Update x86_64-mont5.pl and RSAZ comments a bit.

Back in https://boringssl-review.googlesource.com/c/boringssl/+/33268, I
wrote that I had no idea what the mont5 assembly was doing. In
preparation for fixing up some comments around
BN_mod_exp_mont_consttime, I wanted to understand whether we were still
making assumptions about cache lines.

Happily, for the mont5 code, the answer is no, we are not. We just make
a bunch of masks and apply them in the natural way. But we do require
16-byte alignment on the table, because we use movdqa to read out of it.

I didn't look as closely at RSAZ, but I believe it too is fine. It
fairly quickly tosses $power into an XMM register and builds up masks,
rather than incorporating it into address computations.

(Both scatter5 functions incorporate it into the address, but that's
part of table building, where the index is public. I've updated the
comments to note when the index is secret or public.)

There is one reference to cache lines in the comments of mont5.pl, in
computing $N. However, $N has been unused since
https://boringssl-review.googlesource.com/c/boringssl/+/7244. (There are
references to $N[0] and friends, but those refer to @N, which is a
completely unrelated variable.) Remove it.

Change-Id: I1fac0660dffcd1380572029de2e5baece60cddf6
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/55225
Reviewed-by: Bob Beck <bbe@google.com>
Commit-Queue: Bob Beck <bbe@google.com>
Auto-Submit: David Benjamin <davidben@google.com>
3 files changed
tree: 2c85b3b45d6b66a45071273a6e508d987f6365f6
  1. .github/
  2. crypto/
  3. decrepit/
  4. fuzz/
  5. include/
  6. rust/
  7. ssl/
  8. third_party/
  9. tool/
  10. util/
  11. .clang-format
  12. .gitignore
  15. BUILDING.md
  16. CMakeLists.txt
  17. codereview.settings
  19. FUZZING.md
  20. go.mod
  21. go.sum
  24. OpenSSLConfig.cmake
  25. PORTING.md
  26. README.md
  28. sources.cmake
  29. STYLE.md


BoringSSL is a fork of OpenSSL that is designed to meet Google's needs.

Although BoringSSL is an open source project, it is not intended for general use, as OpenSSL is. We don't recommend that third parties depend upon it. Doing so is likely to be frustrating because there are no guarantees of API or ABI stability.

Programs ship their own copies of BoringSSL when they use it and we update everything as needed when deciding to make API changes. This allows us to mostly avoid compromises in the name of compatibility. It works for us, but it may not work for you.

BoringSSL arose because Google used OpenSSL for many years in various ways and, over time, built up a large number of patches that were maintained while tracking upstream OpenSSL. As Google's product portfolio became more complex, more copies of OpenSSL sprung up and the effort involved in maintaining all these patches in multiple places was growing steadily.

Currently BoringSSL is the SSL library in Chrome/Chromium, Android (but it's not part of the NDK) and a number of other apps/programs.

Project links:

There are other files in this directory which might be helpful: