builder.setUserInfo("mystskey");
builder.setKeyIdentifierType(WSConstants.ISSUER_SERIAL);
builder.setKeyEncAlgo(WSConstants.KEYTRANSPORT_RSAOEP);
Document doc = DOMUtils.createDocument();
builder.prepare(doc, stsProperties.getSignatureCrypto());
Element encryptedKeyElement = builder.getEncryptedKeyElement();
byte[] secret = builder.getEphemeralKey();
EntropyType entropyType = new EntropyType();
entropyType.getAny().add(encryptedKeyElement);