java.lang.NullPointerException Error during the SecurityHelper.prepareSignatureParams() OpenSAML call

Question

I have hit a dead end using the OpenSAML support for preparing a SAML Payload to accomplish a SSO transaction with another service that I am working with. I receive a NullPointerException that is thrown after I use the SecurityHelper.prepareSignatureParams() routine. I have a Stacktrace, but it wold be pretty ugly to append.

Let me first say what I was able to do...

For the purposes of learning the technology and to make sure it would work, I was able to successfully build a SAML payload, sign it using a Certificate and a Private Key that was stored in a Java Key Store file that I created locally on my workstation using the Keytool program with the -genkeypair option.

As I understand things, my JKS file contains a Self Signed Certificate and a Private Key. I was able to open the JKS file, gather the Certificate and the Private Key to build a Signing Certificate. The Signing Certificate was used to sign the SAML Payload that I created You'll see how I did this if you look at the code samples that I'll append.

What isn't working...

I want to use the same SAML support to sign my SAML Payload using a Trusted Certificate that I have for my website that I received from GoDaddy. To do this, I installed the Trusted Certificate into my webserver's keystore at: '\Program Files\Java\jre1.8.0_102\lib\security\cacerts'. I understand that the cacerts file is the KeyStore for our webserver. I installed the Trusted Certificate using the Keytool -importcert command. One big difference is that the Trusted Certificate DOESN'T have a Private Key. So when preparing the Signing Certificate using the Open SAML support, I am not able to add a Private Key to the Credential object (because I don't have one).

When attempting the above for the Trusted Certificate, I am able to get to the part where I am preparing the Signature Parms (SecurityHelper.prepareSignatureParams()). That's where I get the Null Pointer.

If you could take a look at the code that I am using. I am including the code (that signs my payload successfully) that reads from the local JKS file and also the code (that gets the Null Pointer Exception) when I try to using the Trusted Certificate on the server (both cases). There's not much different between the two cases:

//  Signing process using OpenSAML

//  Get instance of an OpenSAML 'KeyStore' object...
KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());

// Read KeyStore as File Input Stream.  This is either the local JKS 
// file or the server's cacerts file.
File ksFile = new File(keyStoreFileName);

//  Open an Input Stream with the Key Store File
FileInputStream ksfInputStream = new FileInputStream(ksFile);

// Load KeyStore.  The keyStorePassord is the password assigned to the keystore,  Usually 'changeit'
// before being changed.
keyStore.load(ksfInputStream, keyStorePassword);

// Close InputFileStream.  No longer needed.
ksfInputStream.close();


// Used to get Entry objects from the Key Store
KeyStore.PrivateKeyEntry pkEntry = null;
KeyStore.TrustedCertificateEntry tcEntry = null;

PrivateKey pk                   = null;
X509Certificate x509Certificate = null;

BasicX509Credential credential  = null;

//  The Java Key Store specific code...
// Get Key Entry From the Key Store.  CertificateAliasName identifies the
// Entry in the KeyStore.  KeyPassword is assigned to the Private Key.
pkEntry = (KeyStore.PrivateKeyEntry) keyStore.getEntry(certificateAliasName,    new KeyStore.PasswordProtection(keyPassword));

//  Get the Private Key from the Entry
pk = pkEntry.getPrivateKey();

//  Get the Certificate from the Entry
x509Certificate = (X509Certificate) pkEntry.getCertificate();

//  Create the Credential.  Assign the X509Certificate and the Privatekey
credential = new BasicX509Credential();
credential.setEntityCertificate(x509Certificate);
credential.setPrivateKey(pk);


//  The Trusted Certificate specific code...
//  Accessing a Certificate that was issued from a trusted source - like GoDaddy.com
//
// Get Certificate Entry From the Key Store.  CertificateAliasName identifies the Entry in the KeyStore.
//  There is NO password as there is no Private Key associate with this Certificate

tcEntry = (TrustedCertificateEntry) keyStore.getEntry(certificateAliasName, null);

//  Get the Certificate from the Entry
x509Certificate = (X509Certificate) tcEntry.getTrustedCertificate();

//  Create the Credential.  There is no Provate Ley to assign into the Credential
credential = new BasicX509Credential();
credential.setEntityCertificate(x509Certificate);


//  Back to code that is not specific to either method...
//
//  Assign the X509Credential object into a Credential Object.  The BasicX509Credential object
// that has a Certificate and a Private Key OR just a Certificate added to it is now saved as a
// Cendential object.
Credential signingCredential = credential;


//  Use the OpenSAML builder to create a signature object.
Signature signingSignature = (Signature)    Configuration.getBuilderFactory().getBuilder(Signature.DEFAULT_ELEMENT_NAME).build    Object(Signature.DEFAULT_ELEMENT_NAME);

//  Set the previously created signing credential
signingSignature.setSigningCredential(signingCredential);

// Get a Global Security Configuration object.
SecurityConfiguration secConfig = Configuration.getGlobalSecurityConfiguration();

// KeyInfoGenerator.  Not sure what this is, but the example I am working from shows
// this being passed as null.
String keyInfoGeneratorProfile = "XMLSignature";

//  Prepare the Signature Parameters.
//
//  This works fine for the JKS version of the KeyStore, but gets a Null Pointer exception when I run to the cacerts file.
SecurityHelper.prepareSignatureParams(signingSignature, signingCredential, secConfig, keyInfoGeneratorProfile <or null>);

