Java Programing

application impose an effective level of trust before running an arbitrary piece of code. And once a security manager is installed, it can’t be replaced. In Java 2, the security manager works in conjunction with an access controller that lets you implement security policies by editing a file. Access policies can be as simple or complex as a particular application warrants. Sometimes it’s sufficient simply to deny access to all resources or to general categories of services such as the filesystem or network. But it’s also possible to make sophisticated decisions based on high-level information. For example, a Java-enabled web browser could use an access policy that lets users specify how much an applet is to be trusted or that allows or denies access to specific resources on a case-by-case basis. Of course, this assumes that the browser can determine which applets it ought to trust. We’ll see how this problem is solved shortly. The integrity of a security manager is based on the protection afforded by the lower levels of the Java security model. Without the guarantees provided by the verifier and the class loader, high-level assertions about the safety of system resources are meaningless. The safety provided by the Java byte-code verifier means that the interpreter can’t be corrupted or subverted, and that Java code has to use components as they are intended. This, in turn, means that a class loader can guarantee that an application is using the core Java system classes and that these classes are the only means of accessing basic system resources. With these restrictions in place, it’s possible to centralize control over those resources with a security manager. 1.6 Application and User-Level Security There’s a fine line between having enough power to do something useful and having all the power to do anything you want. Java provides the foundation for a secure environment in which untrusted code can be quarantined, managed, and safely executed. However, unless you are content with keeping that code in a little black box and running it just for its own benefit, you will have to grant it access to at least some system resources so that it can be useful. Every kind of access carries with it certain risks and benefits. The advantages of granting an untrusted applet access to your windowing system, for example, are that it can display information and let you interact in a useful way. The associated risks are that the applet may instead display something worthless, annoying, or offensive. Since most people can accept that level of risk, graphical applets and the World Wide Web in general are possible. At one extreme, the simple act of running an application gives it a resource, computation time, that it may put to good use or burn frivolously. It’s difficult to prevent an untrusted application from wasting your time, or even attempting a “denial of service” attack. At the other extreme, a powerful, trusted application may justifiably deserve access to all sorts of system resources (e.g., the filesystem, process creation, network interfaces); a malicious application could wreak havoc with these resources. The message here is that important and sometimes complex security issues have to be addressed. In some situations, it may be acceptable to simply ask the user to “okay” requests. Sun’s HotJava web browser can pop up a dialog box and ask the user’s permission for an applet to access an otherwise restricted file. However, we can put only so much burden on our users. An experienced person will quickly grow tired of answering questions; an inexperienced user may not be able to answer the questions correctly. Is it okay for me to grant an applet access to something if I don’t understand what that is? Making decisions about what is dangerous and what is not can be difficult. Even ostensibly harmless access, like displaying a window, can become a threat when paired with the ability for an untrusted application to communicate from your host. The Java Security Manager provides an - 18

Note: If you are looking for good and high quality web space to host and run your application check Lunarwebhost Java Web Hosting services