Chip Authentication via Bidirectional Challenge-Response Digest
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Solution Overview
Problem
Existing secure authentication methods for chips are vulnerable to reverse engineering, tampering, and snooping attacks, which can compromise the security of access authorization and reveal sensitive keys or cryptograms.
Innovation Solution
A method that uses a test device and secured chip to authenticate access through a bidirectional mathematical operation, combining a challenge with a test key, encrypting the result with a common key, and verifying the digest using a cryptographic one-way function to ensure secure access without disclosing keys or cryptograms, even under invasive or snooping attacks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional authentication methods (one-time passwords, challenge-response) are used, then access authorization can be obtained, but the system becomes vulnerable to reverse engineering, tampering, and snooping attacks that can reveal keys and cryptograms
Solution Approach 1:
The invention extracts the test key from the secured chip and stores it only in the test device. The chip retains only the reference digest (cryptographic hash of the test key). This separation removes the sensitive key material from the chip, making it impossible for attackers to extract keys through reverse engineering or tampering, while still enabling secure authentication through digest verification.
Solution Approach 2:
The invention introduces a cryptographic hash function (digest) as an intermediary between the test key and the authentication verification. Instead of directly comparing keys, the system compares cryptographic digests. This intermediary protects the test key from exposure during transmission and storage, preventing snooping attacks from revealing sensitive key material.
2Ease of operation
If the test key is stored in the secured chip for authentication verification, then authentication can be performed, but the key becomes vulnerable to extraction through reverse engineering and physical attacks
Solution Approach 1:
The test key is extracted from the chip's storage and relocated to the test device. The chip stores only the cryptographic digest of the test key, which is computationally infeasible to reverse. This extraction eliminates the risk of key exposure from chip tampering or reverse engineering while preserving authentication functionality.
Solution Approach 2:
The invention uses a disposable test key that exists only in the test device and is never stored in the chip. Even if an attacker compromises the chip, the key cannot be recovered because it was never stored there. This approach treats the key as a temporary, non-recoverable credential that provides security through its transient nature.
3Productivity
If authentication data is transmitted between the test device and chip, then access can be authorized, but captured data may disclose security parameters when analyzed by attackers
Solution Approach 1:
The cryptographic hash function serves as an intermediary that transforms the test key into a digest before transmission. This intermediary ensures that even if the digest is captured during transmission, attackers cannot reverse it to obtain the original key or derive security parameters, thus preventing information loss to attackers.
Solution Approach 2:
The invention converts the potential harm of data transmission into a benefit by using cryptographic hashing. The transmitted digest provides authentication capability while its one-way nature ensures that captured transmission data becomes useless to attackers, turning the transmission vulnerability into a security feature.
4Reliability
If comprehensive authentication protocols are implemented to prevent attacks, then security is improved, but the authentication process becomes more complex and slower
Solution Approach 1:
By extracting the test key from the chip and storing it only in the test device, the invention simplifies the chip's authentication logic to only require digest comparison. This extraction reduces the complexity of the authentication protocol while maintaining strong attack resistance, as the key management complexity is shifted to the test device where it can be handled more securely.
Data Source
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AI summary
A method for authenticating access to a secured chip SC by a test device TD, the test device storing at least one common key CK and one test key TK, the secured chip SC storing the same common key CK and a reference digest F(TK) resulting from a cryptographic function on the test key TK, the method comprising the steps of: - receiving, by the test device TD, a challenge R produced by the secured chip SC, - combining, by the test device TD, the received challenge R with the test key TK by applying a bidirectional mathematical operation (op), encrypting the result (TK op R) with the common key CK, obtaining a cryptogram CK(TK op R), - sending the cryptogram CK(TK op R) to the secured chip SC - decrypting, by the secured chip SC, the cryptogram CK(TK op R) with the common key CK, obtaining an image key TK' representing the test key TK by applying, with the challenge R, the reverse operation (op-1 ) of the mathematical operation (op) previously used by the test device TD, - calculating an expected digest F(TK') of the image key TK' with a cryptographic one-way function, - verifying validity by comparing the expected digest F(TK') with the reference digest F(TK), - if the result of the comparison between the digest F(TK') of the image key TK' and the reference digest F(TK) is positive, accessing, by the test device TD, the secure chip SC in a test mode.