Error creating x.509 certificate

Question

I would like to create an x.509 certificate, so I copy the following codes from Wrox, Beging Cryptography with Java, chapter 6.

import java.io.OutputStreamWriter; import java.math.BigInteger; import java.security.KeyPair; import java.security.cert.X509Certificate; import java.util.Date; import java.util.Enumeration; import org.bouncycastle.asn1.ASN1Set; import org.bouncycastle.asn1.DERObjectIdentifier; import org.bouncycastle.asn1.pkcs.Attribute; import org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers; import org.bouncycastle.asn1.x509.BasicConstraints; import org.bouncycastle.asn1.x509.ExtendedKeyUsage; import org.bouncycastle.asn1.x509.KeyPurposeId; import org.bouncycastle.asn1.x509.KeyUsage; import org.bouncycastle.asn1.x509.X509Extension; import org.bouncycastle.asn1.x509.X509Extensions; import org.bouncycastle.jce.PKCS10CertificationRequest; import org.bouncycastle.openssl.PEMWriter; import org.bouncycastle.x509.X509V3CertificateGenerator; import org.bouncycastle.x509.extension.AuthorityKeyIdentifierStructure; import org.bouncycastle.x509.extension.SubjectKeyIdentifierStructure; import chapter6.PKCS10ExtensionExample; import chapter6.X509V1CreateExample; //example of a basic CA public class PKCS10CertCreateExample { public static X509Certificate[] buildChain() throws Exception { //create the certification request KeyPair pair = chapter7.Utils.generateRSAKeyPair(); PKCS10CertificationRequest request = PKCS10ExtensionExample.generateRequest(pair); //create a root certificate KeyPair rootPair=chapter7.Utils.generateRSAKeyPair(); X509Certificate rootCert = X509V1CreateExample.generateV1Certificate(rootPair); //validate the certification request if(!request.verify("BC")) { System.out.println("request failed to verify!"); System.exit(1); } //create the certificate using the information in the request X509V3CertificateGenerator certGen = new X509V3CertificateGenerator(); certGen.setSerialNumber(BigInteger.valueOf(System.currentTimeMillis())); certGen.setIssuerDN(rootCert.getSubjectX500Principal()); certGen.setNotBefore(new Date(System.currentTimeMillis())); certGen.setNotAfter(new Date(System.currentTimeMillis()+50000)); certGen.setSubjectDN(request.getCertificationRequestInfo().getSubject()); certGen.setPublicKey(request.getPublicKey("BC")); certGen.setSignatureAlgorithm("SHA256WithRSAEncryption"); certGen.addExtension(X509Extensions.AuthorityKeyIdentifier, false, new AuthorityKeyIdentifierStructure(rootCert)); certGen.addExtension(X509Extensions.SubjectKeyIdentifier, false, new SubjectKeyIdentifierStructure(request.getPublicKey("BC"))); certGen.addExtension(X509Extensions.BasicConstraints, true, new BasicConstraints(false)); certGen.addExtension(X509Extensions.KeyUsage, true, new BasicConstraints(false)); certGen.addExtension(X509Extensions.KeyUsage, true, new KeyUsage(KeyUsage.digitalSignature | KeyUsage.keyEncipherment)); certGen.addExtension(X509Extensions.ExtendedKeyUsage, true, new ExtendedKeyUsage(KeyPurposeId.id_kp_serverAuth)); //extract the extension request attribute ASN1Set attributes = request.getCertificationRequestInfo().getAttributes(); for(int i=0;i!=attributes.size();i++) { Attribute attr = Attribute.getInstance(attributes.getObjectAt(i)); //process extension request if(attr.getAttrType().equals(PKCSObjectIdentifiers.pkcs_9_at_extensionRequest)) { X509Extensions extensions = X509Extensions.getInstance(attr.getAttrValues().getObjectAt(0)); Enumeration<?> e = extensions.oids(); while(e.hasMoreElements()) { DERObjectIdentifier oid = (DERObjectIdentifier)e.nextElement(); X509Extension ext = extensions.getExtension(oid); certGen.addExtension(oid, ext.isCritical(), ext.getValue().getOctets()); } } } X509Certificate issuedCert = certGen.generateX509Certificate(rootPair.getPrivate()); return new X509Certificate[]{issuedCert, rootCert}; } public static void main(String[] args) throws Exception { X509Certificate[] chain = buildChain(); PEMWriter pemWrt = new PEMWriter(new OutputStreamWriter(System.out)); pemWrt.writeObject(chain[0]); pemWrt.writeObject(chain[1]); pemWrt.close(); } } 

However, the codes show errors as follows

Exception in thread "main" java.lang.IllegalArgumentException: extension 2.5.29.15 has already been added at org.bouncycastle.asn1.x509.X509ExtensionsGenerator.addExtension (Unknown source) at org.bouncycastle.asn1.x509.X509ExtensionsGenerator. UnknownExtension at org.bouncycastle.x509.X509V3CertificateGenerator.addExtension (Unknown source) in PKCS10CertCreateExample.buildChain (PKCS10CertCreateExample.java:68) in PKCS10CertCreateExample.main (PKCS10CertCreateExreate:reExEx..

please help me..

Answer 1

Googling extension 2.5.29.15 will tell you what is related to KeyUsage

The source code X509V3CertificateGenerator for X509V3CertificateGenerator shows that addExtension() calls X509ExtensionsGenerator.addExtension() , which throws an exception if the added extension is already added.

The source code you provided above does just that, and an exception is thrown:

 certGen.addExtension(X509Extensions.KeyUsage, true, new BasicConstraints(false)); certGen.addExtension(X509Extensions.KeyUsage, true, new KeyUsage(KeyUsage.digitalSignature | KeyUsage.keyEncipherment)); 

This is a bug in the code. You need to delete one of them. I would suggest that first.