Pro PHP Security: From Application Security Principles to the Implementation of XSS Defenses, Second Edition

Summary

In this chapter, we have discussed captchas, challenges that require the user to exercise some sort of intellectual judgment before being permitted to continue; they are designed to block robots or automated attackers from continuing. Captchas might require reading obfuscated text contained in an image, hearing obfuscated speech, or interpreting a set of conditions.

We demonstrated how to create and use a simple text image captcha. Finally, we outlined the problems inherent in using captchas and expecting them to discriminate reliably between human and machine respondents.

In Chapter 10, we will continue with the next problem in practicing secure operations: now that you know that your users are human, how do you go about verifying their ...