User talk:DavidJablon

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[edit] Welcome #2

Hi, thanks for your contributions, and welcome! If you hadn't stumbled across it already, you might be interested in the Cryptography Project on Wikipedia. Cheers! — Matt Crypto 3 July 2005 23:29 (UTC)

[edit] MITM

I disagree with your edits on the MITM page. You make it sound as if public key encryption can be secure in an enviroment where an attacker can perform widespread tampering ('either eavesdropping or tampering or both').

I was trying to point out that if you fear a MITM attack (as the designers of TLS did) you need a physically secure channel for the initial exchange. After your edit, that point was lost. -- Nroets 10:01, 12 July 2005 (UTC)

I think "public key encryption" refers to a fairly narrow subcategory of "public key cryptography", with the latter term embracing a wide variety of tricks. Many different methods use public key cryptography in very different ways to create secure channels in environments where an enemy has full control over the communication channel, given some pretty-well-defined meanings of the word "secure".
In my edits I was trying to show some of the variety of ways that is done. Some use an *initial* (prior) secure channel, as you suggested, but others use a secure channel established after the fact. And "secure" doesn't necessarily imply "private". And some work with keys, others with passwords, etc. Some are two-party, others three or more. Etc.
In any case, I don't see how any points in your edits were lost. Both versions still have a clear reference to the need for a separate "secure" channel. And I don't see how either your text or mine limited "secure" to meaning "physically secure".
Furthermore, I don't see how your text implied that "public key {encryption|cryptography} cannot be secure in an environment where an attacker can perform widespread tampering". If that's what you intended to say, I cannot agree with that remark without further explanation.
That said, I agree that discussing the concept of physical vs. cryptographic security could help to clarify things. If you want to take a pass at fixing it to restore or expand on your viewpoint, feel free to do it on the page or in private email to me. -- User:DavidJablon 10:57, 21 July 2005 (UTC)
Ok, I should not have used the word "physical" (on this page). And I'm not saying my version of the MITM page was faultless.
But people read long Wikipedia articles very fast and they often have very little background. So when you close the 'need for authentication' paragraph with something about public key cryptography, they assume it can solve the problem.
The first sentence (All cryptographic systems ... require an additional exchange ... of some kind of authentication information ...) only applies to public key cryptographic systems. The same goes of the title of the paragraph. I've indicated on the MITM talk page that I feel the page should also be kept applicable to secret key systems.
You were hinting that there are usefull (real world) systems where the secure exchange (transmission) need not be in the beginning (initial). If so, can you give an example. If not, can we use the word 'initial' in the paragraph ? -- Nic Roets 11:34, 22 July 2005 (UTC)
First, public key techniques can be used to solve the problem, and so can symmetric techniques. I think the text says this. But, in at least an historical sense, MITM attack is created by a mis-application or misunderstanding of public key cryptography, so I think it makes sense to highlight such issues.
Regarding the sentence ("All cryptographic systems ..."), I think it clearly applies to both symmetric and asymmetric systems. Regarding real world systems, useful or otherwise, I really wasn't trying to hint anything one way or another. I was correcting an error of fact. Diffie-Hellman, and many other public key systems (e.g. PGP, SSH) may be used in an effectively anonymous manner, where at a subsequent time the parties securely verify, preferrably out-of-band, the values of a shared DH key, or exchanged public keys, to retroactively prove that no MITM was ever present. -- User:DavidJablon 10:59, 22 July 2005 (EDT)
Well for symmetric systems authentication is only half the story. Now we have clarity, I'll fix the page. -- Nic Roets 16:25, 22 July 2005 (UTC)
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