Group Key Formation Using an Untrusted Intermediary
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Solution Overview
Problem
Existing group key formation processes in group communication systems often require a trusted intermediary, which compromises security as the shared symmetric group key may be known to the intermediary and other parties outside the group.
Innovation Solution
A method for creating a group key among a number of parties using an intermediary, where each party shares a cryptographic key with adjacent parties, generates a meeting key, and combines it with an intermediate key computed by the intermediary, forming a group key that is only known to the group members, ensuring the intermediary remains unaware of the key.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a trusted intermediary is used to facilitate group key negotiation, then the ease of operation is improved, but the security is worsened because the intermediary may access or derive the group key
Solution Approach 1:
The patent uses an intermediary to facilitate key exchange between parties, but designs the system so the intermediary cannot derive the final group key. The intermediary helps establish shared secrets between adjacent parties in a ring topology and coordinates the key formation process, yet the final group key is computed locally by each party using their private key and the intermediary's public information, preventing the intermediary from accessing the group key.
2Reliability
If each party shares cryptographic keys with adjacent parties in a ring topology, then the security is improved because the group key is unknown to intermediaries, but the device complexity is worsened due to multiple key management requirements
Solution Approach 1:
The patent segments the key management process into distinct components: each party manages only their own cryptographic key pair and their adjacent party relationships in the ring topology. The overall group key formation is divided into independent steps that can be executed locally by each party, rather than requiring centralized key management. This segmentation reduces the complexity burden on individual devices while maintaining security.
3Productivity
If the group key is formed by combining multiple cryptographic keys including intermediary keys, then the productivity is improved by simplifying the key formation process, but the security is worsened as the intermediary gains knowledge of the group key
Solution Approach 1:
The patent extracts the intermediary's cryptographic keys from the final group key formation process. While the intermediary facilitates the key exchange and their public keys are used in the protocol, the final group key is constructed exclusively from the private keys and shared secrets of the end parties, excluding the intermediary's key material. This extraction ensures the intermediary cannot derive the group key even though they participate in the process.
Data Source
AI summary
A computer-implemented method of creating a group key for a group of N parties using an intermediary, the method includes sharing a cryptographic key of a party with an adjacent party in an ordered ring, wherein each party has another cryptographic key of an adjacent party; generating a meeting key for the party based on combining the cryptographic key of the party with a shared cryptographic key from an adjacent party; sending the meeting key to the intermediary and receiving an intermediate key from the intermediary, wherein the intermediary computes the intermediate key by combining at least two meeting keys of corresponding parties; creating the group key by combining the cryptographic key of the party with the received intermediate key, wherein the created group key includes a combination of at least N−1 of the cryptographic keys of the parties; and using the group key with another party of the group.