Do the weaknesses of SHA-1 weaken the security of Dwolla’s API?

I'd like to share our answer to an interesting question regarding SHA-1 and the authentication scheme implemented by Dwolla's Off-Site Gateway Submit Directly flow:

"I'm looking at the developer stuff on checkout workflow, and see that the "signature" being transmitted between Dwolla and a business website is specified to use the SHA1 hash system. It is my understanding that that method is becoming vulnerable to an attack that has adequate computing power behind it. So, what other hash methods are allowable, for a business interacting with Dwolla? Thanks in advance!"

Though there are some weaknesses with SHA-1, they relate only to hash collisions. This means the weaknesses aren't helpful to attackers who are trying to determine the underlying input(s) of the hash. The only way to obtain the input(s) is by brute force.

In our case, the input of the signature hash is a concatenation of the Application Key, timestamp, and OrderID. These are all provided in the checkout form, so the attacker knows what the input is. What the attacker doesn't have is the Application Secret, which is a 50 character string used as the key in this key-based hash.

In order to forge a signature, the attacker would need to obtain the App Secret by way of brute force. If we assume the search space per character is all alphanumeric characters and 3 symbols ("+", "/", and "="), that leaves us with 65 possible characters. Since the secret is 50 characters long, we can say that an attacker would need to make

or

attempts to exhaust all possibilities.

Let's say an attacker can hash 10 million candidates per second on a single CPU. To exhaust all possibilities, it would take roughly:

Even if he has a large farm of machines running, say 1000 machines, with a collective power of 10 billion hashes/sec, it'd still take roughly:

The sheer size of the Secret string renders brute force an infeasible way to obtain it.  I would recommend reading Jeff Atwood's write up about hashes.

Spotflux doesn't play nice with Tunnelblick

I recently gave Spotflux, a free VPN tunneling service, a try on my Mac.  I loved the experience -- extremely high speed and unlimited bandwidth, but I noticed that I could no longer use my beloved Tunnelblick VPN client.  When attempting to connect to a network with Tunnelblick, it errored out:

  openvpnstart returned with status #226

and left this in the log:

*Tunnelblick: openvpnstart log:
 Loading tun-signed.kext
 stderr from kextload: /Applications/Tunnelblick.app/Contents/Resources/tun-signed.kext failed to load - (libkern/kext) kext (kmod) start/stop routine failed; check the system/kernel logs for errors or try kextutil(8).
 stderr from kextload: /Applications/Tunnelblick.app/Contents/Resources/tun-signed.kext failed to load - (libkern/kext) kext (kmod) start/stop routine failed; check the system/kernel logs for errors or try kextutil(8).
 stderr from kextload: /Applications/Tunnelblick.app/Contents/Resources/tun-signed.kext failed to load - (libkern/kext) kext (kmod) start/stop routine failed; check the system/kernel logs for errors or try kextutil(8).
 stderr from kextload: /Applications/Tunnelblick.app/Contents/Resources/tun-signed.kext failed to load - (libkern/kext) kext (kmod) start/stop routine failed; check the system/kernel logs for errors or try kextutil(8).
 stderr from kextload: /Applications/Tunnelblick.app/Contents/Resources/tun-signed.kext failed to load - (libkern/kext) kext (kmod) start/stop routine failed; check the system/kernel logs for errors or try kextutil(8).
 Error: Unable to load net.tunnelblick.tun and/or net.tunnelblick.tap kexts in 5 tries. Status = 71

Apparently, the kext (driver) that Spotflux loads is incompatible with Tunnelblick and prevents Tunnelblick from loading its own kext. The solution is to unload Spotflux's kext and try connecting via Tunnelblick again.

Let's first run kextstat in Terminal to ensure we've got the offending kext loaded:

 
kextstat | grep spotflux
  121    0 0xffffff7f82231000 0x6000     0x6000     com.spotflux.Spotflux.tun

Then, let's unload it via kextunload.  This requires sudo.

sudo kextunload -b com.spotflux.Spotflux.tun

Once unloaded, Tunnelblick will be able to load its kext and connect as usual!  This will need to be done every time Spotflux is launched and you wish to use Tunnelblick afterwards, unfortunately.

Graph Search: Facebook is Finally Useful

Facebook's Graph Search feature is amazing. I wanted to know which of my new acquaintances and friends from high school go to the university I'll be visiting for a hackathon next week. So, I just started typing my query in a natural way, "my friends who go to Carnegie Melon University", and bam -- I got exactly what I was looking for. No fumbling with drop down menu filters or long advanced search forms. It's like Wolfram Alpha for your intricate network of friends, family and acquaintances.

Of course, not everyone feels the same way about this feature.  Moreover, not everyone feels the same way about Facebook itself.  There's the highly debated issue of users being overly reliant on the online platform, to the point where it's unhealthy.  Critics of Facebook mock it as a tool for narcissists who couldn't care to remember who their friends are.

While I'm cautious of Facebook's potential to be used in a socially unhealthy way, I'm a firm believer that the data amassed by the network can be used to improve social life off the web.  I've made many acquaintances who I haven't yet had the luxury of learning everything about them.  I will probably remember them and the moments we shared together, but easily forget their name and the school they go to or their hometown. Facebook solves this problem.

