From: David Benjamin <davidben@google.com>
Date: Tue, 17 Jul 2018 17:20:28 +0000 (-0400)
Subject: Remove zero special-case in BN_mod_exp_mont.
X-Git-Tag: OpenSSL_1_1_1-pre9~99
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=61ac9fc5c44718bf61ab68328333cc158230d090;p=oweals%2Fopenssl.git

Remove zero special-case in BN_mod_exp_mont.

A number intended to treat the base as secret should not be branching on
whether it is zero. Test-wise, this is covered by existing tests in bnmod.txt.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6733)
---

diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c
index 4e24c94ad3..2c92d7eac9 100644
--- a/crypto/bn/bn_exp.c
+++ b/crypto/bn/bn_exp.c
@@ -356,11 +356,6 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
         aa = val[0];
     } else
         aa = a;
-    if (BN_is_zero(aa)) {
-        BN_zero(rr);
-        ret = 1;
-        goto err;
-    }
     if (!bn_to_mont_fixed_top(val[0], aa, mont, ctx))
         goto err;               /* 1 */