BN_mod_exp_mont is intended to protect the base, but not the exponent. Accordingly, it shouldn't treat a base of zero as special. Change-Id: Ib053e8ce65ab1741973a9f9bfeff8c353567439c Reviewed-on: https://boringssl-review.googlesource.com/27284 Reviewed-by: Adam Langley <agl@google.com>kris/onging/CECPQ3_patch15