Ciphertext Conversion System Using Intermediary Keys

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Solution Overview

Problem

Existing techniques require decryption of symmetric-key encryption ciphertexts to convert them into public-key encryption ciphertexts, exposing plaintext and compromising security.

Innovation Solution

A ciphertext conversion system that generates conversion keys using public-key and symmetric-key encryption schemes, allowing for the conversion of symmetric-key ciphertexts to public-key ciphertexts without decryption through exclusive-OR operations with partial conversion keys.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If existing techniques are used to convert symmetric-key ciphertext to public-key ciphertext, then conversion capability is achieved, but plaintext is exposed and security is compromised

Engineering Contradiction:

Improveciphertext conversion capabilityVSAvoidsecurity

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent introduces a conversion key as an intermediary element that enables transformation from symmetric-key ciphertext to public-key ciphertext without revealing the plaintext. The conversion key combines public-key and symmetric-key components to facilitate secure conversion, acting as a mediator that preserves security while achieving conversion capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The conversion process is segmented into multiple components: a public-key ciphertext portion and a symmetric-key ciphertext portion. This segmentation allows the system to handle conversion in parts, where the public-key portion provides conversion capability and the symmetric-key portion maintains security through key-based encryption without full plaintext exposure.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If decryption is performed to convert ciphertext, then conversion is achieved, but computational resources and time are consumed

Engineering Contradiction:

Improveciphertext conversion capabilityVSAvoidconversion time

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The system performs preliminary actions by pre-generating conversion keys that combine public-key and symmetric-key components. This preliminary key preparation enables faster conversion operations later, as the complex conversion logic is prepared in advance through key generation rather than requiring time-consuming decryption operations during actual conversion.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces the mechanical decryption process with a key-based conversion mechanism. Instead of performing full decryption operations that consume significant computational resources and time, the system uses conversion keys to directly transform ciphertext formats, substituting a more efficient key-driven approach for the slower decryption-based approach.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If decryption is performed for conversion, then conversion capability is achieved, but key generation costs increase

Engineering Contradiction:

Improveciphertext conversion capabilityVSAvoidkey generation cost

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent merges public-key and symmetric-key operations into a unified conversion key structure. By combining these two key types into a single conversion key that enables direct ciphertext transformation, the system reduces the need for separate key generation processes and lowers overall key management costs while maintaining conversion capability.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The conversion key serves multiple functions: it enables ciphertext conversion, maintains security, and reduces computational overhead. This multi-functional design eliminates the need for separate decryption and encryption operations, thereby reducing key generation costs and improving system efficiency.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS20240421975A1Ciphertext conversion system, ciphertext conversion method, and non-transitory computer readable medium

Publication Date: 2024.12.19 MITSUBISHI ELECTRIC CORP

AI summary

A ciphertext conversion system (100) includes a conversion key generation device (600) and a conversion device (700). The conversion key generation device (600) performs encryption of a public-key encryption scheme using a public key and a first decryption enabling condition, so as to generate a first converted public-key ciphertext and a key corresponding to the first converted public-key ciphertext, performs encryption of a symmetric-key encryption scheme using a second symmetric-key encryption secret key as a plaintext and the key corresponding to the first converted public-key ciphertext as a secret key, so as to generate a first partial conversion key, and calculates, as a second partial conversion key, an exclusive-OR of a result of performing encryption using a first symmetric-key encryption secret key and first auxiliary information and a result of performing encryption using the second symmetric-key encryption secret key and second auxiliary information. The conversion device (700) calculates, as at least part of a converted symmetric-key ciphertext, an exclusive-OR of a symmetric-key ciphertext and the second partial conversion key, where the symmetric-key ciphertext is an exclusive-OR of a plaintext and a result of performing encryption using the first symmetric-key encryption secret key and the first auxiliary information.