RFID Block Cipher Initialization Data Diversification
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Solution Overview
Problem
Low-cost RFID tags, especially passive ones, face security issues due to the repetition of pseudo-random sequences generated by block cipher algorithms during successive sessions, compromising authentication security due to fixed initialization data and limited computing power and storage constraints.
Innovation Solution
A method that modifies the initialization data for each session using a session-specific state value, which is smaller in size and stored on the device, allowing the block cipher algorithm to produce different encryption blocks each time, enhancing security and flexibility without increasing memory or computational requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed initialization data is used in block cipher algorithm during successive sessions, then device complexity and memory requirements are kept low, but security is compromised due to sequence repetition
Solution Approach 1:
The patent introduces a dynamic state value that changes with each session, transforming the static initialization data into a dynamic input for the block cipher algorithm. This state value is updated according to a transition function, ensuring that even with fixed initialization data, each session produces a unique pseudo-random sequence, thereby maintaining security without increasing device complexity
Solution Approach 2:
The patent changes the parameter of initialization data by introducing a session-specific state value that modifies the fixed initialization data. This parameter change ensures that the block cipher algorithm produces different outputs for each session while keeping the core initialization data fixed and simple, resolving the contradiction between security and device complexity
2Reliability
If a larger state value is stored to ensure session diversity, then security is improved, but memory constraints of low-cost RFID tags are violated
Solution Approach 1:
The patent uses a state value that is smaller than the full block size required for complete session diversity, but sufficient when combined with the fixed initialization data. This partial action approach provides adequate session diversity while respecting the severe memory constraints of low-cost RFID tags
Solution Approach 2:
The state value serves multiple functions: it provides session diversity, acts as a seed for the transition function, and modifies the fixed initialization data. This multi-functionality allows a small memory footprint to achieve significant security improvement
3Reliability
If initialization data is modified during sessions, then sequence repetition is prevented, but device complexity and energy consumption increase
Solution Approach 1:
The patent performs the modification of initialization data in advance by computing the state value at the beginning of each session before the block cipher algorithm is executed. This preliminary action ensures sequence uniqueness without requiring continuous modifications during the encryption process, thereby minimizing energy consumption
Data Source
Figure 1~2
AI summary
The invention relates to a method of implementing a block encryption algorithm through a device storing a fixed initialization datum (IV), said method being characterized in that it comprises, before execution of a first iteration of said algorithm in the course of a session (So): - a step (EO) of determining a modified initialization datum (IV) by means of a determined function (g) supplied as input by the fixed initialization datum (IV) and a state value (VS0) specific to the session, the state value being stored in the device, said modified initialization datum being intended to be used to implement the first iteration of the algorithm.