FileInputStream in=new FileInputStream(".keystore");
KeyStore ks=KeyStore.getInstance("JKS");
ks.load(in,storepass.toCharArray());
java.security.cert.Certificate c1=ks.getCertificate("caroot");
（2）從密鑰庫中讀取CA的私鑰
PrivateKey caprk=(PrivateKey)ks.getKey(alias,cakeypass.toCharArray());
（3）從CA的證書中提取簽發者的信息
byte[] encod1=c1.getEncoded(); 提取CA證書的編碼
X509CertImpl cimp1=new X509CertImpl(encod1); 用該編碼創建X509CertImpl類型對象
X509CertInfo cinfo1=(X509CertInfo)cimp1.get(X509CertImpl.NAME+"."+X509CertImpl.INFO); 獲取X509CertInfo對象
X500Name issuer=(X500Name)cinfo1.get(X509CertInfo.SUBJECT+"."+CertificateIssuerName.DN_NAME); 獲取X509Name類型的簽發者信息
（4）獲取待簽發的證書
CertificateFactory cf=CertificateFactory.getInstance("X.509");
FileInputStream in2=new FileInputStream("user.csr");
java.security.cert.Certificate c2=cf.generateCertificate(in);
（5）從待簽發的證書中提取證書信息
byte [] encod2=c2.getEncoded();
X509CertImpl cimp2=new X509CertImpl(encod2); 用該編碼創建X509CertImpl類型對象
X509CertInfo cinfo2=(X509CertInfo)cimp2.get(X509CertImpl.NAME+"."+X509CertImpl.INFO); 獲取X509CertInfo對象
（6）設置新證書有效期
Date begindate=new Date(); 獲取當前時間
Date enddate=new Date(begindate.getTime()+3000*24*60*60*1000L); 有效期為3000天
CertificateValidity cv=new CertificateValidity(begindate,enddate); 創建對象
cinfo2.set(X509CertInfo.VALIDITY,cv); 設置有效期
（7）設置新證書序列號
int sn=(int)(begindate.getTime()/1000); 以當前時間為序列號
CertificateSerialNumber csn=new CertificateSerialNumber(sn);
cinfo2.set(X509CertInfo.SERIAL_NUMBER,csn);
（8）設置新證書簽發者
cinfo2.set(X509CertInfo.ISSUER+"."+CertificateIssuerName.DN_NAME,issuer);應用第三步的結果
（9）設置新證書簽名算法信息
AlgorithmId algorithm=new AlgorithmId(AlgorithmId.md5WithRSAEncryption_oid);
cinfo2.set(CertificateAlgorithmId.NAME+"."+CertificateAlgorithmId.ALGORITHM,algorithm);
（10）創建證書並使用CA的私鑰對其簽名
X509CertImpl newcert=new X509CertImpl(cinfo2);
newcert.sign(caprk,"MD5WithRSA"); 使用CA私鑰對其簽名
（11）將新證書寫入密鑰庫
ks.setCertificateEntry("lf_signed",newcert);
FileOutputStream out=new FileOutputStream("newstore");
ks.store(out,"newpass".toCharArray()); 這裏是寫入了新的密鑰庫，也可以使用第七條來增加條目