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secp256k1
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Avoid constructing an invalid signature with probability 1:2^256.

This commit is contained in:
Gregory Maxwell 2014-12-28 19:40:40 -08:00
parent b450c34843
commit d26e26f2f4
1 changed files with 6 additions and 0 deletions
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6
src/ecdsa_impl.h
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@ -198,6 +198,12 @@ static int secp256k1_ecdsa_sig_sign(secp256k1_ecdsa_sig_t *sig, const secp256k1_
secp256k1_fe_get_b32(b, &r.x);
int overflow = 0;
secp256k1_scalar_set_b32(&sig->r, b, &overflow);
if (secp256k1_scalar_is_zero(&sig->r)) {
/* P.x = order is on the curve, so technically sig->r could end up zero, which would be an invalid signature. */
secp256k1_gej_clear(&rp);
secp256k1_ge_clear(&r);
return 0;
}
if (recid)
*recid = (overflow ? 2 : 0) | (secp256k1_fe_is_odd(&r.y) ? 1 : 0);
secp256k1_scalar_t n;