Synchronous Stream Cipher Encryption with Reserved Code Lookup
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Solution Overview
Problem
Existing synchronous stream cipher encryption methods for digital video signals in cinemas require either large memory for lookup tables or extensive digital computation to exclude restricted codes, limiting their practicality and flexibility.
Innovation Solution
A method and system that uses a keystream generator and adders to produce a summed signal stream, combined with minimal lookup tables, to encrypt and decrypt input words while avoiding the use of restricted codes, reducing memory and computational requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If synchronous stream cipher encryption is performed to exclude restricted codes from the data stream, then security against unwanted reception is improved, but device complexity increases due to requirements for large lookup tables or extensive digital computation
Solution Approach 1:
The encryption process is segmented into two independent parts: (1) adding a pseudorandom keystream to the input data using simple adders, and (2) using a compressed lookup table that maps only the necessary non-restricted code combinations. This segmentation allows the system to avoid complex unified encryption algorithms while achieving the same security goal.
Solution Approach 2:
The invention extracts and handles only the essential encryption function by using a keystream generator and simple addition operations, separating the restricted code exclusion function into a dedicated, minimized lookup table. This extraction reduces overall device complexity by eliminating the need for complex integrated encryption algorithms.
2Reliability
If large lookup tables are used to encrypt input words while excluding restricted codes, then encryption security is improved, but memory requirements increase
Solution Approach 1:
The invention extracts only the essential mapping information needed for encryption into a minimized lookup table that contains only valid non-restricted code combinations. By extracting and storing only this essential information rather than complete code tables, memory requirements are dramatically reduced while maintaining encryption security.
Solution Approach 2:
Instead of using a traditional approach where the lookup table contains all possible code mappings and excludes restricted codes through complex logic, the invention inverts the approach by using a compressed table that contains only the valid mappings, thereby reducing memory usage while achieving the same security effect.
3Reliability
If extensive digital computation is performed to exclude restricted codes during encryption, then security is improved, but processing time increases
Solution Approach 1:
The encryption process is divided into simple, parallelizable operations: keystream generation, addition operations, and table lookup. This segmentation eliminates complex sequential computation required by traditional algorithms, significantly reducing processing time while maintaining security through the cryptographic strength of the keystream and mapping function.
Solution Approach 2:
The invention replaces complex mechanical/computational logic for restricted code detection and exclusion with a mathematical approach using addition operations and a pre-computed lookup table. This substitution reduces real-time computational burden while achieving the same security objective.
Data Source
AI summary
A method and apparatus for a signal encryption device constructed to perform synchronous stream cipher encryption for a sequence of input words with restricted codes. The encryption device includes a keystream generator for producing a sequence of pseudorandom words from a key, and an adder that is used to sum the output of the keystream generator and the input words. A lookup table of size substantially twice the number of possible input words provides encrypted codes excluding restricted codes from the summed signal. A signal encryption and decryption system is constructed by including a second keystream generator for producing a second sequence of pseudorandom words from the key, and a second adder to produce a second summed signal from the output of the second keystream generator and the encrypted codes. A corresponding lookup table provides decrypted codes excluding restricted codes from the second summed signal.