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Skype protocol reverse engineered, source available

skype-open-source.blogspot.com

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Re: Skype protocol reverse engineered, source available

#71

Post by LiveTheDream »

Animus7 wrote: post #18

If the goal is to open up Skype, this isn't the way. Even if some insane insomniac de-twiddles the pages upon pages of optimized indirection in this code (which I seriously doubt), all Skype has to do is tweak the protocol or encryption and the researcher is back to square one. It's a losing battle. And that's not even getting into the legality of it it all. How about instead of trying to fruitlessly crack Skype, we…

You may be interested in this[1], open technology for voice and video on the web.

[1] http://news.ycombinator.com/item?id=2605390

Re: Skype protocol reverse engineered, source available

#72

Post by rmc »

jcr wrote: post #44

I wouldn't venture to say this doesn't belong on HN since it really is interesting (if it was actually done correctly), but the files available for download are most likely illegal, were most likely created with pirated tools (IDA Pro/Hex-Rays, and yes, as a customer of theirs for over a dozen years I've reported it), and of course, the usual vilification of reverse engineering. If you're reading this on a desktop or…

The way to do reverse engineering legally is to have one team reverse engineer the target and completely document how it works. Once it's documented, another disconnected team writes a new implementation from the documentation.

So you'd Skype's co-operation to do this? They are able to prevent reverse engineering by not writing the documents?

Re: Skype protocol reverse engineered, source available

#73

Post by muuh-gnu »

jcr wrote: post #39
dmc wrote: post #34

Earlier quoted context omitted.

What about if a developer were to now download the source code available here? Could they, in theory, develop with it as they've never attempted to reverse engineer it themselves? By using ToS, you're limiting enforcement to the people who do the RE, rather than an implementation, surely?

Actually, no. If you look at those files, you're "tainted" and can't be the one who writes a new implementation. The correct way to do reverse engineering for compatibility is to have to completely separate teams. The first does the reverse engineering and writes the specification/documentation. The second completely separate teams takes the specs/docs and writes an entirely new implementation. This is the process us…

> The correct way to do reverse engineering

You should always emphasize that its the correct way _in the US_. As somebody already mentioned, HN readership is international, and said restrictions on reverse engineering do not apply everywhere. Also the author, judging by his name, doesn't seem to be a US citizen.

Re: Skype protocol reverse engineered, source available

#74

Post by prodigal_erik »

jcr wrote: post #70
VMG wrote: post #54

Earlier quoted context omitted.

Why do you assume the tools are pirated?

I think you actually want two answers, the question you asked and "why report it?" The IDA Pro disassembler and the Hex-Rays decompiler are not only very expensive tools, but they are very difficult to purchase. Due to constant problems with piracy, these days they will only sell their products to three areas; (1) governments/law enforcement, (2) very well established corporations (typically well known security resea…

Improving our tools is part of our birthright and responsibility; being able to modify and learn from software is a natural outgrowth of that. We of all people should not respect work intended to discourage collaboration by anyone who isn't "established" (granted the privilege of relating to software as a human being, not just a consumer).

Thank you for the insight into your field. Now I'm sorely tempted to try my hand at decompilation.

Re: Skype protocol reverse engineered, source available

#75

Post by jcr »

rmc wrote: post #72
jcr wrote: post #44

I wouldn't venture to say this doesn't belong on HN since it really is interesting (if it was actually done correctly), but the files available for download are most likely illegal, were most likely created with pirated tools (IDA Pro/Hex-Rays, and yes, as a customer of theirs for over a dozen years I've reported it), and of course, the usual vilification of reverse engineering. If you're reading this on a desktop or…

The way to do reverse engineering legally is to have one team reverse engineer the target and completely document how it works. Once it's documented, another disconnected team writes a new implementation from the documentation. So you'd Skype's co-operation to do this? They are able to prevent reverse engineering by not writing the documents?

If it is done correctly, co-operation from skype is not required. The team that does the reverse engineering will write the specs and documentation from what they learn by examining and analyzing the executable binaries.

