Adaptive Encryption Length Preserving Short Plaintexts
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Solution Overview
Problem
Cryptographic systems face challenges in determining the encryption key used for decrypting ciphertexts, especially when the combination of plaintext and ciphertext character domains does not allow for a sufficient number of keys, leading to unreliable key rollover mechanisms.
Innovation Solution
The system employs a dual encryption method: length-preserving and length-extending encryption, where longer plaintexts are encrypted with a method that maintains the same length, and shorter plaintexts are encrypted with a method that extends the ciphertext length, allowing the decrypting device to determine the encryption method used and retrieve the correct key.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If character domain expansion is used to embed key references in ciphertext, then the number of supported encryption keys increases, but the ciphertext length increases relative to plaintext length
Solution Approach 1:
The patent applies dynamics by making the ciphertext length adaptive rather than fixed. The system dynamically adjusts ciphertext length based on the plaintext length: for longer plaintexts, character domain expansion is used (maintaining ciphertext length equal to plaintext length), while for shorter plaintexts, the system extends ciphertext length to embed sufficient key references. This dynamic approach resolves the contradiction by allowing the system to optimize between key capacity and ciphertext bloat on a per-encryption basis.
Solution Approach 2:
The patent changes the parameter of ciphertext length based on the plaintext length parameter. By establishing a threshold length and applying different encryption strategies above and below this threshold, the system dynamically adjusts the ciphertext-to-plaintext length ratio. This parameter change allows the system to support more keys when necessary (for short plaintexts) while maintaining efficiency when not necessary (for long plaintexts).
2Productivity
If a fixed threshold length is used to select encryption methods, then processing efficiency improves, but flexibility in handling edge cases decreases
Solution Approach 1:
The patent segments the encryption space by dividing plaintexts into two categories based on a threshold length: those above the threshold and those at or below it. This segmentation allows the system to apply different encryption methodologies tailored to each segment's characteristics. The threshold acts as a clean division point that simplifies decision-making (improving efficiency) while still accommodating diverse plaintext lengths (maintaining flexibility through appropriate method selection for each segment).
Data Source
AI summary
Examples discussed herein disclose, among other things, a method. The method includes, among other things, obtaining a plaintext, obtaining a key from a plurality of keys, and determining whether the plaintext is longer than a predefined threshold length. If the plaintext is longer than the predefined threshold length, the method may encrypt the plaintext with the key to generate a first ciphertext having a length of the plaintext, where the character at a predefined position within the first ciphertext belongs to a first subset of characters. And if the plaintext is not longer than the predefined threshold length, the method may encrypt the plaintext with the key to generate a second ciphertext, which is longer than the plaintext, where the character at the same predefined position in the second ciphertext belongs to a second subset of characters.