Threshold Secret Key Blocking Without Public Key Updates
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Solution Overview
Problem
Existing asymmetric cryptography systems are vulnerable to attacks when a user device is compromised, as the attacker can perform illegitimate operations if the secret key is stolen or lost, requiring all devices with the public key to be updated, which poses a security risk.
Innovation Solution
Implement a threshold cryptography scheme where a server partial secret key and a user partial secret key are used, with the validation server determining the validity of cryptographic operations and updating the keys if the device is compromised, ensuring that at least two partial secret keys are required for any operation, and blocking the compromised device without updating the public key.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional asymmetric cryptography is used with a single secret key stored on the user device, then the system is simple to implement, but the system becomes vulnerable when the device is compromised
Solution Approach 1:
The secret key is divided into two separate parts: a server partial secret key stored on the validation server and a user partial secret key stored on the user device. This segmentation ensures that compromising one device does not compromise the entire key, as both parts are needed to perform cryptographic operations.
2Reliability
If the secret key is blocked by invalidating the old key pair and generating a new one, then the compromised device can be secured, but all devices storing the previous public key must be informed, creating a security risk
Solution Approach 1:
The system allows dynamic blocking of the server partial secret key without requiring updates to client devices. The validation server can mark the server partial secret key as blocked, and subsequent cryptographic operations will fail automatically, providing a simple and secure way to invalidate compromised keys without propagating updates to clients.
3Reliability
If the server partial secret key is blocked without updating the public key, then the compromised device is prevented from performing operations, but the public key remains valid for legitimate devices
Solution Approach 1:
The validation server acts as an intermediary between the user device and the cryptographic operation. It receives the user partial secret key from the device, checks whether the server partial secret key is blocked, and only then allows the operation to proceed. This intermediary mechanism enables selective blocking without affecting the public key's validity for legitimate devices.
Data Source
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AI summary
It is provided a method for applying a server partial secret key conditional on blocked status, wherein the server partial secret key (10b) and a user partial secret key (10a) form part of a threshold cryptography scheme (11), the method comprises: receiving (40) a request to apply a server partial secret key (10b) for a requested cryptographic operation for a user device (2); determining (42) that the server partial secret key (10b) can validly be applied by determining that the server partial secret key (10b) is not blocked from being applied; and interacting (44) with the user device (2) to perform the requested cryptographic operation, such that the user device (2) applies the user partial secret key (10a) and the validation server applies the server partial secret key (10b).