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Merge pull request #2131 from sipa/evens

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Only create signatures with even S, and verification mode to check.
This commit is contained in:
Gregory Maxwell
2013-08-15 18:42:28 -07:00
parent 13d3b1c144 a81cd96805
commit 47491a90b6
4 changed files with 43 additions and 17 deletions
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19
src/key.cpp
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@@ -195,9 +195,26 @@ public:
}
bool Sign(const uint256 &hash, std::vector<unsigned char>& vchSig) {
vchSig.clear();
ECDSA_SIG *sig = ECDSA_do_sign((unsigned char*)&hash, sizeof(hash), pkey);
if (sig == NULL)
return false;
if (BN_is_odd(sig->s)) {
// enforce even S values, by negating the value (modulo the order) if odd
BN_CTX *ctx = BN_CTX_new();
BN_CTX_start(ctx);
const EC_GROUP *group = EC_KEY_get0_group(pkey);
BIGNUM *order = BN_CTX_get(ctx);
EC_GROUP_get_order(group, order, ctx);
BN_sub(sig->s, order, sig->s);
BN_CTX_end(ctx);
BN_CTX_free(ctx);
}
unsigned int nSize = ECDSA_size(pkey);
vchSig.resize(nSize); // Make sure it is big enough
assert(ECDSA_sign(0, (unsigned char*)&hash, sizeof(hash), &vchSig[0], &nSize, pkey));
unsigned char *pos = &vchSig[0];
nSize = i2d_ECDSA_SIG(sig, &pos);
ECDSA_SIG_free(sig);
vchSig.resize(nSize); // Shrink to fit actual size
return true;
}