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fix(crypto): Treat edge cases in ecdsa_sign_digest() same as ecdsa_verify_digest() does.

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Andrew Kozlik 2021-07-08 16:31:14 +02:00 committed by Andrew Kozlik
parent bc13566d7b
commit 5d03110a42
1 changed files with 13 additions and 1 deletions
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14
crypto/ecdsa.c
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@ -686,6 +686,13 @@ int ecdsa_sign_digest(const ecdsa_curve *curve, const uint8_t *priv_key,
#endif
bn_read_be(digest, &z);
if (bn_is_zero(&z)) {
// The probability of the digest being all-zero by chance is infinitesimal,
// so this is most likely an indication of a bug. Furthermore, the signature
// has no value, because in this case it can be easily forged for any public
// key, see ecdsa_verify_digest().
return 1;
}
for (i = 0; i < 10000; i++) {
#if USE_RFC6979
@ -713,11 +720,16 @@ int ecdsa_sign_digest(const ecdsa_curve *curve, const uint8_t *priv_key,
continue;
}
bn_read_be(priv_key, s);
if (bn_is_zero(s)) {
// Using an all-zero private key is most likely an indication of a bug.
return 2;
}
// randomize operations to counter side-channel attacks
generate_k_random(&randk, &curve->order);
bn_multiply(&randk, &k, &curve->order); // k*rand
bn_inverse(&k, &curve->order); // (k*rand)^-1
bn_read_be(priv_key, s); // priv
bn_multiply(&R.x, s, &curve->order); // R.x*priv
bn_add(s, &z); // R.x*priv + z
bn_multiply(&k, s, &curve->order); // (k*rand)^-1 (R.x*priv + z)