[Cryptography] RIP Claude Shannon

[Henry Baker]

At 02:50 AM 2/24/2016, Jerry Leichter wrote:
>> As a mental exercise, assume that you have a low-latency, high-bandwidth mechanism to transmit pads, something suitable for use on the Internet.
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>Now -- why can't you optimize by instead of transmitting your pads with this, just transmit the message?
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>Actually, this illustrates when one-time pads might be appropriate:
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>If your communications are *asymmetrical*, so that you have a low-latency, high-bandwidth, *secure* (you left that part out) channel in one direction but not the other.
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>Historically, the asymmetry was often in time:
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>It existed when the system was put in place, but not later.
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>When you prepare your spy, you can give him a large quantity of keying material which he can carry with him.
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>When he needs to report his findings, he has no secure channel to report on, but can create one using the keying material.
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>In fact, any system with pre-shared keys involves the same asymmetry.
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>Cryptographic functions don't eliminate the need for the *secure* "outgoing" channel - they simply "stretch" the initial shared secret immensely so that the "high-bandwidth" part goes away.
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>(Whether "low-latency" is an issue depends on other details - in the classic spy case, it might take days for the one-time pads to reach their destination - but if they were traveling along with the spy, the effective additional latency is zero.)
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>You might think that public-key systems eliminate the whole problem - and for pure secrecy, they do.
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>But if you want to to know *who* you're sending your information to, you need to get the initial trust base out there *somehow*.

The 1x pad random keying material is "freeze dried adjacency".  It is a *resource* that you can stock up on in advance -- kind of like fuel or gold, that you can stockpile in your fallout bunker.

If you've got nothing important to talk about with a friend over a beer, share some key material instead.  Later, when you *do* have something to talk about, you can use some of that key material to gain the advantage of adjacency when discussing over long distances.

When you need to send out a confidential message, you sprinkle some of this fairy dust on the message, and you're good to go.