IDENTITY — Ego management

Identities of "users" in GNUnet are called egos. Egos can be used as pseudonyms ("fake names") or be tied to an organization (for example, "GNU") or even the actual identity of a human. GNUnet users are expected to have many egos. They might have one tied to their real identity, some for organizations they manage, and more for different domains where they want to operate under a pseudonym.

The IDENTITY service allows users to manage their egos. The identity service manages the private keys egos of the local user; it does not manage identities of other users (public keys). Public keys for other users need names to become manageable. GNUnet uses the GNU Name System (GNS) to give names to other users and manage their public keys securely. This chapter is about the IDENTITY service, which is about the management of private keys.

On the network, an ego corresponds to an ECDSA key (over Curve25519, using RFC 6979, as required by GNS). Thus, users can perform actions under a particular ego by using (signing with) a particular private key. Other users can then confirm that the action was really performed by that ego by checking the signature against the respective public key.

The IDENTITY service allows users to associate a human-readable name with each ego. This way, users can use names that will remind them of the purpose of a particular ego. The IDENTITY service will store the respective private keys and allows applications to access key information by name. Users can change the name that is locally (!) associated with an ego. Egos can also be deleted, which means that the private key will be removed and it thus will not be possible to perform actions with that ego in the future.

Additionally, the IDENTITY subsystem can associate service functions with egos. For example, GNS requires the ego that should be used for the shorten zone. GNS will ask IDENTITY for an ego for the "gns-short" service. The IDENTITY service has a mapping of such service strings to the name of the ego that the user wants to use for this service, for example "my-short-zone-ego".

Finally, the IDENTITY API provides access to a special ego, the anonymous ego. The anonymous ego is special in that its private key is not really private, but fixed and known to everyone. Thus, anyone can perform actions as anonymous. This can be useful as with this trick, code does not have to contain a special case to distinguish between anonymous and pseudonymous egos.

libgnunetidentity

Connecting to the service

First, typical clients connect to the identity service using GNUNET_IDENTITY_connect. This function takes a callback as a parameter. If the given callback parameter is non-null, it will be invoked to notify the application about the current state of the identities in the system.

  • First, it will be invoked on all known egos at the time of the connection. For each ego, a handle to the ego and the user’s name for the ego will be passed to the callback. Furthermore, a void ** context argument will be provided which gives the client the opportunity to associate some state with the ego.

  • Second, the callback will be invoked with NULL for the ego, the name and the context. This signals that the (initial) iteration over all egos has completed.

  • Then, the callback will be invoked whenever something changes about an ego. If an ego is renamed, the callback is invoked with the ego handle of the ego that was renamed, and the new name. If an ego is deleted, the callback is invoked with the ego handle and a name of NULL. In the deletion case, the application should also release resources stored in the context.

  • When the application destroys the connection to the identity service using GNUNET_IDENTITY_disconnect, the callback is again invoked with the ego and a name of NULL (equivalent to deletion of the egos). This should again be used to clean up the per-ego context.

The ego handle passed to the callback remains valid until the callback is invoked with a name of NULL, so it is safe to store a reference to the ego’s handle.

Operations on Egos

Given an ego handle, the main operations are to get its associated private key using GNUNET_IDENTITY_ego_get_private_key or its associated public key using GNUNET_IDENTITY_ego_get_public_key.

The other operations on egos are pretty straightforward. Using GNUNET_IDENTITY_create, an application can request the creation of an ego by specifying the desired name. The operation will fail if that name is already in use. Using GNUNET_IDENTITY_rename the name of an existing ego can be changed. Finally, egos can be deleted using GNUNET_IDENTITY_delete. All of these operations will trigger updates to the callback given to the GNUNET_IDENTITY_connect function of all applications that are connected with the identity service at the time. GNUNET_IDENTITY_cancel can be used to cancel the operations before the respective continuations would be called. It is not guaranteed that the operation will not be completed anyway, only the continuation will no longer be called.

The anonymous Ego

A special way to obtain an ego handle is to call GNUNET_IDENTITY_ego_get_anonymous, which returns an ego for the "anonymous" user — anyone knows and can get the private key for this user, so it is suitable for operations that are supposed to be anonymous but require signatures (for example, to avoid a special path in the code). The anonymous ego is always valid and accessing it does not require a connection to the identity service.

Convenience API to lookup a single ego

As applications commonly simply have to lookup a single ego, there is a convenience API to do just that. Use GNUNET_IDENTITY_ego_lookup to lookup a single ego by name. Note that this is the user’s name for the ego, not the service function. The resulting ego will be returned via a callback and will only be valid during that callback. The operation can be canceled via GNUNET_IDENTITY_ego_lookup_cancel (cancellation is only legal before the callback is invoked).

Associating egos with service functions

The GNUNET_IDENTITY_set function is used to associate a particular ego with a service function. The name used by the service and the ego are given as arguments. Afterwards, the service can use its name to lookup the associated ego using GNUNET_IDENTITY_get.

The IDENTITY Client-Service Protocol

A client connecting to the identity service first sends a message with type GNUNET_MESSAGE_TYPE_IDENTITY_START to the service. After that, the client will receive information about changes to the egos by receiving messages of type GNUNET_MESSAGE_TYPE_IDENTITY_UPDATE. Those messages contain the private key of the ego and the user’s name of the ego (or zero bytes for the name to indicate that the ego was deleted). A special bit end_of_list is used to indicate the end of the initial iteration over the identity service’s egos.

The client can trigger changes to the egos by sending CREATE, RENAME or DELETE messages. The CREATE message contains the private key and the desired name. The RENAME message contains the old name and the new name. The DELETE message only needs to include the name of the ego to delete. The service responds to each of these messages with a RESULT_CODE message which indicates success or error of the operation, and possibly a human-readable error message.

Finally, the client can bind the name of a service function to an ego by sending a SET_DEFAULT message with the name of the service function and the private key of the ego. Such bindings can then be resolved using a GET_DEFAULT message, which includes the name of the service function. The identity service will respond to a GET_DEFAULT request with a SET_DEFAULT message containing the respective information, or with a RESULT_CODE to indicate an error.