AES加密算法 - 加密模式
ECB模式
优点:
1.简单；
2.有利于并行计算；
3.误差不会被传送；
缺点:
1.不能隐藏明文的模式；
2.可能对明文进行主动攻击；
CBC模式：
优点：
1.不容易主动攻击,安全性好于ECB,适合传输长度长的报文,是SSL、IPSec的标准。
缺点：
1.不利于并行计算；
2.误差传递；
3.需要初始化向量IV
CFB模式：
优点：
1.隐藏了明文模式;
2.分组密码转化为流模式;
3.可以及时加密传送小于分组的数据;
缺点:
1.不利于并行计算;
2.误差传送：一个明文单元损坏影响多个单元;
3.唯一的IV;
ofb模式：
优点:
1.隐藏了明文模式;
2.分组密码转化为流模式;
3.可以及时加密传送小于分组的数据;
缺点:
1.不利于并行计算;
2.对明文的主动攻击是可能的;
3.误差传送：一个明文单元损坏影响多个单元;
了解这些加密模式之后，再看openssl提供的接口就好理解了。
openssl提供的aes加密接口
以下接口来自“crypto/aes/aes.h”，有openssl源码。
//设置加密和解密器
int AES_set_encrypt_key(const unsigned char *userKey, const int bits,
AES_KEY *key);
int AES_set_decrypt_key(const unsigned char *userKey, const int bits,
AES_KEY *key);
//默认的加密解密方式，参数好理解
void AES_encrypt(const unsigned char *in, unsigned char *out,
const AES_KEY *key);
void AES_decrypt(const unsigned char *in, unsigned char *out,
const AES_KEY *key);
//下面这些也是常用的加密方式，但是参数很多，而源码对于参数使用介绍不多，只能摸索
void AES_ecb_encrypt(const unsigned char *in, unsigned char *out,
const AES_KEY *key, const int enc);
void AES_cbc_encrypt(const unsigned char *in, unsigned char *out,
size_t length, const AES_KEY *key,
unsigned char *ivec, const int enc); //参数相对复杂
void AES_cfb128_encrypt(const unsigned char *in, unsigned char *out,
size_t length, const AES_KEY *key,
unsigned char *ivec, int *num, const int enc);
void AES_cfb1_encrypt(const unsigned char *in, unsigned char *out,
size_t length, const AES_KEY *key,
unsigned char *ivec, int *num, const int enc);
void AES_cfb8_encrypt(const unsigned char *in, unsigned char *out,
size_t length, const AES_KEY *key,
unsigned char *ivec, int *num, const int enc);
void AES_ofb128_encrypt(const unsigned char *in, unsigned char *out,
size_t length, const AES_KEY *key,
unsigned char *ivec, int *num);
void AES_ctr128_encrypt(const unsigned char *in, unsigned char *out,
size_t length, const AES_KEY *key,
unsigned char ivec[AES_BLOCK_SIZE],
unsigned char ecount_buf[AES_BLOCK_SIZE],
unsigned int *num);
从下面这个文件可以看出，AES_encrypt就是ecb加密的方式。而AES_set_encrypt_key和AES_encrypt，它们的实现在"crypto/aes/aes_x86core.c"和"crypto/aes/aes_core.c"，也就是有两个版本，根据平台选择。看源码。
"crypto/aes/aes_ecb.c"
void AES_ecb_encrypt(const unsigned char *in, unsigned char *out,
const AES_KEY *key, const int enc) {
assert(in && out && key);
assert((AES_ENCRYPT == enc)||(AES_DECRYPT == enc));
if (AES_ENCRYPT == enc)
AES_encrypt(in, out, key);
else
AES_decrypt(in, out, key);
}
从这里可以看出，ecb方式的加密，是由AES_encrypt接口实现的。
而cbc的加密方式在另外的地方实现了，下面给出目录以及源代码。
"crypto/aes/aes_cbc.c"
void AES_cbc_encrypt(const unsigned char *in, unsigned char *out, size_t len, const AES_KEY *key, unsigned char *ivec, const int enc) { if (enc) CRYPTO_cbc128_encrypt(in,out,len,key,ivec,(block128_f)AES_encrypt); else CRYPTO_cbc128_decrypt(in,out,len,key,ivec,(block128_f)AES_decrypt); }
从这里看出，cbc加密方式，调用接口CRYPTO_cbc128_decrypt，而它又将AES_encrypt作为参数传入。
"crypto/modes/cbc128.c"
void CRYPTO_cbc128_encrypt(const unsigned char *in, unsigned char *out,
size_t len, const void *key,
unsigned char ivec[16], block128_f block)
{//这里的block就是AES_encrypt
size_t n;
const unsigned char *iv = ivec;
assert(in && out && key && ivec);
#if !defined(OPENSSL_SMALL_FOOTPRINT)
if (STRICT_ALIGNMENT &&
((size_t)in|(size_t)out|(size_t)ivec)%sizeof(size_t) != 0) {
while (len>=16) {
for(n=0; n<16; ++n)
out[n] = in[n] ^ iv[n];//输入与初始化向量进行异或，保存在out
(*block)(out, out, key);//调用AES_encrypt进行加密，异或结果out作为加密输入
//加密输出结果也保存在out里面，
iv = out;//将前一次密文，作为后一次的初始化向量，从而完成加密
len -= 16;
in += 16;
out += 16;
}
} else {
while (len>=16) {
for(n=0; n<16; n+=sizeof(size_t))
*(size_t*)(out+n) =
*(size_t*)(in+n) ^ *(size_t*)(iv+n);
