openssl-aes-ctr使用openmp加速

openssl-aes-ctr
[openmp omp for](#openmp omp for)

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

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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);	   // encrypt
                ctr128_inc_aligned(ivec);				// ivec = ivec + 1
                for (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

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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

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#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：

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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;
# endif

            int 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 */
#endif
    while (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。