openssl-aes-ctr使用openmp加速

openssl-aes-ctr

本文采用openssl-1.1.1w进行开发验证开发；因为aes-ctr加解密模式中，不依赖与上一个模块的加/解密的内容，所以对于aes-ctr加解密模式是比较适合进行并行加速的算法。
其代码如下

void CRYPTO_ctr128_encrypt(const unsigned char *in, unsigned char *out,size_t len, const void *key,unsigned char ivec[16],unsigned char ecount_buf[16], unsigned int *num,block128_f block) {...while (len >= 16) {(*block) (ivec, ecount_buf, key);	   // encryptctr128_inc_aligned(ivec);				// ivec = ivec + 1for (n = 0; n < 16; n += sizeof(size_t))  // out = in ^ ecount_buf*(size_t_aX *)(out + n) =*(size_t_aX *)(in + n)^ *(size_t_aX *)(ecount_buf + n);len -= 16;out += 16;in += 16;n = 0;}...}

从代码不难看出，每层循环，以16字节为一组进行加密；组与组之间不存在关联，下一组变更的只有ivec，所以对其进行加速处理，可以考虑并行处理的方式进行并行处理。

可以提前计算好ivec,ivec+1,ivec+2,…,ivec+255;此处因为单次加解密的长度是4096，所以函数内最长为256组会在一次函数调用中进行加解密。

openmp omp for

参考OpenMP并行编程
使用#pragma omp parallel for 对加密过程进行并行加速处理，处理过程中，在进入for循环前，首先将ivec的值都计算好

int loop = len / 16;
unsigned char * new_ivec[4096]; // 此处有待优化，实际调用长度可能会超过4096
memcpy(new_ivec, ivec, 16);
for (int i = 1; i < loop; i++) {memcpy(new_ivec + 16*i, new_ivec + 16*i - 16, 16);ctr128_inc_aligned(new_ivec + 16*i);
}

然后就是对分组进行并行加密处理

#pragma omp parallel for num_threads (16) private(n)
for (int i = 0; i < loop; i++) {unsigned char current_ecount_buf[16] = {0};(*block) (new_ivec + 16*i, current_ecount_buf, key);unsigned char * current_in = in + 16*i;unsigned char * current_out = out + 16*i;for (n = 0; n < 16; n += sizeof(size_t))*(size_t_aX *)(current_out + n) =*(size_t_aX *)(current_in + n)^ *(size_t_aX *)(current_ecount_buf + n);}

修改过后的函数如下：

void CRYPTO_ctr128m_encrypt(const unsigned char *in, unsigned char *out,size_t len, const void *key,unsigned char ivec[16],unsigned char ecount_buf[16], unsigned int *num,block128_f block)
{unsigned int n;size_t l = 0;n = *num;#if !defined(OPENSSL_SMALL_FOOTPRINT)if (16 % sizeof(size_t) == 0) { /* always true actually */do {while (n && len) {*(out++) = *(in++) ^ ecount_buf[n];--len;n = (n + 1) % 16;}# if defined(STRICT_ALIGNMENT)if (((size_t)in | (size_t)out | (size_t)ecount_buf)% sizeof(size_t) != 0)break;
# endifint loop = len / 16;unsigned char * new_ivec[4096];memcpy(new_ivec, ivec, 16);for (int i = 1; i < loop; i++) {memcpy(new_ivec + 16*i, new_ivec + 16*i - 16, 16);ctr128_inc_aligned(new_ivec + 16*i);}#pragma omp parallel for num_threads (16) private(n)for (int i = 0; i < loop; i++) {unsigned char current_ecount_buf[16] = {0};(*block) (new_ivec + 16*i, current_ecount_buf, key);unsigned char * current_in = in + 16*i;unsigned char * current_out = out + 16*i;for (n = 0; n < 16; n += sizeof(size_t))*(size_t_aX *)(current_out + n) =*(size_t_aX *)(current_in + n)^ *(size_t_aX *)(current_ecount_buf + n);}len -= loop * 16;out += loop * 16;in += loop * 16;n = 0;if (len) {(*block) (ivec, ecount_buf, key);ctr128_inc_aligned(ivec);while (len--) {out[n] = in[n] ^ ecount_buf[n];++n;}}*num = n;return;} while (0);}/* the rest would be commonly eliminated by x86* compiler */
#endifwhile (l < len) {if (n == 0) {(*block) (ivec, ecount_buf, key);ctr128_inc(ivec);}out[l] = in[l] ^ ecount_buf[n];++l;n = (n + 1) % 16;}*num = n;
}

经过以上处理后，需要进行测试，本文采用给openssl，增加enc子命令的方式进行处理，通过增加aria-128-ctrm的方式，而后进行测试验证。
从测试结果看，确实能提高一定的性能，但效果不是很显著，大概可能和加解密时长，占openssl enc整个命令调用时长的占比不是很高，所以没有显著的性能提升。
尽管效果不是很明显，也算是针对openmp和openssl-aes-ctr的一次结合应用。