Use your Chromecast/Roku on a Hotel WiFi

Chromecast and Roku are really wonderful devices which allow you to take all your media with you where ever you go. Especially, if you travel a lot, it's definitely way better to watch something on your Netflix subscription rather than paying exorbitant rates on the hotel's pay-per-view.

But there's a problem. Hotel WiFi's usually use web based authentication (i.e.) their wireless network is usually open and anyone can connect to it. Only when you try and open a webpage, they send you to an authentication page that asks for a username/password (which the hotel will provide you) and/or asks you to accept the terms and conditions.

The problem is that Chromecast and Roku do not have native support for such authentication. But fear not, in this post, i am going to write about a few ways in which you can work around this limitation to enjoy Roku/Chromecast on the hotel's WiFi network.

Find out your device's MAC Address

2 of the 3 workarounds that i mention requires you to know the MAC Address of your Chromecast/Roku device. Here's how you figure it out:

Roku

• Switch it on
• Navigate to Settings->Network->Wireless
• On the bottom right, you can see the MAC Address of the Roku

Chromecast

• Switch it on
• Connect your phone to the hotel WiFi and authenticate it
• Open the Chromecast Setup app on your android phone
• Tap on devices and wait for it to scan
• Tap on your Chromecast device in the list
• Tap "Set Up"
• Tap "I see the code"
• Tap "Set Name"
• The MAC Address of your chromecast will be displayed on the screen now. 

Workaround 1 - Call the Tech Support

Most hotels give you a small sheet of paper with your WiFi username and password. That sheet usually also has a "tech support" phone number. Here is what you can do: Call the tech support number and tell them exactly this: "I would like to use the roku media player device over the hotel WiFi. I wanted to check if you could whitelist the MAC Address of my device to by-pass the authentication page".

Depending on the mood and knowledge of the tech support person, he/she might say okay. But nevertheless, it's gonna take some time before the whitelist happens. And once the whitelist happens, you can enjoy Chromecast/Roku over the hotel WiFi.

Workaround 2 - Spoof your MAC and authenticate from your laptop

The whole web authentication system works around MAC addresses. Once you enter your username and password, your MAC and IP addresses are going to be whitelisted for a certain amount of time (about 24 hours) and your device will be allowed to access the internet in that time period.

One key weakness about this authentication mechanism is that MAC address is easily spoof'able. So we are going to to assign your Roku/Chromecast's MAC address to your laptop and perform the authentication like usual and then make use of that whitelist to access the internet from your Roku/Chromecast. Here are the steps (follow them precisely to the word):

• Find the MAC address of your Roku/Chromecast using the steps above. Note it down.
• Open the terminal (assumes linux).
• Run "ifconfig" and note down the MAC Address of the laptop. [1]
• Run this command: "sudo ifconfig wlan0 down".
• Disconnect from the WiFi network on the laptop.
• Run this command: "sudo ifconfig wlan0 hw ether <mac address of roku>".
• IMPORTANT: Turn off the Roku/Chromecast by unplugging it.
• Run this command: "sudo ifconfig wlan0 up".
• Connect to the Hotel's WiFi network on the laptop.
• Open the browser and navigate to google.com (or any other website).
• It will ask for authentication, provide username/password that the hotel gave you.
• Type google.com again and verify that you can access Google.
• Run this command: "sudo ifconfig wlan0 down".
• Disconnect from the WiFi network on the laptop.
• Run this command: "sudo ifconfig wlan0 hw ether <mac address of your laptop from step [1] above>".
• Run this command: "sudo ifconfig wlan0 up".
• Now you can plug your Chromecast/Roku back in and connect to the Hotel's WiFi network on that. It should now be connected to the internet!

You will have to repeat these steps after the whitelist expires (usually about once a day).

Note: The above two work arounds will connect your Chromecast/Roku directly to the hotel's WiFi 

Workaround 3 - Set up your own WiFi network

Buy a portable WiFi adapter and use that to share your Hotel's WiFi through your own access point.

Hope this helps!

-Vignesh

Introducing Super Secure File - One File, Completely Secure, Access Anywhere!

Super Secure File gets you a really secure password protected file that you can access anywhere with an internet connection. Smartphone, Tablet, Laptop, SmartTV, anything!

To cut to the chase and create your Super Secure File, go to: http://secure.foamsnet.com.

How does it work?

Super Secure File basically uses Google Drive to store your encrypted file and does all the encryption and decryption locally in Javascript. The key never ever leaves your computer. Once you close the tab, boom, the key is gone. Nobody knows the key but you (and probably your spouse if you are married).

Motivation

This is not a big feat or anything, this is merely a mashup of a few libraries to prove a point to myself. The motive behind this app is to build a secure mechanism to store my passwords and credit card numbers on the cloud so that I can access it anywhere. I do not trust anyone who links me up to a server when it comes to information like this. Which is why i wanted a completely static HTML page with no server access whatsoever to provide me with this functionality.

Feel free to examine the source code here (and please let me know if you find anything utterly stupid): https://github.com/vickyg3/super-secure-file

Hosting and Links

Since this is a static page, I have not hosted this on my server. This is merely hosted as a github page (if you look at the repo, you'll see the default branch to be gh-pages and not master). Hosting it as a github page also proves that it has no server interaction whatsoever and cannot steal your key by any mean.

