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ecc.c: fix infinite loop. #282

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ecc.c: fix infinite loop. #282

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10 changes: 10 additions & 0 deletions ecc/ecc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -625,6 +625,16 @@ int ecc_ecdsa_validate(const uint32_t *x, const uint32_t *y, const uint32_t *e,
if (isZero(r) || isZero(s))
return -1;

/* r and s must be in [1, n-1]; otherwise fieldInv(s) below can loop
* forever when s is a multiple of the order n (e.g. s == n). sub()
* returns borrow == 1 iff the value is < n. */
{
uint32_t tmp_cmp[8];
if (sub(r, ecc_order_m, tmp_cmp, arrayLength) == 0 ||
sub(s, ecc_order_m, tmp_cmp, arrayLength) == 0)
return -1;
}

// 3. Calculate w = s^{-1} \pmod{n}
fieldInv(s, ecc_order_m, ecc_order_r, w);

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