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A Crypto Challenge For The Telegram Developers

thoughtcrime.org

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Re: A Crypto Challenge For The Telegram Developers

#41

Post by velis_vel »

nwh wrote: post #28
utnick wrote: post #14

Earlier quoted context omitted.

How is the key image impossible to describe? There are only 4 possible colors per cell. You just describe it like 0,1,2,3,2,0, etc Just as if you were reading off the real key.

From just asking around, most people described the key image to me in terms of the darkest portions and ignored the parts that were lighter. It's easier for the example image to say that there's a dark L and lighter X shape in the center and then assume that the rest is the same. At least, that's how people did when I presented it to them as a challenge.

> There's also not that many possible images anyway, there's 8 rows with 8 columns, and 4 possible colours for each pixel. Even not assuming any fuzzy matching (human comparison) it's still very possible to generate keys with colliding image hashes.

Uh, 4^(8*8)=2^128 is a pretty large number.

Re: A Crypto Challenge For The Telegram Developers

#42

Post by chetanahuja »

meowface wrote: post #6

Even if Telegram's explanation did stand up to scrutiny and was ran by experienced cryptographers, the fact that its core code is closed source makes it utterly worthless from a security perspective. They can tout their own security all they like, but if no one else can independently verify it then it means nothing. So far they've only published the source to their client, but their servers do all of the actual proce…

"but their servers do all of the actual processing and cryptography"

I realize t'is the season to to piling on to the hapless Telegram folks, but I think that assertion is wrong.

Re: A Crypto Challenge For The Telegram Developers

#43

Post by xnyhps »

moxie wrote: post #25
xnyhps wrote: post #18

Earlier quoted context omitted.

Well, not entirely the same framing. For $200k one could probably brute-force an 896-bit RSA key. ;)

I don't actually think that's true. At least, not within the time limits they defined. The $75k 896bit RSA factoring prize went unclaimed for 20 years, for instance.

Yeah, when I started actually trying to back it up, I noticed I was probably a factor 5 off.

Namely, if you look at the keylength.com values for asymmetric key sizes, 768 in 2009 ago should come close to the difficulty of 896 today. The RSA 768 challenge was broken in 2009 (http://eprint.iacr.org/2010/006), which cost them "the equivalent of almost 2000 years of computing on a single core 2.2GHz AMD Opteron". Renting that amount of time Amazon EC2's $0.06/hour instances would be $1 million.

Re: A Crypto Challenge For The Telegram Developers

#44

Post by fleitz »

wodenokoto wrote: post #20
ge0rg wrote: post #3

tl;dr: moxie uses ancient, known broken crypto primitives (Dual_EC_DRBG, RSA with 896 bits, MD2 and XOR) to construct a chat protocol which is unbreakable if framed in the same way the Telegram developers did with their challenge. "If they can’t demonstrate a break in this obviously broken protocol using the same contest framework they’ve setup, then we’ll know that their contest is bullshit." Also, a call to arms to…

I still don't get it. If an insecure protocol with an insecure implementation can send messages that others can't read, how is it insecure?

It's only secure if attackers have eg. You aren't using Wifi, your network is fully secured, no one has access to any router along the way, etc.

Lets put it this way, if you're using Telegram / MarlinSpikeGram and you and I are in the same coffeeshop I can read your messages.

Re: A Crypto Challenge For The Telegram Developers

#45

Post by javajosh »

Funny. But actually, the simplest contest that accurately describes Telegram's insanity is simply this:

::Given an unknown function f and a single output y, compute the input x that maps to y.::

Ready? Here's the output: ROSEBUD. Now I'll give $100k to anyone who can tell me x. Good luck!

Re: A Crypto Challenge For The Telegram Developers

#46

Post by nwh »

velis_vel wrote: post #41
nwh wrote: post #28

Earlier quoted context omitted.

From just asking around, most people described the key image to me in terms of the darkest portions and ignored the parts that were lighter. It's easier for the example image to say that there's a dark L and lighter X shape in the center and then assume that the rest is the same. At least, that's how people did when I presented it to them as a challenge.

> There's also not that many possible images anyway, there's 8 rows with 8 columns, and 4 possible colours for each pixel. Even not assuming any fuzzy matching (human comparison) it's still very possible to generate keys with colliding image hashes. Uh, 4^(8*8)=2^128 is a pretty large number.

So it is, I've removed that. I need to sleep more.

Re: A Crypto Challenge For The Telegram Developers

#47

Post by fleitz »

jagermo wrote: post #33
MagicWishMonkey wrote: post #19

Earlier quoted context omitted.

People need to stop posting his shit here, it's basically linkbait he's using to pimp his Whisper service. He's the worst kind of troll.

Moxie? He is kind of a real expert in everything crypto and, instead of using the phrase "military grade encryption", WhisperSystems actually explains what they do and how they do it. His posts are very well written and understandable, even for non pros (with a pinch of sarcasm, but that's how I like it). So, where exactly is he trolling?

I think you'd be more likely to find him trolling on the ocean.

http://www.blueanarchy.org/holdfast/

Re: A Crypto Challenge For The Telegram Developers

#48

Post by clebio »

ColinWright wrote: post #27
wodenokoto wrote: post #20

Earlier quoted context omitted.

I still don't get it. If an insecure protocol with an insecure implementation can send messages that others can't read, how is it insecure?

The problem is not whether the protocol is secure - the problem is that there's no way we can tell. Historically, that means that it's likely not to be secure. With regards this counter-challenge. The crypto here is known to be poor. If this counter-challenge cannot be broken, then it shows that the challenge issued by Telegram is no proof of security. SO in short, * we don't know if no one can read the Telegram-ency…

This is an excellent answer. You get right to the core of it, quite clearly, which is that this has naught to do with the crypto itself. But that:

> If this counter-challenge cannot be broken, then it shows that the challenge issued by Telegram is no proof of security.

Re: A Crypto Challenge For The Telegram Developers

#49

Post by svantana »

im3w1l wrote: post #11

Using an NSA backdoored RNG is pretty redundant. A cell phone cannot be secured against NSA. They'll just activate their keylogger and grab the plaintext before it has even been encrypted.

That gives me an idea: messaging apps shouldn't use the default OS keyboard, but write their own. In that case, NSA would need to target that messaging app specifically.

Re: A Crypto Challenge For The Telegram Developers

#50

Post by utnick »

finnn wrote: post #10
meowface wrote: post #6

Even if Telegram's explanation did stand up to scrutiny and was ran by experienced cryptographers, the fact that its core code is closed source makes it utterly worthless from a security perspective. They can tout their own security all they like, but if no one else can independently verify it then it means nothing. So far they've only published the source to their client, but their servers do all of the actual proce…

Wait the crypto is done server side? I haven't really looked into Telegram much, but that's fucking silly. Lavabit all over again.

its not done server side
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