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

In 1992 the rc2 and rc4 algorithms were approved for

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Unformatted text preview: s 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 ----------- Of course, it is ludicrous to estimate computing power 35 years in the future. Breakthroughs in some science-fiction technology could make these numbers look like a joke. Conversely, physical limitations unknown at the present time could make them unrealistically optimistic. In cryptography it is wise to be pessimistic. Fielding an algorithm with an 80-bit key seems extremely short-sighted. Insist on at least 112-bit keys. Table 7.1 Average Time Estimates for a Hardware Brute-Force Attack in 1995 Length of Key in Bits Cost $100 K 40 56 64 80 70,000 years 7000 years 112 128 1019 years 1018 years 1017 years 1016 years 1015 years 1014 years 1013 years 1014 years 2 seconds 35 hours 1 year 1013 $1 M .2 seconds 3.5 hours 37 days years 1012 $10 M .02 seconds 21 minutes 4 days 700 years years $100 1011 M 2 milliseconds 2 minutes 9 hours 70 years years 1010 $1 G .2 milliseconds 13 seconds 1 hour 7 years years 5.4 109 $10 G .02 milliseconds 1 second minutes 245 days years $100 108 G 2 microseconds .1 second 32 seconds 24 days years $1 T .2 microseconds .01 second 3 seconds 2.4 days 6 hours $10 T .02 microseconds 1 millisecond .3 second 107 years 106 years 1012 years 1011 years If an attacker wants to break a key badly enough, all he has to do is spend money. Consequently, it seems prudent to try to estimate the minimum “value” of a key: How much value can be trusted to a single key before it makes economic sense to try to break? To give an extreme example, if an encrypted message is worth $1.39, then it wouldn’t make much financial sense to set a $10-million cracker to the task of recovering the key. On the other hand, i...
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