Add bn_mul_small and bn_sqr_small.

As part of excising BIGNUM from EC scalars, we will need a "words"
version of BN_mod_mul_montgomery. That, in turn, requires BN_sqr and
BN_mul for cases where we don't have bn_mul_mont.

BN_sqr and BN_mul have a lot of logic in there, with the most complex
cases being not even remotely constant time. Fortunately, those only
apply to RSA-sized numbers, not EC-sized numbers. (With the exception, I
believe, of 32-bit P-521 which just barely exceeds the cutoff.) Imposing
a limit also makes it easier to stack-allocate temporaries (BN_CTX
serves a similar purpose in BIGNUM).

Extract bn_mul_small and bn_sqr_small and test them as part of
bn_tests.txt. Later changes will build on these.

If we end up reusing these functions for RSA in the future (though that
would require tending to the egregiously non-constant-time code in the
no-asm build), we probably want to extract a version where there is an
explicit tmp parameter as in bn_sqr_normal rather than the stack bits.

Change-Id: If414981eefe12d6664ab2f5e991a359534aa7532
Reviewed-by: Adam Langley <>
4 files changed
tree: 3208df721c92bba8731a9b6f9d4bc6471638e212
  1. .clang-format
  2. .github/
  3. .gitignore
  6. CMakeLists.txt
  14. codereview.settings
  15. crypto/
  16. decrepit/
  17. fipstools/
  18. fuzz/
  19. include/
  20. infra/
  21. sources.cmake
  22. ssl/
  23. third_party/
  24. tool/
  25. util/


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: