AESNI(4) FreeBSD Kernel Interfaces Manual AESNI(4)


aesnidriver for the AES accelerator on Intel CPUs


To compile this driver into the kernel, place the following lines in your kernel configuration file:

device crypto
device aesni

Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):



Starting with some models of Core i5/i7, Intel processors implement a new set of instructions called AESNI. The set of six instructions accelerates the calculation of the key schedule for key lengths of 128, 192, and 256 of the Advanced Encryption Standard (AES) symmetric cipher, and provides a hardware implementation of the regular and the last encryption and decryption rounds.

The processor capability is reported as AESNI in the Features2 line at boot. The aesni driver does not attach on systems that lack the required CPU capability.

The aesni driver registers itself to accelerate AES operations for crypto(4). Besides speed, the advantage of using the aesni driver is that the AESNI operation is data-independent, thus eliminating some attack vectors based on measuring cache use and timings typically present in table-driven implementations.


The aesni driver first appeared in FreeBSD 9.0.


The aesni driver was written by Konstantin Belousov <kib@FreeBSD.org>. The key schedule calculation code was adopted from the sample provided by Intel and used in the analogous OpenBSD driver.
September 6, 2010 FreeBSD