program linked with lcrypto is many times slower than openssl command

问题

I have a simple C program for aes256 encryption. It is linked with openssl library (-lcrypto). The core of the program are following few lines:

AES_set_encrypt_key(key32 ,256 ,&aes_ks3);

while( len = fread( buf ,1 ,4096, fp) ){
    if( 4096 != len )
        break;
    AES_cbc_encrypt(buf ,buf ,len ,&aes_ks3 ,iv ,AES_ENCRYPT);
    fwrite(buf ,1 ,len ,wfp);
}

AES_cbc_encrypt(buf ,buf ,len+padding_len ,&aes_ks3, iv,AES_ENCRYPT);
fwrite(buf ,1 ,len+padding_len ,wfp);

I am only using standard openssl library functions for encryption (ie. I am not using my own functions). I can encrypt same file, using same key and IV with openssl command:

openssl enc -aes-256-cbc -in FILE.in -out FILE.out -K $key -iv $iv

And I get identical output file (thus verifying that my program works correctly).

However, my program consistently runs is 4-5 times slower than the openssl command. They are both using the same routines, abd are both linked with the same library.

How is that possible?

How can I investigate why?

UPDATE:

Here are the actual numbers for encrypting same file with 1) openssl, 2) my program:

1) openssl:

real    0m0.238s
user    0m0.196s
sys     0m0.040s

2) my program:

real    0m1.006s
user    0m0.964s
sys     0m0.040s

回答1:

By calling the AES functions directly, you lose all the optimizations provided by the EVP layer. In particular, the EVP layer supports AES intrinsics, which makes a huge difference on CPUs that support them.

来源：https://stackoverflow.com/questions/34993514/program-linked-with-lcrypto-is-many-times-slower-than-openssl-command