AESNI

AES-NI, short for AES New Instructions, is a set of dedicated hardware instructions added to several x86 processors to accelerate the Advanced Encryption Standard (AES). By implementing core AES rounds and key-generation steps in hardware, AES-NI speeds up encryption and decryption and reduces CPU overhead for cryptographic tasks such as TLS handshakes, disk encryption, and VPN traffic. The instruction set comprises six instructions: AESENC, AESENCLAST, AESDEC, AESDECLAST, AESKEYGENASSIST, and AESIMC. These perform the main AES round transformations, the final round, the inverse operations for decryption, and the AES key schedule, respectively. For Galois/Counter Mode (GCM) authentication, carry-less multiply instructions in the PCLMULQDQ family are frequently used alongside AES-NI, though they are separate hardware features.

AES-NI first appeared with Intel's Westmere microarchitecture around 2010, and AMD later implemented compatible instructions in its processors. Since then, most modern Intel and AMD CPUs expose AES-NI, and software cryptographic libraries can detect and automatically exploit it when available.

With AES-NI, software AES routines can execute more efficiently than pure software implementations, yielding performance improvements in encryption-heavy workloads. It does not change AES security parameters or algorithms; it simply accelerates them. Adoption depends on hardware support and on compiler and library support to enable the instructions.