Block Cipher Mode Non-Standard Buffer Encryption

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Solution Overview

Problem

Existing block ciphers, such as AES, require message padding to encrypt data of non-standard sizes, which reveals the message length to attackers, compromising security.

Innovation Solution

The method modifies block cipher modes to encrypt data of sizes not multiples of the standard block size by creating an intermediate block cipher of a non-standard size, allowing encryption without padding and enhancing security by preventing clear data leakage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If message padding is used to encrypt data of non-standard sizes, then encryption can be performed on any message length, but the message size is revealed to attackers

Engineering Contradiction:

Improveencryption capability for any message lengthVSAvoidmessage size leakage

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediary component - a buffer of non-standard size that acts as a mediator between the message and the block cipher. This buffer absorbs the size mismatch without requiring standard padding, thereby preventing message size leakage while still enabling encryption of arbitrary length messages.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the parameter of block size from the fixed standard size to a non-standard size that matches the actual message length. By modifying this critical parameter, the system eliminates the need for padding and prevents attackers from inferring message size from the ciphertext structure.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If standard block cipher modes are used, then encryption is simple and well-defined, but the fixed block size multiple property helps attackers understand the cipher structure

Engineering Contradiction:

Improvesimplicity of encryptionVSAvoidcipher structure vulnerability

Core Design Contradiction:

Ease of operationVSObject-affected harmful factors

Solution Approach 1:

The patent applies asymmetry by using a non-standard buffer size that breaks the symmetric pattern of fixed block size multiples. This asymmetric approach maintains operational simplicity while confusing attackers who rely on predictable block size patterns to analyze cipher structure.

Inventive Principle:

Principle #4Asymmetry

3Ease of manufacture

If padding is concatenated to messages, then messages can be encrypted, but the padded message size is always a multiple of block size

Engineering Contradiction:

Improveencryption process feasibilityVSAvoidoriginal message size information

Core Design Contradiction:

Ease of manufactureVSLoss of information

Solution Approach 1:

The patent extracts the padding operation entirely from the encryption process. Instead of adding padding bits to reach block size multiples, the system uses a buffer that exactly matches the message length, removing the harmful padding step while preserving encryption feasibility.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS8687803B2Operational mode for block ciphers

Publication Date: 2014.04.01 APPLE INC

AI summary

In the field of computer enabled cryptography, such as a keyed block cipher having a plurality of sequenced rounds, the cipher is hardened against attack by a protection process. The protection process uses block lengths that are larger or smaller than and not an integer multiple of those of an associated standard cipher, and without using message padding. This is operative in conjunction with standard block ciphers such as the AES, DES or triple DES ciphers, and also with various block cipher cryptographic modes such as CBC or EBC.