Capacitor-Powered Charge Pump for Secure Chip Card Memory Writing
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Solution Overview
Problem
Existing countermeasures for protecting microcircuit cards against fault injection attacks, such as writing a predetermined value in non-volatile memory, are vulnerable to attackers who can detect increased current consumption and cut off power supply, rendering the card unusable.
Innovation Solution
A module that includes a capacitor to supply a charge pump and control means only during an attack, making the discharge of the capacitor undetectable and ensuring that the control means are powered, thereby preventing attackers from bypassing the countermeasure by cutting off power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a charge pump is charged to write a predetermined value in non-volatile memory when an attack is detected, then the card becomes unusable and the attack is countered, but the current consumption increases significantly which can be detected by SPA analysis
Solution Approach 1:
The capacitor is pre-charged during normal operation from the power supply before an attack occurs. When an attack is detected, the already-charged capacitor immediately powers the charge pump without requiring additional current from the power supply, thus avoiding detectable current consumption spikes while still enabling the protective writing operation.
2Object-affected harmful factors
If the power supply to the card is cut off when unusual current consumption is detected, then the attacker can bypass the countermeasure, but the card becomes unusable
Solution Approach 1:
The capacitor acts as an intermediary energy storage element between the power supply and the charge pump. During an attack, the capacitor maintains power supply to the charge pump and control means independently of the main power supply, preventing attackers from bypassing the countermeasure by cutting off the main power supply while ensuring the card can complete the protective writing operation.
3Object-affected harmful factors
If a capacitor is used to supply the charge pump during an attack, then the discharge can be detected by analyzing consumption, but the solution allows power cutting attacks to succeed
Solution Approach 1:
The capacitor is pre-charged during normal operation when no attack is detected, so its discharge during an attack cannot be distinguished from normal operational variations. This preliminary charging masks the capacitor discharge signature, making it undetectable through SPA analysis, while simultaneously ensuring the capacitor can immediately power the charge pump if a power cutting attack occurs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents attackers from disrupting the writing process in non-volatile memory cells, ensuring the microcircuit card remains operational and secure by masking the capacitor discharge and powering the control means during attacks.
Implementation Method 1
a capacitor (140) supplied in normal operation by a voltage VCC... the capacitor (140) being adapted to supply the charge pump (120) only when an attack is detected
Data Source
Figure 1~2
Figure 3
AI summary
This microcircuit board includes: - means for detecting an attack on the board; - control means (130) capable of charging a charge pump (120) capable of applying a programming voltage (UP) to control a write in a cell (110) of a non-volatile memory when an attack is detected; and - a capacitor (140) arranged to be powered in normal operation and to power said charge pump (120) only when an attack is detected; the board (100) being characterized in that said capacitor (140) also powers said control means (130) when an attack is detected.