A method and apparatus for providing user key material from a server to a client is disclosed. The method comprises receiving a first message from the client in a server, the first message having a user key material request, an access token and an identifier of a transport key (TrK-ID), validating the user key material request according to the access token, generating a response having user key material responsive to the user key material request, encrypting the response according to the transport key (TrK), and transmitting a second message comprising the response from the server to the client. The client decrypts the second message according to the transport key (TrK) and validates the second message using the identifier of the transport key (TrK-ID).