Modified CTRT Encryption Scheme for Stronger Key Lengths
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Solution Overview
Problem
The existing All Or Nothing Transform (AONT) scheme, specifically the Counter Transform (CTRT) algorithm, is restricted by the condition k≤l for block length l and key length k of a block cipher, limiting its implementation with stronger key lengths like AES's 192 and 256-bit keys due to compatibility issues.
Innovation Solution
A modified CTRT scheme that segments an original bit sequence into input blocks, encrypts them using a key longer than the block length, concatenates intermediate blocks, and applies an invertible transformation function to produce output blocks, allowing for key lengths greater than the block length, thereby overcoming the k≤l restriction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the CTRT scheme is used with traditional block ciphers like DES, then the restriction k≤l is satisfied, but stronger key lengths like AES's 192 and 256 bits cannot be used
Solution Approach 1:
The patent divides the encryption process into multiple stages: first encrypting data blocks with a key derived from a random bit sequence, then applying an additional transformation layer. This segmentation allows the system to accommodate key lengths greater than block lengths by separating the key derivation and encryption functions.
Solution Approach 2:
The patent changes the fundamental parameter relationship from k≤l to k>l by introducing a random bit sequence of length k that is longer than the block length l. The key is derived from this random sequence, and the encryption process is modified to handle this parameter change, enabling stronger key lengths like AES-256.
2Reliability
If data is split into multiple fragments using threshold splitting, then security is improved, but data size increases about n-fold
Solution Approach 1:
The patent applies the All Or Nothing Transform (AONT) as a preliminary transformation step before splitting data into fragments. This AONT layer is added to the encryption process, transforming the data in advance to ensure that even if fragments are compromised, the original data cannot be recovered without all fragments.
Solution Approach 2:
The patent combines multiple encryption layers: traditional block cipher encryption with AONT transformation. This composite approach integrates the security benefits of both methods, achieving strong security without the need for excessive data splitting, thus controlling data size growth.
3Ease of manufacture
If OAEP scheme is used for AONT transformation, then compatibility with computer implementation is improved, but calculation cost increases due to hash value expansion
Solution Approach 1:
The patent extracts and removes the computationally expensive hash value expansion process from the encryption scheme. Instead of using OAEP's hash-based transformation, the patent employs a simpler AONT approach that achieves the same security goals without the heavy computational overhead, thus reducing energy consumption and calculation cost.
Data Source
AI summary
A data processing apparatus includes a processing circuit configured to segment an original bit sequence into a plurality of input blocks each having a first block length, create a random bit sequence, encrypt respective ones of the plurality of input blocks with a block cipher scheme using a key (having a key length larger than the first block length) based on the random bit sequence to derive intermediate blocks, concatenate every predetermined number of intermediate blocks to form one or more output blocks, compute an invertible transformation function on the one or more output blocks and the random bit sequence to derive a further output block, and output an encrypted bit sequence including those output blocks.