So, all you need is to remember your password and one of these URLs (they all redirect to the same Github Page): http://bit.ly/securefile or http://bit.ly/supersecurefile or http://secure.foamsnet.com or http://vickyg3.github.io/super-secure-file/super_secure_file.html

Get your Super Secure File and make your life a little easier! :-)


-Vignesh

VLC Media Player: Automatically Skip Songs in Indian Movies!

I watch a lot of movies. Really a lot. And VLC Media Player is my (and many others') favorite. Indian movies are plagued with songs in irrelevant times and most of the time it just interrupts the pace/flow of the movie. No offense to music lovers/music makers, I like listening to songs in general. But I don't like them in the middle of an important scene in the movie.

The Problem

Whenever a song starts, inevitably I try to use the seek bar (using the seek bar is really one of the big pain points of any media player as it almost never takes you to where you want) and seek to the end of the song. Most of the time I end up seeking either just after the song (thereby missing something important) or to some portion in between the song (thereby having to wait for some more time for the song to end).

As an engineer, I naturally wondered, Wouldn't it be wonderful to have an automated way (preferably a keyboard shortcut) to just skip the song and move to the more important stuff?

This is exactly what I sat down to solve. Based on this xkcd, it seemed like it would be worth the time.And I (sort of) have a perfect solution that helps me skip songs automatically in the press of a button in VLC Media Player.

The Solution

As hard as the problem might seem, I ended up using a very simple heuristic. Start analyzing the audio stream, and whenever there is a silence for about a second or so, it's likely that the song ends there. I just came up with this heuristic based on the fact that most Indian movie songs are continuous (either lyric or the music goes on throughout the song without any breaks) and when the song ends, there is usually a small interval of silence before the next scene starts. And if there is a silence somewhere in between the song, just do the analysis again and it will take you to the next silence which is most likely the end of the song.

Is it perfect? Absolutely not. It's not even a solution, it's more of a heuristic (aka hack) which exploits some pattern in the Indian movie songs. And in my observation (I have been using this for quite a while now), It seems to be working correctly 99% of the time.

Implementation Details

Note: This section has technical jibber-jabber. If all you care about is how to use the script in your VLC media player, skip ahead to the "Usage" section.

First things first, I chose VLC media player, because that's the one I use. If you aren't using it, then you should start using it too. To begin with, we need to query VLC Media Player.

The overall flow goes something like this:

1. Get the name of the file that VLC is currently playing
2. Get the time point of the current playback from VLC
3. Analyze the audio stream of the file and detect the next silence beginning from the time point of current playback
4. Seek VLC to the determined duration where silence was detected (this is likely the end point of our song)

As complex as these steps might seem, they are fairly trivial to accomplish. To perform steps 1, 2 and 4 all we need to do is enable the HTTP interface in VLC. Once that's done, it is straightforward to get details of playback and control the player through a simple HTTP interface. The 2nd step is a little more tricky as it involves analysis of the audio stream of a file. Fortunately, we have a swiss army knife in our hands which will not only analyze the audio stream, but pin point us to the exact location of silence that we are looking for. The tool is none other than FFmpeg. The silence detect filter in ffmpeg has been used to accomplish this.

Here is a rough sketch of the ffmpeg command that I use:

ffmpeg -ss <start_time> -i <input_file> -t 600 -vn -af silencedetect=noise=0.1 -f null -

Let me break that up:

• -ss <start_time> :- seeks to the specified time in the input file. this value for this is obtained from VLC's HTTP interface
• -i <input_file> :- absolute path of the file that VLC is currently playing. this value is obtained from VLC's HTTP interface
• -t 600 :- analyzes only 600 seconds (10 minutes) of audio to detect for silence (as Indian movie songs are hardly longer than 10 minutes).
• -vn :- ignore the video
• -af silencedetect=noise=0.1 :- enable the silence detection filter with a threshold of 0.1dB. this value was picked by trial and error.
• -f null - :- just print the output of the filter in stdout rather than a file.

We then grep for the exact duration and then seek VLC based on this output.

Code

The code is in github here: https://github.com/vickyg3/scripts/blob/master/song_skipper.py

Look into the variables on top of the file and change them as per your environment if required.

Usage

To use this script, you need to install the following (fairly straightforward if you are tech-savy, but doable even if you are not).

• Install Python - Download Python 2.x (do NOT download 3.x)
• Enable HTTP Interface in VLC. Click on the link for instructions on how to do this. (you only need to do this once).
• Install FFmpeg
• Download the script from here: https://raw.github.com/vickyg3/scripts/master/song_skipper.py

Once you do the above steps, all you need to do is to bind a keyboard shortcut such that the script will execute. For Mac, I used Keyboard Maestro to set up a global keyboard shortcut which will invoke the script. There should be an equivalent program for Windows/Linux too. So that whenever a song starts, I merely use the keyboard shortcut to skip it.

Hope you enjoy it.

-Vignesh

Education is a cure for all problems. Donate for the cause of Educating kids: Computer Kindness Foundation is helping schools to build Libraries. Follow the link to contribute.

Announcing Social Photos v2!

I have been working on this side project for quite a while now and I am happy to announce that it is launch ready now!

Visit http://socialphotos.net to manage all your digital photos across Social Networks in one roof using a simple intuitive user interface.

