MVK_1 MVK_1 - 1 month ago 14
C Question

EVP Interface with AES-NI support

When using the OpenSSL crypto libraries in C/C++, does the EVP interface automatically support AES-NI hardware acceleration (assuming processor support)? Referring to this, it appears command-line OpenSSL does have support. I was wondering if there were specific function calls that I had to use to take advantage of this support.

For instance, if I use

EVP_EncryptInit_ex(ctx, type, imp, key, iv)
, do any of these parameters have to specify NI acceleration? I.e. will
EVP_EncryptInit_ex(ctx, EVP_aes_256_cbc(), NULL, key, iv)
do the trick?

Thanks!

jww jww
Answer

When using the OpenSSL crypto libraries in C/C++, does the EVP interface automatically support AES-NI

Yes. EVP_* is the official/supported way to ensure AES-NI is used (if available). In fact, EVP is the only way to access hardware acceleration in general.

EVP_* is also the only way to obtain other hardware accelerations, like engaging Intel's ia32's SHA acceleration under Skylark; ARM's Crypto extensions available in ARMv8; and VIA's ia32 Padlock extensions on their processors.

Using low level AES routines (like AES_encrypt and AES_decrypt) are software only-implementations, and they will never use hardware acceleration like AES-NI. Also see Dr. Henson's response on the OpenSSL mailing list at Verify AES-NI use at runtime?.


Related questions are (1) how to determine if AES-NI is being used; and (2) what are the benchmarking results. For that, see How can I check if OpenSSL is support/use the Intel AES-NI?

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