david wong

Hey! I'm David, a security consultant at Cryptography Services, the crypto team of NCC Group . This is my blog about cryptography and security and other related topics that I find interesting.

To the moon

posted November 2013

There we are, bitcoins reached the 1000$/btc bar. We are living history. The price of 1mBTC is 1$ now. I don't know what to think anymore. I've been following bitcoins since they were bellow 20$. Reading everything on /r/bitcoin and HN. I would never have imagined that. comment on this story

Bitecoin and Litecoin reach a new peak!

posted November 2013

Bitcoin reached 877$/bitcoin today. I had 11 bitcoins that I bought for 450$ in total (40$/bitcoin) and which I lost trading and losing my wallet as well. I'm raging every time I think of the free holidays I could have paid myself with them.

But not all is lost, I have some litecoins and they just reached a peak of 14$ / litecoin. They're following bitcoins' rate closely and they're just waiting to become "mainstream" as well to boom.

Fingers crossed.

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Satoshi's original paper on Bitcoin

posted November 2013

8 pages of simple explanations

and a "explain me like I'm 5" post on http://www.reddit.com/r/Bitcoin/comments/1reu69/if_you_have_not_read_satoshi_nakamotos_original/cdmlnfd?context=1" target="_blank">reddit :

Bitcoin is a giant public ledger saying who sent what coins to whom. People have private keys, which they use to sign coin transfers. It's easy to verify signatures. That way only you can give away your coins. But that doesn't prevent you from giving the same coins to multiple people. For that we have the ledger, which puts all the transfers in a particular order that everyone agrees on so you can't pay someone with coins you already spent. Transactions are published on a p2p network. To put them in order, people take sets of transactions, add a random number, and make a cryptographic hash of the whole thing. (Feed data into a hash function and you get an unpredictable number.) If the hash is a low enough number it's a valid block and it becomes part of the blockchain. If it's too high, you change the random number and try again. The block also includes the hash of the previous block, so that puts everything in sequence. It takes a lot of tries to get a low-enough number, so only one block is published every ten minutes or so, by some random person who got lucky. This puts everything in order. It's expensive to do that, so when someone successfully generates a block, they get paid by a special bitcoin transaction that awards them some brand-new coins. That's mining.
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Newegg trial: Crypto legend takes the stand, goes for knockout patent punch

posted November 2013

"We've heard a good bit in this courtroom about public key encryption," said Albright. "Are you familiar with that?" "Yes, I am," said Diffie, in what surely qualified as the biggest understatement of the trial. "And how is it that you're familiar with public key encryption?" "I invented it."

A nice piece of journalism about how Diffie stood out in court to "knock out the Jones patent with "clear and convincing" evidence (which is the standard for invalidating a patent).".

Learning more about the guy who is behind the Diffie-Hellman">http://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange">Diffie-Hellman handshake.

more info here comment on this story


posted November 2013

So after a long night staying up and coding I finally handed in my project including my report in LaTeX.

I'm not really proud of what I did, I felt like I could have done much better if given more time (okay I slacked and I had enough time).

BUT, as I already said earlier, I've accomplished a lot and even though I'm done with this project I still kinda want to keep working on it.

Things that I've learned doing this class :

  • C is awful. But now I know the basics. I wish we had one more project to code in C to really get it though.
  • Makefile? Headers? I still don't really get the structure of a C project (and I'm ashamed).
  • I know Linux! Okay I don't know Linux that much, but I'm getting really causy there. I installed debian on a VM and I'm considering setting up a dual boot on my laptop now.
  • Emacs emacs! I was postponing learning it because I was afraid, and just forced myself to use it for this project and goshh am I fast when I use it. When I go back to Sublime Text I just want to C-M-F, C-A, C-K, C-Y...
  • LaTeX! As a Math major I've always been ashamed not knowing it. Now that I got a taste of it I'm wondering if I should use it to write my book on.
  • Svn and Git. I'm not a stranger anymore! And I use them for all my websites as well now :)

I think that's it, but I feel like I've learned a lot and I wished this course was a year thing rather than a semester thing.

The course is not over yet though and next week we'll dive into java for... a quick swim since it will be our last week.

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I'm turning nuts

posted November 2013

I feel like I've been doing a hackaton these past few days trying to finish my sudoku solver. I had to hand it in 2 hours ago but still haven't finished... I really hope this won't affect my grade too much.

I've been learning a lot of Emacs, C, using gcov, gprof, LaTeX... I'm so confused right now and my code has became so dense that it's hard for me to debug it.

