.. SPDX-License-Identifier: GPL-2.0

Digital TV Conditional Access Interface (CI API)
================================================


.. note::

   This documentation is outdated.

This document describes the usage of the high level CI API as
in accordance to the Linux DVB API. This is a not a documentation for the,
existing low level CI API.

.. note::

   For the Twinhan/Twinhan clones, the dst_ca module handles the CI
   hardware handling.This module is loaded automatically if a CI
   (Common Interface, that holds the CAM (Conditional Access Module)
   is detected.

ca_zap
~~~~~~

A userspace application, like ``ca_zap`` is required to handle encrypted
MPEG-TS streams.

The ``ca_zap`` userland application is in charge of sending the
descrambling related information to the Conditional Access Module (CAM).

This application requires the following to function properly as of now.

a) Tune to a valid channel, with szap.

  eg: $ szap -c channels.conf -r "TMC" -x

b) a channels.conf containing a valid PMT PID

  eg: TMC:11996:h:0:27500:278:512:650:321

  here 278 is a valid PMT PID. the rest of the values are the
  same ones that szap uses.

c) after running a szap, you have to run ca_zap, for the
   descrambler to function,

  eg: $ ca_zap channels.conf "TMC"

d) Hopefully enjoy your favourite subscribed channel as you do with
   a FTA card.

.. note::

  Currently ca_zap, and dst_test, both are meant for demonstration
  purposes only, they can become full fledged applications if necessary.


Cards that fall in this category
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

At present the cards that fall in this category are the Twinhan and its
clones, these cards are available as VVMER, Tomato, Hercules, Orange and
so on.

CI modules that are supported
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The CI module support is largely dependent upon the firmware on the cards
Some cards do support almost all of the available CI modules. There is
nothing much that can be done in order to make additional CI modules
working with these cards.

Modules that have been tested by this driver at present are

(1) Irdeto 1 and 2 from SCM
(2) Viaccess from SCM
(3) Dragoncam

The High level CI API
~~~~~~~~~~~~~~~~~~~~~

For the programmer
^^^^^^^^^^^^^^^^^^

With the High Level CI approach any new card with almost any random
architecture can be implemented with this style, the definitions
inside the switch statement can be easily adapted for any card, thereby
eliminating the need for any additional ioctls.

The disadvantage is that the driver/hardware has to manage the rest. For
the application programmer it would be as simple as sending/receiving an
array to/from the CI ioctls as defined in the Linux DVB API. No changes
have been made in the API to accommodate this feature.


Why the need for another CI interface?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is one of the most commonly asked question. Well a nice question.
Strictly speaking this is not a new interface.

The CI interface is defined in the DVB API in ca.h as:

.. code-block:: c

	typedef struct ca_slot_info {
		int num;               /* slot number */

		int type;              /* CA interface this slot supports */
	#define CA_CI            1     /* CI high level interface */
	#define CA_CI_LINK       2     /* CI link layer level interface */
	#define CA_CI_PHYS       4     /* CI physical layer level interface */
	#define CA_DESCR         8     /* built-in descrambler */
	#define CA_SC          128     /* simple smart card interface */

		unsigned int flags;
	#define CA_CI_MODULE_PRESENT 1 /* module (or card) inserted */
	#define CA_CI_MODULE_READY   2
	} ca_slot_info_t;

This CI interface follows the CI high level interface, which is not
implemented by most applications. Hence this area is revisited.

This CI interface is quite different in the case that it tries to
accommodate all other CI based devices, that fall into the other categories.

This means that this CI interface handles the EN50221 style tags in the
Application layer only and no session management is taken care of by the
application. The driver/hardware will take care of all that.

This interface is purely an EN50221 interface exchanging APDU's. This
means that no session management, link layer or a transport layer do
exist in this case in the application to driver communication. It is
as simple as that. The driver/hardware has to take care of that.

With this High Level CI interface, the interface can be defined with the
regular ioctls.

All these ioctls are also valid for the High level CI interface

#define CA_RESET          _IO('o', 128)
#define CA_GET_CAP        _IOR('o', 129, ca_caps_t)
#define CA_GET_SLOT_INFO  _IOR('o', 130, ca_slot_info_t)
#define CA_GET_DESCR_INFO _IOR('o', 131, ca_descr_info_t)
#define CA_GET_MSG        _IOR('o', 132, ca_msg_t)
#define CA_SEND_MSG       _IOW('o', 133, ca_msg_t)
#define CA_SET_DESCR      _IOW('o', 134, ca_descr_t)


On querying the device, the device yields information thus:

.. code-block:: none

	CA_GET_SLOT_INFO
	----------------------------
	Command = [info]
	APP: Number=[1]
	APP: Type=[1]
	APP: flags=[1]
	APP: CI High level interface
	APP: CA/CI Module Present

	CA_GET_CAP
	----------------------------
	Command = [caps]
	APP: Slots=[1]
	APP: Type=[1]
	APP: Descrambler keys=[16]
	APP: Type=[1]

	CA_SEND_MSG
	----------------------------
	Descriptors(Program Level)=[ 09 06 06 04 05 50 ff f1]
	Found CA descriptor @ program level

	(20) ES type=[2] ES pid=[201]  ES length =[0 (0x0)]
	(25) ES type=[4] ES pid=[301]  ES length =[0 (0x0)]
	ca_message length is 25 (0x19) bytes
	EN50221 CA MSG=[ 9f 80 32 19 03 01 2d d1 f0 08 01 09 06 06 04 05 50 ff f1 02 e0 c9 00 00 04 e1 2d 00 00]


Not all ioctl's are implemented in the driver from the API, the other
features of the hardware that cannot be implemented by the API are achieved
using the CA_GET_MSG and CA_SEND_MSG ioctls. An EN50221 style wrapper is
used to exchange the data to maintain compatibility with other hardware.

.. code-block:: c

	/* a message to/from a CI-CAM */
	typedef struct ca_msg {
		unsigned int index;
		unsigned int type;
		unsigned int length;
		unsigned char msg[256];
	} ca_msg_t;


The flow of data can be described thus,

.. code-block:: none

	App (User)
	-----
	parse
	  |
	  |
	  v
	en50221 APDU (package)
   --------------------------------------
   |	  |				| High Level CI driver
   |	  |				|
   |	  v				|
   |	en50221 APDU (unpackage)	|
   |	  |				|
   |	  |				|
   |	  v				|
   |	sanity checks			|
   |	  |				|
   |	  |				|
   |	  v				|
   |	do (H/W dep)			|
   --------------------------------------
	  |    Hardware
	  |
	  v


The High Level CI interface uses the EN50221 DVB standard, following a
standard ensures futureproofness.