Description
Botan before 3.6.0, when certain GCC versions are used, has a compiler-induced secret-dependent operation in lib/utils/donna128.h in donna128 (used in Chacha-Poly1305 and x25519). An addition can be skipped if a carry is not set. This was observed for GCC 11.3.0 with -O2 on MIPS, and GCC on x86-i386. (Only 32-bit processors can be affected.)
References
github.com/...ommit/53b0cfde580e86b03d0d27a488b6c134f662e957
github.com/randombit/botan/compare/3.5.0...3.6.0
news.ycombinator.com/item?id=41887153
