Broadcast Encryption Key Revocation Management
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Solution Overview
Problem
Existing broadcast encryption methods are inefficient for managing key revocation in large populations, as they require significant bandwidth and are vulnerable to collusion, especially when dealing with a small percentage of cancelled subscribers, leading to impractical bandwidth usage and security issues.
Innovation Solution
A method utilizing a key generation engine, encryption engine, and decryption engine that generates random values and blinding factors to create a constant-size ciphertext, allowing only non-revoked devices to compute the final key through tree-based key derivation and pairing operations, ensuring collusion resistance and efficient bandwidth usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If individual Cancel messages are sent to each cancelled subscriber, then key revocation is achieved, but bandwidth consumption becomes proportional to the number of cancelled subscribers
Solution Approach 1:
The patent combines multiple individual Cancel messages into a single aggregated message that can be broadcast to all subscribers simultaneously. This merging approach maintains the effectiveness of key revocation while reducing bandwidth consumption from O(n) to O(1), where n is the number of cancelled subscribers.
Solution Approach 2:
The invention creates a universal message format that serves multiple functions: it addresses all cancelled subscribers in a single transmission, provides addressing information for message validation, and enables efficient key distribution to remaining subscribers. This multi-functional message structure eliminates the need for separate individual messages.
2Quantity of substance
If a global message with addressing information is used, then bandwidth consumption is reduced, but any terminal can decrypt and retrieve the new key regardless of whether it is addressed to it
Solution Approach 1:
The patent implements local quality by giving each subscriber a unique decryption capability based on their individual credentials. While the message is broadcast globally, only the intended recipient(s) possess the specific local key material needed to decrypt it. This is achieved through subscriber-specific key pairs where the private key is stored locally in each terminal.
Solution Approach 2:
The invention introduces cryptographic key pairs as intermediaries between the broadcast message and the subscriber terminals. The public key acts as a mediator that allows anyone to encrypt the message, while the private key (stored locally in authorized terminals) acts as a mediator that allows only specific terminals to decrypt it. This intermediary mechanism resolves the contradiction between global broadcast and selective access.
3Device complexity
If state-of-the art broadcast encryption schemes are used, then key management is simplified, but ciphertext grows linearly with the number of revoked users or decryption keys depend linearly on the number of users
Solution Approach 1:
The patent performs preliminary action by pre-distributing public keys to all subscribers during system initialization, before any revocation events occur. This preliminary setup creates a foundation that enables efficient revocation handling later, where only the necessary minimal information needs to be transmitted. The pre-established key infrastructure eliminates the need for linear growth in ciphertext or key sizes during revocation operations.
Data Source
AI summary
The present invention concerns the field of broadcast encryptionmethod, i.e. a method to organize the distribution of keys into a group of users so that it is possible to manage the revocation of one member of the group in an efficient way. The proposed solution is a private encryption key ciphertext constant collusion-resistant broadcast encryption. The main idea behind the invention is to mix the notion of efficient tree-based key derivation (also called subset management) with individual and personalized key blinding thus achieving a full collusion-resistant broadcast encryption system. The key de-blinding is performed at the last moment thanks to a cryptographic technique called pairings (also known as bilinear maps) resulting in a global key commonly shared by all authorized (non-revoked) devices. It should be noted that only non-revoked devices can compute the final key (this is achieved through subset management and related subset key derivation technique) and perform the de-blinding (which is performed with one pairing).