How does Pay-TV Work?
Satellite television services are divided into two categories: (i) subscription-based satellite television, and (ii) FTA (open) satellite television. The main difference between these services is the existence -or not- of an obligation to pay, either to rebroadcast or to access the audio and video content broadcast by the satellite system. This difference has important implications in the technical configuration, management, and security of satellite television content. This chapter describes the characteristics and operation of both service types.
Subscription-Based satellite television
Subscription-based satellite television service, also known as subscription satellite television, operates from a direct-to-home (DTH) system for the distribution of television signals broadcast directly to the public from geostationary satellites. To guarantee the protection of the content being broadcast via satellite signals, DTH services use Conditional Access Systems or CAS.
The purpose of CAS is to manage and protect the content of television broadcasters that are being distributed by the subscription television service provider, encrypting audio and video signals in order to avoid non-authorized access to said content. Usually, to acquire pay television services, users must purchase or rent a decoder or set-top-box
(STB) and an official smart card from the DTH service provider. Smart cards are used to manage and store the rights to decode content based on the service or programming package acquired by the subscriber.
CAS encrypts television signals and the content of DTH services by means of keys known as Control Words (CWs), which are constantly being updated (every few seconds) and transmitted through the network. DTH operators invest in cutting-edge technology to keep these keys periodically updated. The keys are received by the STB in order to decrypt the audio and video content when the subscriber wishes to watch a given signal. CWs are encrypted in turn to avoid their interception and utilization by unauthorized third parties to access the protected content. To this effect, CWs are transmitted by means of encrypted packages called Entitlement Control Messages (ECMs), and the keys being encrypted by ECMs are called transmission keys. Transmission keys are stored in the memory of the smart cards included in the STB. DTH operators have the ability to change the transmission keys, as applicable, through administrator-level commands.
Figure 1 describes the process to receive content protected by the CAS. When a subscriber wants to watch a given signal, the STB receives an ECM from the DTH provider and sends it to the smart card. The smart card decrypts the ECM using the transmission key that is currently valid and then queries its database to find the rights assigned to
the ECM to watch the signal in question (it determines if the subscriber has acquired the rights to see this specific signal). If the rights match, the smart card sends the CW to the STB. The CW must be encrypted again to protect the communication between the smart card and the STB. This process of protecting the satellite signal is called pairing.
Free-to-Air (FTA) Satellite Television services allow the reception of satellite signals that, by decision of the holder of the rights to that particular content, are broadcast with no encryption and thus are not protected by a CAS. Taking
this into account, FTA content may be received and watched by any device connected to a satellite receiver. These decoding devices or STBs do not have the ability to decrypt signals, so they can only receive FTA signals. These devices are usually known as “FTA devices” by the industry (Figure 2).
Illegal devices are those that have the ability to decrypt signals from subscription/based satellite television systems without due authorization or which could be modified for that purpose. These devices have been commonly sold under the label of “FTA devices”. FTA devices are exclusively designed to allow the reception of unencrypted satellite signals or signals not protected by CAS (free content), whereas illicit devices allow illegal access to encrypted satellite signals.