Re: Skype protocol reverse engineered, source available

#76

Post by pflats »

rmc wrote: post #72
jcr wrote: post #44

I wouldn't venture to say this doesn't belong on HN since it really is interesting (if it was actually done correctly), but the files available for download are most likely illegal, were most likely created with pirated tools (IDA Pro/Hex-Rays, and yes, as a customer of theirs for over a dozen years I've reported it), and of course, the usual vilification of reverse engineering. If you're reading this on a desktop or…

The way to do reverse engineering legally is to have one team reverse engineer the target and completely document how it works. Once it's documented, another disconnected team writes a new implementation from the documentation. So you'd Skype's co-operation to do this? They are able to prevent reverse engineering by not writing the documents?

Not at all.

Suppose you and I work for the same company. I bust open Skype through decompilation, reading memory, the network, whatever trick I want. With that, I write documentation for how Skype's protocols work.

You read my documentation, and implement it in a new program. Since we haven't talked, and you've never seen a line of Skype's code, you haven't infringed on any copyrights.

It is important to note, though, that this does not necessarily protect us against a patent suit.

Re: Skype protocol reverse engineered, source available

#78

Post by VMG »

jcr wrote: post #70
VMG wrote: post #54

Earlier quoted context omitted.

Why do you assume the tools are pirated?

I think you actually want two answers, the question you asked and "why report it?" The IDA Pro disassembler and the Hex-Rays decompiler are not only very expensive tools, but they are very difficult to purchase. Due to constant problems with piracy, these days they will only sell their products to three areas; (1) governments/law enforcement, (2) very well established corporations (typically well known security resea…

Thanks for your insight. The spelling errors in the blog posts aren't the hallmark of professionalism either, but what about the information in comment header?

    /*\
    |*|
    |*| Skype 4142 Decompression v1.002 by Sean O'Neil.
    |*| Copyright (c) 2004-2009 by VEST Corporation.
    |*| All rights reserved. Strictly Confidential!
    |*|
    |*| Date: 29.10.2009
    |*|
    \*/
is this just a special brand of stupid?

edit: some info about this corporation and Sean O'Neil: http://en.wikipedia.org/wiki/VEST

the official web page points to beach resort?!?

edit2: same guy: http://cryptolib.com/ciphers/skype/

Re: Skype protocol reverse engineered, source available

#79

Post by Iv »

jcr wrote: post #44

I wouldn't venture to say this doesn't belong on HN since it really is interesting (if it was actually done correctly), but the files available for download are most likely illegal, were most likely created with pirated tools (IDA Pro/Hex-Rays, and yes, as a customer of theirs for over a dozen years I've reported it), and of course, the usual vilification of reverse engineering. If you're reading this on a desktop or…

"The way to do reverse engineering legally is to have one team reverse engineer the target and completely document how it works. Once it's documented, another disconnected team writes a new implementation from the documentation."

Yes, it is a common silly practice that stems from the real madness that are copyright laws. Considering that the documentation passed between the two teams contain all the informations to make the software work correctly, I wonder what makes it different from a source code. I could easily write a code generator that would be fed a "documentation" file and generate the C code that creates the final program. Hell, a C program is a specification on how to generate a given binary code. I wonder how often this really happens behind the doors at these "clean room implementation" teams.

Re: Skype protocol reverse engineered, source available

#80

Post by tene »

peterwwillis wrote: post #58
Animus7 wrote: post #18

If the goal is to open up Skype, this isn't the way. Even if some insane insomniac de-twiddles the pages upon pages of optimized indirection in this code (which I seriously doubt), all Skype has to do is tweak the protocol or encryption and the researcher is back to square one. It's a losing battle. And that's not even getting into the legality of it it all. How about instead of trying to fruitlessly crack Skype, we…

> How about instead of trying to fruitlessly crack Skype, we spend the time making something that's both open and better? There's value in making an open client that works with the existing network (for example, Microsoft recently killed the Skype integration plug-in for Asterix).

"Asterisk"
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