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:
“...one of my motivating forces has been to recreate the world I know into a world I wish I could be in. Hence my optimism and happy endings. But I’ve never dreamed I could actually reshape the real world.”
—Kristin Hunter (b. 1931)
“The climate of Ohio is perfect, considered as the home of an ideal republican people. Climate has much to do with national character.... A climate which permits labor out-of-doors every month in the year and which requires industry to secure comfort—to provide food, shelter, clothing, fuel, etc.—is the very climate which secures the highest civilization.”
—Rutherford Birchard Hayes (1822–1893)
“People between twenty and forty are not sympathetic. The child has the capacity to do but it can’t know. It only knows when it is no longer able to do—after forty. Between twenty and forty the will of the child to do gets stronger, more dangerous, but it has not begun to learn to know yet. Since his capacity to do is forced into channels of evil through environment and pressures, man is strong before he is moral. The world’s anguish is caused by people between twenty and forty.”
—William Faulkner (1897–1962)
“Friends, both the imaginary ones you build for yourself out of phrases taken from a living writer, or real ones from college, and relatives, despite all the waste of ceremony and fakery and the fact that out of an hour of conversation you may have only five minutes in which the old entente reappears, are the only real means for foreign ideas to enter your brain.”
—Nicholson Baker (b. 1957)
“I find ... that he is happiest of whom the world sais least, good or bad.”
—Thomas Jefferson (1743–1826)