Features Include:

• Transfer Photos
• Transfer Albums
• Download selective albums as a zip file
• View Slideshow of your albums
• Monitor progress in a simple pane
• And much more!

Please do feel free to give feedbacks/suggestions. Use it and Share it!

http://socialphotos.net

-Vignesh

Solving Boggle (Scramble with Friends) with a Bot!

Headnote

I am always fascinated by Android games, especially puzzle games. This is how it usually works with me and a puzzle game. I start playing them with random friends. They beat me and I beat them on and off. Then I sit and think, this is so monotonic and algorithmic that a human being shouldn't be sitting and doing it. Then I sit with the computer (with my favorite monkeyrunner Jython in it) and try to come up with a simple algorithm for it. Then i plug in the standard monkeyrunner code to actually feed the output of the program back to the device. Then I usually become #1 among my friends in the leaderboard (often even in the global leaderboard) ;-)

This is one such scenario. Zynga's Scramble with Friends has been really popular among my friends off late. So i hit this routine cycle and ended up with a beautiful bot which usually scores a centum (like the one TamBrahm parents force their kids to get in Mathematics).

With that out of the way, let's begin.

Objective of the Game

The game consists of a 4x4 grid of letters. You have to form as many words you can by starting from a letter and by moving to one of the (upto) 8 adjacent letters. Dead simple, but really interesting and addictive.

The first thing needed to solve this is a dictionary of words. I went on the internet and downloaded a plain text dictionary file which had about 170k words in it. Good enough to start with.

Algorithm - Breadth First Search

The number of valid words is usually very limited. In most games, the total number of valid words is usually < 400. So, a simple Breadth First Search (BFS) will do starting with single letter elements and then add the neighbors recursively. One key insight is, if you come across a prefix that never occurs in the dictionary, you can discard that prefix at that point instead of adding it to the traversal queue.

A rough sketch of the algorithm is as follows:

• queue = [all 16 characters]
• while queue is not empty:
• word = head of queue
• if word is in dictionary output it [1]
• for all neighbors adjacent to the last character of word
• new_word = word + neighbor
• if dictionary has words with prefix new_word, add new_word to the queue [2]

That's it. Straightforward implementation of a BFS-like algorithm.

Choice of Data Structure

The key to solving this problem efficiently lies in choosing a good data structure for implementing the dictionary. The dictionary needs to support two major operations. One is looking up if a word exists. This is used for step [1] in the above algorithm. The other operation is, given a prefix, check if there is atleast one word containing that prefix in the dictionary. This is used for step [2] in the algorithm mentioned above.

Array ?

One good looking candidate is using a simple array (note that the dictionary is already sorted for us). Look up can be performed using simple binary search. Prefix checking can also be performed using a modified binary search (if search succeeds, then prefix exists. if search fails, prefix existence can be determined by looking at the bounds in which the search failed). Also, note that the dictionary has ~173k words. So, searching is gonna take log(173k) which is approximately 18 hits in the worst case. This is a totally fair deal.

Trie ?

Another possibility is using the Trie, whose raison-d'etre (very reason for existence) is to implement such dictionaries. The Trie implementation is also fairly trivial (since we require only two major operations apart from Trie construction). In the Trie, both the operations are gonna take as many hits as the length of the word or the prefix being looked up. So asymptotically, both these data structures are more or less similar and we don't have a big advantage in using either one over the other since our output is always gonna be < 400 words.

I decided to go with the Trie. After reading this article about Trie implementations in Python, I decided to quickly write my own implementation of Trie. Also, this made life simpler as I couldn't quickly find any good resources about using external libraries within monkeyrunner.

Implementation Quirks

Since I had already used monkeyrunner a few times before, implementation turned out to be pretty straightforward. The following are a few implementation quirks and nuances that the script deals with:

• Input is manually entered as a raw row-major string of length 16.
• If the same word can be formed by two different combinations, only one combination is actually considered valid. This is overcome by storing a list of already found words in another Trie.
• Even though the script finds smaller words first (because of BFS), it actually starts outputting words of length >= 5 first and then after it has exhausted all the lengthier words, it then outputs the smaller words in the reverse order of length (4,3,2). This is to maximize points in case we don't find time to output all the words.
• The game offers three lifelines. I found the freeze option to be useful to the bot (as each freeze gives you 15 additional seconds of game time). So, the script automatically taps on the freeze lifeline every 30 seconds.
• We also need to store the co-ordinate of each letter in the queue along with the letters themselves in order to simulate the output in the device.
• The co-ordinates are hard-coded for Nexus 7 portrait mode.

Code

The whole implementation can be found here: https://github.com/vickyg3/scripts/tree/master/scramble_bot

Sample Video

Here is the exciting part. This is how it looks like when my bot plays the game:

It's always a very nice feelings to watch you script do such beautiful things.

-Vignesh

Wanna do some good deed? Visit http://www.computerkindness.org (Or look for the banner in the top-right of this page).

C++ COW Craziness

Note: This isn't one of those Linus'ish articles that bitches about C++. I like C++ and I would just like to point out one of the many nuances in the language that could affect the performance of your program without your knowledge.


C++ STL's string class promises Copy-on-write. What that means is that, you can make as many copies of the string, but the actual memory duplication will happen only when one of the strings are actually written to (i.e.) no memory duplication will be made for copies that are made for pure reads. Or atleast that's what I thought, until I discovered today that, if you use the [ ] operator on the string, you rig the COW functionality of it forever. It is something that you normally don't do, but doing so could cost you a lot of performance. Let's run through an example.

string s1(1024 * 1024 * 16, 'g');
for(int i = 0; i < 1000; i++) {
  string s2 = s1;
}

This runs in 19 milliseconds. That's because (obviously) there are no actual copies made. Just 1000 pointers being created to the existing 16 megabytes of data. Now, lets try modifiying the copied string.

string s1(1024 * 1024 * 16, 'g');
for(int i = 0; i < 1000; i++) {
  string s2 = s1;
  s2[0] = 'v';
}

This runs in 4.3 seconds. That's right, from 19 milliseconds to 4.3 seconds for making 1000 actual copies of 16 MB of data. This is the expected behavior, a copy is done when you try to write to it. Next comes the weird part, consider the following code:

string s1(1024 * 1024 * 16, 'g');
for(int i = 0; i < 1000; i++) {
  string s2 = s1;
  s2[0];
}

Guess how much time this should take? Intuitively it seems like this should hit the COW fast path (i.e.) no actual copies, because there is no "write" here. This takes 4.3 seconds too! The problem behind the [ ] operator is that, you can easily stash away a pointer to some portion of the string and modify it later thereby screwing up the state. So, it is impossible to perform COW once you use the [ ] operator on a string. The following snippet illustrates this:

string s1("hello");
char *p = &s1[2];
string s2 = s1;
*p = 'v';

You see what happened there? You stashed away a pointer to the middle of the string and then tried to change it later after the copy. This is sort of an indirect write, and there is no way for the compiler to determine this. So, the moment is sees the [ ] operator, it removes the COW functionality for that string. One way to do such a read without rigging the COW functionality is to do a crazy cast like this:

string s1(1024 * 1024 * 16, 'g');
const_cast<const string &>(s1)[0];
for(int i = 0; i < 1000; i++) {
  string s2 = s1;
}

This snippet takes the fast COW path and runs in 20 milliseconds. The takeaway from this article is that, do not use the [ ] (or the .at()) operator on strings, especially large string that could be copied later on. Even though you think you're doing an harmless read, you are rigging the COW functionality of that string forever. You are paying the price for that pointer you stashed away (or may be even released long back) without knowing.

 -Vignesh

Convert your keyboard into an Android game controller!

I have been gifted with a new android phone. It's the big G branded Galaxy Nexus. Its blazingly fast and awesome to use (especially after years of HTC Wildfire usage). Right from day one, i have been really addicted to this game called Temple Runner which wasn't compatible with my old phone.

The game is very straightforward to play and it involves only 4 different operations. Swipe up, left, right and down. Coming from a strong keyboard background, I was never 100% comfortable with touch interfaces as i was with keyboard. And these 4 operations sounded analogous to the accelerate, brake and turn operations while playing a racing game in the computer keyboard.

That got me thinking, is there a way to make the computer keyboard into a game controller for my Android phone? Turns out its fairly straightforward. In this post i'll explain exactly how to do that.

Ingredients

• Android phone (obviously)
• USB cable connected in debugging mode
• Android SDK installed
• Very very basic python english

There's a tool named monkeyrunner which enables us to send operations from the computer to the phone via a very simple Python API (monkeyrunner tool is a part of Android SDK). A sample code for a controller would look like this:

Code until line 7 is fairly straightforward to understand. The only thing that i would like to explain here is the device object. It is an object of the MonkeyDevice class. This class has all the API methods that you need to use in order to simulate the operations. For example, device.touch(100, 200, MonkeyDevice.DOWN_AND_UP) will simulate a touch event at co-ordinate 100, 200 (with the origin being top left). As simple as that!

You can find the detailed documentation of the monkey device class to know about other methods like drag, type, etc.

The full code which i used for playing Temple Run game is given below:

One point to note is that, the sys.stdin.read(1) line will read one character and wait for the enter key to be pressed. This could be annoying given that you are writing a game controller. In order to avoid the enter key press, if you are on linux run "stty raw" before running this script and if on windows use the getch function in msvcrt module.

-Vignesh

How I hacked an android game with Python and OCR!

Math Workout is a famous android game. In fact, it features in the top 5 of google listings for many math game + android related queries. The objective of the game is very very simple. It will fire simple math questions one after the other and you'll have to tap in the correct answer. Its a race against time among other users of the app in the world.

Here's how the app looks like and a few screenshots of questions:

As you can see, the game is fairly straigtforward. So its the time that you have to beat. A naive approach to that would be having a calculator or a computer near by and feeding in the questions to determine the answer and feeding it back to the phone. Totally manual!

Thats when the programming neurons of my brains started itching me that this could be automated and cheated by some mean. Come on think, think! So i sat on to solve this problem during my weekend and started thinking about ways i could attack this problem.

These are the steps that came into my mind in the first thought:

1. Grab a screenshot of every question
2. Crop the screenshot so that only the question is visible
3. Run the cropped image through an OCR engine
4. Parse the result and evaluate it
5. Identify the co-ordinates of the resulting number and appropriately simulate touch events in the phone

Bummer! Every step looked a bit complex in itself at first sight. Then came along a bit of googling, and voila, i found the perfect tool that i needed to perform steps 1, 2 and 5. It is the monkeyrunner tool that comes along with the Android SDK. It opens up a Python API through which i can grab and crop screenshots, simulate touch events given an (x,y) co-ordinate. Exactly what i wanted.



Now, I have the cropped image that has the question in hand. Next step is to run it through an OCR engine. Again googling told me that ocrad is an useful OCR command line tool that was available as a part of the GNU project. I installed it and found that it cannot process png images. So i had to run the image through a converter before passing it to ocrad. This small piece of shell script helped me accomplish that:


To keep things simple, the shell script is invoked from python using os.popen(). Now, I have the actual expression as a python string. As you can see from the sample screenshots, few questions can be solved by a direct "eval" whereas others require some processing. Basic operations like addition, subtraction, multiplication and division can be solved using "eval". Whereas questions like "10% of 20", "square root of 9" needs some processing. Thats what this following if else block does:



Now that the expression is evaluated and we have the result in hand, all that's left is to go through the result character by character and simulate touch events in corresponding positions in the screen. I managed to identify the co-ordinates of each number in the screen by trial and error and hard coded those values within two functions named getx() and gety() which will take a character and return its corresponding x and y co-ordinates respectively, and the simulation happens. Here is the code snippet:



To orchestrate this whole process and play the game fully automatically other cosmetic additions like coping up with the frame rate of the phone and taking care of screenshot/ocr lags are to be considered. These are handled by minor if conditions and sleeps for very small amounts of time.

The end result is as you see in the below screenshot :-P

Here is a video of how the game looks like when it is being played by my script:

Though these steps seem like computationally a bit expensive, in practice i found them to be really fast. The script was able to answer approximately 2 questions per second (with an explicit sleep of 0.2 seconds between two questions - which leads to 2 questions every 0.8 seconds). A C/C++ program might run faster than this, but i stopped here as i have accomplished what i wanted. Overall it was a fun filled Sunday! :-)

Here is a link to the full source code of the automated script: auto_math_workout.py (you can find ocr.sh from the gist above in this page - rest of the source code is in the link)

Any comments/feedbacks are welcome! :-)

-Vignesh

Replacing Lightweight Web Services with Twitter Bots!

Foresight
Here is a vague idea. I'm not sure if i can even call it an idea. I always had the tendency to create lightweight information portals as usable web-based services with a very simple user interface. It just used to get things done and nothing more.

Practical Use Case
For example, let us consider a simple problem of "PNR Status Enquiry" in Indian Trains (for the uninitiated: PNR status is nothing but the current status of a waitlisted ticket in Indian Trains). First of all, such a system is really useful because the official Indian Railways websites are a bit clogged and they don't provide any alert services. Also, their websites are not so catchy and mobile compatible, and we definitely don't want to switch on the computer just to check the PNR status.

Before today, if i was asked to build such a system, i would go for an elegant google-like web page, where there is just a text box and a button for the user to enter the PNR number and click go. The resultant page will be again a simple HTML table with the ticket details (of course all of them scrapped from one of the railway websites - pretty sure that this isn't legal, although i am not aware of any laws against site scraping).

Do we really need web for this?
But this thought stuck me today. Web is a wonderful platform, at times too good to host silly and redundant stuff like this. Tomorrow i may have to build a similar system for Buses or Aeroplanes requiring me to add more and more pages with almost same functionality but different information sources. We don't need the web for such silly things. My idea is that, why not use "Twitter" as a platform for such web services. I've heard of facebook as a platform before for many applications and games (Farmville), so why not twitter as a platform too?

Twitter as a Platform
So what exactly do i mean by twitter as a platform? Let us redesign the same PNR status enquiry system using what i mean by twitter as a platform. Instead of having a web page for inputs, lets host a twitter bot, say @pnrbot. Now, whenever you need to enquire the status of a PNR number, all you have to do is post a tweet mentioning that bot, for example "@pnrbot 1234567890" (where 1234567890 is the PNR number you wish to enquire).

Now, as long as your tweets are public, the bot can read your tweet almost instantaneously thanks to the vast amount of real time APIs provided by twitter. Now the bot does the usual site scraping from the railways website for your PNR status and it posts it as a reply to your tweet. Simple isn't it? To take it a level further, the bot can also autotweet your PNR status every day until your journey date, which is not very easy in the case of a web based app. Also, since you will not be following the bot and the bot will not be following you, you will not clutter any of your friends' timeline with this tweet as it won't appear in their timeline.

If any of the input data is sensitive and not to be exposed, then the same design can be adopted by just switching the term "tweet" with "Direct Message" (although in that case, both you and the bot need to be following each other, which can be easily accomplished).

Pros of the Platform
Twitter is a part of our day to day life since the inception of mobile internet. So, you get many useful information from such bots interactively rather than opening your webpage and waiting for the page to load. Moreover, twitter is known for its notifications. If you have activated SMS alerts for @ mentions, then you don't even need to have internet to make use of such a bot. You can just send the tweet through an SMS and read the reply from the bot as SMS. Also, twitter has email notifications which may also be of good use. As mentioned in the example, you can have one input with multiple periodical outputs (like time based notifications, etc.) which is not so easy to implement in web based systems.

Developer Standpoint
So from a developer standpoint, what do we ultimately gain by choosing Twitter as a platform over Web for lightweight services? The answer is quite simple and really advantageous. For one, you need not host a web server for lightweight web services. All you need to do is run a script that will act as the bot. The script will also be really lightweight since twitter APIs does all the pushing for you (no polling). You offload majority of the user interface and load to twitter and do only the actual processing in your server.

From the implementation perspective, it'd be really great to have a good library/framework in a nice scripting language (like php or python) for building such a bot so that the possible features (like twitter API access, etc.) could be abstracted out thereby the developers actually have to write just the logic of their actual bot and nothing extra.

Closing Thoughts
I am pretty sure such bots already exists. By building more and more of interactive bots Twitter can really stand tall as a good platform not just for communication but also for instantaneous information retrieval.

P.S.: I am in the process of developing a simple such bot as a proof-of-concept. I am also highly determined to come up with a generic twitter bot library as i mentioned in the post. So as always, interested developers are welcome to carry on if you like the idea!

-Vignesh

Orkut Deja Vu - The Technical Side!

Its been almost two months now since I first launched "Orkut Deja Vu" - A series of web applications and a chrome extension that helps you move your memories from orkut to facebook. Personally, I think the application was a good hit. In this article i will try and explain the technical side of it and the various hurdles faced on the due course of development.


Note: This article is for the technically inclined and if you don't want the technical details and just want to use the application, visit http://orkutdejavu.foamsnet.com!


Java and My server!


To begin with it, my server is a VPS running linux with a humble 700MB RAM and a shared processor. My search for an Orkut API ended with orkut os client - An official API provided by Google. This is more of a library than an API and only the java implementation of the library was very sophisticated (though there were php implementations, they weren't that good). Ever since i started learning computer science, if there was one thing i hated, it was java (now don't even get me started about perl).


So there lied the first problem in front of my eyes: Running java in my server. I didn't want to take up the pain of setting up JSP for this sake and decided to just call the java program that does the orkut calls from PHP using shell_exec. I know it isn't a safe option, but since there is no user passed data and the calls are hard-coded, i was sure that there was no injection vulnerabilities. Yet this approach isn't very efficient as it spawns a separate java vm for every exec call, but it was a compromise that i had to make for not setting up a java based server.


OAuth - The headache!


The orkut library's OAuth implementation was really messy. Fortunately, it had a method to explicitly set an OAuth access token obtained from elsewhere. That said, I used Zend OAuth library in PHP to perform the 3 legged OAuth and use that access token in the java programs. There were totally four java programs: one each to fetch the user's orkut name, albums list, photos and scraps. The java programs printed the output as JSON if it was successful or nothing if there was an exception. PHP then parses that JSON. I used JSON so that all the escaping will be taken care by the JSON libraries and thereby ensuring safety of data transmission.


Photo Album Migrator


The photo album migration was quite straight forward without much hurdles. All i had to do was integrate the following: Image gallery, Facebook API, Orkut API and write some simple javascript that made AJAX calls to transfer the photos. This was quite a cakewalk as i was already very familiar with the Facebook graph API.

Scrapbook Downloader


Again, the programming side of this was quite straight forward. But there was one major challenge involved in designing this. The java program generates a html file containing the scraps which is then converted to PDF. HTML to PDF conversion is CPU intensive and hence needs to be done with care. I could have used a resource manager like Sun Grid Engine, but i did not want to make things complex for a simple job to be done. Also, the conversion is not done programatically by a library as all the PHP PDF libraries were memory-wise very expensive (a file with ~100 scraps always exceeded PHP's memory limit of 64MB). So, I used a external command line utility (wkhtmltopdf) to accomplish this conversion. Again it was a simple shell_exec with hard-coded arguments.

Testimonials Migrator


This was the really challenging part. There was no Orkut API that gave access to users' testimonials. But i didn't want to give up. I really wanted to pull off a tool that can migrate testimonials to facebook. So I thought of attacking this problem from the heart of orkut - the orkut website. Obviously, the first thing that came to my mind was a Google Chrome extension. The extension will inject a javascript into orkut.com website and add a "Post to Facebook" button beneath eacch of your testimonials.


The first hurdle in accomplishing this was that there were two versions of orkut (old and new) with different page structures. I didn't want to write two different scripts to handle the versions. Instead i wrote another script that detects the version and if it is new, it prompted the user to redirect to the older version in order to use the extension. The next job was to understand orkut's DOM so that I can place the buttons. This ended up being quite an easy job too.


Another glitch in chrome extensions is that we cannot specify images directly in CSS for content scripts(for e.g.: background: url(a.jpg); is not possible), as the CSS will run in the scope of the website. So, it has to be either done programatically using javascript or encode the image in base64 and hard code it in the CSS. I chose the first option. From this point, it was fairly straight forward. When the user clicks on the post button, store the corresponding testimonial using HTML5's local storage and create a new tab where the user can choose the posting options. Again, the facebook authentication and API usage here were simple as i had enough exposure already.


Epilogue


Though it seems like a simple app, huge amount of thoughts are put into every single aspect in design of the application and the entire development process was a fun journey with a great learning curve. This application has made me feel my web presence. Web is really a great platform for amateur developers like me. I have got around 20 new followers in twitter and a person from brazil appreciating me for this application. I have really been motivated a lot by this and hope to continue the same stride in creating usable applications as this one!


