使用java代码实现自签rsa根证书，并使用根证书签发加密证书

可以使用Java的KeyPairGenerator和Certificate类来实现自签RSA根证书的生成和使用根证书签发加密证书的过程。以下是一个简单的示例代码：

import java.security.*;
import java.security.cert.*;
import java.util.Date;

public class CertGenerator {
    public static void main(String[] args) throws Exception {
        // 生成RSA密钥对
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();

        // 生成自签根证书
        X509Certificate rootCert = generateRootCert(keyPair);

        // 生成加密证书
        X509Certificate encCert = generateEncCert(keyPair.getPrivate(), rootCert);

        // 输出证书信息
        System.out.println("Root certificate:");
        System.out.println(rootCert);
        System.out.println("Encrypted certificate:");
        System.out.println(encCert);
    }

    private static X509Certificate generateRootCert(KeyPair keyPair) throws Exception {
        // 构造证书请求
        X509CertInfo certInfo = new X509CertInfo();
        certInfo.set(X509CertInfo.VERSION, new CertificateVersion(CertificateVersion.V3));
        certInfo.set(X509CertInfo.SERIAL_NUMBER, new CertificateSerialNumber(new java.util.Random().nextInt() & 0x7fffffff));
        certInfo.set(X509CertInfo.SUBJECT, new X500Name("CN=Root"));
        certInfo.set(X509CertInfo.ISSUER, new X500Name("CN=Root"));
        certInfo.set(X509CertInfo.KEY, new CertificateX509Key(keyPair.getPublic()));
        certInfo.set(X509CertInfo.VALIDITY, new CertificateValidity(new Date(), new Date(System.currentTimeMillis() + 365L * 24L * 60L * 60L * 1000L)));
        certInfo.set(X509CertInfo.ALGORITHM_ID, new CertificateAlgorithmId(new AlgorithmId(AlgorithmId.sha256WithRSAEncryption_oid)));

        // 签名证书请求
        X509CertImpl cert = new X509CertImpl(certInfo);
        cert.sign(keyPair.getPrivate(), "SHA256withRSA");

        return cert;
    }

    private static X509Certificate generateEncCert(PrivateKey privateKey, X509Certificate rootCert) throws Exception {
        // 构造证书请求
        X509CertInfo certInfo = new X509CertInfo();
        certInfo.set(X509CertInfo.VERSION, new CertificateVersion(CertificateVersion.V3));
        certInfo.set(X509CertInfo.SERIAL_NUMBER, new CertificateSerialNumber(new java.util.Random().nextInt() & 0x7fffffff));
        certInfo.set(X509CertInfo.SUBJECT, new X500Name("CN=Encrypted"));
        certInfo.set(X509CertInfo.ISSUER, rootCert.getSubjectDN());
        certInfo.set(X509CertInfo.KEY, new CertificateX509Key(rootCert.getPublicKey()));
        certInfo.set(X509CertInfo.VALIDITY, new CertificateValidity(new Date(), new Date(System.currentTimeMillis() + 365L * 24L * 60L * 60L * 1000L)));
        certInfo.set(X509CertInfo.ALGORITHM_ID, new CertificateAlgorithmId(new AlgorithmId(AlgorithmId.sha256WithRSAEncryption_oid)));

        // 签名证书请求
        X509CertImpl cert = new X509CertImpl(certInfo);
        cert.sign(privateKey, "SHA256withRSA");

        return cert;
    }
}

这段代码会生成一个2048位的RSA密钥对，然后使用该密钥对生成一个自签的根证书和一个使用根证书签发的加密证书。其中，generateRootCert方法用于生成自签根证书，generateEncCert方法用于生成加密证书。注意，这里使用的是SHA256withRSA算法进行签名。