RC5-64

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This time, the challenge to find the key for the 64-bit encryption is 256 times harder than the 56-bit challenge — 34 quadrillion keys compared to 72 quadrillion keys. Although there are over 600,000 users running Distributed.net's Bovine software for the RC5-64 project, the project has been running for more than 1000 days and they have yet to find the secret key. Until this day comes, users can see RC5-64's progress daily; it takes between 3 minutes and 12 hours for most computers to process the data blocks. One need not be online but once every few days so the computer can connect to Distributed.net's proxy keyservers and obtain more data. If the computer doesn't have access to the Internet at the moment but is done processing blocks, the Bovine software can start checking randomly-created blocks. Thus, the computer¹s idle time is never wasted.

Fig. 2: RC5-64's architecture

Distributed.net has created an interesting, efficient architecture for RC5-64 (see figure 2), the most notable aspect being that each block is sent out only once to a unique user. RC5-64 has a pyramid architecture consisting of keyservers and clients. (distributed.net faq-o-matic) The master keyserver is at the top of the pyramid and has the most important job: it keeps track of the keyblocks, or the data that needs to be processed. Thus, the master keyserver distributes the keyblocks as needed and doesn't send out keyblocks that have already been checked.

Under the master keyserver are the main Bovine proxy keyservers. These keyservers are mediators between the master keyserver and the clients. The proxy keyservers request large blocks of keys — superblocks — from the master keyserver. The superblocks are broken down by the proxies and sent to the clients. The clients check the blocks and return them to the proxies, which then return them to the master keyserver.

An analogy that might clarify the process is a person going to their local library to get a book. The book isn't in, so he requests the book from the librarian. The librarian then in turn asks a larger library or county library for the book. The larger library will send the book to the smaller library, and the librarian will give the person that specific book. When the person is done with the book, it is returned to the librarian, who returns it to the bigger library.

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