Perform the RSA CRT reductions with Montgomery reduction.

The first step of RSA with the CRT optimization is to reduce our input
modulo p and q. We can do this in constant-time[*] with Montgomery
reduction. When p and q are the same size, Montgomery reduction's bounds
hold. We need two rounds of it because the first round gives us an
unwanted R^-1.

This does not appear to have a measurable impact on performance. Also
add a long TODO describing how to make the rest of the function
constant-time[*] which hopefully we'll get to later. RSA blinding should
protect us from it all, but make this constant-time anyway.

Since this and the follow-up work will special-case weird keys, add a
test that we don't break those unintentionally. (Though I am not above
breaking them intentionally someday...)

Thanks to Andres Erbsen for discussions on how to do this bit properly.

[*] Ignoring the pervasive bn_correct_top problem for the moment.

Change-Id: Ide099a9db8249cb6549be99c5f8791a39692ea81
Reviewed-on: https://boringssl-review.googlesource.com/24204
Reviewed-by: Adam Langley <agl@google.com>
2 files changed
tree: 19ef101a465899de18396224af82a3059e11b435
  1. .github/
  2. crypto/
  3. decrepit/
  4. fipstools/
  5. fuzz/
  6. include/
  7. infra/
  8. ssl/
  9. third_party/
  10. tool/
  11. util/
  12. .clang-format
  13. .gitignore
  14. API-CONVENTIONS.md
  15. BUILDING.md
  16. CMakeLists.txt
  17. codereview.settings
  18. CONTRIBUTING.md
  19. FUZZING.md
  20. INCORPORATING.md
  21. LICENSE
  22. PORTING.md
  23. README.md
  24. sources.cmake
  25. 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: