Techzone
A bunch of useful tutorials around the latest softwares and hardwares
Total Immersion: Augmented reality meets paper ad
Jun 19th 2010
You might ask yourself what a good old French rocker Johnny Halliday (better known in USA as Smet thanks to star fashion designer Chrisitian Audigier )has something to do with augmented reality.
This question is legit but here is the answer: the French TV magazine Tele 7 jours are offering a pretty nice feature: if you place the cover of the magazine in front of your webcam you will have the pleasure to see our french rocker appear on the magazine’s cover playing a private concert for you; nice isn’t it? Indeed the French augmented reality specialized company Total Immersion really did a great job.
Tutorial: Using TV Out with an iPod Touch 2G/ iPhone 123G for selfwritten apps with XCode
Apr 13th 2010
Here we are again with a typical problem when using an iPhone or an iPod Touch: you have built a nice app with XCode and would like to show it to everyone during a presentation. Unfortunately you don’t have the magic “Steve Job” cable that will allow you to show to the whole audience what you are currently doing on your iPod Touch.
Only the Video app allows a direct video output onto the cable. This is so frustrating! But fortunately here is a solution. This solution is based on jailbreaking your device and installing a special app that will over a private Apple API output the screen buffer directly onto the cable. It’s really worth trying it out and will give your presentation a new dimension, because not so many people are using this technique. More >
What can you do with bytes ? Thibault tells you
Apr 11th 2010
Ever wanted to know what you could do with a ByteArray ? Thibault Imbert (visit his website ByteArray.org) gives you the answers and opens you the mysterious world of bits and bytes in Actionscript 3. His book will contain 7 chapters around concepts like encoders, parsers or even emulators.
If you are beginning to learn Actionscript 3, have no clue why ByteArrays are so important or if you wonder how to make an image encoder or how to send data over sockets, then this book is for you!
Thibault was kind enough to let us download the first chapter called “The first bits. The complete book will be available on his website. And by the way, don’t hesitate to check his other Actionscript 3 tuts and articles, this will show you the power of Actionscript 3 😉
How to quickly convert MP4 files to MP3 with Automator
May 6th 2009
In this article you will discover two pretty nice workarounds to edit MP4 files and to convert them into an MP3 that any MP3 player is available to play.
The idea to write this article came after a friend of mine asked me to find a very quick solution to convert tens (or was it tons 😉 ) of MP4 files in MP3 files.
Don’t forget that your Mac will help you to do a lot of stupid file converting without even having a strong knowledge about codecs and QuickTime headers. More >
Web 3.0 Innovative Semantic Interactions with Spotlets
Dec 21st 2008
Here and there you have certainly have heard of the new semantic web and Web 3.0. Web 2.0 was the socalled “community Web” corresponding to the numerous blogs, social networks and other APIs to let other people use the functions of a website.
That was indeed very interesting but a major problem was the correct information retrieval. That’s the point were semantic will play a major role in the future. Semantics try to find out from a combination of words, what the user wanted to say or to formulate.
More >
BeatMaker review
Sep 24th 2008
Composing music on your iPhone is really funny and really addictive. Let’s take a look on Intua’s new iPhone software: BeatMaker. Click here for the English version (Translated by Google)
Wii Fit Balance Board Hacked :) Part 2/2
Jun 15th 2008
After our first video, many people came up with several comments asking if other movements were possible, because in the first video (http://youtube.com/watch?v=lKUDU9lE–E) we were only going backwards and forwards. Yes! it is also possible to do circular movements and you can actually turn surf around/over a city with Google Earth. In order to illustrate this, we (Simon Bergweiler and myself) have recorded another video in which we are also showing how to move your avatar in World of Warcraft. We are planning a next video, with new cool interactions, so stay tuned!
Wii Fit Balance Board Hacked :) Part 1/2
May 20th 2008
After hours of testing and C# coding, you can now use your Wii Balance Board as a new input device. Simon Bergweiler and myself posted a Youtube video of our application and its usage with Google Earth, Microsoft Virtual Earth and Second Life. Have fun !
P.S: If you wanna have more explanation on how it works, feel free to contact us on the email displayed in the video.
