Control Word Encryption Using Nonce-Derived Keys
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Solution Overview
Problem
In conditional access systems for content delivery, secure transfer of control words between encryptors and conditional access systems is lacking, especially when different parties provide encryption and CA platforms, leading to potential misappropriation or theft of control words.
Innovation Solution
The use of digital certificates and secure hardware elements, such as tamper-resistant modules, to authenticate and encrypt control words, ensuring secure communication and authorization between SimulCrypt Synchronizer (SCS) and Entitlement Control Message Generators (ECMGs), with global secret keys stored in hardware and derived nonces for encryption and authentication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control words are transferred in clear between encryptor and CA systems, then communication simplicity is maintained, but security is compromised leading to potential misappropriation or theft of control words
Solution Approach 1:
A secure communication module acts as an intermediary between the encryptor and CA systems, establishing authenticated secure channels (such as TLS/SSL connections) to transfer control words. This intermediary layer provides encryption and authentication mechanisms that protect control word transmission while maintaining a standardized interface for participating systems.
Solution Approach 2:
The patent replaces clear-text control word transfer with cryptographic protection mechanisms. Control words are encrypted using robust encryption algorithms (e.g., AES-256) and transmitted through secured channels, substituting the simple but insecure mechanical transfer method with cryptographically protected communication protocols.
2Reliability
If multiple CA providers share control words for content security, then content protection is improved, but control over who can access control words deteriorates
Solution Approach 1:
The patent segments the control word distribution by creating separate secure communication channels for each CA provider. Each CA system receives control words through its own authenticated secure connection, allowing individual access control policies to be applied to each participant while maintaining content protection across all providers.
Solution Approach 2:
Different security policies and authentication mechanisms can be applied to different CA providers based on their specific requirements and trust levels. Each CA system can have customized security parameters, certificate authorities, and authentication methods tailored to their organizational needs while still participating in the SimulCrypt content protection system.
3Reliability
If software-based protection mechanisms are used for control words, then ease of implementation is maintained, but security deteriorates as these mechanisms can be compromised
Solution Approach 1:
A dedicated secure communication module serves as an intermediary that handles all cryptographic operations for control word protection. This modular approach isolates the complex security implementation in a separate component that can be independently secured, tested, and maintained, while the rest of the SimulCrypt system continues to operate with standard software interfaces.
Data Source
AI summary
In accordance with a method for communicating a control word (CW) from a client such as an encryptor to a server such as the entitlement control message generator (ECMG) of a conditional access system (CAS), communication is established between the client and server over a secure connection. A control word to be encrypted is received by the client and encrypted using a first and second key. The first key is a global secret key (GSK) that is known to the client and the server without being communicated over the secure connection. The second key is a control word encryption key (CWEK) that is derived from a locally generated client nonce (CN) and a server nonce (SN) obtained from the server over the secure connection. The encrypted control word (ECW) is sent to the server over the secure connection.