david wong

Hey! I'm David, a security engineer at the Blockchain team of Facebook, previously a security consultant for the Cryptography Services of NCC Group. I'm also the author of the Real World Cryptography book. This is my blog about cryptography and security and other related topics that I find interesting.

Quick access to articles on this page:

more on the next page...

Nodster day 3 posted April 2014

I can't stop coding this thing. What I've done today:

  • This is the query I'm using in google now : [your search] mp3 -facebook -youtube -soundcloud -last.fm -amazon -dailymotion -bleep
  • I'm now parsing google and the following links with jQuery: $(body).find('a') and then looking for good links with a regex. This is so much more quicker!
  • There is still a part that is taking some time though, it's the metadata fetching. I still have to get every mp3 independently and download enough bits to learn its metadatas...

But it is working quite well as it is!

EDIT: I'm now fetching the metadata in parallel and it's super fast! I've also fixed a ton.

comment on this story

Nodster day 2 posted April 2014

Okay. I'm not gonna talk too much about my new node-webkit project Nodster because I also have a lot of studies to do (exams next week!).

nodster

The problems

  • I'm still not streaming the mp3s properly. I think that I'll never be able to do it through the html5 audio and I need to look up other solutions. The do it yourself approach seems appealing and I'm gonna look into node speaker and node lame.
  • I'm using node google to crawl google and get links. It's not working properly and I'll have to dig into crawling google myself.
  • I'm parsing pages with a regex, it really seems to be slowing everything and I'm gonna look into using a dom parser. I heard about cheerio, is it good?

What does the app do?

  • Right now it's crawling google and avoiding useless websites like youtube, facebook, soundcloud, etc...
  • Then it goes one step deeper and looks for .mp3
  • It checks each mp3 for size (thanks to the headers) and download a bit of each to get metadata.
  • Displays the metadata and a link to play the file
  • If the link is clicked, the mp3 is downloaded to a buffer.mp3 and played.

The main problem is that it's slow, and it's not finding enough links. I could try to parse bing, yahoo and a list of mp3 finders. Or I could maybe try to optimize the requests to google...

Anyway, this app is bringing me a lot of problems to solve and it's pretty interesting :) some people have already forked it and someone has already requested a pull, so if you wanna help. Come and fork it!

2 comments

Nodster (node-webkit) posted April 2014

As always when I have to study for exams I find a gazillion other things to do.

Last night I downloaded node-webkit. I've been slacking when doing QT and WxPython because they were boring. And I thought that node-webkit would be as well. One hello world later and I was amazed at how easy it was to create desktop application with it!

Spent my day trying to figure out what are pipes, streams, websockets... I have to admit I have a long way to go but I really enjoyed this session of node.js.

I had this idea of a free spotify that would just get mp3s from google. There are a lot of legal issues around so I'm wondering if I should really keep this one, but here is what I did today: Nodster (Node-webkit + Napster).

nodster nodster2

The code is not pretty as I was trying and discovering new things all along. The design is crappy but this is obviously because I had other better things to code first :) I want to get the metadata of the mp3s to sort them more easily (most of them seems to have metadatas) but I have trouble figuring out how to do it.

Also it uses mp3skull.com to find mp3s, there are a lot others but eventually I wanted to just use google and crawl hard.

I could also add pictures for albums and... so many things to do!

If you want to help, fork away :)

2 comments

How to store passwords? Hash or KDF? posted April 2014

I remember a time where people would advise to just hash the password with md5 before storing it into a database.

Then md5 became a bad choice because of the rainbow tables (precomputed tables of md5). The concept of salt helped (adding a secret value to passwords before hashing them).

But hash were never meant for encrypting passwords. As KDF. But KDF seems to be better a fit for that kind of task.

See Ty's blog post "please stop hashing passwords". He makes good points and advise using those following KDFs for the job:

  • bcrypt
  • scrypt
  • pbkdf2

Scrypt is the one used in Litecoin by the way.

comment on this story

Procrastination posted April 2014

Procrastination

I've read a LOT of stuff about procrastination. I have techniques:

I think those are all my techniques, I can't really think of any others.

2 Ideas

A few months ago I started counting my calories intake, and I lost weight! It's magic. As soon as you start counting the bad stuff, you realize how much you're doing of it. I've had this idea for quite a long time, a slack counter, that times how long you slack per day. It compares that to the average. I don't know how to implement that, but a cellphone app would be the best suited I think. We always carry it, so we just have to launch the app and start a timer when we procrastinate. This + a firefox/chrome app that recognizes websites that are "time consumer" to add to your statistics. I'm sure that would help me work more!

