Split ec_point_mul_scalar into two operations.

While it appears that we internally support constant-time
dual multiplication, it is not actually constant-time. Integrating the
two operations means we hit the doubling branch. Instead, replace the
constant-time functions with single multiplication functions, one for
arbitrary points and one for the base point. This simplifies timing
analysis of the EC_METHODs.

This CL only changes the wrapper functions. A subsequent CL will change
the EC_METHOD hooks. We conservatively assume EC_POINT_mul callers
expect secret scalars and split it into two multiplications and an
addition if needed.

Update-Note: EC_POINT_mul may get slower if called with both g_scalar
and p_scalar non-NULL. If the scalars were secret, this plugs a timing
leak (note neither ECDH nor ECDSA signing use such an operation). If
acting on public scalars, notably ECDSA verify, this slowdown is not
inherently necessary. If necessary, we can expose a public version of
ec_point_mul_scalar_public, but callers should be using BoringSSL's
ECDSA verify API instead.

Change-Id: I9c20b660ce4b58dc633588cfd5b2e97a40203ec3
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/36224
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>
8 files changed
tree: 947423e4348de22b85242b7e1bbc405df3d82ffb
  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
  15. BUILDING.md
  16. CMakeLists.txt
  17. codereview.settings
  19. FUZZING.md
  20. go.mod
  23. PORTING.md
  24. README.md
  25. sources.cmake
  26. 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.

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