From a52926189155d906d8c11ff97cbc1e5191d202cd Mon Sep 17 00:00:00 2001 From: Geoff Thorpe Date: Wed, 30 Apr 2014 11:39:24 -0400 Subject: [PATCH] bignum: fix boundary condition in montgomery logic It's not clear whether this inconsistency could lead to an actual computation error, but it involved a BIGNUM being passed around the montgomery logic in an inconsistent state. This was found using flags -DBN_DEBUG -DBN_DEBUG_RAND, and working backwards from this assertion in 'ectest'; ectest: bn_mul.c:960: BN_mul: Assertion `(_bnum2->top == 0) || (_bnum2->d[_bnum2->top - 1] != 0)' failed Signed-off-by: Geoff Thorpe --- crypto/bn/bn_exp.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c index baeda372cf..ea2bd0a898 100644 --- a/crypto/bn/bn_exp.c +++ b/crypto/bn/bn_exp.c @@ -494,6 +494,9 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p, r->d[0] = (0-m->d[0])&BN_MASK2; for(i=1;id[i] = (~m->d[i])&BN_MASK2; r->top = j; + /* Upper words will be zero if the corresponding words of 'm' + * were 0xfff[...], so decrement r->top accordingly. */ + bn_correct_top(r); } else #endif -- 2.25.1