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manipulation techniques to present the verdict to the user (how good their guess was). For educational purposes, we also dump the entire XML response into a textarea element, for those who want to look at SOAP data in more detail. Enabling the PrivilegeManager in Firefox

As we noted earlier, the PrivilegeManager can be configured not to respond to our programmatic pleas. To find out whether a Firefox browser is configured this way, type “about:config” into the address bar to reveal the preferences list. Use the filter textbox to find the entry signed.applets.codebase_principal_support. If the value is true, then our code above will work. If not, we won’t be able to contact Google. Earlier versions of Mozilla required that the configuration be edited by hand, followed by a complete browser restart. In Firefox, double-clicking the relevant row in the preferences list will toggle the preference value between true and false. Changes made in this way will take place immediately, without needing to restart the browser, or even refresh the page, if the preferences are opened in a separate tab. Signing Mozilla client code

Because Internet Explorer bypasses the PrivilegeManager, the application functions smoothly enough in that browser. However, in Mozilla the user is confronted with the scary-looking dialog twice (assuming that the browser is configured to use the PrivilegeManager), making this sort of web service approach rather problematic for Mozilla users. They can prevent it from reappearing by selecting the

“Remember my decision” checkbox (see figure 7.5), but we developers have no control over that (and quite rightly so!).

There is a solution, but it requires the application to be packaged in a way that is very specific to Mozilla. Web applications may be signed by digital certificates. To be signed, however, they must be delivered to Mozilla browsers in JAR files, that is, compressed zip archives with all scripts, HTML pages, images, and other resources in one place. JAR files are signed with digital certificates of the variety sold by companies such as Thawte and VeriSign. Resources inside signed JAR files are referred to using a special URL syntax, such as

jar:http://myserver/mySignedJar.jar|/path/to/someWebPage.html

When the user downloads a signed web application, they are asked once whether they want to allow it to grant any privileges that it asks for, and that is that. Licensed to jonathan zheng

Protecting confidential data

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Mozilla provides free downloadable tools for signing JAR files. For users who want to simply experiment with this technology, unauthenticated digital certificates can be generated by tools such as the keytool utility that ships with the Sun Java Development Kit (JDK). We, however, recommend using a certificate from a recognized authority for live deployments.

Signed JAR files are not portable. They will only work in Mozilla browsers. For that reason, we won’t pursue them in any greater detail here. If you’re interested in exploring this approach further, have a look at the URLs in the Resources section.

This concludes our discussion on interacting with remote services using Ajax. We’ve reached to the point where our application is running in the browser, exchanging data with its server and possibly with third-party servers as well. That data is unlikely to execute malicious code on your machine, but it may be a security risk of a different kind, particularly if the data is confidential. In the next section, we’ll see how to safeguard your users’ data from prying eyes. 7.3 Protecting confidential data

The web browser that your user is sitting in front of does not enjoy a direct connection to your server. When data is submitted to the server, it is routed across many intermediate nodes (routers and proxy servers, for instance) on the Internet before it finds your server. Ordinary HTTP data is transmitted in plain text, allowing any intermediate node to read the data in the packets.