDataBuf,buf,iRemain,ctr_buf,ctr_inc,en_ctx);//iv has been changed, ctx has been changed!!! memcpy(pDataBuf,buf,iRemain); } printf("encrypt =\n"); print_hex(DataBuf,fsize); //Decrypt pDataBuf = DataBuf; uint8 iv4[] = {0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, 0x00,0x00,0x00,0x00,0x00,0x00}; //uint8 buf3[256]={'\0'}; //aes_decrypt_ctx de_ctx[1]; //aes_decrypt_key128(key,de_ctx); aes_encrypt_key128(key,en_ctx); ctr_init(iv4,iv4+4,ctr_buf);//we set iv as the nouce aes_ctr_decrypt(pDataBuf,buf3,16,ctr_buf,ctr_inc,en_ctx); printf("decrypt =\n"); print_hex(buf3,fsize); printf("\n"); } 输出如下(CBC未去掉Padding):
参考资料: 如您对AES/DEX加密解密有兴趣,建议阅读:Java DES加密和解密,Java AES加密和解密两篇文章。 |
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