OcrV1, PascalFrancis, Checkpoint, bibRecord, 000347

CAPTCHA challenge strings : problems and improvements

Identifieur interne : 000347 ( PascalFrancis/Checkpoint ); précédent : 000346; suivant : 000348

CAPTCHA challenge strings : problems and improvements

Auteurs : Jon Bentley [États-Unis] ; Colin Mallows [États-Unis]

Source :

Proceedings of SPIE, the International Society for Optical Engineering [ 0277-786X ] ; 2006.

RBID : Pascal:07-0377977

Descripteurs français

Pascal (Inist)
- Etude expérimentale, Reconnaissance optique caractère, Dictionnaire, Consonne, Voyelle, Psychologie, Reconnaissance forme, 4230S.
Wicri :
- topic : Dictionnaire, Psychologie.

English descriptors

KwdEn :
- Consonant, Dictionaries, Experimental study, Optical character recognition, Pattern recognition, Psychology, Vowel.

Abstract

A CAPTCHA is a Completely Automated Public Test to tell Computers and Humans Apart. Typical CAPTCHAs present a challenge string consisting of a visually distorted sequence of letters and perhaps numbers, which in theory only a human can read. Attackers of CAPTCHAs have two primary points of leverage: Optical Character Recognition (OCR) can identify some characters, while nonuniform probabilities make other characters relatively easy to guess. This paper uses a mathematical theory of assurance to characterize the probability that a correct answer to a CAPTCHA is not just a lucky guess. We examine the three most common types of challenge strings, dictionary words, Markov text, and random strings, and find substantial weaknesses in each. We therefore propose improvements to Markov text, and new challenges based on the consonant-vowel-consonant (CVC) trigrams of psychology. Theory and experiment together quantify problems in current challenges and the improvements offered by modifications.

Affiliations:

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Le document en format XML

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CAPTCHA challenge strings : problems and improvements

CAPTCHA challenge strings : problems and improvements

Source :

Descripteurs français

English descriptors

Abstract

Links toward previous steps (curation, corpus...)

Links to Exploration step

Le document en format XML

Pour manipuler ce document sous Unix (Dilib)

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