根据椭圆曲线点的x和y值生成PublicKey [英] Generating PublicKey from x and y values of elliptic curve point

问题描述

我正试图在我的应用程序中生成一个共享机密，如下所示:

I am trying to generate a shared secret in my app like this:

public static byte[] generateSharedSecret(PrivateKey privateKey PublicKey publicKey) {
    KeyAgreement keyAgreement = KeyAgreement.getInstance("ECDH", "SC");
    keyAgreement.init(privateKey);
    keyAgreement.doPhase(publicKey, true);
    return keyAgreement.generateSecret();
} 

这工作正常，但是我在这里使用的PublicKey应该来自后端.

This is working fine, but the PublicKey I use here should be coming from the backend.

后端只是向我发送椭圆曲线上某点的x和y值，现在我应该据此生成PublicKey.但我只是想不通！如何仅从这两个值创建PublicKey实例?

The backend just sends me the x and y value of a point on an elliptic curve and now I am supposed to generate the PublicKey from that. But I just can't figure it out! How can I create a PublicKey instance just from those two values?

推荐答案

实际上非常简单！但是除了x和y值之外，您还需要做其他事情.您还需要一个ECParameterSpec！ ECParameterSpec描述您正在使用的椭圆曲线，您的应用必须使用与后端相同的ECParameterSpec！

It's actually quite simple! But you need one more thing besides the x and y values. You also need an ECParameterSpec! The ECParameterSpec describes the elliptic curve you are using and your app has to use the same ECParameterSpec as your backend does!

使用x和y值可以创建ECPoint实例，并且可以与ECParameterSpec一起创建ECPublicKeySpec:

With the x and y values you can create an ECPoint instance and together with your ECParameterSpec you can create an ECPublicKeySpec:

ECParameterSpec ecParameters = ...;
BigInteger x = ...;
BigInteger y = ...;

ECPoint ecPoint = new ECPoint(x, y);
ECPublicKeySpec keySpec = new ECPublicKeySpec(ecPoint, ecParameters);

现在使用ECPublicKeySpec，您可以使用KeyFactory生成PublicKey:

And now with that ECPublicKeySpec you can generate the PublicKey using a KeyFactory:

KeyFactory keyFactory = KeyFactory.getInstance("EC");
PublicKey publicKey = keyFactory.generatePublic(keySpec);

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