Function SigHasLowR

src/key.cpp:202–212

Check that the sig has a low R value and will be less than 71 bytes

// Check that the sig has a low R value and will be less than 71 bytes
bool SigHasLowR(const secp256k1_ecdsa_signature* sig)
{
    unsigned char compact_sig[64];
    secp256k1_ecdsa_signature_serialize_compact(secp256k1_context_sign, compact_sig, sig);

    // In DER serialization, all values are interpreted as big-endian, signed integers. The highest bit in the integer indicates
    // its signed-ness; 0 is positive, 1 is negative. When the value is interpreted as a negative integer, it must be converted
    // to a positive value by prepending a 0x00 byte so that the highest bit is 0. We can avoid this prepending by ensuring that
    // our highest bit is always 0, and thus we must check that the first byte is less than 0x80.
    return compact_sig[0] < 0x80;
}

uint256 CKey::ECDH(const CPubKey& pubkey) const {
    assert(fValid);