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bignum: fix boundary condition in montgomery logic

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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

(Imported from upstream's 3cc546a3bbcbf26cd14fc45fb133d36820ed0a75)
This commit is contained in:
Adam Langley 2014-06-20 12:00:00 -07:00
parent 6a57f92195
commit eceb33d3af
1 changed files with 3 additions and 0 deletions
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3
crypto/bn/exponentiation.c
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@ -692,6 +692,9 @@ int BN_mod_exp_mont(BIGNUM *rr, const BIGNUM *a, const BIGNUM *p,
for (i = 1; i < j; i++) for (i = 1; i < j; i++)
r->d[i] = (~m->d[i]) & BN_MASK2; r->d[i] = (~m->d[i]) & BN_MASK2;
r->top = j; 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 if (!BN_to_montgomery(r, BN_value_one(), mont, ctx)) { } else if (!BN_to_montgomery(r, BN_value_one(), mont, ctx)) {
goto err; goto err;
} }