Untrinsics is a single-header, portable implementation of commonly used Intel intrinsics — especially for cryptographic operations like AES — in plain, portable C.
It's ideal for environments where hardware intrinsics are unavailable, like embedded systems, WebAssembly, or just cross-platform sanity.
📦 Header-only
💻 No dependencies
🔐 Crypto-friendly
📐 Bit-accurate with Intel’s original instructions
- ✅ Drop-in replacements for a wide range of Intel intrinsics
- 🔐 AES-specific instructions like
_mm_aesenc_si128,_mm_aesdec_si128,_mm_aeskeygenassist_si128, etc. - 📦 Implements
__m128iwith dual access as bytes, 32-bit words, and 64-bit words - 🛠 Bitwise ops, shifting, and shuffle operations
- 🧪 Suitable for test suites and cross-platform builds
Simply include the header in your project:
#include "untrinsics.h"That’s it. No linking, no build flags, no fuss.
Because sometimes you want or need Intel-style cryptographic instructions without depending on a specific CPU or compiler. This is particularly useful for:
- Writing portable crypto test vectors
- Cross-platform development (e.g., targeting WebAssembly)
- Understanding how AES and its building blocks work internally
- Educational and debugging use
Unlike larger projects like SIMDe (SIMD Everywhere), which aim to comprehensively emulate a wide array of SIMD intrinsics across platforms, Untrinsics is deliberately focused and compact.
It targets a small set of the most commonly used operations in cryptographic implementations, making it lightweight, easy to audit and trivial to include in existing projects.
The emulated instructions include mitigations against timing-based side channels. However, this is a best-effort approach and does not replace hardware countermeasures or CPU-specific assembly code.
Because constant-time operation incurs significant performance costs, some AES instructions do not run in constant time by default; additional mitigations can be enabled by defining UNTRINSICS_MITIGATE before including this file. Note that these performance costs might lead users to disable cryptographic features entirely. If constant-time behavior is critical, effective mitigations—such as masking and bitslicing—should be applied at higher levels in your implementation.
Public Domain.
No copyright.
No license.
No attribution required.
Use it however you like.
Open issues, suggest features, or just say hi. PRs are welcome!