JAVA对数字证书的常用操作

一：需要包含的包    

 import  java.security. * ;
     import  java.io. * ;
     import  java.util. * ;
     import  java.security. * ;
     import  java.security.cert. * ;
     import  sun.security.x509. * 
     import  java.security.cert.Certificate;
     import  java.security.cert.CertificateFactory; 
二：从文件中读取证书
    用keytool将.keystore中的证书写入文件中，然后从该文件中读取证书信息    

  CertificateFactory cf = CertificateFactory.getInstance( " X.509 " );
    FileInputStream in = new  FileInputStream( " out.csr " );
    Certificate c = cf.generateCertificate(in);

    String s = c.toString();

 
三：从密钥库中直接读取证书
    

 String pass = " 123456 " ;
    FileInputStream in = new  FileInputStream( " .keystore " );
    KeyStore ks = KeyStore.getInstance( " JKS " );
    ks.load(in,pass.toCharArray());
    java.security.cert.Certificate c = ks.getCertificate(alias); // alias为条目的别名
 
四：JAVA程序中显示证书指定信息
    

  System.out.println( " 输出证书信息:\n " + c.toString());
    System.out.println( " 版本号: " + t.getVersion());
    System.out.println( " 序列号: " + t.getSerialNumber().toString( 16 ));
    System.out.println( " 主体名： " + t.getSubjectDN());
    System.out.println( " 签发者： " + t.getIssuerDN());
    System.out.println( " 有效期： " + t.getNotBefore());
    System.out.println( " 签名算法： " + t.getSigAlgName());
     byte  [] sig = t.getSignature(); // 签名值  
     PublicKey pk = t.getPublicKey();
     byte  [] pkenc = pk.getEncoded();  
    System.out.println( " 公钥 " );
     for ( int  i = 0 ;i < pkenc.length;i ++ )System.out.print(pkenc[i] + " , " );
 
五：JAVA程序列出密钥库所有条目
    

 String pass = " 123456 " ;
    FileInputStream in = new  FileInputStream( " .keystore " );
    KeyStore ks = KeyStore.getInstance( " JKS " );
    ks.load(in,pass.toCharArray());
    Enumeration e = ks.aliases();
     while (e.hasMoreElements())
    java.security.cert.Certificate c = ks.getCertificate((String)e.nextElement());
 
六：JAVA程序修改密钥库口令
    

 String oldpass = " 123456 " ;
    String newpass = " 654321 " ;
    FileInputStream in = new  FileInputStream( " .keystore " );
    KeyStore ks = KeyStore.getInstance( " JKS " );
    ks.load(in,oldpass.toCharArray());
    in.close();
    FileOutputStream output = new  FileOutputStream( " .keystore " );
    ks.store(output,newpass.toCharArray());
    output.close();
 
七：JAVA程序修改密钥库条目的口令及添加条目     

 FileInputStream in = new  FileInputStream( " .keystore " );
    KeyStore ks = KeyStore.getInstance( " JKS " );
    ks.load(in,storepass.toCharArray());
    Certificate [] cchain = ks.getCertificate(alias);获取别名对应条目的证书链
    PrivateKey pk = (PrivateKey)ks.getKey(alias,oldkeypass.toCharArray());获取别名对应条目的私钥
    ks.setKeyEntry(alias,pk,newkeypass.toCharArray(),cchain);向密钥库中添加条目
 
    第一个参数指定所添加条目的别名，假如使用已存在别名将覆盖已存在条目，使用新别名将增加一个新条目，第二个参数为条目的私钥，第三个为设置的新口令，第四个为该私钥的公钥的证书链
    FileOutputStream output=new FileOutputStream("another");
    ks.store(output,storepass.toCharArray())将keystore对象内容写入新文件

八：JAVA程序检验别名和删除条目
    

  FileInputStream in = new  FileInputStream( " .keystore " );
    KeyStore ks = KeyStore.getInstance( " JKS " );
    ks.load(in,storepass.toCharArray());
    ks.containsAlias( " sage " );检验条目是否在密钥库中，存在返回true
    ks.deleteEntry( " sage " );删除别名对应的条目
    FileOutputStream output = new  FileOutputStream( " .keystore " );
    ks.store(output,storepass.toCharArray())将keystore对象内容写入文件,条目删除成功
 
九：JAVA程序签发数字证书
   （1）从密钥库中读取CA的证书       

  FileInputStream in = new  FileInputStream( " .keystore " );
    KeyStore ks = KeyStore.getInstance( " JKS " );
    ks.load(in,storepass.toCharArray());
    java.security.cert.Certificate c1 = ks.getCertificate( " caroot " );
 
