CAPTCHA: Using Hard AI Problems for Security

Abstract

Abstract. We introduce captcha, an automated test that humans can pass, but current computer programs can't pass: any program that has high success over a captcha can be used to solve an unsolved Artificial Intelligence (AI) problem. We provide several novel constructions of captchas. Since captchas have many applications in practical security, our approach introduces a new class of hard problems that can be exploited for security purposes. Much like research in cryptography has had a positive impact on algorithms for factoring and discrete log, we hope that the use of hard AI problems for security purposes allows us to advance the field of Artificial Intelligence. We introduce two families of AI problems that can be used to construct captchas and we show that solutions to such problems can be used for steganographic communication. captchas based on these AI problem families, then, imply a win-win situation: either the problems remain unsolved and there is a way to differentiate humans from computers, or the problems are solved and there is a way to communicate covertly on some channels.

Hardness Amplification of Weakly Verifiable Puzzles

“…We show that, even in this setting, if no efficient algorithm can solve a single puzzle with probability much more than ε, then no efficient algorithm can simultaneously solve n puzzles with probability much more than ε n , which is essentially optimal. 1 We also show that the weak verifiability property is essential for obtaining such a general hardness amplification result: We exhibit an example of puzzles that are not even weakly verifiable, and where the probability of solving multiple instances is the same as the probability of solving a single instance.…”

“…One example of weakly verifiable puzzles is the notion of computer-generated inverse Turing tests, or CAPTCHAs [11,1]. These are distribution of puzzles that are easily solvable by humans, but are assumed to be solvable by computers only with small (albeit noticeable) probability.…”

“…Still, CAPTCHAs are weakly verifiable, as it is possible to efficiently generate a CAPTCHA together with its unique solution. In the work of von-Ahn et al [1], they suggests sequential repetition as a method of hardness amplification for CAPTCHAs. Our work indicates that parallel repetition can be used as well.…”

User identity issues in mashups for learning experiences using IMS Learning Design

“…Current anti-spam technologies, such as "captchas" [14], precludes the possibility of creating user accounts automatically in the external service. Thus, a different approach is required.…”

Enforcing Email Addresses Privacy Using Tokens

“…Another often mentioned technology in relation to spam is captcha (Completely Automated Public Turing Test to Tell Computer and Humans Apart) [3]. It is not a technology to counter spam per se but nowadays it is often used to prevent bots from accessing certain information or pages.…”