Variable Pre-Key Reduction for Symmetric Block Cipher Compatibility
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Solution Overview
Problem
Existing digital rights management (DRM) systems face challenges in efficiently handling variable-sized 'pre-key' bits from public key and hashing algorithms when used with symmetric block ciphers, requiring a systematic method to reduce these bits to a fixed size for secure content decryption.
Innovation Solution
An apparatus and method that includes instructions to selectively use some bits of a variable-sized pre-key to generate a reduced key for decryption, using logical operations like exclusive-OR, while discarding other bits, allowing for flexible key size reduction and secure content decryption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable-length pre-key bits from public key or hashing algorithms are used directly, then the key size can be large and flexible, but the symmetric block cipher requires a fixed-size key creating incompatibility
Solution Approach 1:
The patent transforms the variable-length pre-key into a fixed-length key by changing the parameter of key length through systematic processing. The method accepts pre-keys of various lengths (e.g., 256 bits from SHA-256, 512 bits from SHA-512) and systematically processes them to produce a uniform fixed-length output key that matches symmetric cipher requirements, thereby resolving the parameter mismatch between asymmetric/hash functions and symmetric ciphers.
Solution Approach 2:
The patent introduces an intermediary key processing function that acts as a mediator between the variable-length pre-key from public key infrastructure or hashing algorithms and the fixed-length key requirement of symmetric block ciphers. This intermediary systematically processes the pre-key through defined operations to produce a compatible fixed-length key, enabling seamless integration of different cryptographic systems without direct connection.
2Reliability
If all pre-key bits are used to generate the decryption key, then maximum entropy and security are achieved, but processing time increases
Solution Approach 1:
The patent applies partial action by systematically selecting and processing only the necessary portion of pre-key bits required to generate the fixed-length decryption key. Rather than unnecessarily processing all available pre-key bits, the method performs exactly the required amount of processing to produce the correct key length, optimizing the balance between security (using sufficient entropy) and processing efficiency (avoiding excessive computation).
Data Source
AI summary
A method and apparatus for reducing a variable number of pre-key bits to a fix key size is disclosed. The resulting key is used with a symmetric block cipher to descramble content. By being able to directly adapt a large and variable number of bits, it is possible to use cryptographic algorithms that were not thought possible, such as the output of modem public key and hashing functions, in order to create a key to directly use with a symmetric block cipher. Some or all of the pre-key bits may be used in the creation of the key.