This is done in preparation of generalizing the optimization to all our
EC_METHODs.
Wycheproof happily does cover the case where x needed a reduction, but
they don't appear to check x being just above or below n, only x = p - 1
(adjusted downwards). Also we can tailor the test vectors a bit to the
x == r*z^2 (mod p) strategy to make sure we don't mess that up.
Additionally, the scenario is different for n > p. There is also the
nuisance of EC_FELEM vs EC_SCALAR having different widths. All our
built-in curves are well-behaved (same width, and consistently p < n),
but secp160r1 is reachable from custom curves and violates both
properties. Generate some tests to cover it as well.
Change-Id: Iefa5ebfe689a81870be21f04f5962ab161d38dab
Reviewed-on: https://boringssl-review.googlesource.com/c/32985
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>
fbec517255
