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+",");

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trueks.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);}