SHA instruction set
extensions to the x86 instruction set architecture
A SHA instruction set is a set of extensions to the ARM, Power, RISC-V and x86 instruction set architecture which support hardware acceleration of the Secure Hash Algorithm (SHA) family.
ARM
SHA-1 and SHA-256 instructions appeared as optional features (FEAT_SHA1 and FEAT_SHA256) in the Arm V8.0 architecture introduced in 2011. The instructions are:
SHA-1: SHA1C, SHA1H, SHA1M, SHA1P, SHA1SU0, SHA1SU1
SHA-256: SHA256H, SHA256H2, SHA256SU0, SHA256SU1
SHA-512 and SHA-3 instructions appeared as optional features (FEAT_SHA512 and FEAT_SHA3) in the Arm V8.2 architecture. The instructions are:
SHA-512: SHA512H, SHA512H2, SHA512SU0, SHA512SU1
SHA-3: EOR3, RAX1, XAR, BCAX
A scalable vector extension (SVE) version of the SHA-3 instructions appeared as an optional feature (FEAT_SVE_SHA3) in the Arm V9.0 architecture.
Power
Vector instructions for the Sigma functions for SHA-256 (vshasigmaw) and SHA-512 (vshasigmad) were added in the specification for Power ISA v.2.07 released in May 2013. The same instruction performs either Σ₀, Σ₁, σ₀ or σ₁ as described in the SHA-2 standard (FIPS-180-4) depending on parameters.
RISC-V
SHA2 instructions are part of the Zknh extension part of the RISC-V Cryptography Extensions Volume I: Scalar & Entropy Source Instructions ratified in November 2021.
As SHA-512 is defined on 64-bit words, the instructions for SHA-512 differ in RV32 and RV64, with some RV32 instructions for SHA-512 split the elementary sigma operations in half in order to operate on a single 32-bit register.
The instructions are:
SHA-256 (RV32 and RV64): sha256sig0 (SHA-256 σ₀), sha256sig1 (SHA-256 σ₁), sha256sum0 (SHA-256 Σ₀), sha256sum1 (SHA-256 Σ₁)
SHA-512 (RV32): sha512sig0h (high half of SHA-512 σ₀), sha512sig0l (low half of SHA-512 σ₀), sha512sig1h (high half of SHA-512 σ₁), sha512sig1l (low half of SHA-512 σ₁), sha512sum0r (SHA-512 Σ₀), sha512sum1r (SHA-512 Σ₁)
SHA-512 (RV64): sha512sig0 (SHA-512 σ₀), sha512sig1 (SHA-512 σ₁), sha512sum0 (SHA-512 Σ₀), sha512sum1 (SHA-512 Σ₁)
x86 architecture processors
The original SSE-based extensions added four instructions supporting SHA-1 and three for SHA-256 and were specified in 2013 by Intel. Instructions for SHA-512 were introduced in Arrow Lake and Lunar Lake in 2024.
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