OTP Memory Playback Attack Prevention
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Solution Overview
Problem
Existing methods for protecting authorization information in non-volatile memory are vulnerable to playback attacks, where an attacker can replace new authorization information with old information, allowing unauthorized access to content.
Innovation Solution
A method using a one-time programmable (OTP) memory where a new digital signature is computed over new information and the current state of the OTP memory, with specific bits being programmed based on the new information and current state, ensuring only valid signatures are used for access, thereby preventing unauthorized access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If authorization information is stored in non-volatile memory with digital signatures, then data security is improved, but the system becomes vulnerable to playback attacks where old signatures can be reused
Solution Approach 1:
The patent applies preliminary action by programming a OTP bit to an unprogrammable state before the digital signature becomes valid. This ensures that once the signature is written to memory, the corresponding OTP bit cannot be changed, preventing attackers from creating alternative valid signatures. The sequence is: compute signature, write signature to memory, then program OTP bit - ensuring the OTP constraint is in place before the signature is activated.
Solution Approach 2:
The patent changes the state parameter of the OTP memory from programmable to unprogrammable. By transitioning the OTP bit from a writable state to a fixed unprogrammable state, the system creates an irreversible constraint that binds the authorization information to a specific signature. This parameter change ensures that the authorization data cannot be paired with alternative signatures, preventing playback attacks.
2Object-affected harmful factors
If the OTP bit is programmed before saving the signature, then security against playback attacks is improved, but system reliability deteriorates due to potential programming failures
Solution Approach 1:
The patent applies preliminary action in a controlled sequence: first compute the signature, then write it to memory, and only after successful memory writing does it program the OTP bit. This sequencing ensures that if OTP programming fails, the signature remains in memory and can be used with a different OTP bit, maintaining system reliability while still preventing playback attacks.
Solution Approach 2:
The patent provides a cushioning mechanism by maintaining the ability to use alternative OTP bits if programming fails. The system is designed to handle OTP programming failures by allowing retry with different bits, ensuring that the authorization process can complete successfully even if individual OTP bits cannot be programmed, thus cushioning against reliability issues.
3Object-affected harmful factors
If multiple OTP bits are programmed for each signature update, then security against playback attacks is enhanced, but device complexity increases
Solution Approach 1:
The patent segments the security function by using individual OTP bits for different authorization information entries. Each authorization entry is associated with a specific OTP bit, allowing independent management and verification. This segmentation simplifies the overall system by breaking down the complex task of securing multiple authorization entries into manageable individual bit operations.
Data Source
AI summary
A method for data security includes receiving, in a processor having a one-time programmable (OTP) memory, which includes multiple bits and has a current state defined by the bits of the OTP that have been programmed, new information to be written to a data memory. Based on the new information and the current state, at least one further bit of the OTP memory is selected to be programmed, thereby defining a new state of the OTP memory. A new digital signature is computed over the new information and the new state. The new information and the new digital signature are saved in the data memory. After saving the new information and the new digital signature in the data memory, the at least one further bit of the OTP memory is programmed, whereby the new state becomes the current state. Related apparatus and methods are also disclosed.