typedef void (*SilcKeyAgreementCallback)(SilcClient client,
                                             SilcClientConnection conn,
                                             SilcClientEntry client_entry,
                                             SilcKeyAgreementStatus status,
                                             SilcSKEKeyMaterial *key,
                                             void *context);

    Key agreement callback that is called after the key agreement protocol
    has been performed. This is called also if error occurred during the
    key agreement protocol. The `key' is the allocated key material and
    the caller is responsible of freeing it. The `key' is NULL if error
    has occurred. The application can freely use the `key' to whatever
    purpose it needs. See lib/silcske/silcske.h for the definition of
    the SilcSKEKeyMaterial structure.