Rather than recompute values the same as in key generation, where
possible, we check differently. In particular, most RSA values are
modular inverses of some value. Check each of them by multiplying and
using our naive constant-time division function.
Median of 29 RSA keygens: 0m0.218s -> 0m0.205s
(Accuracy beyond 0.1s is questionable.)
Bug: 238
Change-Id: Iaca19f12c045457013def844a17bf502ed09136e
Reviewed-on: https://boringssl-review.googlesource.com/26373
Reviewed-by: Adam Langley <alangley@gmail.com>