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

In still other words the one time pad see section 15

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Unformatted text preview: epeating one-zero pattern. Given my general level of paranoia, I recommend overwriting a deleted file seven times: the first time with all ones, the second time with all zeros, and five times with a cryptographically secure pseudo-random sequence. Recent developments at the National Institute of Standards and Technology with electron-tunneling microscopes suggest even that might not be enough. Honestly, if your data is sufficiently valuable, assume that it is impossible to erase data completely off magnetic media. Burn or shred the media; it’s cheaper to buy media new than to lose your secrets. Previous Table of Contents Next Products | Contact Us | About Us | Privacy | Ad Info | Home Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc. All rights reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy statement. To access the contents, click the chapter and section titles. Applied Cryptography, Second Edition: Protocols, Algorthms, and Source Code in C (cloth) Go! Keyword Brief Full Advanced Search Search Tips (Publisher: John Wiley & Sons, Inc.) Author(s): Bruce Schneier ISBN: 0471128457 Publication Date: 01/01/96 Search this book: Go! Previous Table of Contents Next ----------- Part III Cryptographic Algorithms Chapter 11 Mathematical Background 11.1 Information Theory Modern information theory was first published in 1948 by Claude Elmwood Shannon [1431, 1432]. (His papers have been reprinted by the IEEE Press [1433].) For a good mathematical treatment of the topic, consult [593]. In this section, I will just sketch some important ideas. Entropy and Uncertainty Information theory defines the amount of information in a message as the minimum number of bits needed to encode all possible meanings of that message, assuming all messages are equally likely. For example, the day-of-the-week field in a database contains no more than 3 bits of information, because the information can be encoded with 3 bits: 000 001 010 011 100 101 = = = = = = Sunday Monday Tuesday Wednesday Thursday Friday 110 = Saturday 111 is unused If this information were represented by corresponding ASCII character strings, it would take up more memory space but would not contain any more information. Similarly, the “sex” field of a database contains only 1 bit of information, even though it m...
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