Discuss the doubling case in windowed Booth representation.

Using signed digits for point multiplication halves the size of the table,
which is a valuable optimization. However, it is dependent on the curve whether
the doubling case in point addition is reachable. Assuming my reasoning is
valid, the condition for the standard table strategy is:

  The non-trivial doubling case in single-point scalar multiplication may occur
  if and only if the 2^(w-1) bit of the group order is zero.

It would be nice to transcribe this to Coq someday but, for now, check in a
proof in prose. The condition also does not apply to EC_GFp_nistz256_method's
multi-level tables.

This file is now 91% comments by line count.

Change-Id: I29b394289793db957f99e80734e10ed59a96fcec
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/36364
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
1 file changed
tree: 29f758b05cfc804eeb842482ab7853e25aab37fc
  1. .github/
  2. crypto/
  3. decrepit/
  4. fipstools/
  5. fuzz/
  6. include/
  7. ssl/
  8. third_party/
  9. tool/
  10. util/
  11. .clang-format
  12. .gitignore
  13. API-CONVENTIONS.md
  14. BREAKING-CHANGES.md
  15. BUILDING.md
  16. CMakeLists.txt
  17. codereview.settings
  18. CONTRIBUTING.md
  19. FUZZING.md
  20. go.mod
  21. INCORPORATING.md
  22. LICENSE
  23. PORTING.md
  24. README.md
  25. sources.cmake
  26. 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.

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