sun.security.util.DerValue not available on IBM SDKs

[Heiner Westphal]

Hello!
Im using xml-security java 1.1.0 on an AIX with
IBM SDK 1.4.1.
In org.apache.xml.security.keys.content.x509.XMLX509SKI
an object of class sun.security.util.DerValue is used, which
should not be according to
http://java.sun.com/products/jdk/faq/faq-sun-packages.html
When I'm trying to read a specific certificate I get:
Exception in thread "main" java.lang.NoClassDefFoundError:
sun/security/util/DerValue.
This does not happen, if I use a selfsigned cert created with
keytool and keyalg=DSA.
If anyone knows a quick workaround, please tell me.
P.S.: The calling code is attached, trace below.
trace is (sorry, no line numbers,
... means org.apache.xml.security.):
Exception in thread "main" java.lang.NoClassDefFoundError: 
sun/security/util/DerValue
 at ...keys.content.x509.XMLX509SKI.getSKIBytesFromCert(Unknown Source)
 at ...keys.content.x509.XMLX509SKI.<init>(Unknown Source)
 at ...keys.keyresolver.implementations.X509SKIResolver.
                         engineResolveX509Certificate(Unknown Source)
 at ...keys.keyresolver.KeyResolver.resolveX509Certificate(Unknown Source)
 at ...keys.KeyInfo.getX509CertificateFromStaticResolvers(Unknown Source)
 at ...keys.KeyInfo.getX509Certificate(Unknown Source)
- HERE starts my custom code, see attachement -

    /**
     * Get a certificate that matches the given keyinfo.
     * @param keyInfo Keyinfo to check against.
     * @return certificate that matches the keyinfo.
     * @throws MyErrorException If no certificate was found just
     *                          because there was no matching, or because
     *                          the keystore was broken.
     */
    private X509Certificate getCertificate(final KeyInfo keyInfo)
        throws MyErrorException {
        if (keyInfo != null) {
            if (keyInfo.containsX509Data()) {
                X509Certificate cert;
                try {
                    StorageResolver storageResolver =
                        new StorageResolver(new KeyStoreResolver(keyStore));
                    keyInfo.addStorageResolver(storageResolver);
                    cert = keyInfo.getX509Certificate();  // HERE!
                } catch (StorageResolverException e) {
                    throw new MyErrorException(e);
                } catch (KeyResolverException e) {
                    throw new MyErrorException(e);
                }
                return cert;
            } else {
                throw new MyErrorException(
                    "Message contains no KeyInfo. " + "Cannot check dsig.");
            }
        } else {
            throw new MyErrorException(
                "Message contains no X509Data. " + "Cannot check dsig.");
        }
    }