Distributed Decryption With Zero-Knowledge Key-Share Verification
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Solution Overview
Problem
Existing distributed decryption systems are vulnerable to attacks from malicious parties who can perform offline guessing attacks to obtain partial information about secret decryption keys, compromising security against chosen-ciphertext attacks.
Innovation Solution
Implementing a zero-knowledge proof mechanism where parties verify the authenticity of key shares using non-interactive zero-knowledge proofs, ensuring that only legitimate parties can participate in decryption, thereby preventing malicious actors from extracting information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If distributed decryption is implemented without zero-knowledge proofs, then decryption functionality is provided, but security against offline guessing attacks is compromised
Solution Approach 1:
The system performs preliminary verification by requiring parties to provide zero-knowledge proofs of knowledge of their key shares before the actual decryption operation. This preliminary action prevents malicious parties from participating in decryption without possessing valid key shares, thereby blocking offline guessing attacks before they can compromise security.
Solution Approach 2:
Zero-knowledge proofs serve as an intermediary mechanism that allows verification of key share authenticity without revealing the actual key shares. This intermediary enables secure verification while maintaining the confidentiality of cryptographic secrets, resolving the contradiction between security and complexity.
2Reliability
If zero-knowledge proofs are required for key share verification, then security against malicious parties is improved, but communication overhead increases
Solution Approach 1:
The patent extracts the verification function from the decryption process itself by using separate zero-knowledge proofs. This separation allows the verification to be performed independently and efficiently, reducing the communication overhead during the actual decryption operation while maintaining security against malicious parties.
3Ease of operation
If key shares are distributed without verification, then ease of key distribution is maintained, but vulnerability to chosen-ciphertext attacks increases
Solution Approach 1:
The system applies preliminary anti-action by implementing zero-knowledge proof verification before allowing parties to use their key shares for decryption. This preemptive measure counteracts potential chosen-ciphertext attacks by ensuring that only legitimate key holders can participate in the decryption process, thereby neutralizing the vulnerability before it can be exploited.
Data Source
AI summary
A method for distributed asymmetric decryption between a first party and a second party, each holding a different respective share of a secret key, is provided. The method comprises receiving, at the second party: a zero-knowledge proof of knowledge; and a plurality of inputs associated with a ciphertext to be decrypted, wherein the ciphertext is encrypted with a public key associated with the secret key. The method further comprises checking, by the second party, that the zero-knowledge proof of knowledge was generated based on the first party's share of the secret key; and, in response to determining that the zero-knowledge proof of knowledge was generated based on the first party's share of the secret key, sending, by the second party, information derived from the second party's share of the secret key. An example system for implementing the method is also provided. The system comprises a client device configured for performing distributed asymmetric decryption with a network device that holds a second share of a secret key, wherein the client device comprises a memory storing a first share of the secret key and wherein the client device is configured to act as the first party. The system further comprises the network device, which is configured to act as the second party.