For your question: Session keys and key rotation? Den 25 sep 2013 16:11 skrev "John Young" <j...@pipeline.com>:
> NSA Technical Journal published "The Unbreakable Cipher" in Spring 1961. > > http://www.nsa.gov/public_info/_files/tech_journals/The_Unbreakable_Cipher.pdf > > Excerpts: > > [Quote] > > David Kahn, "Lyen Otuu Wllwgh WI Etjown" pp. 71, 83, 84, 86, > 88 and 90 of the *New York Times Magazine *November 13, 1960 > says that an unbreakable cipher system can be made from one > time key "that is absolutely random and never repeats." ... > > For each cipher system there is an upper bound to the amount of > traffic it can protect against cryptanalytic attack. What is > "cryptanalytic attack"? It is a process applied to cipher text > in order to extract information, especially information > contained in the messages and intended to be kept secret. > If some of the information is gotten by other means and this > results in more being extracted from the cipher, this is (at > least partially) a successful attack. If certain phrases can be > recognized when they are present, this is successful cryptanalysis. > If a priori probabilities on possible contents are altered by > examination of the cipher, this is cryptanalytic progress. > If in making trial decipherments it is possible to pick out > the correct one then cryptanalysis is successful. ... > > Another example is that of Mr. Kahn, one-time key. Here the > limit is quite clear; it is the amount of key on hand. The key arrives > in finite "messages," so there is only a finite amount on hand at > anyone time, and this limits the amount of traffic which can be sent > securely. Of course another shipment of key raises this bound, but > technically another cipher system is now in effect, for by my > definition a cipher system is a message. A sequence of messages > is a sequence of cipher systems, related perhaps, but not the same. ... > > [Answer to the question:] "Does there exist an unbreakable cipher" > would be this, "Every cipher is breakable, given enough traffic, and > every cipher is unbreakable, if the traffic volume is restricted > enough." > > [End quote] > > Is this conclusion still valid? If so, what could be done to restrict > traffic > volume to assure unbreakablility? And how to sufficiently test that. > Presuming that NSA and cohorts have investigated this effect. > > _______________________________________________ > cryptography mailing list > cryptography@randombit.net > http://lists.randombit.net/mailman/listinfo/cryptography > >
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