Java Tutorial/Security/CertificateFactory

Creating a Certification Path

import java.io.FileInputStream;
import java.security.KeyStore;
import java.security.cert.CertPath;
import java.security.cert.Certificate;
import java.security.cert.CertificateFactory;
import java.util.Arrays;
public class Main {
  public static void main(String[] argv) throws Exception {
    FileInputStream is = new FileInputStream("your.keystore");
    KeyStore keystore = KeyStore.getInstance(KeyStore.getDefaultType());
    keystore.load(is, "my-keystore-password".toCharArray());
    String alias = "myalias";
    Certificate cert = keystore.getCertificate(alias);
    CertificateFactory certFact = CertificateFactory.getInstance("X.509");
    CertPath path = certFact.generateCertPath(Arrays.asList(new Certificate[]{cert}));
  }
}

Importing a Certificate from a File

import java.io.File;
import java.io.FileInputStream;
import java.security.cert.CertificateFactory;
public class Main {
  public static void main(String[] argv) throws Exception {
    FileInputStream is = new FileInputStream(new File("your"));
    CertificateFactory cf = CertificateFactory.getInstance("X.509");
    java.security.cert.Certificate cert = cf.generateCertificate(is);
  }
}

reading multiple certificates with a CertificateFactory.

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.math.BigInteger;
import java.security.InvalidKeyException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;
import java.security.Security;
import java.security.SignatureException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import java.util.Iterator;
import javax.security.auth.x500.X500Principal;
import org.bouncycastle.x509.X509V1CertificateGenerator;
public class MainClass {
  public static void main(String[] args) throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    KeyPair pair = generateRSAKeyPair();
    ByteArrayOutputStream bOut = new ByteArrayOutputStream();
    bOut.write(generateV1Certificate(pair).getEncoded());
    bOut.close();
    InputStream in = new ByteArrayInputStream(bOut.toByteArray());
    CertificateFactory fact = CertificateFactory.getInstance("X.509", "BC");
    X509Certificate x509Cert;
    Collection collection = new ArrayList();
    while ((x509Cert = (X509Certificate) fact.generateCertificate(in)) != null) {
      collection.add(x509Cert);
    }
    Iterator it = collection.iterator();
    while (it.hasNext()) {
      System.out.println("version: " + ((X509Certificate) it.next()).getVersion());
    }
  }
  public static X509Certificate generateV1Certificate(KeyPair pair) throws InvalidKeyException,
      NoSuchProviderException, SignatureException {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    X509V1CertificateGenerator certGen = new X509V1CertificateGenerator();
    certGen.setSerialNumber(BigInteger.valueOf(System.currentTimeMillis()));
    certGen.setIssuerDN(new X500Principal("CN=Test Certificate"));
    certGen.setNotBefore(new Date(System.currentTimeMillis() - 10000));
    certGen.setNotAfter(new Date(System.currentTimeMillis() + 10000));
    certGen.setSubjectDN(new X500Principal("CN=Test Certificate"));
    certGen.setPublicKey(pair.getPublic());
    certGen.setSignatureAlgorithm("SHA256WithRSAEncryption");
    return certGen.generateX509Certificate(pair.getPrivate(), "BC");
  }
  public static KeyPair generateRSAKeyPair() throws Exception {
    KeyPairGenerator kpGen = KeyPairGenerator.getInstance("RSA", "BC");
    kpGen.initialize(1024, new SecureRandom());
    return kpGen.generateKeyPair();
  }
}

Using the CertificateFactory Class

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.math.BigInteger;
import java.security.InvalidKeyException;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;
import java.security.Security;
import java.security.SignatureException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.Date;
import javax.security.auth.x500.X500Principal;
import org.bouncycastle.x509.X509V1CertificateGenerator;
public class MainClass {
  public static void main(String[] args) throws Exception {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    KeyPair pair = generateRSAKeyPair();
    ByteArrayOutputStream bOut = new ByteArrayOutputStream();
    bOut.write(generateV1Certificate(pair).getEncoded());
    bOut.close();
    InputStream in = new ByteArrayInputStream(bOut.toByteArray());
    CertificateFactory fact = CertificateFactory.getInstance("X.509", "BC");
    X509Certificate x509Cert = (X509Certificate) fact.generateCertificate(in);
    System.out.println("issuer: " + x509Cert.getIssuerX500Principal());
  }
  public static X509Certificate generateV1Certificate(KeyPair pair) throws InvalidKeyException,
      NoSuchProviderException, SignatureException {
    Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    X509V1CertificateGenerator certGen = new X509V1CertificateGenerator();
    certGen.setSerialNumber(BigInteger.valueOf(System.currentTimeMillis()));
    certGen.setIssuerDN(new X500Principal("CN=Test Certificate"));
    certGen.setNotBefore(new Date(System.currentTimeMillis() - 10000));
    certGen.setNotAfter(new Date(System.currentTimeMillis() + 10000));
    certGen.setSubjectDN(new X500Principal("CN=Test Certificate"));
    certGen.setPublicKey(pair.getPublic());
    certGen.setSignatureAlgorithm("SHA256WithRSAEncryption");
    return certGen.generateX509Certificate(pair.getPrivate(), "BC");
  }
  public static KeyPair generateRSAKeyPair() throws Exception {
    KeyPairGenerator kpGen = KeyPairGenerator.getInstance("RSA", "BC");
    kpGen.initialize(1024, new SecureRandom());
    return kpGen.generateKeyPair();
  }
}