As the creator said, you need to trim the high bytes of the key with zeros!
I think it's obvious that he has his own custom deterministic wallet. Based on an existing one or completely new one from scratch.
That said, I'm not sure it can sign a message with that tool.
Maybe. And it’s not even necessary, just add your own salt, and that will be enough - going over SEED will be useless.
string seed = Timer::getSeed(32);
//seed = "bla bla bla";// Mnemonic code words
string salt = "Bitcoin seed";// = "VanitySearch";
unsigned char hseed[64];
pbkdf2_hmac_sha512(hseed, 64, (const uint8_t *)seed.c_str(), seed.length(),
(const uint8_t *)salt.c_str(), salt.length(),
//2048);// 2048 rounds of hashing required by the BIP 39 Standard ???
//2048);// Used 2048 rounds ???
//0);// Used 0 rounds !!!
1024);// Electrum ?