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applied cryptography - protocols, algorithms, and source code in c

The objective of the new system was primarily to

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Unformatted text preview: ile security on a computer network, using only symmetric cryptography [515, 1027]. This protocol is less important in the actual mechanisms and more in its overall philosophy: By automating the generation, distribution, installation, storage, changing, and destruction of keys, the protocol went a long way to ensure the security of the underlying cryptographic algorithms. This protocol provides three things: secure communications between a server and several terminals, secure file storage at the server, and secure communication among servers. The protocol doesn’t really provide for direct terminal-to-terminal communication, although it can be modified to do that. Each server on the network is attached to a cryptographic facility, which does all of the encrypting and decrypting. Each server has a Master Key, KM0, and two variants, KM1 and KM2, both of which are simple variants of KM0. These keys are used to encrypt other keys and to generate new keys. Each terminal has a Master Terminal Key, KMT, which is used to exchange keys with other terminals. The servers store KMT, encrypted with KM1. All other keys, such as those used to encrypt files of keys (called KNF), are stored in encrypted form under KM2. The master key, KM0, is stored in some nonvolatile security module. Today that could be either a ROM key or a magnetic card, or it could be typed in by the user (probably as a text string and then key crunched). KM1 and KM2 are not stored anywhere in the system, but are computed from KM0 whenever they are needed. Session keys, for communication among servers, are generated with a pseudo-random process in the server. Keys to encrypt files for storage (KNF) are generated in the same manner. The heart of the protocol is a tamper-resistant module, called a cryptographic facility. At both the server and the terminal, all encryption and decryption takes place within this facility. The most important keys, those used to generate the actual encryption keys, are stored in this module. These keys can never be read once they are stored. And they are...
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