private byte[] computeKey(WSTrustVersion wstVer, final RequestSecurityTokenResponse rstr, final RequestedProofToken proofToken, final RequestSecurityToken rst) throws WSTrustException, UnsupportedOperationException {
// get ComputeKey algorithm URI, client entropy, server entropy and compute
// the SecretKey
final URI computedKey = proofToken.getComputedKey();
final Entropy clientEntropy = rst.getEntropy();
final Entropy serverEntropy = rstr.getEntropy();
final BinarySecret clientBinarySecret = clientEntropy.getBinarySecret();
final BinarySecret serverBinarySecret = serverEntropy.getBinarySecret();
byte [] clientEntropyBytes = null;
byte [] serverEntropyBytes = null;
if(clientBinarySecret!=null){
clientEntropyBytes = clientBinarySecret.getRawValue();
}