//  I need to set into the SigningSignature object the signing algorithm.  This is required when using the TrustedCertificate
signingSignature.setSignatureAlgorithm(SignatureConstants.ALGO_ID_SIGNATURE_RSA_SHA256);



//  This is my code that builds a SAML Response.  The SAML Payload contains data
// about the SSO session that I will be creating...
Response samlResponse = createSamlResponse.buildSamlResponseMessage();

//  Sign the Response using the Certificate that was created earlier
samlResponse.setSignature(signingSignature);



// Get the marshaller factory to marshall the SamlResponse
MarshallerFactory marshallerFactory = Configuration.getMarshallerFactory();
Marshaller responseMarshaller = marshallerFactory.getMarshaller(samlResponse);

// Marshall the Response
Element responseElement = responseElement =     responseMarshaller.marshall(samlResponse);

//  Sign the Object...
Signer.signObject(signingSignature);

NOTE: My attempt to sign a SAML Payload was modeled after an OPENSAML example that I found here: https://narendrakadali.wordpress.com/2011/06/05/sign-assertion-using-opensaml/

Hoping that someone can show me the error of my ways or what I am missing.

Thanks for any suggestions.

EDIT (01/26/2016)

I was able to get past the NULL pointer I was receiving while preparing the Signature Params (SecurityHelper.prepareSignatureParams()). Code changes included updating my xmlsec.jar file to version 2.0.8 (xmlsec-2.0.8.jar) and I explicitly setting the signature algorithm to SHA256 when using the Trusted Certificate (from GoDaddy). See my code example for the use of:

signingSignature.setSignatureAlgorithm(SignatureConstants.ALGO_ID_SIGNATURE_RSA_SHA256);

The above changes allows the SAML payload to be built and sent to the connection endpoint.

However, I am still not establishing the SSO connection to my endpoint.

Here's what I see happening:

During processing while the SAML payload is being constructed and specifically, the SAML payload's Signature is being signed:

Signer.signObject(signature);

I get an an error message from SAML:

ERROR: org.opensaml.xml.signature.Signer - An error occured computing the digital signature

The stack trace (just the ending portion):

org.apache.xml.security.signature.XMLSignatureException: Sorry, you supplied the wrong key type for this operation! You supplied a null but a java.security.PrivateKey is needed.
at org.apache.xml.security.algorithms.implementations.SignatureBaseRSA.engineInitSign(SignatureBaseRSA.java:149)
at org.apache.xml.security.algorithms.implementations.SignatureBaseRSA.engineInitSign(SignatureBaseRSA.java:165)
at org.apache.xml.security.algorithms.SignatureAlgorithm.initSign(SignatureAlgorithm.java:238)
at org.apache.xml.security.signature.XMLSignature.sign(XMLSignature.java:631)
at org.opensaml.xml.signature.Signer.signObject(Signer.java:77)

I searched the error messages, but I am not coming up with much.

I don't understand the root of the error message - That the wrong key type was supplied (null) and that OpenSAML seems to be expecting a java.Security.PrivateKey.

When using the Trusted Certificate, I don't have a Private Key, Correct? How would I be able to provide a Private Key? In the case of the Trusted Certificate I read a Trusted Certificate (TrustedCertificateEntry) from the KeyStore. The TrustedCertificateEntry object allows me to access the Certificate, but there's no method for obtaining a Private Key (as well there shouldn't be).

However, when I use my Self Signed Certificate to perform the signing operation, I understand that I do have both the Certificate (the Public Key) and the Private Key contained in the JKS file (the KeyStore). I think that's why when I read from the JKS file, I am able to read a Private Key Entry (KeyStore.PrivateKeyEntry) that has methods for accessing both the Public Key (the Certificate) and the Private Key.

What am I missing about the Trusted Certificate case? The OpenSAML support seems to be expecting a Private key to be able to compute the Signature.

In the case of the Trusted Certificate, is there a way to package the original Private Key into my Key Store (along with the Trusted Certificate)? I am not sure if this is what is normally done or even possible.

Hopefully some guidance as to what I am doing here, Please!

EDIT (01/26/2017) - 2 to provide additional detail.

I'll share a portion of the SAML payload that gets sent...

In the case of the Self Signed Certificate, I see a SignatureValue tag and a X509Certificate tag. Both have binary data included within the begin and end of the tag.

In the case of the Trusted Certificate, I've got an empty Signature Value tag that looks like:

<ds:SignatureValue/>

The Certificate tag is still present and contains the certificate bytes.

So, looking at the error I see from OpenSAML, it is more obvious that it can't compute a Signature using the data that is available in the Trusted Certificate.

Answer 1

Ok, this quite a long question. As I understand the root of the problem is the message "Sorry, you supplied the wrong key type for this operation! You supplied a null but a java.security.PrivateKey is needed." You are trying to sign a message using a public key. This is not possible. Just looking logically on it, signing using a public key would not provide any proof that the signer is intended as it is available to everyone.

What you need to do is sign using a private key. in your case you have generated a public and private key on you computer, then sent CSR to the CA and recieved a certificate signed by the CA. You should use the privat key from you local computer to sign the message and send the CA signed certificate to the recipient so they can use it to confirm your signature.

In this blog post of mine I explain how to obtain credentials, including the private key from a Java keystore.