从私钥导出ECDSA公钥

Question

我试图从私钥中生成一个公共ECDSA密钥，但我还没有在互联网上找到多少关于如何实现这一点的帮助。几乎所有的事情都是为了从公钥规范生成公钥，我不知道如何得到它。到目前为止，我总结了以下内容：

public void setPublic() throws GeneralSecurityException {
    ECNamedCurveParameterSpec params = ECNamedCurveTable.getParameterSpec("secp256k1");
    KeyFactory fact = KeyFactory.getInstance("ECDSA", "BC");
    ECCurve curve = params.getCurve();
    java.security.spec.EllipticCurve ellipticCurve = EC5Util.convertCurve(curve, params.getSeed());
    java.security.spec.ECPoint point = ECPointUtil.decodePoint(ellipticCurve, this.privateKey.getEncoded());
    java.security.spec.ECParameterSpec params2=EC5Util.convertSpec(ellipticCurve, params);
    java.security.spec.ECPublicKeySpec keySpec = new java.security.spec.ECPublicKeySpec(point,params2);
    this.publicKey = fact.generatePublic(keySpec);
}

但是，在运行时，我会出现以下错误：

Exception in thread "main" java.lang.IllegalArgumentException: Invalid point encoding 0x30
at org.bouncycastle.math.ec.ECCurve.decodePoint(Unknown Source)
at org.bouncycastle.jce.ECPointUtil.decodePoint(Unknown Source)
at Wallet.Wallet.setPublic(Wallet.java:125)

我做错了什么？有更好/更简单的方法吗？

编辑：我已经设法编译了一些代码，但它不能正常工作：

public void setPublic() throws GeneralSecurityException {
    BigInteger privKey = new BigInteger(getHex(privateKey.getEncoded()),16);
    X9ECParameters ecp = SECNamedCurves.getByName("secp256k1");
    ECPoint curvePt = ecp.getG().multiply(privKey);
    BigInteger x = curvePt.getX().toBigInteger();
    BigInteger y = curvePt.getY().toBigInteger();
    byte[] xBytes = removeSignByte(x.toByteArray());
    byte[] yBytes = removeSignByte(y.toByteArray());
    byte[] pubKeyBytes = new byte[65];
    pubKeyBytes[0] = new Byte("04");
    System.arraycopy(xBytes, 0, pubKeyBytes, 1, xBytes.length);
    System.arraycopy(yBytes, 0, pubKeyBytes, 33, xBytes.length);




    ECNamedCurveParameterSpec params = ECNamedCurveTable.getParameterSpec("secp256k1");
    KeyFactory fact = KeyFactory.getInstance("ECDSA", "BC");
    ECCurve curve = params.getCurve();
    java.security.spec.EllipticCurve ellipticCurve = EC5Util.convertCurve(curve, params.getSeed());
    java.security.spec.ECPoint point = ECPointUtil.decodePoint(ellipticCurve, pubKeyBytes);
    java.security.spec.ECParameterSpec params2 = EC5Util.convertSpec(ellipticCurve, params);
    java.security.spec.ECPublicKeySpec keySpec = new java.security.spec.ECPublicKeySpec(point,params2);
    this.publicKey = fact.generatePublic(keySpec);
}

private byte[] removeSignByte(byte[] arr)
{
    if(arr.length==33)
    {
        byte[] newArr = new byte[32];
        System.arraycopy(arr, 1, newArr, 0, newArr.length);
        return newArr;
    }
    return arr;
}

当我运行它时，它会生成一个公钥，但它不是私钥对应的公钥。

Answer 1

我在静态编程语言中遇到了同样的问题，所以，如果它对任何人有帮助，下面是我如何从静态编程语言中的ECDSA私人密钥中导出PublicKey。这段代码基于列夫·诺布洛克的Java答案，然后反复试验直到成功。

在我的例子中，我知道我的密钥使用了secp256k1曲线，所以我可以对这部分进行硬编码。我没有费心学习如何将其推广到其他曲线。

import java.security.KeyFactory
import java.security.KeyPair
import java.security.PrivateKey
import java.security.PublicKey
import org.bouncycastle.asn1.pkcs.PrivateKeyInfo
import org.bouncycastle.jce.ECNamedCurveTable
import org.bouncycastle.jce.interfaces.ECPrivateKey
import org.bouncycastle.jce.spec.ECNamedCurveParameterSpec
import org.bouncycastle.jce.spec.ECPublicKeySpec
import org.bouncycastle.math.ec.ECPoint
import org.bouncycastle.openssl.jcajce.JcaPEMKeyConverter
import org.bouncycastle.openssl.PEMParser

