Question

I cannot find any code/doc describing how to sign a CSR using BC. As input I have a CSR as a byte array and would like to get the cert in PEM and/or DER format.

I have gotten this far

def signCSR(csrData:Array[Byte], ca:CACertificate, caPassword:String) = {
  val csr = new PKCS10CertificationRequestHolder(csrData)
  val spi = csr.getSubjectPublicKeyInfo

  val ks = new java.security.spec.X509EncodedKeySpec(spi.getDEREncoded())
  val kf = java.security.KeyFactory.getInstance("RSA")
  val pk = kf.generatePublic(ks)

  val (caCert, caPriv) = parsePKCS12(ca.pkcs12data, caPassword)

  val fromDate : java.util.Date = new java.util.Date // FixMe
  val toDate = fromDate // FixMe
  val issuer = PrincipalUtil.getIssuerX509Principal(caCert)
  val contentSigner = new JcaContentSignerBuilder("SHA256WithRSAEncryption").setProvider(BC).build(caPriv)
  val serial = BigInt(CertSerialnumber.nextSerialNumber)
  val certgen = new JcaX509v3CertificateBuilder(new X500Name(issuer.getName), serial.bigInteger, fromDate, toDate, csr.getSubject, pk)

I have trouble figuring out get from a certificate generator to store this in PEM or DER format.

Or am I going down the wrong path all together?

Answer 1

Ok … I was looking to do the same stuff and for the life of me I couldn’t figure out how. The APIs all talk about generating the key pairs and then generating the cert but not how to sign a CSR. Somehow, quite by chance – here’s what I found.

Since PKCS10 represents the format of the request (of the CSR), you first need to put your CSR into a PKCS10Holder. Then, you pass it to a CertificateBuilder (since CertificateGenerator is deprecated). The way you pass it is to call getSubject on the holder.

Here’s the code (Java, please adapt as you need):

public static X509Certificate sign(PKCS10CertificationRequest inputCSR, PrivateKey caPrivate, KeyPair pair)
        throws InvalidKeyException, NoSuchAlgorithmException,
        NoSuchProviderException, SignatureException, IOException,
        OperatorCreationException, CertificateException {   

    AlgorithmIdentifier sigAlgId = new DefaultSignatureAlgorithmIdentifierFinder()
            .find("SHA1withRSA");
    AlgorithmIdentifier digAlgId = new DefaultDigestAlgorithmIdentifierFinder()
            .find(sigAlgId);

    AsymmetricKeyParameter foo = PrivateKeyFactory.createKey(caPrivate
            .getEncoded());
    SubjectPublicKeyInfo keyInfo = SubjectPublicKeyInfo.getInstance(pair
            .getPublic().getEncoded());

    PKCS10CertificationRequestHolder pk10Holder = new PKCS10CertificationRequestHolder(inputCSR);
    //in newer version of BC such as 1.51, this is 
    //PKCS10CertificationRequest pk10Holder = new PKCS10CertificationRequest(inputCSR);

    X509v3CertificateBuilder myCertificateGenerator = new X509v3CertificateBuilder(
            new X500Name("CN=issuer"), new BigInteger("1"), new Date(
                    System.currentTimeMillis()), new Date(
                    System.currentTimeMillis() + 30 * 365 * 24 * 60 * 60
                            * 1000), pk10Holder.getSubject(), keyInfo);

    ContentSigner sigGen = new BcRSAContentSignerBuilder(sigAlgId, digAlgId)
            .build(foo);        

    X509CertificateHolder holder = myCertificateGenerator.build(sigGen);
    X509CertificateStructure eeX509CertificateStructure = holder.toASN1Structure(); 
    //in newer version of BC such as 1.51, this is 
    //org.spongycastle.asn1.x509.Certificate eeX509CertificateStructure = holder.toASN1Structure(); 

    CertificateFactory cf = CertificateFactory.getInstance("X.509", "BC");

    // Read Certificate
    InputStream is1 = new ByteArrayInputStream(eeX509CertificateStructure.getEncoded());
    X509Certificate theCert = (X509Certificate) cf.generateCertificate(is1);
    is1.close();
    return theCert;
    //return null;
}

As you can see, I’ve generated the request outside this method, but passed it in. Then, I have the PKCS10CertificationRequestHolder to accept this as a constructor arg.

Next, in the X509v3CertificateBuilder arguments, you’ll see the pk10Holder.getSubject – this is apparently all you need? If something is missing, please let me know too!!! It worked for me. The cert I generated correctly had the DN info I needed.

Wikipedia has a killer section on PKCS – http://en.wikipedia.org/wiki/PKCS