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 secure, channels, real and/or world:
“The objects of a financier are, then, to secure an ample revenue; to impose it with judgment and equality; to employ it economically; and, when necessity obliges him to make use of credit, to secure its foundations in that instance, and for ever, by the clearness and candour of his proceedings, the exactness of his calculations, and the solidity of his funds.”
—Edmund Burke (17291797)
“The enthusiastic uprising of the people in our cause, is our great reliance; and we can not safely give it any check, even though it overflows, and runs in channels not laid down in any chart.”
—Abraham Lincoln (18091865)
“Your real statesman is first of all, and chief of all, a great human being, with an eye for all the great fields on which men like himself struggle, with unflagging, pathetic hope, toward better things.... He is a guide, a counselor, a mentor, a servant, a friend of mankind.”
—Woodrow Wilson (18561924)
“If only it were Gods will that printed and written materials have as much influence on the people as the princes and their censors fear! Considering the countless good books we have, the world would have changed for the better a long time ago.”
—Franz Grillparzer (17911872)