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

If the encrypted files are database files this

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Unformatted text preview: ation layer, then it can be independent of the type of communication network used. It is still end-to-end encryption, but the encryption implementation does not have to bother about line codes, synchronization between modems, physical interfaces, and so forth. In the early days of electromechanical cryptography, encryption and decryption took place entirely offline; this is only one step removed from that. Encryption at these high layers interacts with the user software. This software is different for different computer architectures, and so the encryption must be optimized for different computer systems. Encryption can occur in the software itself or in specialized hardware. In the latter case, the computer will send the data to the specialized hardware for encryption before sending it to lower layers of the communication architecture for transmission. This process requires some intelligence and is not suitable for dumb terminals. Additionally, there may be compatibility problems with different types of computers. The major disadvantage of end-to-end encryption is that it allows traffic analysis. Traffic analysis is the analysis of encrypted messages: where they come from, where they go to, how long they are, when they are sent, how frequent or infrequent they are, whether they coincide with outside events like meetings, and more. A lot of good information is buried in that data, and a cryptanalyst will want to get his hands on it. Table 10.3 presents the positive and negative aspects of end-to-end encryption. Combining the Two Table 10.4, primarily from [1244], compares link-by-link and end-to-end encryption. Combining the two, while most expensive, is the most effective way of securing a network. Encryption of each physical link makes any analysis of the routing information impossible, while end-to-end encryption reduces the threat of unencrypted data at the various nodes in the network. Key management for the two schemes can be completely separate: The network managers can take care of encryption at the physical level, while the individual users have responsib...
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