This package contains the JAP client which acts as a local proxy between your browser and the insecure Internet. All requests for web pages are handled by JAP and are encrypted several times. The encrypted messages are sent through a chain of intermediate servers (named Mixes) to the final destination on the Internet.
Multiple layers of encryption protect all messages. A Mix collects messages in a batch, totally changes their appearance (removes one layer of encryption) and forwards them all at the same time, but in a different order. An adversary may observe all communication links, however he cannot determine a relation between incoming and outgoing packets. A surfer remains anonymous within the group of all users of the service.
Demonstrably, the system protects your privacy as long as the Mix works correctly. Unfortunately nobody knows whether a certain Mix is actually trustworthy or not. Therefore we use a whole chain of Mixes. Each message passes through several Mixes and the entire chain of Mixes has to be corrupt to successfully observe the user's activities. The chaining effectively prevents single Mixes from observing. This is the meaning of strong anonymity: Even the anonymity service itself cannot spy on its users.
For further information see http://anon.inf.tu-dresden.de/