Ok, I was able to find out, why I get a wrong y coordinate (leading zeros in Hex-String brings up this crap). Validation seems to be okay.

But my problem afterward (which I didn't mention to this point, because I thought it will solve itself when I have a correct y-coordinate) is, that if I try to save this public key as PEM, I only get -----BEGIN PUBLIC KEY----- MFowMFow-----END PUBLIC KEY----- as result. This was also my result with wrong y and failed validation. Benjamin Schäfer schrieb am Dienstag, 14. September 2021 um 18:04:26 UTC+2: > Hi there, > > I'm trying to retrieve a public key, given x and y with the following code: > > //x and y came from a webservice > std::string x = > "40BA49FCBA45C7EEB2261B1BE0EBC7C14D6484B9EF8A23B060EBE67F97252BBC"; > std::string y = > "00987BA49DF364A0C9926F2B6DE1BAF46068A13A2C5C9812B2F3451F48B75719EE"; > std::string pt = x + y; > CryptoPP::HexDecoder decoder; > decoder.Put((byte*)pt.data(), pt.size()); > decoder.MessageEnd(); > > CryptoPP::ECP::Point q; > size_t len = decoder.MaxRetrievable(); > > q.identity = false; > q.x.Decode(decoder, len / 2); > q.y.Decode(decoder, len / 2); //Wrong value > > CryptoPP::ECDSA<CryptoPP::ECP, CryptoPP::SHA256>::PublicKey publicKey; > publicKey.Initialize(CryptoPP::ASN1::brainpoolP256r1(), q); > > After Initializing the public key, I try to validate it: > > CryptoPP::ECDSA<CryptoPP::ECP, CryptoPP::SHA256>::Verifier > verifier(publicKey); > > CryptoPP::AutoSeededRandomPool prng; > bool result = publicKey.Validate(prng, 3); > > result is always false and I tried to get the int-values of x and y with > the following: > > const CryptoPP::ECP::Point& qq = publicKey.GetPublicElement(); > std::ostringstream cou; > cou << "Q.x: " << qq.x; > cou << "Q.y: " << qq.y; > OutputDebugStringA(cou.str().c_str()); > > While x seems to be okay, y is not. And I don't know what to do... Is > there anybody with a similar problem and a possible solution? > > > Best regards > -- You received this message because you are subscribed to the Google Groups "Crypto++ Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to cryptopp-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/cryptopp-users/f193b607-7e7a-4fed-a3e5-5768642d5314n%40googlegroups.com.