Universal Ciphertext Transformation via Intermediary Keys

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Solution Overview

Problem

Conventional ciphertext transformation schemes are limited in transforming ciphertext from one public key encryption scheme into another, requiring time and increased costs for designing proxy re-encryption, and cannot universally transform ciphertext of existing public key encryption schemes.

Innovation Solution

A transformation key generation apparatus and method that uses probabilistic circuit or function secret sharing to generate a transformation key for converting ciphertext from one public key encryption scheme to another, enabling the transformation of ciphertext between different public key encryption schemes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional ciphertext transformation schemes are used, then ciphertext can be transformed between specific encryption schemes, but the transformation is limited to formats specified by the scheme and cannot universally transform any public key encryption scheme

Engineering Contradiction:

Improvetransformation compatibilityVSAvoidscheme design complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent introduces a transformation key as an intermediary element that enables ciphertext transformation between different public key encryption schemes. The transformation key acts as a mediator that bridges the source encryption scheme and the destination encryption scheme, allowing universal transformation without requiring custom proxy re-encryption design for each scheme pair. This resolves the contradiction by providing a general-purpose transformation mechanism that works across different schemes.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent creates a universal ciphertext transformation framework that can transform ciphertext from any public key encryption scheme to any other public key encryption scheme. The transformation apparatus and method are designed to be scheme-agnostic, accepting ciphertext from various source schemes and producing ciphertext compatible with various destination schemes, thereby achieving multi-functionality and broad adaptability without increasing design complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If proxy re-encryption is designed from scratch for specific encryption schemes, then ciphertext transformation between those schemes is possible, but it takes time and increases introduction cost

Engineering Contradiction:

Improvetransformation capabilityVSAvoiddesign time

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The patent performs preliminary action by pre-generating transformation keys that can be used for ciphertext transformation. Instead of designing proxy re-encryption from scratch when transformation is needed, the transformation keys are prepared in advance using the transformation key generation apparatus. This eliminates the need for time-consuming custom design for each transformation scenario, as the universal transformation framework is already in place.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The transformation key generation apparatus enables self-service by automatically generating transformation keys without requiring manual proxy re-encryption design. The system can autonomously produce the necessary transformation credentials using the transformation key generation method, eliminating the need for expert intervention or custom scheme design, thereby reducing both time and cost.

Inventive Principle:

Principle #25Self-service

3Adaptability or versatility

If conventional ciphertext transformation is used, then transformation within the same scheme format is possible, but transformation of existing public key encryption schemes into other public key encryption schemes is not possible

Engineering Contradiction:

Improvecross-scheme transformationVSAvoidtransformation security

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The transformation key serves as a secure intermediary that enables cross-scheme transformation while maintaining security. The transformation key is generated using cryptographically secure methods and is used to transform ciphertext from source scheme to destination scheme without exposing the underlying plaintext or private keys. This intermediary mechanism ensures that transformation security is maintained even when operating across different encryption schemes with potentially different security properties.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS11450238B2Conversion key generation apparatus, encrypted text conversion apparatus, decryption apparatus, encrypted text conversion system, conversion key generation method, encrypted text conversion method, decryption method, and program

Publication Date: 2022.09.20 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

A transformation key generation apparatus has key generation means for receiving a decryption key sks of a first public key encryption scheme Σs and a public key pkd of a second public key encryption scheme Σd, and generating a transformation key utks→d for transforming first ciphertext cts of the first public key encryption scheme Σs into second ciphertext tct of the second public key encryption scheme Σd by using a probabilistic circuit or function secret sharing.