Free-To-Air receivers generally use the same technology standards (such as DVB-S, MPEG-2) as those used by pay-TV networks such as Echostar’s Dish Network and BCE’s Bell TV. FTA receivers, however, lack the smartcard readers or decryption modules designed for the reception of pay-TV programming, since the receivers are designed only for reception of unencrypted transmissions.

On occasion, where a pay-TV service’s encryption system has been very seriously compromised, to the extent that it can be emulated in software and without the presence of a valid access card, hackers have been able to reverse engineer an FTA receiver’s software and add the necessary emulation to allow unauthorized reception of pay TV channels. Manufacturers, importers, and distributors of FTA receivers officially do not condone this practice and some will not sell to or support individuals who they believe will be using their products for this purpose. Use of third-party software will void the manufactures warranty.

Unlike traditional methods of pirate decryption that involve altered smart cards used with satellite receivers manufactured and distributed by the provider, piracy involving FTA receivers require only an update to the receiver’s firmware. Electronic countermeasures that disable access cards may not have the same or any effect on FTA receivers because they are not capable of being updated remotely. The firmware in receivers themselves cannot be overwritten with malicious code via satellite as provider-issued receivers are.

FTA receivers also have the advantage of being able to receive programming from multiple providers plus legitimate free-to-air DVB broadcasts which are not part of any package, a valuable capability which is conspicuously absent from most “package receivers” sold by DBS providers. DVB-S is an international standard and thus the industry-imposed restriction that a Bell TV receiver is not interchangeable with a Dish Network receiver (the same box) and neither are interchangeable with a GlobeCast World TV receiver (also DVB) is an artificial one created by providers and not respected by either pirates or legitimate unencrypted FTA viewers.

Periodically, a provider will change the processes in which its encryption information is sent. When this happens, illegitimate viewing is disrupted. Third-party coders may release an updated altered version of the FTA receiver software on internet forums, sometimes hours to days after the countermeasure is implemented, although some countermeasures have allowed the encryption to remain secure for several months or longer. The receivers, meanwhile, remain able to receive unencrypted DVB-S broadcasts and (for some HDTV models) terrestrial (over-the-air) ATSC programming. The same is not true of standard subscription TV receivers, whereby unsubscribing from a pay-TV package causes loss of all channels.

The use of renewable security allows providers to send new smart cards to all subscribers as existing compromised encryption schemes (such as Nagravision 1 and 2) are replaced with new schemes (currently Nagravision 3). This “card swap” process can provide pay-TV operators with more effective control over pirate decryption, but at the expense of replacing smart cards in all existing subscribed receivers. While this approach is used by most providers, deployments tend to be slowed due to cost.

While smart-card piracy often involves individuals who re-program access cards for others (usually for a price), piracy using FTA receivers involves third-party software that is relatively easy to upload to the receiver and can even be uploaded using a USB device, network, or serial link (a process called “flashing”). Most such firmware is distributed freely on the Internet. Websites that third-party coders use to share this software often have anywhere from 50,000 to over 200,000 registered users.

Another method of pirate decryption that has become popular recently is known as Internet Key Sharing (IKS). This is accomplished by an Ethernet cable hooked to the receiver that allows updated decryption keys to be fed to the unit directly from the internet. The DVB-S common scrambling system and the various conditional access systems are based on the use of a legitimately subscribed smart cards which generates a continuous stream of cryptographic key usable to decrypt one channel on a receiver. A key-sharing scheme operates by redistributing these keys in real-time to multiple receivers in an unlimited number of locations so that one valid smartcard may serve almost 10000 viewers.

As of June 2009 this was the only active pirate decryption system still in widespread use in North American satellite TV, due to the shutdown of the compromised Nagravision 2 system by providers such as Dish Network and Bell TV.

However, this is limited by the interval of the stream of keys or also called CW (Control Words). Usually, the interval for the renewal of the CWs is ±10 seconds, but other systems (i.e. NDS3) have CW intervals of 5 seconds or less. Each channel usually has a different set of CWs for decryption and thus each box currently watching a specific channel must periodically request the current CWs from the server/smart-card for that specific channel. So arguably, the sharing of the card might not be unlimited. There are some restrictions to this like the frequency of CW changes and also the latency of the network. If the CWs do not arrive in time, there could be a freeze or crackle in the picture.

There are of course other more costly possibilities like having several legitimately subscribed cards each handling a few channels and a CW caching server.

The dependence on an external server also potentially compromises privacy for individual viewers, as well as rendering the system incompatible with many receiver models which lack the ability to connect to an outside network and/or lack the ability to set or modify the various keys or identifiers used in communication between the card and receiver.

Credit : http://en.wikipedia.org