An extended Ethernet LAN is built by connecting several Ethernet segments by means of suitable devices (repeaters, bridges, etc.). A common way to make this interconnection is through a main segment, called the backbone, that joins each of the departments (or, perhaps, building floors) within the owner premises. In this kind of network, data transmission in the backbone is very sensitive to either eavesdropping or manipulation. The implementation of a cryptographic system that protects transmission (providing for both confidentiality and integrity of transmitted data) in this kind of network is addressed. The operation of the proposed system and the specific troubles encountered in implementing it in the local network of the Polytechnic University of Catalonia are presented. An analysis of the functionality of the ciphering bridges is provided and their implementation is studied in detail. Finally, the more relevant results and conclusions are given.>

An implementation of a security protocol in an extended LAN environment is described. The protocol has a hierarchical architecture. At the first level, the session key is disposed of, in the second level there are the master keys, and at the highest level there are the public and private key of the manager and the CryptoNet's keys. The relations between them, the right time to do the keys' renewal, and the appropriate form in which to do it are also characteristics that make it possible to obtain security based on two very well known algorithms such as the DES and RSA.>