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Pieter Wuille a545127fbc
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README.md

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