Adding Certificates to CMS Signed Data

Question

I am currently using the java Bouncy Castle libraries in order to create CMS signed data (or PKCS7 signed data). I seem however to be stuck with adding certificates (even though the certificate signer is properly added).

I checked out this question about properly signing data, but it didn't respond the needs of my SCEP server. The code I used was from EJBCA but doesn't seem to add certificates to the PKCS7 signed data.

When I parse the signed data with the openssl cms tool, I see that the "certificates" field is "EMPTY". Additionally, when I try to the print the certs with openssl pkcs7 [...] -print_certs, I get nothing.

Here is how I sign my data with Bouncy Castle (it's a lot code but enough to reproduce the issue):

CMSEnvelopedDataGenerator edGen = new CMSEnvelopedDataGenerator();
CMSTypedData msg;
List<X509Certificate> certList = new ArrayList<>();
// Make sure the certificate is not null
if (this.certificate != null) {
    certList.add((X509Certificate) this.certificate);
}

/**
* Create the signed CMS message to be contained inside the envelope
* this message does not contain any message, and no signerInfo
**/
CMSSignedDataGenerator gen = new CMSSignedDataGenerator();
Collection<JcaX509CertificateHolder> x509CertificateHolder = new ArrayList<>();
try {
    for (X509Certificate certificate : certList) {
        x509CertificateHolder.add(new JcaX509CertificateHolder(certificate));
    }
    CollectionStore<JcaX509CertificateHolder> store = new CollectionStore<>(x509CertificateHolder);
    gen.addCertificates(store);
} catch (Handle all exceptions) {}

This snippet of code above should normally add certificates. I took this from EJBCA.

Here is how I complete the signed data:

CMSSignedDataGenerator gen1 = new CMSSignedDataGenerator();
// I add ALL of my attributes here
// Once they're added...
Certificate caCert = this.caCertificate;
try {
    String provider = BouncyCastleProvider.PROVIDER_NAME;
    ContentSigner contentSigner = new JcaContentSignerBuilder(signatureAlgorithmName).
            setProvider(provider).
            build(signerKey);
    JcaDigestCalculatorProviderBuilder calculatorProviderBuilder = new JcaDigestCalculatorProviderBuilder().
            setProvider(provider);
    JcaSignerInfoGeneratorBuilder builder = new JcaSignerInfoGeneratorBuilder(calculatorProviderBuilder.build());
    builder.setSignedAttributeGenerator(new DefaultSignedAttributeTableGenerator(new AttributeTable(attributes)));
    gen1.addSignerInfoGenerator(builder.build(contentSigner, (X509Certificate) ca));
} catch (Handle all exceptions) {}

// Create the signed data
CMSSignedData sd = gen1.generate(msg, true);
byte[] results = sd.getEncoded();

The bytes array results is the DER formatted PKCS7 signed data... but no certificate is added.

Am I missing something? Thank you for your help!

Answer 1

The CMSSignedDataGenerator gen1 has to explicitly add the certificate, which I wasn't aware of.

It can simply be done by:

• Adding the certificates to a List of X509Certificates;
• Converting that List into a Collection of JcaX509CertificateHolder;
• Adding this collection to a CollectionStore of JcaX509CertificateHolder;
• Adding the store the CMSSignedDataGenerator.

Code sample:

 CMSSignedDataGenerator gen1 = new CMSSignedDataGenerator();
 List<X509Certificate> certificates = new ArrayList<>();

 // I chose to add the CA certificate
 certificates.add((X509Certificate) this.caCertificate);

 // In this case, this is a certificate that I need to add
 if (this.certificate != null)
     certificates.add((X509Certificate) this.certificate);

 // This is the recipient certificate
 if (this.recipientCert != null)
     certificates.add((X509Certificate) this.recipientCert);
 Collection<JcaX509CertificateHolder> x509CertificateHolder = new ArrayList<>();

 // Of course, we need to handle the exceptions...
 for (X509Certificate certificate : certificates) {
     x509CertificateHolder.add(new JcaX509CertificateHolder(certificate));
 }
 CollectionStore<JcaX509CertificateHolder> store = new CollectionStore<>(x509CertificateHolder);

// The final stage.
 gen1.addCertificates(store);

Hope this helps anyone in the future.