Secure Channels in The Real World
There are no perfectly secure channels in the real world. There are, at best, only ways to make insecure channels (e.g., couriers, homing pigeons, diplomatic bags, etc.) less insecure: padlocks (between courier wrists and a briefcase), loyalty tests, security investigations, and guns for courier personnel, diplomatic immunity for diplomatic bags, and so forth.
In 1976, two researchers proposed a key exchange technique (now named after them) — Diffie–Hellman key exchange (D-H). This protocol allows two parties to generate a key only known to them, under the assumption that a certain mathematical problem (e.g., the Diffie–Hellman problem in their proposal) is computationally infeasible (i.e., very very hard) to solve, and that the two parties have access to an authentic channel. In short, that an eavesdropper—conventionally termed 'Eve', who can listen to all messages exchanged by the two parties, but who can not modify the messages—will not learn the exchanged key. Such a key exchange was impossible with any previously known cryptographic schemes based on symmetric ciphers, because with these schemes it is necessary that the two parties exchange a secret key at some prior time, hence they require a confidential channel at that time which is just what we are attempting to build.
It is important to note that most cryptographic techniques are trivially breakable if keys are not exchanged securely or, if they actually were so exchanged, if those keys become known in some other way — burglary or extortion, for instance. An actually secure channel will not be required if an insecure channel can be used to securely exchange keys, and if burglary, bribery, or threat aren't used. The eternal problem has been and of course remains — even with modern key exchange protocols — how to know when an insecure channel worked securely (or alternatively, and perhaps more importantly, when it did not), and whether anyone has actually been bribed or threatened or simply lost a notebook (or a notebook computer) with key information in it. These are hard problems in the real world and no solutions are known — only expedients, jury rigs, and workarounds.
Read more about this topic: Secure Channel
Famous quotes containing the words real world, secure, channels, real and/or world:
“When truth is nothing but the truth, it’s unnatural, it’s an abstraction that resembles nothing in the real world. In nature there are always so many other irrelevant things mixed up with the essential truth. That’s why art moves you—precisely because it’s unadulterated with all the irrelevancies of real life.”
—Aldous Huxley (1894–1963)
“... is it not clear that to give to such women as desire it and can devote themselves to literary and scientific pursuits all the advantages enjoyed by men of the same class will lessen essentially the number of thoughtless, idle, vain and frivolous women and thus secure the [sic] society the services of those who now hang as dead weight?”
—Sarah M. Grimke (1792–1873)
“Television is becoming a collage—there are so many channels that you move through them making a collage yourself. In that sense, everyone sees something a bit different.”
—David Hockney (b. 1937)
“I’m real ambivalent about [working mothers]. Those of use who have been in the women’s movement for a long time know that we’ve talked a good game of “go out and fulfill your dreams” and “be everything you were meant to be.” But by the same token, we want daughters-in-law who are going to stay home and raise our grandchildren.”
—Erma Bombeck (20th century)
“That the world is not the embodiment of an eternal rationality can be conclusively proved by the fact that the piece of the world that we know—I mean our human reason—is not so very rational. And if it is not eternally and completely wise and rational, then the rest of the world will not be either; here the conclusion a minori ad majus, a parte ad totum applies, and does so with decisive force.”
—Friedrich Nietzsche (1844–1900)