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Conditional Access Systems
- 1. Introduction to Conditional Access Systems Namith CM
- 2. What is CAS? A Conditional Access System is the collection of security components in the end-to-end pipeline of broadcast media, from source headend equipments to client devices. PayTV systems generate revenue by enabling media content rights exclusively to viewers who pay for it. “Paid channels” or channels with premium content, which are not available free-to-air. Video-on-demand and movie-on-demand services. In simple terms, in general, all devices in the network can theoretically get access to all the available (free-to-air and encrypted) media contents/streams. But only those devices with some specific keys can view the encrypted/protected contents. The secure management of these keys in the open network, is the prime responsibility of a CAS vendor.
- 3. Types of CAS in PayTV systems Smartcard based solution Smartcard contains proprietary security logic for decryption. Proven and tested, and most widely accepted solution. Recovery time after hacking is high, since cards need to be replaced. CAM-based solution Similar to smartcard based, but the device is just provided with a slot for CAM module, and any smartcard (meeting CAM requirements) should be able to work. More open standard, but poor adoption by market leaders. Cardless or full-software solution SoC level security features are used by software modules. Relatively newer technology, cheaper and growing in popularity. Recovery time after hacking is very low, hence discouraging hackers.
- 4. CAS for Broadcast Networks The next few slides explain the end-to-end management of secure content. This is a very generalized and simplistic explanation (intended for engineers with DVB background), and not specific to any particular CAS vendor. The basic concept would be similar for all Broadcast CAS systems, with slight variations in the number of levels for key encryption, key ladder logic, encryption/scrambling algorithms used, etc.
- 5. Scrambling and Descrambling Free-to-air service Scrambled service Scrambler Control Word (CW) Random key, from a Random Number Generator Can this key be sent to STB clients without encryption? Think about ECM! Should it same for all users? Think about bandwidth! Scrambled service Descrambler Free-to-air service @ Headend Mux @ STB Client How frequently should this key be changed? Think about brute-force attacks!
- 6. Why is CW shared? ESPN (free-to-air) ESPN (user-1) Scrambler CW-1 CW-2 CW-3 CW-4 ESPN (user-2) ESPN (user-3) ESPN (user-4) Bandwidth wastage. Millions of users. Impractical! Multiple CW impractical, so use common CW per service
- 7. Why is ECM shared? Encryptor Key-1 Key-2 Key-3 Key-4 CW ECM (user-1) ECM (user-2) ECM (user-3) ECM (user-4) Multiple ECM impractical, so use common ECM per service Bandwidth wastage. Millions of users. Will run short of PIDs. Even if sent on same PID, the overhead to encrypt & send so many million ECMs so frequently is too high. Thus impractical!
- 8. End-to-end Key Handling (Headend) CW Kser1 CWenc CWenc ECM Kusr1 K-ser1enc K-ser1enc EMM KserN K-serNenc K-serNenc Kusr1 Khw from SoC/smartcard db K-usr1enc K-usr1enc AUTH Common to all User-specific or group-specific, common PID User-specific, common PID … … Free-to-air service Scrambled serviceScrambler Common to all CW
- 9. K-usr1 End-to-end Key Handling (STB Client) K-usr1enc AUTH K-ser1enc EMM K-serNenc … CWenc ECM Khw from SoC or smartcard K-usr1K-usr1enc K-ser1enc K-ser1 CWenc CW Free-to-air serviceScrambled service Descrambler CW K-serNenc K-serN …
- 10. Simulcrypt MUX Scrambler CW- generator & Simulcrypt Synchronizer (SCG) PID/Tables generator & multiplexer Free-to-air service Scrambled service CAS-1 EMM g ECMg CAS-2 EMM g ECMg ECM-1 EMM-1 ECM-2 EMM-2 CW CAT CA descriptors EMM-1 PID (CAS- 1) EMM-2 PID (CAS- 2) PMT CA descriptors ECM-1 PID (CAS- 1) ECM-2 PID (CAS- 2) EMM-1 EMM-2 ECM-1 ECM-2 Enables coexistence of multiple CA systems operating simultaneously in the same network.