fun getECPrivateKeyFromPEM(privatePem: String): ECPrivateKey {
    val pemParser = PEMParser(privatePem.reader())
    val privateKeyInfo = pemParser.readObject() as PrivateKeyInfo
    return JcaPEMKeyConverter().getPrivateKey(privateKeyInfo) as ECPrivateKey
}

fun getKeyPairFromECPrivateKey(privateKey: ECPrivateKey): KeyPair {
    val keyFactory: KeyFactory = KeyFactory.getInstance("ECDSA", "BC")
    val spec: ECNamedCurveParameterSpec = ECNamedCurveTable.getParameterSpec("secp256k1")
    val Q: ECPoint = spec.getG().multiply(privateKey.getD())
    val publicKey: PublicKey = keyFactory.generatePublic(ECPublicKeySpec(Q, spec))
    return KeyPair(publicKey, privateKey)
}

这是我的测试背带：

import java.io.StringWriter
import org.bouncycastle.openssl.jcajce.JcaPEMWriter

fun main() {
    val privatePem = """
       |-----BEGIN PRIVATE KEY-----
       |MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg55EMdhNJX+YN/bjN
       |Eof91oKqEqD0QidEsRMhHBwSRjShRANCAARnSFpE0LDugORBWlSJz0Zf9e0mR9s6
       |tlxSeo1Nbd2vv9LDedm+l/CfZpbyYvPm49DAKDhkUHFIVDd2SsiPrRa7
       |-----END PRIVATE KEY-----
    """.trimMargin()
    val privateKey: ECPrivateKey = getECPrivateKeyFromPEM(privatePem)
    val pair: KeyPair = getKeyPairFromECPrivateKey(privateKey)
    val pems: String = StringWriter().use {
        val pemWriter = JcaPEMWriter(it)
        pemWriter.writeObject(pair.getPublic())
        pemWriter.writeObject(pair.getPrivate())
        pemWriter.flush()
        it.toString()
    }
    println(pems)
}

这个打印出来：

-----BEGIN PUBLIC KEY-----
MFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEcE4HMAHLDvPr6xHKsjhPXJzTdxLlRRR8
BfYnI2TGb0QLTFyyXm13CeYiLnxbkGhSvz9ZRo0zGQygKPVpgiThSw==
-----END PUBLIC KEY-----
-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIOeRDHYTSV/mDf24zRKH/daCqhKg9EInRLETIRwcEkY0oAoGCCqGSM49
AwEHoUQDQgAEZ0haRNCw7oDkQVpUic9GX/XtJkfbOrZcUnqNTW3dr7/Sw3nZvpfw
n2aW8mLz5uPQwCg4ZFBxSFQ3dkrIj60Wuw==
-----END EC PRIVATE KEY-----

Answer 2

在前面的答案的基础上，我们可以将其扩展到以下情况，即所有给定的都是满足BCECPrivateKey接口的私钥：

DerivePubKeyFromPrivKey(BCECPrivateKey definingKey, Provider provider) {

    KeyFactory keyFactory = KeyFactory.getInstance("EC", provider);

    BigInteger d = definingKey.getD();
    org.bouncycastle.jce.spec.ECParameterSpec ecSpec = 
    definingKey.getParameters();
    ECPoint Q = definingKey.getParameters().getG().multiply(d);

    org.bouncycastle.jce.spec.ECPublicKeySpec pubSpec = new 
    org.bouncycastle.jce.spec.ECPublicKeySpec(Q, ecSpec);
    PublicKey publicKeyGenerated = keyFactory.generatePublic(pubSpec);
    return publicKeyGenerated;
}

Answer 3

因此，过了一段时间，我想出了一个解决方案，并决定发布它，以防其他人与我有相同的问题：

KeyFactory keyFactory = KeyFactory.getInstance("ECDSA", "BC");
    ECParameterSpec ecSpec = ECNamedCurveTable.getParameterSpec("secp256k1");

    ECPoint Q = ecSpec.getG().multiply(((org.bouncycastle.jce.interfaces.ECPrivateKey) this.privateKey).getD());

    ECPublicKeySpec pubSpec = new ECPublicKeySpec(Q, ecSpec);
    PublicKey publicKeyGenerated = keyFactory.generatePublic(pubSpec);
    this.publicKey = publicKeyGenerated;

编辑：根据@MaartenBodewes注释删除了解码ECPoint的代码。