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AES-NI Hardware Acceleration

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On x86/x86-64 CPUs that support the AES-NI instruction set, Qt-AES can use native hardware instructions for a significant throughput improvement over the pure software implementation.

Note

AES-NI is only supported on x86/x86-64. Enabling it on any other architecture will produce a CMake configure error.

Windows / MSVC: MSVC does not require a separate compiler flag to enable AES-NI intrinsics — they are available by default on x64 targets. The -maes flag check in CMakeLists.txt is a no-op under MSVC, which is expected and correct.

What is accelerated

All five modes are hardware-accelerated:

Mode Encrypt Decrypt
ECB ✅ ✅
CBC ✅ ✅
CTR ✅ ✅
CFB ✅ ✅
OFB ✅ ✅

CFB and OFB use the forward AES cipher for both encrypt and decrypt (as the standard requires), so they take the encryption key schedule in both directions.

Enabling AES-NI

Pass -DQTAES_ENABLE_AESNI=ON at configure time:

cmake -B build \
  -DQTAES_ENABLE_AESNI=ON \
  -DQTAES_ENABLE_TESTS=ON \
  -DCMAKE_PREFIX_PATH=/path/to/Qt
cmake --build build
ctest --test-dir build -V

Runtime detection

Even with QTAES_ENABLE_AESNI=ON, the library queries the CPU at runtime via CPUID. If the running CPU does not support AES-NI the library silently falls back to the software implementation — no code changes are required.

API transparency

AES-NI is entirely transparent to the caller. The same encode() / decode() API is used regardless of whether hardware acceleration is active. Ciphertext produced by the hardware path is identical to the software path and fully interoperable.