RE: [EMAIL PROTECTED]: Skype security evaluation]

2005-11-13 Thread Marcel Popescu
 Do you have some articles about these protocols?

The authoritative reference for TLS is the TLS RFC 
(http://www.ietf.org/rfc/rfc2246.txt). The authoritative reference for IPsec

is of course the IPsec RFC (http://www.ietf.org/rfc/rfc2401.txt). As to why 
they wouldn't use these as they stand, synchronized protocols often require 
finer control over the data block size than these offer, but modification is

easy enough, and would certainly have caused fewer concerns than a roll your

own.

[Marcel] Thanks, and appreciated, but I haven't made myself clear. I meant:
is there a page by one of the known names in the field saying something
like: if you want to do this, then you should use these protocols? Like
Peter said: they should have used TLS or YASSL for the handshake and IPSEC +
ESP for the transport. Is there a place where one trying to implement a
secure system could go and find out the basic components he needs? With pros
and cons, preferably?

[Marcel] Maybe this is too much to ask, I don't know. That's pretty much the
point :)

Thanks,
Marcel




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RE: [EMAIL PROTECTED]: Skype security evaluation]

2005-11-03 Thread Marcel Popescu
 From: [EMAIL PROTECTED] [mailto:owner-
 [EMAIL PROTECTED] On Behalf Of Peter Gutmann

 I can't understand why they didn't just use TLS for the handshake (maybe
 YASSL) and IPsec sliding-window + ESP for the transport (there's a free
 minimal implementation of this whose name escapes me for use by people who
 want to avoid the IKE nightmare).  Established, proven protocols and
 implementations are there for the taking, but instead they had to go out
 and try and assemble something with their own three hands (sigh).

Do you have some articles about these protocols? I can't find anything on
your webpage, and a newbie (like myself) can't distinguish between well
designed and badly designed protocols. Can you recommend such a collection
of well designed protocols for various purposes? With implementation caveats
if possible?

(I haven't looked at it in a long time - is Handbook of Applied Cryptography
a good reference for this?)

Thanks,
Marcel


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RE: That's gratitude for ya...

2005-02-17 Thread Marcel Popescu
 From: [EMAIL PROTECTED] [mailto:owner-
 [EMAIL PROTECTED] On Behalf Of Rich Salz

 The other day I sent Amir Herzberg a private note saying I thought his
 new tool was pretty neat, and though I'm sure he's heard it a lot,
 thanks.  He said nope, nobody else has said it, and I was stunned.

My apologies. I've been using Amir's tool since he posted the link, but I
haven't thought of sending a thank you note :(

Amir, I also think it's neat. :)

Marcel


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RE: Cryptography Research wants piracy speed bump on HD DVDs

2005-01-05 Thread Marcel Popescu
 From: [EMAIL PROTECTED] [mailto:owner-
 [EMAIL PROTECTED] On Behalf Of Adam Back
 Sent: Wednesday, December 22, 2004 11:48 PM

 I would think the simplest canonical counter-attack would be to make a
 p2p app that compares diffs in the binary output (efficiently rsync
 style) accumulates enough bits to strip the disk watermark, p2p rips
 and publishes.  QED.

Why not the way it happens right now - re-encoding? Few people post DVD
images of movies on p2p networks, and even when they do, I prefer a DivX or
XviD variant. (Much better given my 'net bandwidth.) I strongly doubt
there's any chance of a watermark surviving an unknown re-encoding process
(DivX has dozens of parameters you can change).

Marcel



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Re: Approximate hashes

2004-09-01 Thread Marcel Popescu
From: Marcel Popescu [EMAIL PROTECTED]

 Hence my question: is there some approximate hash function (which I
could
 use instead of SHA-1) which can verify that a text hashes very close to
a
 value? So that if I change, say, tabs into spaces, I won't get exactly the
 same value, but I would get a good enough?

I just had an idea. Would this work?

- let S be the input string, whose hash I want to verify
- make S uppercase
- remove everything but A-Z, 0-9, and common punctuation (!;:',.?)
- calculate the SHA1 hash of the result

This should keep any insignificant changes out of the final result. Does
anyone know of a mail transformation which could upset it? Can anyone see a
way to attack this by letting a significantly different message collide on
the same hash? (I'm ignoring the recent discoveries - they're not that
practical, I'm only trying to fight spam, not the government.)

Thanks,
Marcel

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Re: Approximate hashes

2004-09-01 Thread Marcel Popescu
From: Hal Finney [EMAIL PROTECTED]

 As you are probably aware, existing hashcash implementations do not base
 the stamp on the message content.  Instead they only lock the stamp to
 the receiver's email address.  Then the receiver keeps a list of the
 hashcash stamps he has seen recently, to prevent reuse.  I'm not sure
 what you hope to gain by locking the stamp to the message content.

Me dumb, sorry. I was actually thinking of some other thing I wanted to do
about spam (which involved the whole content), and haven't re-read the
hashcash site in about a week.

You are perfectly right, of course. Windows spam victims, here I come! g

Thanks,
Marcel

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Re: Looking for mirror (or: better) sites to host my crypto/security lectures

2004-05-25 Thread Marcel Popescu
From: Amir Herzberg [EMAIL PROTECTED]

 So, if anyone has a reliable ftp server where I could post the lectures
 (and update them via ftp), please let me know.

You might also want to look into installing a tracker and sharing them with
BitTorrent http://bitconjurer.org/BitTorrent/ - it should help with the
bandwidth requirements for anyone making them available.

Mark

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