Re-encryption Key Generation Device for Attribute-Based Proxy-Re-Encryption

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Solution Overview

Problem

Attribute-based proxy-re-encryption schemes increase the size of ciphertext during re-encryption due to the inclusion of a random matrix.

Innovation Solution

A re-encryption key generation device that randomizes and encrypts a decryption key using attribute-based encryption, eliminating the need for a random matrix in the re-encrypted ciphertext.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a random matrix is included in a re-encrypted ciphertext to enable attribute-based proxy-re-encryption, then the functionality of changing decryption authority is improved, but the size of the ciphertext increases

Engineering Contradiction:

Improvedecryption authority changing functionalityVSAvoidciphertext size

Core Design Contradiction:

Adaptability or versatilityVSVolume of stationary object

Solution Approach 1:

The patent extracts the random matrix from the re-encrypted ciphertext and relocates it to the re-encryption key. This separation allows the re-encrypted ciphertext to be stored more efficiently while the re-encryption key (which is not frequently updated) contains the random matrix needed for future re-encryption operations. The decryption authority changing functionality is preserved because the random matrix remains accessible through the re-encryption key when needed.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The random matrix is generated and stored in advance in the re-encryption key during the key generation phase, before any re-encryption operations are performed. This preliminary action eliminates the need to include the random matrix in each re-encrypted ciphertext, as it is already prepared and stored separately. The functionality is maintained because the pre-stored random matrix can be used when re-encryption is needed.

Inventive Principle:

Principle #10Preliminary action

2Volume of stationary object

If the ciphertext size is reduced by eliminating the random matrix, then storage efficiency is improved, but the complexity of key management increases

Engineering Contradiction:

Improveciphertext sizeVSAvoidkey management complexity

Core Design Contradiction:

Volume of stationary objectVSDevice complexity

Solution Approach 1:

The patent moves the random matrix from the ciphertext dimension to the key dimension, creating a separate storage dimension for cryptographic parameters. This dimensional separation allows ciphertext to be stored compactly while keys are managed separately with their own storage structure. The increased key management complexity is isolated to the key dimension and does not affect ciphertext storage efficiency.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS11349654B2Re-encryption key generation device, re-encryption device, re-encrypted ciphertext decryption device, and cryptographic system

Publication Date: 2022.05.31 MITSUBISHI ELECTRIC CORP

AI summary

A key generation device generates a decryption key dkx having a tag-added decryption key and a decryption key adkx. The tag-added decryption key includes a decryption key tdkx in which a key attribute x is set and a tag tgφ required to decrypt a ciphertext with the decryption key tdkx. In the decryption key adkx, the key attribute x is set. An encryption device generates an original ciphertext octy in which a ciphertext attribute y corresponding to the key attribute x is set and which can be decrypted with the tag-added decryption key. A re-encryption key generation device encrypts the decryption key tdkx by an attribute-based encryption scheme using a ciphertext attribute y′, so as to generate a re-encryption key rkx,y′ which is a key for generating a re-encrypted ciphertext rcty′ which can be decrypted with a decryption key adkx′ in which a key attribute x′ corresponding to the ciphertext attribute y′ is set.