HELP: Create new encryption with coordinates of PUK and BrainpoolP256R1 Curve

[kheinrich188]

Hey,
I need to encrypt a jwt with coordinates of a public key by using the BrainpoolP256R1 curve.

So what I got from API is:

{
     ...
    "kty": "EC",
    "crv": "BP-256",
    "x": "QLpJ_LpFx-6yJhsb4OvHwU1khLnviiOwYOvmf5clK7w",
    "y": "AJh7pJ3zZKDJkm8rbeG69GBooTosXJgSsvNFH0i3Vxnu"
}

In a reference implementation seeing below they using this x and y coordinates to create the new encryption

C# reference code:

...
Console.Out.WriteLine($"Coordinates: {encJson["x"]} {encJson["y"]}");

X9ECParameters x9EC = ECNamedCurveTable.GetByOid(TeleTrusTObjectIdentifiers.BrainpoolP256R1);
ECDomainParameters domainParams = new ECDomainParameters(x9EC.Curve, x9EC.G, x9EC.N, x9EC.H, x9EC.GetSeed());

var x = new BigInteger(1, Base64Url.Decode(encJson["x"].ToString()));
var y = new BigInteger(1, Base64Url.Decode(encJson["y"].ToString()));
var ecPoint = domainParams.Curve.CreatePoint(x, y);

var key = new ECPublicKeyParameters(ecPoint, domainParams);
....

However, is it possible to archive this with your library and if yes how can we do this with these x and y values?

[larabr]

Hi @kheinrich188 , OpenPGP.js is not a generic crypto library, it deals with OpenPGP messages specifically. Unless you have a recipient OpenPGP key to encrypt to (which doesn't seem to be the case), this is not the right tool for you.

BrainpoolP256R1 is supported natively by NodeCrypto, but if you need to run the code in the browser, you can try the elliptic library, even though it is not constant time (hence there might be more secure alternatives).

[kheinrich188]

Thanks a lot for your quick answer.

Clear now for me