Transistor Mobility Codeword Storage Against Die-Thinning Attacks
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Solution Overview
Problem
Existing methods for securely storing codewords in integrated circuits are vulnerable to unauthorized access, as techniques such as extracting and thinning the die can alter physical characteristics, allowing unauthorized extraction of the codeword.
Innovation Solution
The codeword is stored using transistors with mobilities that change upon physical stress, making unauthorized access destructive to the codeword, and transistors are arranged in susceptible locations like edges or corners to enhance this security, with W/L ratios less than 1 to emphasize mobility differences and stress layers applied to set predetermined codewords.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the codeword is stored using physical characteristics of transistors, then the codeword can be permanently fixed, but unauthorized access techniques can extract and thin the die to measure and obtain the secret codeword
Solution Approach 1:
The patent applies preliminary anti-action by pre-configuring the transistor mobility values during manufacturing to encode the secret codeword. The mobility values are set such that any physical stress or damage during unauthorized access attempts will alter these values, thereby destroying the codeword before it can be extracted. This proactive setup ensures that the codeword is inherently protected against reverse engineering.
Solution Approach 2:
The patent utilizes parameter changes by encoding the codeword in the mobility parameter of transistors. Since mobility is a physical characteristic that can be permanently altered by stress or damage, any attempt to access the codeword through physical means will change the mobility parameter, thereby destroying the stored information. This transforms the physical state of the transistor into a security feature.
2Reliability
If the transistors are arranged in susceptible locations to undergo physical stress, then the codeword can be destroyed upon unauthorized access, but the circuit design becomes more complex
Solution Approach 1:
The patent applies local quality by placing transistors in specific locations on the die that are inherently more susceptible to physical stress during unauthorized access attempts. These locations, such as edges or corners, are deliberately chosen because they are more likely to undergo deformation or stress when the die is thinned or manipulated. This localized vulnerability ensures that physical attacks on these specific areas will destroy the codeword stored in those transistors.
3Reliability
If the W/L ratios of transistors are set to enhance mobility differences, then the codeword storage capability is improved, but the current consumption may increase
Solution Approach 1:
The patent applies parameter changes by optimizing the W/L ratios of transistors to enhance mobility differences while controlling current consumption. By carefully selecting W/L values, the design achieves sufficient mobility differentiation for reliable codeword storage without excessive current draw. This parameter optimization balances security requirements with energy efficiency.
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
This approach renders unauthorized access ineffective by altering the codeword upon attempted manipulation, ensuring secure storage through inherent transistor mobility changes and stress-induced modifications.
Implementation Method 1
the value of the codeword is determined by the mobility of at least a first transistor of the plurality of transistors
Implementation Method 2
the attempt to break open the packaging of the integrated circuit and to thin the backside of the die results in a change in the physical stress within the transistors, thereby forcing a change in the mobility of the transistors
Implementation Method 3
The plurality of transistors may form a circuit that is stable in two different states (bi-stable), and the mobilities of the transistors may bias the bi-stable towards one of the states
Data Source
AI summary
The invention discloses an integrated circuit (10) for securely storing a codeword. The value of the codeword is dependent on the mobility (μA, μB, μC) of at least one transistor (TRA, TRB, TRC) of the integrated circuit. The invention further discloses a reader means (15), a method for determining the value of the codeword from the integrated circuit (10), and a method for altering the value of the codeword.