Obfuscated Character CAPTCHA with Substitute Hints
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Solution Overview
Problem
Recent advances in machine vision and OCR technologies have made it increasingly difficult for traditional character-based CAPTCHA schemes to distinguish between humans and computers, while audio CAPTCHA schemes are also being defeated by automated programs, necessitating a more robust security mechanism.
Innovation Solution
The implementation of a CAPTCHA system that incorporates obfuscated characters with substitute characters, where users are provided with indications of which characters to substitute, along with adjustable difficulty levels and multi-modal presentations (visual and audio) to enhance human recognition and thwart automated programs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional character-based CAPTCHA schemes are used, then implementation simplicity is maintained, but security effectiveness deteriorates due to advances in machine vision and OCR technologies
Solution Approach 1:
The patent introduces obfuscated characters as intermediaries between the CAPTCHA system and automated programs. These obfuscated characters serve as a mediator that humans can interpret through contextual clues while automated OCR systems struggle to recognize, thereby resolving the contradiction between maintaining simplicity and improving security effectiveness.
Solution Approach 2:
The patent changes the parameter of character recognizability by introducing obfuscation techniques that alter the visual appearance of characters while preserving their identity through contextual hints. This parameter change makes the CAPTCHA resistant to automated recognition systems while remaining solvable by humans, thus improving security without significantly increasing complexity.
2Reliability
If audio CAPTCHA schemes are implemented, then human recognition capability is enhanced, but automation resistance deteriorates as automated programs can also process audio
Solution Approach 1:
The patent implements a multi-functional CAPTCHA system that can operate in both visual and audio modes, making it universal across different user preferences and capabilities. The visual mode with obfuscated characters provides automation resistance, while the audio mode maintains ease of operation for users who prefer auditory interfaces, thus resolving the contradiction between automation resistance and ease of operation.
3Reliability
If obfuscated characters with substitute characters are used, then security against automated programs is improved, but user recognition accuracy may deteriorate due to character distortion
Solution Approach 1:
The patent applies local quality by providing different levels of obfuscation to different characters in the CAPTCHA string. Some characters are highly obfuscated to challenge automated programs, while others remain relatively clear to serve as anchors for human recognition. This localized differentiation ensures that security effectiveness is improved without completely compromising user recognition accuracy.
Solution Approach 2:
The patent incorporates feedback mechanisms where users can request hints or explanations for obfuscated characters, and the system provides contextual clues about the substitute characters. This feedback loop helps users overcome the difficulty of recognizing distorted characters while maintaining the security challenge against automated programs, thus balancing security effectiveness with recognition accuracy.
Data Source
AI summary
A method for determining if a user of a computer system is a human. A processor receives an indication that a computer security program is needed and acquires at least one image depicting a first string of characters including at least a first and second set of one or more characters. A processor assigns a substitute character to be used as input for each of the second set of one or more characters. A processor presents the at least one image and an indication of the substitute character and when to use the substitute character to the user. A processor receives a second string of characters from the user. A processor determines whether the second string of characters substantially matches the first string of characters based on the substitute character assigned to each of the second set of one or more characters and determines whether the user is a human.