Yesterday, suddenly, I found something really stupid in my sudoku grid generation that I couldn't fix. A day after, I found the solution, randomly, fixing it created a huge load of other issues. I have been re-inspecting my whole code all day long and I'm stressed by this deadline that I already passed.

Gosh that is a hard course.

And... because of this, I missed a day writing on my new application. I was on a 9-day strike :(

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What is the enlightenment I'm supposed to attain after studying finite automata?

posted November 2013

I'm studying automata, it's sort of a "logical" subject that reminds me of studying mathematics. It looks cool, it only asks your brain to think, not to memorize, and you don't really know what's the real use of it.

If you want to take a peak at what I'm studying, you can find a similar course on Coursera given by Jeff Ullman from Stanford (yes, obviously I should have moved to the US and attend Stanford).

Well, someone nicely asked what I was thinking on Stackoverflow, and someone else nicely answered.

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NSA infected 50,000 computer networks with malicious software

posted November 2013

Example about Belgium:

One example of this type of hacking was discovered in September 2013 at the Belgium telecom provider Belgacom. For a number of years the British intelligence service - GCHQ – has been installing this malicious software in the Belgacom network in order to tap their customer’s telephone and data traffic. The Belgacom network was infiltrated by GCHQ through a process of luring employees to a false Linkedin page.
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posted November 2013

I have an exam of Réseaux (Network) tomorrow and the slides of my prof are... how could I say this... not really clear. We have practical applications classes but they were... organized in the worst possible way. The subject did seem interesting at first but I felt like I learned nothing. Hopefully for the past few weeks I've been using the wonderful online course An Introduction to Computer Networks given by Nick McKeown and Philip Levis both very competent profs from Stanford. It seems like I should have gone there for my master of Cryptography :) Anyway, I'm doing with what I have here and I feel blessed studying Cryptography right when free online courses started becoming a thing.

The course is available here.

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posted November 2013

Bullrun or BULLRUN is a clandestine, highly classified decryption program run by the United States National Security Agency (NSA). The British signals intelligence agency Government Communications Headquarters (GCHQ) has a similar program codenamed Edgehill. According to the NSA's BULLRUN Classification Guide, which was published by The Guardian, BULLRUN is not a Sensitive Compartmented Information (SCI) control system or compartment, but the codeword has to be shown in the classification line, after all other classification and dissemination markings. Information about the program's existence was leaked in 2013 by Edward Snowden.

from https://en.wikipedia.org/wiki/Bullrun_%28decryption_program%29" target="_blank">wikipedia.

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Sudoku Solver

posted November 2013

My Programmmation class first part is about coding a sudoku solver. We have to do everything in english, we have to commit with svn, we have to write a final report with LaTeX.

Every week we're given some vague guidelines and we have to dive deep into C to first, understand what we have to do, and secondly, find solutions in a language we've never really played with before. We have to turn in what we did every week, if our code doesn't compile it's a zero, if it does compile it goes through a multitude of tests that quickly decrease your grade (out of 20). Let's just say I spent many nights and early mornings coding and I started the first week with a 2/20.

It felt like a crash course, it felt unfair at times, but holy cow did I learn some C in a really short amount of time. Props to my professor for that, and I wish I had more courses like that. I might not get the best grade out of this course but I sure learn the most things there.

I've also committed everything I've done on a public git repo so everyone can see how it looks like here :


You can compile with make, learn how to use with ./sudoku -h

It can read sudokus of different sizes from 1x1 to 64x64 as long as it is presented like this :

#this is a comment

5 3 _ _ 7 _ _ _ _

6 _ _ 1 9 5 _ _ _

_ 9 8 _ _ _ _ 6 _

8 _ _ _ 6 _ _ _ 3

4 _ _ 8 _ 3 _ _ 1

7 _ _ _ 2 _ _ _ 6

_ 6 _ _ _ _ 2 8 _

_ _ _ 4 1 9 _ _ 5

_ _ _ _ 8 _ _ 7 9

One more list

posted November 2013

It's time for a new list of random things I noticed about Bordeaux :

  • Many 2€ kebab places. Also, kebab here are made with a Lebanese bread, like a crepe, and not with the half of an Arabic bread like in Lyon.
  • It's raining, A LOT. It's raining at least once a week, but usually way more than once a week.
  • It's not that cold. I just came back from a week in Lyon and oh my god was it cold there, you can feel winter coming, but in Bordeaux ? Chill, you don't need that jacket.
  • There are no Bordelais. Most people I run into come from other places in France. I actually only met one Bordelaise and it was during my first week here.
  • The city is really not that big. In 30 minutes you feel like you've seen most of it.
  • We have Velov' in Lyon, Velib' in Paris, here it's Vcub. Those free bikes you can rent pretty much anywhere.