tree 8a8f7d82d86ecc8bf6472398a1cbec84eac83be5
parent 7361ee42cfff6039585c49a82e4b585cb633d5e3
author Brian Smith <brian@briansmith.org> 1592250157 -0500
committer CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org> 1593529446 +0000

Use |crypto_word_t| and |size_t| more consistently in ECC scalar recoding.

Use |crypto_word_t| as the type for secret values in scalar recoding.
Use |size_t| as the type of array indexes in scalar recoding. Use
explicit casts where a larger type is (losslessly) truncated to a
smaller type. With this change, |uint64_t| is no longer used in the
p256.c when building in 32-bit mode, |unsigned| is not used in any of
the affected modules, and |uint8_t| and |char| are no longer used for
secret values in the ECC recoding.

When given the choice of doing non-array-indexing arithmetic (e.g. shifts)
on |size_t| values or |crypto_word_t| values, prefer doing it on
|crypto_word_t| values. More generally, try to use |size_t| only for
sizes and array indexes.

This is part of a bigger project to minimize the use of types other than
|crypto_word_t| for secret values. This is also part of a larger project
make the ECC code more consistent.

Avoid changing the loop indexing in the P-256 scalar multiplication from
|int| to |size_t|. The P-224 code does use |size_t| but it is less clear
than the P-256 code where |i - 1| results in a negative/underflowed
value when |i| is zero.

Change-Id: I78cb404455c2340a4f8c9688d36c0d425bfcc50b
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/41685
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>