(*block)(out, out, key);
iv = out;
len -= 16;
in += 16;
out += 16;
}
}
#endif
while (len) {
for(n=0; n<16 && n<len; ++n)
out[n] = in[n] ^ iv[n];//in和iv异或
for(; n<16; ++n)//如果in长度不是16的整数倍
out[n] = iv[n];//最后的out直接用iv初始化，其实也就相当于out与0进行异或
(*block)(out, out, key);
iv = out;
if (len<=16) break;//加密结束
len -= 16;
in += 16;
out += 16;
}
memcpy(ivec,iv,16);
}
//从上面的源码可以看出，cbc本质上和ecb差别不大，唯一区别是将前一次加密结果，与要加密的内容异或。因此，cbc的并行性较差，因为每次都要等待前一次的结果，而ecb则不用，速度较快。其主要区别仍然看文章开头，原理图看参考链接。
调用实例：
int aes_encrypt(char* in, char* key, char* out)//, int olen)
{
if(!in || !key || !out) return 0;
AES_KEY aes;
if(AES_set_encrypt_key((unsigned char*)key, 128, &aes) < 0)
{
return 0;
}
int len=strlen(in)/<span style="font-family: 'Hiragino Sans GB W3', 'Hiragino Sans GB', Arial, Helvetica, simsun, u5b8bu4f53;">AES_BLOCK_SIZE*</span><span style="font-family: 'Hiragino Sans GB W3', 'Hiragino Sans GB', Arial, Helvetica, simsun, u5b8bu4f53;">AES_BLOCK_SIZE</span><span style="font-family: 'Hiragino Sans GB W3', 'Hiragino Sans GB', Arial, Helvetica, simsun, u5b8bu4f53;">, en_len=0;</span><span style="font-family: 'Hiragino Sans GB W3', 'Hiragino Sans GB', Arial, Helvetica, simsun, u5b8bu4f53;">
</span> while(en_len<len)//输入输出字符串够长，并且是AES_BLOCK_SIZE的整数倍，需要严格限制
{
AES_encrypt((unsigned char*)in, (unsigned char*)out, &aes);
in+=AES_BLOCK_SIZE;
out+=AES_BLOCK_SIZE;
en_len+=AES_BLOCK_SIZE;
}
return 1;
}
int aes_decrypt(char* in, char* key, char* out)
{
if(!in || !key || !out) return 0;
AES_KEY aes;
if(AES_set_decrypt_key((unsigned char*)key, 128, &aes) < 0)
{
return 0;
}
int len=strlen(in), en_len=0;
while(en_len<len)
{
AES_decrypt((unsigned char*)in, (unsigned char*)out, &aes);
in+=AES_BLOCK_SIZE;
out+=AES_BLOCK_SIZE;
en_len+=AES_BLOCK_SIZE;
}
return 1;
}
最近遇到一个坑，
AES_encrypt <pre code_snippet_id="232583" snippet_file_name="blog_20140312_1_226454" name="code" class="cpp" style="color: rgb(55, 42, 24); font-size: 16px; line-height: 28px;">AES_decrypt
就是这两个函数让我折腾了四五天，心力憔悴，几近崩溃，也许是走火入魔了，因为遇到了挑战，非要干掉它，而不是绕过！
int aes_encrypt(char* in, char* key, char* out)//, int olen)
{
if(!in || !key || !out) return 0;
AES_KEY aes;
if(AES_set_encrypt_key((unsigned char*)key, 128, &aes) < 0)
{
return 0;
}
<pre code_snippet_id="232583" snippet_file_name="blog_20140312_1_226454" name="code" class="cpp" style="color: rgb(55, 42, 24); font-size: 16px; line-height: 28px;"> int len=strlen(in)/<span style="font-family: 'Hiragino Sans GB W3', 'Hiragino Sans GB', Arial, Helvetica, simsun, u5b8bu4f53;">AES_BLOCK_SIZE*</span><span style="font-family: 'Hiragino Sans GB W3', 'Hiragino Sans GB', Arial, Helvetica, simsun, u5b8bu4f53;">AES_BLOCK_SIZE</span><span style="font-family: 'Hiragino Sans GB W3', 'Hiragino Sans GB', Arial, Helvetica, simsun, u5b8bu4f53;">, en_len=0;</span>
char *lptmp = new char[len+1];
memset(lptmp, '\0', len+1);
while(en_len<len)//输入输出字符串够长，并且是AES_BLOCK_SIZE的整数倍，需要严格限制
{
AES_encrypt((unsigned char*)in, (unsigned char*)lptmp, &aes);
in+=AES_BLOCK_SIZE;
<span style="font-family: 'Hiragino Sans GB W3', 'Hiragino Sans GB', Arial, Helvetica, simsun, u5b8bu4f53;">lptmp</span><span style="font-family: 'Hiragino Sans GB W3', 'Hiragino Sans GB', Arial, Helvetica, simsun, u5b8bu4f53;">+=AES_BLOCK_SIZE;</span>
en_len+=AES_BLOCK_SIZE;
<span style="color:#372a18;"> //hex(lptmp) </span><strong><span style="color:#ff0000;">那么就发现第一个数据块加密的结果是对的，后面就错误了，加密后的数据很多是0，查了openssl的</span></strong>
<strong><span style="color:#ff0000;"> //源代码这个aes这块的加解密是线程安全的，有谁知道原因？</span></strong>
}
if(lptmp)
{delete []lptmp;
lptmp = NULL;
}
return 1;
}