This post will not be complete without a heartfelt thanks to all those who supported me on due course of development and all those who used and shared this with your friends!


-Vignesh

Playing With Technology - Break Bob's Account!

Folks,

In this edition of Playing With Technology, we have yet another simple challenge. Go ahead and enjoy it!

Scenario

Bob is a famous underworld hacker. His systems are known to be of proven security. He has recently launched a public website to which only very few of his friends have access. He has an admin account where he manages all the user accounts. Your goal is to login into the admin account and find the secret key! Bob generally is too confident about is system's secureness and hence he chooses only passwords of length 4. Also, he enforces an hourly limit of 30 hits to his website. As with the previous hack, clues and hints can lie anywhere and everywhere!

Bob's Website: http://foamsnet.com/pwt/bob_account/
Username: admin
Password Length: 4
Hourly Limit: 30 requests per hour!

Once you find the key, Post it as a comment in this post. I will approve all the comments once i reveal the answer and will aggregate all the correct responses along with the answer.

-Vignesh

PWT Solution - Reach Alice's Website

Hey guys,

Thanks for the overwhelming response for the first PWT post. Here is the solution and explanation for "Reach Alice's Website" hack.

You can view the question here.

To give away the solution in a briefly, it is about "HTTP Referer field in the request". HTTP requests can have a field known as the "Referer" which will contain the URL of the point of origin of that particular request. By looking at the Referer, the current page can find out where that particular request came from. Since it is easily forgeable (like in this hack), referers are generally used only for statistical purposes and none of the application level logic will rely on this field.

So yeah, the solution is, just send a HTTP request with the "Referer" set as "http://www.fakehackersworld.com" and you will get the key.

Here is a sample request without the Referer field set:


Here is a sample request with the Referer field set:


List of persons who completed this task

Please view their original comments to see how they did it.

• Varunkumar Nagarajan


• Viswabharathi


• Raghav


• Azhagu Selvan SP

Congrats to all of you !

The good response that i have got for this post will definitely keep me going about PWT! Thanks guys!

-Vignesh

Playing with Technology (PWT) - Reach Alice's Website !

Hey folks,

This is my first series called "Playing with Technology (PWT)". I will post an interesting real time question related to some technology for you to play around with. It will involve anything and everything i am familiar with. You may have to write scripts, perform hacks, etc. There are no rewards involved. It is just to share the minimal knowledge i possess in the form of an interactive series.

PWT will kick off today with a very simple real time hack that i call as "Reach Alice's Website". Go ahead and enjoy the hack.

Scenario

Alice (yes, our same good old friend Alice) owns a website. Recently, her website was acquired by Hackers World Inc. (http://www.fakehackersworld.com). The CEO of Hackers World considers this acquisition as a very confidential one and decides that all traffic to Alice website should only come through Hackers World website. But the sad part is that, Hackers World website is accessible only to the employees of Hackers World. Your goal, being a hacker, is to somehow reach Alice's website through Hackers World website and acquire the secret key from there!

Alice's Website: http://foamsnet.com/pwt/visit_alice_site
Hackers World Website: http://www.fakehackersworld.com

Remember clues can be lying/hiding in anywhere!

Once you find the key, Post it as a comment in this post. I will approve all the comments once i reveal the answer and will aggregate all the correct responses along with the answer.

Update: The solution has been posted here

-Vignesh

root - The king of kings - Question (Part 1)

After these many years of linux, i have finally found something that root cannot do but a non-root user can do! Yes, its true and it was difficult for myself to believe this in the first place. Its like the phrase, “I saw binary numbers floating in my dreams, wait a second, i think i saw a two!”.

I have always not liked the fact that root is the king of linux and he never respects anyone else. Of course we need a system administrator who should be able to control the entire system, but at the same time, using a system administrator account should not be considered as dangerous, as many of the linux distros warn me.

Consider a simple case, root executes rm -rf * from a directory that is owned by xxxxxx and permissions set to 700. root will be able to successfully do this as he has no limits (which is the cause of the danger). I feel that root should still respect the permissions and not be able to do this in one step. If he really knows that he wants to do it, first he should change the permissions of the file (say to 720) and then perform the rm. By this, it requires two mistakes to screw up, rather than one. But the point is, root should respect permissions and he should modify the permissions when he clearly knows what he is doing and must not be entitled to do anything arbitrarily.

Now, to the actual topic. Here’s what a normal linux user would think is always true:

user@user$ marry me
fuck off!
user@user$ sudo marry me
with pleasure sir!

The point of the above statements is that, no matter what, root can always do anything and everything, unless i recently found one exception. I was able to run a command as non root but not as root.

user@user$ touch foo
user@user$ sudo touch foo
touch: Permission denied

Can anyone figure out how on earth could this happen ? (Yes it is really possible!). I’m posting this as two parts (Question and Answer). I will post the scenario i came up with along with the explanation how it is theoretically correct in the next part. If you know of such a scenario, please share it on comments :-)

-Vignesh

Bom Sabado - The orkut virus !!

If you are still one among those who give a damn about orkut, then this might be one thing that your really care about. Today, orkut has been hit by a vulnerability that is really a security threat for your account.