When I'm really in trouble, and I can't seem to get motivated, I always take my iPod out and start a 30 minute timer. I do that, and then I find something to work on, anything, and I don't have to be efficient or know right away how I'm gonna work on it. I just have to do it, non-stop, to focus for just 30 minutes. And when the timer stops, I'm usually motivated enough to either keep going, or take a small break and start a bigger timer. I had the idea of implementing a 30 minute timer + a chain system, everyday you can start this 30 minute timer once and if you do work non-stop for 30 minutes while it runs, you will validate a day. Try validating the most days in a row!

Other techniques ?

This article brings 3 good points:

There are two ways to look at any task. You can do something because you see it as a way to end up better off than you are now – as an achievement or accomplishment. As in, if I complete this project successfully I will impress my boss, or if I work out regularly I will look amazing. Psychologists call this a promotion focus

when we say things like “I just can’t get out of bed early in the morning, “ or “I just can’t get myself to exercise,” what we really mean is that we can’t get ourselves to feel like doing these things.

Making an if-then plan is more than just deciding what specific steps you need to take to complete a project – it’s also deciding where and when you will take them.
If it is 2pm, then I will stop what I’m doing and start work on the report Bob asked for.

You have to let go

This article helped/helps me a lot. Every time I fall into a procrastination period (because it's a disease you'll have to live with for the rest of your life :D), I read that article.

I hadn’t figured out the skill that would save me from the procrastination.
Until I learned about letting go.

Learn from the pro

Katia Verresen is a "Mental Energy coach" for CEOs and founders. Here's a nice article about her and interesting stuff she has to say about being efficient, in the zone.

Verresen is a big fan of a tactic called “calendar blocking,” and she encourages her clients to identify the chunks of time on their calendars when they have the most physical energy for work.

The mood you wake up in is critical. Consider it to be the default font for your entire day.

For a marathon runner, people say that the day before and the day before that are the most important. If you mess up with your sleep one day, you'll feel the consequences until two days after.

Verresen actually tells her clients that if they haven’t gotten enough sleep, they shouldn’t take their emotions seriously the next day.

“Mental energy is the ability to separate yourself from your thoughts,” Verresen says. “Everyday, we have millions of thoughts that cause stress, anxiety, depression — that can stall you out in a million different ways — but you don’t have to believe them.”

“The best way to reset your mental energy is to get it up and out into the physical world,” Verresen says. “Screens don’t count. You should put whatever it is that’s bothering you or that you need to get done up on a white board. Write it down and stick it up on a wall.

I sometime stop what I'm doing to do the dishes. It clears my mind.

Verresen advises her clients to block off two slots ranging between 90 minutes to 2 hours every week as mental white space. They need to literally put it on their calendar and make sure they aren’t interrupted or disturbed during this time — ideally they shouldn’t have meetings right afterwards either.

I do this by doing my laundry. I take a paper and a pen with me and I go do my laundry for an hour.

comment on this story

Gröbner basis on numb3rs posted April 2014

It doesn't seem to be the only appearance of the Gröbner basis on the show:

In the Season 4 opening episode 'Trust Metric' (2007) of the television crime drama NUMB3RS, math genius Charlie Eppes mentions that he used Gröbner bases in an attempt to derive an equation describing friendship.

From wolfram alpha

comment on this story

An awesome explanation of the Fourier Transform posted April 2014

I've run into this über cool explanation of the Fourier Transform thanks to mtodd's blog

Here's a bit from the introduction:

What does the Fourier Transform do? Given a smoothie, it finds the recipe.
How? Run the smoothie through filters to extract each ingredient.
Why? Recipes are easier to analyze, compare, and modify than the smoothie itself.
How do we get the smoothie back? Blend the ingredients.

And cool examples of what can be done with the Fourier Transform:

  • If earthquake vibrations can be separated into "ingredients" (vibrations of different speeds & strengths), buildings can be designed to avoid interacting with the strongest ones.
  • If sound waves can be separated into ingredients (bass and treble frequencies), we can boost the parts we care about, and hide the ones we don't. The crackle of random noise can be removed. Maybe similar "sound recipes" can be compared (music recognition services compare recipes, not the raw audio clips).
  • If computer data can be represented with oscillating patterns, perhaps the least-important ones can be ignored. This "lossy compression" can drastically shrink file sizes (and why JPEG and MP3 files are much smaller than raw .bmp or .wav files).
  • If a radio wave is our signal, we can use filters to listen to a particular channel. In the smoothie world, imagine each person paid attention to a different ingredient: Adam looks for apples, Bob looks for bananas, and Charlie gets cauliflower (sorry bud).
comment on this story