（2）从密钥库中读取CA的私钥
    

 PrivateKey caprk = (PrivateKey)ks.getKey(alias,cakeypass.toCharArray());
 
 （3）从CA的证书中提取签发者的信息   

   byte [] encod1 = c1.getEncoded();    提取CA证书的编码
    X509CertImpl cimp1 = new  X509CertImpl(encod1);  用该编码创建X509CertImpl类型对象
    X509CertInfo cinfo1 = (X509CertInfo)cimp1.get(X509CertImpl.NAME + " . " + X509CertImpl.INFO);  获取X509CertInfo对象
    X500Name issuer = (X500Name)cinfo1.get(X509CertInfo.SUBJECT + " . " + CertificateIssuerName.DN_NAME); 获取X509Name类型的签发者信息
 
    （4）获取待签发的证书
   

  CertificateFactory cf = CertificateFactory.getInstance( " X.509 " );
    FileInputStream in2 = new  FileInputStream( " user.csr " );
    java.security.cert.Certificate c2 = cf.generateCertificate(in);
 
    （5）从待签发的证书中提取证书信息
  

    byte  [] encod2 = c2.getEncoded();
    X509CertImpl cimp2 = new  X509CertImpl(encod2);  用该编码创建X509CertImpl类型对象
    X509CertInfo cinfo2 = (X509CertInfo)cimp2.get(X509CertImpl.NAME + " . " + X509CertImpl.INFO);  获取X509CertInfo对象 

    （6）设置新证书有效期
   

  Date begindate = new  Date(); 获取当前时间
    Date enddate = new  Date(begindate.getTime() + 3000 * 24 * 60 * 60 * 1000L ); 有效期为3000天
    CertificateValidity cv = new  CertificateValidity(begindate,enddate); 创建对象
    cinfo2.set(X509CertInfo.VALIDITY,cv);  设置有效期
 
    （7）设置新证书序列号
  

    int  sn = ( int )(begindate.getTime() / 1000 );    以当前时间为序列号
    CertificateSerialNumber csn = new  CertificateSerialNumber(sn);
    cinfo2.set(X509CertInfo.SERIAL_NUMBER,csn);
 
    （8）设置新证书签发者
    cinfo2.set(X509CertInfo.ISSUER+"."+CertificateIssuerName.DN_NAME,issuer);应用第三步的结果
    （9）设置新证书签名算法信息
    AlgorithmId algorithm=new AlgorithmId(AlgorithmId.md5WithRSAEncryption_oid);
    cinfo2.set(CertificateAlgorithmId.NAME+"."+CertificateAlgorithmId.ALGORITHM,algorithm);
    （10）创建证书并使用CA的私钥对其签名
    X509CertImpl newcert=new X509CertImpl(cinfo2);
    newcert.sign(caprk,"MD5WithRSA"); 使用CA私钥对其签名
    （11）将新证书写入密钥库 

    ks.setCertificateEntry( " lf_signed " ,newcert);
    FileOutputStream out = new  FileOutputStream( " newstore " );
    ks.store(out, " newpass " .toCharArray());  这里是写入了新的密钥库，也可以使用第七条来增加条目
 
十：数字证书的检验
    （1）验证证书的有效期
 （a）获取X509Certificate类型对象
  

 CertificateFactory cf = CertificateFactory.getInstance( " X.509 " );
    FileInputStream in1 = new  FileInputStream( " aa.crt " );
  java.security.cert.Certificate  c1 = cf.generateCertificate(in1);
 X509Certificate t = (X509Certificate)c1;
  in2.close();
 
        （b）获取日期
 Date TimeNow=new Date();
 （c）检验有效性
 

  try  {
    t.checkValidity(TimeNow);
           System.out.println( " OK " );
 } catch (CertificateExpiredException e)  {   // 过期 
     System.out.println( " Expired " );
    System.out.println(e.getMessage());
 } catch ((CertificateNotYetValidException e)  {  // 尚未生效 
     System.out.println( " Too early " );
    System.out.println(e.getMessage());} 
 
     （2）验证证书签名的有效性
 （a）获取CA证书
       

   CertificateFactory cf = CertificateFactory.getInstance( " X.509 " );
     FileInputStream in2 = new  FileInputStream( " caroot.crt " );
   java.security.cert.Certificate  cac = cf.generateCertificate(in2);
  in2.close();
 
 （c）获取CA的公钥
  PublicKey pbk=cac.getPublicKey();
 （b）获取待检验的证书（上步已经获取了，就是C1）
 （c）检验证书
        

   boolean  pass = false ;
          try  {
      c1.verify(pbk);
             pass = true ;
         } catch (Exception e)  {
             pass = false ;
             System.out.println(e);
  }