Direct Youtube link:http://youtube.com/watch?v=lKUDU9lE–E
When tagging makes fun: ESP games
May 20th 2008
Tagging picture is sometimes not very funny, but if you turn this into a twoplayer game. you will get Google Image Labeler: on a random principle, a partner is found by Google Image Labeler. If your partner suggests the same words or definitions for a displayed image, you will win points. More >
Top 5 best Flash resources
May 10th 2008
Ever wanted to know how a cool animation was implemented, but never knew which thirdparty class was used? Here is a top 5 of musthave Flash resources. More >
DIY: How to build a car holder for iPod Nano 3G
Apr 9th 2008
Readers of my blog already knows it : I like my iPod Nano Fatty. The 3G version of the iPod was certainly one of the best iPods because you had every interface / menu and preview in the same orientation and there was no need to turn your iPod to watch a film (like the new Nano ones). More >
Second Life Multilanguage support
Sep 11th 2007
When you are flying around in Second Life you have certainly noticed that there are no support for multilanguage, meaning everything is in English and there is no option to change it. The following tutorial will explain how by using textures and the Linden Scripting Language it is possible to make a multilanguage support for your world including an adaptive language change for dialog boxes. More > 
Ipod Nano 3g Full Review
Sep 11th 2007
As you may have now seen, the new Nano 3 G was released a few weeks ago. The reviews on the internet concerning the iPod are sometime biased by enthousiastic geeks or early adopters. The following review is 100% objective 

Usability 



The new iPod is about 7 cm high and 5.2 cm wide. It’s weight: only 49.2 grams! Although the screen is pretty small it’s a pleasure to watch TV shows or video clips on it. There is no visual difficulty concerning the usage of menus. But for someone who has big thumbs the usage of the click wheel might be adventurous: you will never know if you are going to select the next/previous track or going to change the volume. I would say the click wheel is very sensitive. More > 
RSA DiffieHellman explained in 3 minutes
Apr 1st 2007
Cryptosystems explained
I was always upset to see that cryptography was made so difficult because so many cryptical maths signs were used.
I wrote this tiny article to easily explain how RSA and Diffie Hellman key exchange are working. This article is not targeted on mathematics fans so they won’t find something new here;) I hope it can help you to start in the cryptosystem field.
Modulo calculation
The first thing to know in cryptography, is how to handle with modulo calculations. Modulo, what ? No fear it’s very easy to understand.
Just take this example : when a friend of you is telling : “I’ll be back home in 32 hours” how are you converting this in days ?
32 hours = 24 hours + 8 hours
This is equivalent to write : 32 = 24×1 + 8 . Unconsciously you made : 32 divided by 24 and the remainder is 8
So if we turn this in a mathematical way you can write : 32 mod 24 = 8
Another example : If you say “I have a train in 125 minutes“. How are you proceeding to know how many hour(s) and minutes you have to wait ? Very easy : you are going to divide 125 by 60 and then 5 will remain. You have two “full” hours and 5 minutes :
125 = 60×2 + 5 . You can also write : 125 mod 60 = 5
Here is another example : 125 mod 32 = 29. Why ? because 125 = 32 x 3 + 29
Just think about “doing 3 packets of 32 starting at 125 ” and if the remainder is not 0, the number remaining (the red one) will be the solution of your equation.
24 mod 12 = 0 because we have a remainder that equals 0 => 24 = 2 x 12 + 0
Prime numbers
Many properties in cryptography are based on multiplication and factorization of prime numbers. A primer number is a whole number (integer) that can only be divided evenly by itself.
e.g. 2, 3, 5, 7,11,13,17,19,23,27 are prime numbers
24 is not a prime number because it can be divided by 2,3,4,8,12
Generating big prime numbers enables us to have a higher security because they are very hard to find ( due to the property of being divisible by itself). Make the test by yourself : find a prime number higher than 2000. You will need a few seconds to verify the divisors so do computers for very huge prime numbers.
If you are interested, here is a page listing the 1000 first prime numbers : http://primes.utm.edu/lists/small/1000.txt
The DiffieHellman key exchange
It’s always a problem when you want to share a key to another person, because you can’t be sure that the “line” or transmission mode is sure enough. That’s why DiffieHellman key exchange algorithm was created. The following picture explains the whole process :
RSA
The acronym RSA stands for Ron Rivest, Adi Shamir and Leon Adleman, the three “inventor” of this system. It was in 1977.
RSA is very easy to understand. We will have two persons (say Alice and Bob). They want to communicate together but don’t want to be listened by someone else. So Alice will need to encrypt her message and Bob to decrypt it.
We will first choose two prime numbers p and q so that p and q have no common divider. In other words the greatest common divider of p and q is 1.
Finding p and q
Let’s take as an example p = 7 and q = 3. It’s clear that gcd(7,3) = 1
Now we are going to find n. n equals p x q . So in our example we will have :
n = p x q = 7 x 3 = 21
Alice also needs to compute her private (or so called secret) key and the public key. Bob will also have a private key. With his secret/private key and Alice’s public key Bob will be able to decipher Alice’s message.
In order to compute both keys we need to find e and d so that: e x d mod phi(n) = 1.
Don’t panic 😉
phi(n) = (p1)(q1) = (71)(31) = 12
Now we must find e so that e has no common factor with phi(n). We can also say that gcd(e,phi(n)) = 1 or gcd(e,12).
Let’s take e = 7 ( a quick check gives uses gcd(7, 12) = 1 ) for the sake of showing how the process works.
Now we need to find out d . Finding d is perhaps the most tricky thing of the whole RSA algorithm.
We can write this : 7 d mod 12. To solve this we simply write :
12 = 7 x 1 + 5 (then we pull down the numbers 5 and 2 )
7 = 5 x 1 + 2
5 = 2 x 2 + 1 => Stop !
Extended Euclidean Algorithm
When you have a 1 on the most right side of your equation you stop ! What we just did is called “Extended Euclidean algorithm”. “Funny” name, but easy to solve 😉 Now that we have the number 1 on the right side we can “invert” our equation by writing :
1 = 5 – 2 x 2
and then you will replace by 2 by 7 = 5 x 1 + 2
1 = 5 – ( 7 – 5 x 1) x 2
1 = 5 x 3 – 2 x 7
and now we will replace 5 by 5 = 12 – 7 x 1
1 = (12 – 7 x 1) x 3 – 2 x 7
and by replacing 2 by 5 = 12 – 7 x 1
If we group the 7s and the 12s we have :
1 = 12 x 3 – 5 x 7
What we in fact were trying to reach is a result with following form 1 = 12 x A – 5 x B with A and B unknown. These two unknown numbers are in maths called Bezout coefficients.
Don’t forget that we are working in the ensemble Z12. We can “erase” 3 x 12 because we already have seen that 3 x 12 = 36 and 36 mod 12 = 0
Now we are going to watch the 5 x 7 part. we see the number 5 coming from e . But we want d !
we can now write in this form : 5 + 12 = 7 . This is called the inverse of 5 mod 12. So inverse of 5 mod 12 = 7
and d is going to be : 7 + 12 because we have in our equation mod 12
this gives d = 19.
What happens next if instead of 5 we had a positive number such as 3 ? You would have calculated : d = 3 + 12 = 15
We can now check our result : e x d = 7 x 19 = 133 . And if we decompose 133 we have : 133 = 12 x 11 + 1 The remainder is 1, our calculation is correct.
Let’s encrypt !
In order to simplify the calculation, we are going to take following values for n, p, q, e and d. We take 5 for the value of e because gcd(5,phi(n)) = gcd(5,12) = 1. This will simplify the process.
To sum up : n = 21 p = 7 q = 3 e= 5 d = 19
The couple (d,n) represents the private key (decrypting key)
The couple (e,n) represent the public key (encrypting key)
Now we are going to compute a message say a number m = 12 (we take this value because this value must be smaller than n) and c our encrypted message that is going to be sent to Bob.
We just need to write
The result of this formula is : c = 12 ^{5}mod 21 and then we see c = 3
Decrypting is easy, you just need d ( the private key) and apply following formula :
So 3^{5} mod 21 = 12 <=> m = 12 Bingo 😉
What you just need to know about RSA :
Encrypting
with the couple (e,n) the public key
Decrypting
with the couple (d,n) the private key
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