The virus is called "Bom Sabado", meaning "Good Saturday" in portugese. This is yet another XSS attack, thereby making it the second XSS attack on a major website this week. Earlier this week, Twitter faced a similar attack. There is no official update from google yet on this issue.

What does it do?

When you open orkut and if you are affected by this virus (which could be possible if one of your friends are already affected), a piece of javascript will automatically run doing the following:

• Makes your browser hang for a moment


• Adds you to the attacker's communities (orkut equivalent of facebook fan pages) without your consent


• Sends a scrap (orkut equivalent of facebook wall) to all your friends without your consent, with the text "Bom Sabado" and a piece of code that will do the same set of actions when your friend log in to his/her account

How to prevent this?

• Unlike the twitter XSS attack, this is a severe one that steals your cookies and thereby impersonate your session. If you have logged in to orkut anytime today, clear your cookies and cache of your browser.


• To be safe, change your google account password and security question. To do this, go to https://www.google.com/accounts


• Do not visit orkut until google officially says that they have fixed it. For updates, keep looking here


• If your account seems to be behaving crazy or if its totally compromised, then see here for a solution.


• Delete your orkut account and join facebook !

I badly want to use orkut now!

If you badly want to use it now, then you can use this minor hack to do that. The virus seems to be loading the malicious javascript code from tptools.org and hence you can tweak this to point to something else in your hosts file.

Edit your hosts file (Windows - C:\windows\system32\drivers\etc\hosts; Linux - /etc/hosts) and add the following lines: 127.0.0.1 tptools.org
127.0.0.1 www.tptools.org
This tweak will make tptools.org will to resolve to your own system and hence the javascript will fail to load. Note that you are at your own risk, i am not responsible if your account gets compromised even after you make this tweak !!

I will try to update this post once there are some official responses from google.

-Vignesh

Twitter onMouseOver Saga - XSS and much more !!

There cannot be a better time for me to write about XSS as the famous twitter recently came across with an XSS vulnerability that was exploited by many all around the world by forcing users to redirect to some illegal site or post/retweet stuff without their consent, etc. What the hell was wrong with twitter ? Why did all this happen ? In this article, i have tried to answer these questions.



First let us be clear with the terminology. XSS stands for Cross Site Scripting (It is not called CSS because CSS already refers to Cascading Style Sheets). XSS is a way of injecting malicious code into a web page so that the users are troubled, user data is stolen, etc. If you don’t understand what that means, read along, you’ll understand it by the end of this article.

Before going into XSS, let me give a brief introduction about what Client Side Scripting is. Client side scripting (I don’t want to abbreviate this as it will again end up as CSS!) is nothing but a piece of code that gets executed within your web browser. When you open a website, the website is rendered as HTML along with some Client Side Scripts. For example, you click on a piece of text and a pop up appears saying “hello world”, then it is a simple script that has been run within your browser. An example of a client side scripting is JavaScript.

JavaScript can do things like redirecting the user to another website, accessing personal data (in the form of cookies, etc.) and much more. Twitter gets data from the user (in the form of status updates) and displays them in your timeline. Since client side scripts are nothing but pieces of code embedded along with HTML, the displaying part of twitter has to be clever enough to distinguish scripts and escape them (a simple example of escaping is to replace > with &gt; and < with &lt; as that will avoid the browser from misinterpreting data posted by user as an HTML tag - another simple example would be using printf(“\\n”) in C to literally print \n in the screen and not a new line).

Similarly, JavaScript code has to be escaped properly before being displayed or else there is a possibility that the browser will misinterpret the data posted by the user as JavaScript and start executing it which might cause potential damage. If the escaping is not done properly, then the attacker (usually the person who is always one step ahead of the developer) will be clever enough to exploit that display method to inject malicious JavaScript code to cause damage. Such an improper display mechanism is known as a XSS vulnerability and the attacks exploiting XSS vulnerabilities are known as XSS attacks. Twitter faced one such attack two days back.

Now to better understand how XSS attacks are performed, lets call our friends Alice, Bob and Oscar for help. So the following sequence of steps explain how an XSS attack is performed:

• Bob hosts a website (in this case www.twitter.com) where users are allowed to make posts


• Bob's website has an XSS vulnerability (in this case the javascript onMouseOver function vulnerability)


• Alice and Oscar are users of Bob's website and Alice can view updates posted by Oscar (in twitter lingo, Alice is following Oscar)


• Oscar spots the XSS vulnerability in Bob's website and decides to exploit it. So he makes a post that exploits the vulnerability (in our case redirect the user to some illegal website when he moves the mouse over the post)


• Alice eagerly opens Bob's website and is redirected to a totally unexpected website as she accidentally moved the mouse over Oscar's post (to be worse, while her mom is watching from behind ;-))


• There is also a possibility that Oscar can exploit the vulnerability and steal Alice's session information (cookies) and impersonate Alice


• Thus, Alice is screwed (as always) !!

It is really bad that a website in the scale of twitter had such a vulnerability. But after all, no product is perfect. An official blog post from twitter said that this bug was created as a result of fixing some other issue. I personally feel that a company like twitter cannot afford to give such a lame excuse for it could have caused many celebrities profiles to have posted spam tweets and much more damage. Nevertheless, sites like twitter, facebook, etc. are the primary target for attackers these days and hence security precautions always has to be the number one priority.

Read more about this on twitter's official blog here.

-Vignesh