Simplify Montgomery RR precomputation.

Use equivalent but simpler math, and explain the simpler math. Move the
discussion of multipying-vs-doubling to be after the discussion of
squaring-vs-doubling so that the discussion order follows the code
order, and so that we can combine the multipying-vs-doubling discussion
with the explanation of why no multiply/doubling is needed at all.
Expand the existing discussion to be a little more explicit.

Retain |threshold|, but change the type of |threshold| was changed to
|int| to avoid a signed/unsigned comparison in the added assertion
(|bn_mod_lshift_consttime| takes the shift count as an |int| anyway).

Change-Id: I24e4687e76944a34a8621b5f2fdee15a5201ac88
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/63906
Reviewed-by: Bob Beck <bbe@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: Bob Beck <bbe@google.com>
2 files changed
tree: 2185d24dbf38ef9fee4387878c3db3a0a5df1208
  1. .github/
  2. cmake/
  3. crypto/
  4. decrepit/
  5. fuzz/
  6. include/
  7. pki/
  8. rust/
  9. ssl/
  10. third_party/
  11. tool/
  12. util/
  13. .clang-format
  14. .gitignore
  15. API-CONVENTIONS.md
  16. BREAKING-CHANGES.md
  17. BUILDING.md
  18. CMakeLists.txt
  19. codereview.settings
  20. CONTRIBUTING.md
  21. FUZZING.md
  22. go.mod
  23. go.sum
  24. INCORPORATING.md
  25. LICENSE
  26. PORTING.md
  27. README.md
  28. SANDBOXING.md
  29. sources.cmake
  30. STYLE.md
README.md

BoringSSL

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: