Re: Re: Retrieving public key from x and y

> 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.

Something sounds sideways. We probably need to see your code.

If I had to hazard a guess, I'd say there's something wrong with the
public key. The fields are empty.

The following works as expected for me.

$ cat test.cxx
#include <iostream>
#include <string>

#include "cryptlib.h"
#include "filters.h"
#include "eccrypto.h"
#include "osrng.h"
#include "files.h"
#include "sha.h"
#include "hex.h"

#include "pem.h"

int main(int argc, char* argv[])
{
    using namespace CryptoPP;

    AutoSeededRandomPool prng;
    ECDSA<ECP, SHA256>::PrivateKey skey;
    skey.Initialize(prng, ASN1::secp256k1());

    ECDSA<ECP, SHA256>::PublicKey pkey;
    skey.MakePublicKey(pkey);

    FileSink fs("pubkey.pem");
    PEM_Save(fs, pkey);

    return 0;
}

Compiling it:

$ g++ -DNDEBUG -g2 -O3 -fPIC -pthread -pipe test.cxx ./libcryptopp.a -o test.exe

Running it:

$ ./test.exe
$ cat pubkey.pem
-----BEGIN PUBLIC KEY-----
MFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEpqAXeayRz3sez/raCNqrx5dRp9GLrRaP
TmRu7a5OqBiJk7V34UolfNSRsDW6iWGmzlsUFJs4Ui+XYv493sS3ng==
-----END PUBLIC KEY-----

And cross check with OpenSSL:

$ openssl ec -in pubkey.pem -inform PEM -pubin -text
read EC key
Public-Key: (256 bit)
pub:
    04:a6:a0:17:79:ac:91:cf:7b:1e:cf:fa:da:08:da:
    ab:c7:97:51:a7:d1:8b:ad:16:8f:4e:64:6e:ed:ae:
    4e:a8:18:89:93:b5:77:e1:4a:25:7c:d4:91:b0:35:
    ba:89:61:a6:ce:5b:14:14:9b:38:52:2f:97:62:fe:
    3d:de:c4:b7:9e
ASN1 OID: secp256k1

Jeff

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