tree d5aa9138c127b7f1ecd5510e2952f7791a69bb06
parent d035730ac7ebb82fbf1895fea50c29048bb6edb2
author Brian Smith <brian@briansmith.org> 1459057351 -1000
committer David Benjamin <davidben@google.com> 1461022486 +0000

Require the public exponent to be available in RSA blinding.

Require the public exponent to be available unless
|RSA_FLAG_NO_BLINDING| is set on the key. Also, document this.

If the public exponent |e| is not available, then we could compute it
from |p|, |q|, and |d|. However, there's no reasonable situation in
which we'd have |p| or |q| but not |e|; either we have all the CRT
parameters, or we have (e, d, n), or we have only (d, n). The
calculation to compute |e| exposes the private key to risk of side
channel attacks.

Also, it was particularly wasteful to compute |e| for each
|BN_BLINDING| created, instead of just once before the first
|BN_BLINDING| was created.

|BN_BLINDING| now no longer needs to contain a duplicate copy of |e|,
so it is now more space-efficient.

Note that the condition |b->e != NULL| in |bn_blinding_update| was
always true since commit cbf56a5683ddda831ff91c46ea48d1fba545db66.

Change-Id: Ic2fd6980e0d359dcd53772a7c31bdd0267e316b4
Reviewed-on: https://boringssl-review.googlesource.com/7594
Reviewed-by: David Benjamin <davidben@google.com>