如何在 Java 中存储和重用密钥对？

Question

我想生成一个密钥对并重新使用它。

public static KeyPair generateKeyPair() throws Exception {
        KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
        generator.initialize(2048, new SecureRandom());
        KeyPair pair = generator.generateKeyPair();

        return pair;
}

我该怎么做？

Answer 1

这里有点问题：Java的重点几乎完全放在 TLS 和实现 TLS 所需的密码学上。对于 TLS，需要私钥和证书。所以你会遇到这样的情况：

必须生成一个（伪造的）自签名证书以与您的 public 密钥一起使用或；
必须找到另一种方法来存储没有证书的私钥。

但是，对于 (2.)，您很快就会得到一种不太兼容的方法。如果您想这样做，您可以创建一个使用 PBE / CBC 加密的 PKCS#8 加密私钥。

所以这里有一些代码可以创建自签名证书并使用它来存储密钥。请注意到期日期，为了安全起见，您可以将其设置为 100 年（或者您实际上可以进行一些密钥管理）。

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.math.BigInteger;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.KeyStore;
import java.security.KeyStore.Entry;
import java.security.KeyStore.PrivateKeyEntry;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.Provider;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Security;
import java.security.UnrecoverableEntryException;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.util.Calendar;
import java.util.Date;

import org.bouncycastle.asn1.x500.X500Name;
import org.bouncycastle.asn1.x509.SubjectPublicKeyInfo;
import org.bouncycastle.cert.X509CertificateHolder;
import org.bouncycastle.cert.X509v3CertificateBuilder;
import org.bouncycastle.cert.jcajce.JcaX509CertificateConverter;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.operator.ContentSigner;
import org.bouncycastle.operator.OperatorCreationException;
import org.bouncycastle.operator.jcajce.JcaContentSignerBuilder;

public class StoreKeyPair {
    public static KeyPair generateKeyPair() throws Exception {
        KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
        generator.initialize(2048, new SecureRandom());
        KeyPair pair = generator.generateKeyPair();

        return pair;
    }

    public static Certificate selfSign(KeyPair keyPair, String subjectDN)
            throws OperatorCreationException, CertificateException, IOException
    {
        Provider bcProvider = new BouncyCastleProvider();
        Security.addProvider(bcProvider);

        long now = System.currentTimeMillis();
        Date startDate = new Date(now);

        X500Name dnName = new X500Name(subjectDN);

        // Using the current timestamp as the certificate serial number
        BigInteger certSerialNumber = new BigInteger(Long.toString(now));

        Calendar calendar = Calendar.getInstance();
        calendar.setTime(startDate);
        // 1 Yr validity
        calendar.add(Calendar.YEAR, 1);

        Date endDate = calendar.getTime();

        // Use appropriate signature algorithm based on your keyPair algorithm.
        String signatureAlgorithm = "SHA256WithRSA";

        SubjectPublicKeyInfo subjectPublicKeyInfo = SubjectPublicKeyInfo.getInstance(keyPair
                .getPublic().getEncoded());

        X509v3CertificateBuilder certificateBuilder = new X509v3CertificateBuilder(dnName,
                certSerialNumber, startDate, endDate, dnName, subjectPublicKeyInfo);

        ContentSigner contentSigner = new JcaContentSignerBuilder(signatureAlgorithm).setProvider(
                bcProvider).build(keyPair.getPrivate());

        X509CertificateHolder certificateHolder = certificateBuilder.build(contentSigner);

        Certificate selfSignedCert = new JcaX509CertificateConverter()
                .getCertificate(certificateHolder);

        return selfSignedCert;
    }

    public static void main(String[] args) throws Exception {
        KeyPair generatedKeyPair = generateKeyPair();

        String filename = "test_gen_self_signed.pkcs12";
        char[] password = "test".toCharArray();

        storeToPKCS12(filename, password, generatedKeyPair);

        KeyPair retrievedKeyPair = loadFromPKCS12(filename, password);

        // you can validate by generating a signature and verifying it or by
        // comparing the moduli by first casting to RSAPublicKey, e.g.:

        RSAPublicKey pubKey = (RSAPublicKey) generatedKeyPair.getPublic();
        RSAPrivateKey privKey = (RSAPrivateKey) retrievedKeyPair.getPrivate();
        System.out.println(pubKey.getModulus().equals(privKey.getModulus()));
    }

    private static KeyPair loadFromPKCS12(String filename, char[] password)
            throws KeyStoreException, NoSuchAlgorithmException, CertificateException,
            FileNotFoundException, IOException, UnrecoverableEntryException {
        KeyStore pkcs12KeyStore = KeyStore.getInstance("PKCS12");

        try (FileInputStream fis = new FileInputStream(filename);) {
            pkcs12KeyStore.load(fis, password);
        }

        KeyStore.ProtectionParameter param = new KeyStore.PasswordProtection(password);
        Entry entry = pkcs12KeyStore.getEntry("owlstead", param);
        if (!(entry instanceof PrivateKeyEntry)) {
            throw new KeyStoreException("That's not a private key!");
        }
        PrivateKeyEntry privKeyEntry = (PrivateKeyEntry) entry;
        PublicKey publicKey = privKeyEntry.getCertificate().getPublicKey();
        PrivateKey privateKey = privKeyEntry.getPrivateKey();
        return new KeyPair(publicKey, privateKey);
    }

    private static void storeToPKCS12(
            String filename, char[] password,
            KeyPair generatedKeyPair) throws KeyStoreException, IOException,
            NoSuchAlgorithmException, CertificateException, FileNotFoundException,
            OperatorCreationException {

        Certificate selfSignedCertificate = selfSign(generatedKeyPair, "CN=owlstead");

        KeyStore pkcs12KeyStore = KeyStore.getInstance("PKCS12");
        pkcs12KeyStore.load(null, null);

        KeyStore.Entry entry = new PrivateKeyEntry(generatedKeyPair.getPrivate(),
                new Certificate[] { selfSignedCertificate });
        KeyStore.ProtectionParameter param = new KeyStore.PasswordProtection(password);

        pkcs12KeyStore.setEntry("owlstead", entry, param);

        try (FileOutputStream fos = new FileOutputStream(filename)) {
            pkcs12KeyStore.store(fos, password);
        }
    }
}

请注意，我懒得正确处理异常。

此代码使用 this answer 的略微改动版本，请参阅我的评论以了解我更改代码的原因。

public 密钥当然也可以单独存储。只需调用 getEncoded 并存储生成的 SubjectPublicKeyInfo 结构。

如何在 Java 中存储和重用密钥对？

How to store and reuse keypair in Java?

java

cryptography

keystore