如何使用 Bouncy Castle 创建与 OpenSSH 兼容的 ED25519 密钥？

Question

如何创建可用于 SSH 的 OpenSSH ED25519 私钥？ 目标是为您的 OpenSSH 客户端提供与.ssh/id_ed25519中相同格式的密钥文件。

这是我目前的方法，它不会创建兼容的：

import org.bouncycastle.asn1.x9.X9ECParameters;
import org.bouncycastle.crypto.ec.CustomNamedCurves;
import org.bouncycastle.crypto.params.AsymmetricKeyParameter;
import org.bouncycastle.crypto.util.OpenSSHPrivateKeyUtil;
import org.bouncycastle.crypto.util.PrivateKeyFactory;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.jce.spec.ECParameterSpec;
import org.bouncycastle.util.io.pem.PemObject;
import org.bouncycastle.util.io.pem.PemWriter;

import java.io.StringWriter;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.Security;

public class Test {
    static {
        Security.removeProvider("BC");provider
        Security.insertProviderAt(new BouncyCastleProvider(), 1);
    }

    public static String createCurve25519PEM() {
        try {
            X9ECParameters curveParams = CustomNamedCurves.getByName("Curve25519");
            ECParameterSpec ecSpec = new ECParameterSpec(curveParams.getCurve(), curveParams.getG(), curveParams.getN(), curveParams.getH(), curveParams.getSeed());
            KeyPairGenerator kpg = KeyPairGenerator.getInstance("EC", new BouncyCastleProvider());
            kpg.initialize(ecSpec);
            KeyPair keypair = kpg.generateKeyPair();

            AsymmetricKeyParameter akp = PrivateKeyFactory.createKey(keypair.getPrivate().getEncoded());
            byte[] content = OpenSSHPrivateKeyUtil.encodePrivateKey(akp);
            PemObject o = new PemObject("OPENSSH PRIVATE KEY", content);
            StringWriter sw = new StringWriter();
            PemWriter w = new PemWriter(sw);
            w.writeObject(o);
            w.close();
            Log.d("createCurve25519PEM", "key: " + sw.toString());
            return sw.toString();
        } catch (Exception e) {
            Log.d("createCurve25519PEM", e.toString());
        }
        return null;
    }
}

output 看起来像这样：

-----BEGIN OPENSSH PRIVATE KEY-----
MIIBTwIBAQQgA8BjYjSjUgM4PahSZQx3i9DWcEdGiGnBoA0tXCUENzKggeEwgd4C
AQEwKwYHKoZIzj0BAQIgf////////////////////////////////////////+0w
RAQgKqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqmEkUoUQEIHtCXtCXtCXtCXtC
XtCXtCXtCXtCXtCXtCYLXpx3EMhkBEEEKqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq
qqqqqqqtJFogrhmhuKCGtOAe3Sx3SNFMkj1Nfm18YbIp6cWifs7T2QIgEAAAAAAA
AAAAAAAAAAAAABTe+d6i95zWWBJjGlz10+0CAQihRANCAARl0Kc+dO0Er1dpu6mh
/lZmTw3/DMKPLTzjosX2u7hQswV+U9o0WOYFd1JOqsGdkLfYuGmdZzWdk74dvV1O
+w5T
-----END OPENSSH PRIVATE KEY-----

..但不幸的是，SSH 不接受。

Answer 1

以这种方式使用“Curve25519”以 X9 使用的简短 Weierstrass形式提供给您； 这不适用于 Ed25519，它被定义为使用扭曲的爱德华形式。 此外，通过 JCA 不幸的ECParameterSpec class 将其填塞，给出了原始的 X9 定义的“显式”表示，该表示现在已经过时并且几乎从未用于使用Weierstrass 曲线的算法。 因此，您创建的数据对于 PEM 类型 OPENSSH PRIVATE KEY 不正确； 它对 OpenSSL 的“传统”PEM 类型 EC PRIVATE KEY 有效，并且OpenSSL （它仍然支持但不喜欢“param_enc 显式”）能够读取该类型的内容，尽管它不能用于互操作与其他任何东西。

您需要将 JCA 与算法“ED25519”（不是“EC”“ECDSA”“ECDH”“ECMQV”等都是 X9/SECG）一起使用，如下所示：

    KeyPair pair = KeyPairGenerator.getInstance("ED25519","BC") .generateKeyPair();
    AsymmetricKeyParameter bprv = PrivateKeyFactory.createKey(pair.getPrivate().getEncoded());
    // then proceed as you already have; I have simplified for my test environment
    byte[] oprv = OpenSSHPrivateKeyUtil.encodePrivateKey(bprv);
    PemWriter w = new PemWriter(new OutputStreamWriter(System.out));
    w.writeObject(new PemObject("OPENSSH PRIVATE KEY", oprv)); w.close();

    // BTW if you pass an actual Provider to .getInstance (rather than a String, or letting it search)
    // you don't actually need to have put that Provider in the searchlist
    // Also in Java 15 up you can use the SunEC provider (normally searched by default)
    // but since you still need other Bouncy pieces why bother

或者由于您已经依赖于 Bouncy，请使用轻量级 API：

    AsymmetricCipherKeyPairGenerator gen = new Ed25519KeyPairGenerator(); 
    gen.init(new KeyGenerationParameters(new SecureRandom(), 255));
    AsymmetricKeyParameter bprv = gen.generateKeyPair().getPrivate();
    // ditto