tree 13df35142658248ccb145553ad55c3ce04595ae7
parent 10458977f6a803859808365fad071731369f655a
author David Benjamin <davidben@google.com> 1667594237 -0400
committer Boringssl LUCI CQ <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com> 1667740466 +0000

Skip the field inversion when just measuring output size.

https://boringssl-review.googlesource.com/c/boringssl/+/41084
inadvertently added a somewhat expensive operation (field inversion) in
the path of EC_POINT_point2oct when passed with buf == NULL. The result
is a caller that calls the function twice, first to measure and then to
serialize, actually ends up doing the field inversion twice.

Fix this by removing the dual-use calling convention from the internal
function and just have a separate function to measure the output size
separately. It's slightly subtle because EC_POINT_point2oct would check
for the point at infinity by way of converting to affine coordinates, so
we do need to repeat that check.

As part of this, add a unit test for
https://boringssl-review.googlesource.com/6488, which rejected the point
at infinity way back.

Change-Id: I3b6c0f95cced9c00489386f064a2c3f0bb1776f8
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/55065
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>