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

Manual encryption of selected files is the only

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Unformatted text preview: d files are not structured as records and fields, such as text files, retrieval is easier: The entire file is decrypted before use. If the encrypted files are database files, this solution is problematic. Decrypting the entire database to access a single record is inefficient, but encrypting records independently might be susceptible to a block-replay kind of attack. In addition, you must make sure the unencrypted file is erased after encryption (see Section 10.9). For further details and insights, consult [425,569]. Dereferencing Keys When encrypting a large hard drive, you have two options. You can encrypt all the data using a single key. This gives a cryptanalyst a large amount of ciphertext to analyze and makes it impossible to allow multiple users to see only parts of the drive. Or, you can encrypt each file with a different key, forcing users to memorize a different key for each file. The solution is to encrypt each file with a separate key, and to encrypt the keys with another key known by the users. Each user only has to remember that one key. Different users can have different subsets of the file-encryption keys encrypted with their key. And there can even be a master key under which every file-encryption key is encrypted. This is even more secure because the file-encryption keys are random and less susceptible to a dictionary attack. Driver-Level vs. File-Level Encryption There are two ways to encrypt a hard drive: at the file level and at the driver level. Encryption at the file level means that every file is encrypted separately. To use a file that’s been encrypted, you must first decrypt the file, then use it, and then re-encrypt it. Driver-level encryption maintains a logical drive on the user’s machine that has all data on it encrypted. If done well, this can provide security that, beyond choosing good passwords, requires little worry on the part of the user. The driver must be considerably more complex than a simple file-encryption program, however, because it must deal with the issues of being an installed device driv...
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