Tamper-Evident Printed Document Verification via Selective Hashing
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Solution Overview
Problem
Current methods fail to render printed documents tamper evident, as standard hash algorithms are ineffective due to lossy printing processes and the inclusion of unprinted information, and are vulnerable to compensating changes that evade detection.
Innovation Solution
A system that generates an integrity verification code (IVC) by excluding undeterminable document elements from the hash calculation, allowing only a subset of document elements, such as printable characters, to be hashed, and applying consistent rules for other characters, thereby tolerating changes and eliminating hiding places for compensating changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard hash algorithms are applied to printed documents, then the hash calculation includes all document elements, but this causes false alarms due to lossy printing processes and unprinted information
Solution Approach 1:
The patent extracts only the printable characters from the document and excludes unprinted elements (metadata, formatting commands, etc.) from the hash calculation. This extraction resolves the contradiction by ensuring that only determinable document content is hashed, preventing false alarms from unprinted information while maintaining detection reliability for actual tampering.
Solution Approach 2:
The patent applies different treatment to different parts of the document: printable characters are included in the hash, while unprinted elements are excluded. This local differentiation resolves the measurement precision issue by ensuring consistent hashing only where the printing process preserves determinability.
2Reliability
If all document elements are included in hash calculation, then complete document integrity is verified, but compensating changes can evade detection
Solution Approach 1:
By extracting and excluding unprinted elements from the hash calculation, the patent eliminates the hiding places where compensating changes could be inserted. This resolves the contradiction by ensuring that only the printable content—where changes are detectable—is verified, preventing compensating changes from evading detection.
3Ease of operation
If printing process is used to create documents, then documents are accessible in physical form, but the printing process is lossy and creates unprinted information
Solution Approach 1:
The patent accepts the lossy nature of printing by extracting only the printable characters for hashing, while intentionally excluding the lost unprinted information (metadata, formatting commands). This resolves the contradiction by adapting the verification process to work with the limitations of the printing process, maintaining ease of physical document access while achieving reliable verification.
Data Source
AI summary
A system and method are disclosed for rendering printed documents tamper evident. Examples render classes of documents tamper evident with cryptographic level security or detect tampering events, where such security was previously unavailable, for example, in documents printed using common printers without special paper or ink. Examples enable proving the date of document content without the need for expensive third party archival, including documents held, since their creation, entirely in secrecy or in untrustworthy environments, such as on easily-altered, publicly-accessible internet sites. Examples can use a document's prior registration date in a blockchain to establish a no-later than date-of-existence for that document. Examples can extend the useful life of integrity verification algorithms, such as hash functions, even when applied to binary executable files. Examples can efficiently identify whether multiple document versions are substantially similar, even if they are not identical, thus potentially reducing storage space requirements.