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IKE keying daemon charon

The charon keying daemon was built from scratch to implement the IKEv2 protocol for strongSwan.

Most of its code is located in the libcharon library, making the IKE daemon core available to other programs such as charon-systemd, charon-svc, charon-cmd or the Android app.

Architecture

      +---------------------------------+       +----------------------------+
      |          Credentials            |       |          Backends          |
      +---------------------------------+       +----------------------------+

       +------------+    +-----------+        +------+            +----------+
       |  receiver  |    |           |        |      |  +------+  | CHILD_SA |
       +----+-------+    | Scheduler |        | IKE- |  | IKE- |--+----------+
            |            |           |        | SA   |--| SA   |  | CHILD_SA |
    +-------+--+         +-----------+        |      |  +------+  +----------+
 <->|  socket  |               |              | Man- |
    +-------+--+         +-----------+        | ager |  +------+  +----------+
            |            |           |        |      |  | IKE- |--| CHILD_SA |
       +----+-------+    | Processor |--------|      |--| SA   |  +----------+
       |   sender   |    |           |        |      |  +------+
       +------------+    +-----------+        +------+

      +---------------------------------+       +----------------------------+
      |               Bus               |       |      Kernel Interface      |
      +---------------------------------+       +----------------------------+
             |                    |                           |
      +-------------+     +-------------+                     V
      | File-Logger |     |  Sys-Logger |                  //////
      +-------------+     +-------------+
Processor The threading is realized with the help of a thread pool (called processor), which contains a fixed amount of precreated threads. All threads in the daemon originate from the processor. To delegate work to a thread, jobs are queued to the processor for asynchronous execution.
Scheduler The scheduler is responsible to execute timed events. Jobs may be queued to the scheduler to get executed at a defined time (e.g. rekeying). The scheduler does not execute the jobs itself, it queues them to the processor.
IKE_SA Manager The IKE_SA manager manages all IKE_SAs. It further handles the synchronization: Each IKE_SA must be checked out strictly and checked in again after use. The manager guarantees that only one thread may check out a single IKE_SA. This allows us to write the (complex) IKE_SAs routines non-threadsave.
IKE_SA The IKE_SA contain the state and the logic of each IKE_SA and handle the messages.
CHILD_SA The CHILD_SA contains state about an IPsec security association and manages them. An IKE_SA may have multiple CHILD_SAs. Communication to the kernel takes place here through the kernel interface.
Kernel Interface The kernel interface installs IPsec security associations, policies, routes and virtual addresses. It further provides methods to enumerate interfaces and may notify the daemon about state changes at lower layers.
Bus The bus receives signals from the different threads and relays them to interested listeners. Debugging signals, but also important state changes or error messages are sent over the bus.
Controller The controller provides a simple API for plugins to control the daemon (e.g. initiate IKE_SA, close IKE_SA, ...).
Backends Backends are pluggable modules which provide configuration. They have to implement an API which the daemon core uses to get configuration.
Credentials Provides trustchain verification and credential serving using registered plugins.

Plugins

The daemon loads plugins at startup. These implement the plugin_t interface (source:src/libstrongswan/plugins/plugin.h). Each plugin registers itself at the daemon to hook in functionality.

  +-------------------------------------+
  | charon                  +---+ +-----+------+
  |                         |   | |   stroke   |
  |                         |   | +-----+------+
  | +-------------+         |   | +-----+------+
  | | bus         |  ---->  | p | |    smp     |
  | +-------------+         | l | +-----+------+
  | +-------------+  <----  | u | +-----+------+
  | | controller  |         | g | |    sql     |
  | +-------------+  ---->  | i | +-----+------+
  | +-------------+         | n | +-----+------+
  | | credentials |  <----  |   | |  eap_aka   |
  | +-------------+         | l | +-----+------+
  | +-------------+  ---->  | o | +-----+------+
  | | backends    |         | a | |  eap_sim   |
  | +-------------+  <----  | d | +-----+------+
  | +-------------+         | e | +-----+------+
  | | eap         |  ---->  | r | |  eap_md5   |
  | +-------------+         |   | +-----+------+
  |                         |   | +-----+------+
  |                         |   | |eap_identity|
  |                         +---+ +-----+------+
  +-------------------------------------+

There is a growing list of available plugins (see source:src/libcharon/plugins).