Decryption Condition Addition Device Matrix Restriction
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Solution Overview
Problem
In proxy re-encryption schemes, the generation of a re-encryption key requires access to a user secret key or master secret key, leading to increased key accesses and inefficiencies.
Innovation Solution
A decryption condition is restricted by adding a row and a column to the secret distribution matrix in the ciphertext, eliminating the need for a re-encryption key.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a re-encryption key is used to change the decryption condition of a ciphertext, then the decryption condition can be changed, but the number of accesses to the user secret key or master secret key increases
Solution Approach 1:
The invention segments the decryption condition change process into two independent parts: (1) the original ciphertext with its secret distribution matrix, and (2) an additional access structure that can be added without requiring the secret key. This allows the decryption condition to be modified by simply adding structural elements rather than generating new re-encryption keys that require secret key access.
Solution Approach 2:
The invention performs preliminary action by pre-defining the additional access structure that will be added to the secret distribution matrix. This additional structure is prepared in advance with predetermined values, so when decryption condition changes are needed, no time-consuming key generation or secret key access is required - the pre-prepared structure is simply integrated.
2Reliability
If a re-encryption key is generated to restrict decryption conditions, then security is improved, but the complexity of the system increases due to key management
Solution Approach 1:
The invention extracts the decryption condition restriction functionality from the re-encryption key generation process. Instead of requiring a re-encryption key to impose restrictions, the invention directly adds an additional access structure to the ciphertext's secret distribution matrix, separating the restriction mechanism from secret key dependencies.
Solution Approach 2:
The additional access structure serves as an intermediary element between the original ciphertext and the decryption process. This intermediary structure with predetermined values enables decryption condition restrictions without requiring direct interaction with secret keys or complex re-encryption key management protocols.
3Adaptability or versatility
If the secret distribution matrix is modified by adding rows and columns related to restriction conditions, then decryption condition restriction is achieved, but the ciphertext size increases
Solution Approach 1:
The invention changes parameters of the secret distribution matrix by adding rows and columns with predetermined values rather than arbitrary data. These additional parameters are structured to provide decryption condition restrictions while maintaining efficiency, as the predetermined values allow for optimized storage and processing compared to general matrix expansions.
Data Source
AI summary
A decryption condition addition device (300) acquires an original ciphertext cts in which a secret distribution matrix M is set as information specifying a decryption condition and acquires an additional access structure S+ which is a restriction condition to restrict the decryption condition of the original ciphertext cts. The decryption condition addition device (300) adds a row and a column which are indicated in the additional access structure S+ to the secret distribution matrix M set in the original ciphertext cts, and thereby generates an updated ciphertext cts, for which the decryption condition of the original ciphertext cts is restricted.