ctaes
Simple C module for constant-time AES encryption and decryption.
Features:
- Simple, pure C code without any dependencies.
- No tables or data-dependent branches whatsoever, but using bit sliced approach from https://eprint.iacr.org/2009/129.pdf.
- Very small object code: slightly over 4k of executable code when compiled with -Os.
- Slower than implementations based on precomputed tables or specialized instructions, but can do ~15 MB/s on modern CPUs.
Performance
Compiled with GCC 5.3.1 with -O3, on an Intel(R) Core(TM) i7-4800MQ CPU, numbers in CPU cycles:
| Algorithm | Key schedule | Encryption per byte | Decryption per byte |
|---|---|---|---|
| AES-128 | 2.8k | 154 | 161 |
| AES-192 | 3.1k | 169 | 181 |
| AES-256 | 4.0k | 191 | 203 |
Build steps
Object code:
$ gcc -O3 ctaes.c -c -o ctaes.o
Tests:
$ gcc -O3 ctaes.c test.c -o test
Benchmark:
$ gcc -O3 ctaes.c bench.c -o bench
Review
Results of a formal review of the code can be found in http://bitcoin.sipa.be/ctaes/review.zip