Stream Cipher Pseudo-Random Sequence Generation Using Nonlinear Filtering
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Solution Overview
Problem
Existing stream cipher techniques face difficulties in generating high-quality pseudo-random sequences, particularly in selecting appropriate nonlinear feedback functions and controlling sequence phases, which affects their security and efficiency.
Innovation Solution
A method and device implementing a stream cipher using a linear feedback shift register with 16 31-bit state variables, performing N-round operations involving bit restructuring, nonlinear state filtering, and variable initialization and work mode operations to generate a 32-bit pseudo-random sequence, utilizing a key expansion unit and control unit to manage the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nonlinear feedback functions are used to generate pseudo-random sequences, then cryptography properties are improved, but device complexity and difficulty of selection increase
Solution Approach 1:
The system divides the pseudo-random sequence generation into two independent parts: a linear feedback shift register (LFSR) that generates a base sequence, and a separate nonlinear filtering function that processes this sequence. This segmentation allows the linear LFSR to handle the complex feedback function selection while the nonlinear filtering provides the required cryptographic properties, thus resolving the contradiction between reliability and device complexity.
2Ease of operation
If linear shift register sequences are used, then generation simplicity is improved, but sequence phase control and security deteriorate
Solution Approach 1:
The patent introduces a nonlinear filtering function as an intermediary between the simple linear shift register and the final pseudo-random sequence output. This intermediary component enhances the security and phase control capabilities without complicating the basic LFSR structure, allowing the system to maintain generation simplicity while improving reliability through the filtering stage.
3Adaptability or versatility
If clock control sequences are used, then sequence generation flexibility is improved, but linear complexity increases
Solution Approach 1:
The system employs a dynamic nonlinear filtering function that can adapt its operation based on the input from the LFSR, providing sequence generation flexibility. However, the core LFSR maintains a fixed, simple structure with well-understood linear complexity characteristics. This dynamic filtering layer provides adaptability without increasing the fundamental linear complexity of the sequence generation mechanism.
Data Source
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AI summary
The present invention discloses a method and a device for implementing stream cipher. The method includes: implementing a key expansion operation with a pre-set 128-bit initial key and 128-bit initial vector, to obtain 16 31-bit state variables; implementing N-round operations using the state variables, wherein N is a positive integer and in turn each round of operation includes: bit restructuring, nonlinear state filtering operation and variable initialization mode operation; processing the output results after the N-round operations in turn using bit restructuring, nonlinear state filtering operation and discarding the output, as well as the variable work mode operation; implementing the following steps in each clock tick and respectively in turn: bit restructuring, nonlinear state filtering operation, XOR operation, and variable work mode operations, to obtain 32-bit pseudo-random sequence. Application of the method and device described in this invention can be simple and convenient way to obtain the required pseudo-random sequence, and has a high security.