Function NegateSignatureS

src/test/script_tests.cpp:148–178

}; // struct ScriptTest

void static NegateSignatureS(std::vector<unsigned char>& vchSig) {
    // Parse the signature.
    std::vector<unsigned char> r, s;
    r = std::vector<unsigned char>(vchSig.begin() + 4, vchSig.begin() + 4 + vchSig[3]);
    s = std::vector<unsigned char>(vchSig.begin() + 6 + vchSig[3], vchSig.begin() + 6 + vchSig[3] + vchSig[5 + vchSig[3]]);

    while (s.size() < 33) {
        s.insert(s.begin(), 0x00);
    }
    assert(s[0] == 0);
    // Perform mod-n negation of s by (ab)using libsecp256k1
    // (note that this function is meant to be used for negating secret keys,
    //  but it works for any non-zero scalar modulo the group order, i.e. also for s)
    int ret = secp256k1_ec_seckey_negate(secp256k1_context_static, s.data() + 1);
    assert(ret);

    if (s[1] < 0x80) {
        s.erase(s.begin());
    }

    // Reconstruct the signature.
    vchSig.clear();
    vchSig.push_back(0x30);
    vchSig.push_back(4 + r.size() + s.size());
    vchSig.push_back(0x02);
    vchSig.push_back(r.size());
    vchSig.insert(vchSig.end(), r.begin(), r.end());
    vchSig.push_back(0x02);
    vchSig.push_back(s.size());
    vchSig.insert(vchSig.end(), s.begin(), s.end());
}

namespace
{