Hardware Acceleration

Botan provides built-in support for hardware acceleration of certain algorithms on certain platforms. These alternate implementations use special CPU instructions that are not available on all platforms and either speed up the algorithm or improve security in terms of side channel resistance.

A “base” software implementation is always provided. For example, for the AES-128 block cipher three implementations are available. All of the AES-128 implementations are immune to common cache/timing based side channels.

  • If AES hardware support is available (AES-NI, POWER8, Aarch64) use that

  • If 128-bit SIMD with byte shuffles are available (SSSE3, NEON, or Altivec), use the vperm technique published by Mike Hamburg at CHES 2009

  • If no hardware or SIMD support, fall back to a constant time bitsliced implementation

The following sections list the platforms and algorithms for which hardware acceleration is available. If the CPU specific optimizations are available at runtime, they are automatically used if enabled in the build. If not, the base implementation is used.

x86

On x86-64 and x86-32 platforms, the following CPU specific optimizations are available:

Algorithm

Extension

Module

Added in

AES

VAES-AVX2

AES-NI

SSSE3

aes_vaes

aes_ni

aes_vperm

3.6.0

1.9.3

1.9.10

AES-GCM

CLMUL

SSSE3

ghash_cpu

ghash_vperm

1.11.6

1.9.10

Argon2

AVX2

SSSE3

argon2_avx2

argon2_ssse3

3.0.0

2.19.2

ChaCha

AVX512 (x86-64 only)

AVX2

SSE2

chacha_avx512

chacha_avx2

chacha_simd32

3.1.0

2.8.0

1.11.32

IDEA

SSE2

idea_sse2

1.9.4

KMAC

BMI2

keccak_perm_bmi2

3.2.0

NOEKEON

SSE2

noekeon_simd

1.9.4

RDRAND

RDRAND

processor_rng

1.11.31

RDSEED

RDSEED

rdseed

1.11.36

Serpent

AVX512 (x86-64 only)

AVX2

SSE2

serpent_avx512

serpent_avx2

serpent_simd

3.1.0

2.8.0

1.9.0

SHACAL2

Intel SHA Extensions

AVX2

shacal2_x86

shacal2_avx2

2.3.0

2.13.0

SHAKE

BMI2

keccak_perm_bmi2

2.13.0

SHA-1

Intel SHA Extensions

SSE2

sha1_x86

sha1_sse2

2.2.0

1.7.12

SHA-256

Intel SHA Extensions

BMI2

sha2_32_x86

sha2_32_bmi2

2.2.0

2.7.0

SHA-3

BMI2

keccak_perm_bmi2

2.10.0

SM4

GFNI

sm4_gfni

3.6.0

ARM

On arm64 and arm32 platforms, the following CPU specific optimizations are available:

Algorithm

Extension

Module

Added in

AES

NEON

aes_armv8

1.9.3

AES-GCM

PMULL (arm64 only)

NEON

ghash_cpu

ghash_vperm

2.3.0

2.12.0

ChaCha

NEON

chacha_simd32

2.8.0

NOEKEON

NEON

noekeon_simd

1.9.4

Serpent

NEON

serpent_simd

1.9.2

SHACAL2

NEON

ARMv8 Cryptography Extensions (arm64 only)

shacal2_simd

shacal2_armv8

2.3.0

2.13.0

SHA-1

ARMv8 Cryptography Extensions (arm64 only)

sha1_armv8

2.2.0

SHA-256

ARMv8 Cryptography Extensions (arm64 only)

sha2_32_armv8

2.2.0

SHA-384

ARMv8 Cryptography Extensions (arm64 only)

sha2_64_armv8

3.3.0

SHA-512

ARMv8 Cryptography Extensions (arm64 only)

sha2_64_armv8

3.3.0

SM4

ARMv8 Cryptography Extensions (arm64 only)

sm4_armv8

2.8.0

PowerPC

On ppc64 and ppc32 platforms, the following CPU specific optimizations are available:

Algorithm

Extension

Module

Added in

AES

POWER8/POWER9

AltiVec

aes_power8

aes_vperm

2.14.0

2.12.0

AES-GCM

AltiVec

ghash_vperm

2.12.0

ChaCha

AltiVec

chacha_simd32

2.8.0

DARN

POWER9

processor_rng

2.15.0

Serpent

AltiVec

serpent_simd

1.9.2

SHACAL2

AltiVec

shacal2_simd

2.3.0

NOEKEON

AltiVec

noekeon_simd

1.9.4

Configuring Acceleration

Hardware acceleration can be disabled at during configuring the build by passing certain --disable-* options to configure.py. This will cause the base software implementation to be used instead of the hardware accelerated one. The following options are currently supported:

--disable-sse2

disable SSE2 intrinsics

--disable-ssse3

disable SSSE3 intrinsics

--disable-sse4.1

disable SSE4.1 intrinsics

--disable-sse4.2

disable SSE4.2 intrinsics

--disable-avx2

disable AVX2 intrinsics

--disable-bmi2

disable BMI2 intrinsics

--disable-rdrand

disable RDRAND intrinsics

--disable-rdseed

disable RDSEED intrinsics

--disable-aes-ni

disable AES-NI intrinsics

--disable-sha-ni

disable SHA-NI intrinsics

--disable-altivec

disable AltiVec intrinsics

--disable-neon

disable NEON intrinsics

--disable-armv8crypto

disable ARMv8 Crypto intrinsics

--disable-powercrypto

disable POWER Crypto intrinsics

Additionally, --disable-modules=MODS can be used to remove a certain module, if desirable.

Last but not least, the BOTAN_CLEAR_CPUID environment variable can be set to a non-empty value at runtime to cause Botan to clear the CPUID bits for the CPU extensions it uses.