However, the fact that Facebook wields so much power, that it single-handedly controls personal, and sometimes private information about nearly everyone, coupled with the perceived lack of transparency about what Facebook does with that data gives rise to the suspicion that they may have a nefarious agenda --  they may be exploiting this data by selling it to nosy corporations or giving direct access to snooping intelligence agencies like the NSA.  

By building Graph Search, Facebook has given me a reason to believe that the data it amassed doesn't have to be used for "evil" -- it can be used for good. Its collection, aggregation, and analysis of social data undoubtedly comes at the cost of privacy, but the insights gained are powerful and beneficial.

At the end of the day, Facebook is solving a complex problem: digesting the massive amount of data submitted voluntarily by hundreds of millions of people around the world, and making it useful.  They've done just that with Graph Search.

Morpheus

The following is an excerpt from my blog post in the Dwolla Blog where I recounted my experience at the largest hackathon in Texas, HackTX.

A screenshot from Morpheus.

Morpheus, whose name bears no relation to the well known leader in the human fight against dystopian robot overlords from The Matrix, but instead is named after the Greek god of dreams and sleep, is a platform that brings distributed computing to mobile devices.  Mobile devices, such as Apple and Android smartphones and tablets, are exponentially increasing in processing power.  If we consider the fact that in my pocket lies an HTC One which contains a 1.7 GHz quad-core Snapdragon processor, (which truly is mind-blowing, because the last time I shopped for computer components, a few years ago, Intel was just rolling out their first Quad Core processors and the world was going nuts over it) and we also consider that 80% of the time, my phone is resting idly in my pocket or missing underneath my bed, we realize that the true potential of its is being wasted 90% of the time.  The other 10% is wasted because I use my phone to check my Facebook news feed and text my buddies.  Now, imagine if your phone could instead be used to work in a cluster of other computing devices to tackle large computational problems, like those being solved by Folding@Home, a project that takes advantage of the powerful Playstation 3's gamers have sitting in their homes to simulate protein folding, design medical drugs, and understand molecular dynamics to save human lives.  The true power of Morpheus is realized when you consider that smartphones and tablets are growing in their ubiquity.  Think about the impact that billions of super-quick devices could have if they were used for a purpose greater than taking selfies and tweeting about what you're about to buy from the supermarket.

"But do you really think people will drain their battery just because of the philanthropic goodness of their hearts?"  you may be inclined to ask.  Morpheus answers this in two ways: a) participants only leave their phone to compute when charging at night, and b) researchers will pay participants, using Dwolla, for the work their phone does.  This brings an interesting twist to the Folding @ Home model, which relies on gamers to rack up their energy bill and subject their PS3 to computational slavery for nothing except the knowledge that they're doing good in this world.  With Morpheus, researchers and even commercial enterprises can leverage the immense power hidden away in everyone's pockets to solve their problems.  Imagine IBM renting your phone for the night so it can compute the Answer to Life, The Universe, and Everything in just a fraction of the 7.5 million years it took Deep Thought to do so.

The Morpheus team! 

So, in essence, you get paid while you sleep just for running a simple app on your phone during the night. This simple idea is mind-bogglingly cool and has a ton of potential to do good for the world. I'm hopeful that the Morpheus team, uTexas students Eduardo Saenz, Bulat Bazarbayev, Comyar Zaheri Brandon Lee, and Sudheesh Katkam, will take this beyond HackTX and launch this in the wild, real world. Very well done, gentlemen.

Python: Glide, instead of move, mouse cursor from one point to another

I couldn't find a function in pywin32 to smoothly glide a pointer from one point to another, instead of simply "moving" the cursor by making it jump from its current position to a given position.  I needed a way to make the mouse sort of "glide" from point A to point B at a seemingly natural pace, so here's my solution:

import time
import win32api

MOUSE_SPEED = .4 #seconds

def mouse_glide_to(x,y):
    """Smooth glides mouse from current position to point x,y with default timing and speed"""
    x1,y1 = win32api.GetCursorPos()
    smooth_glide_mouse(x1,y1, x, y, MOUSE_SPEED)

def smooth_glide_mouse(x1,y1,x2,y2, t, intervals):
    """Smoothly glides mouse from x1,y1, to x2,y2 in time t using intervals amount of intervals"""
    distance_x = x2-x1
    distance_y = y2-y1
    for n in range(0, intervals+1):
        move_mouse(x1 + n * (distance_x/intervals), y1 + n * (distance_y/intervals))
        time.sleep(t*1.0/intervals)

def move_mouse(x, y):
    win32api.SetCursorPos((x,y))

mouse_glide_to(x,y) will move the cursor from its current position to point (x,y) in MOUSE_SPEED seconds. It works perfectly!

Road Runner (SMC Networks) routers - practically NO security

Upon registering for Time Warner's Road Runner internet service, customers are offered a router manufactured by SMC Networks.  The router ships with WEP encryption enabled by default, using a 128-bit key based on its MAC address.   While WEP encryption is already the most insecure form of wireless encryption out there,  SMC Networks amplifies this weakness further by not generating a random WEP key; something which a home user almost never changes unless forced to do so during first time installation, whether it is because he or she is ignorant about the risks of a vulnerable network, or because he or she simply doesn't know how to or care enough to change it.  While a randomly generated WEP key can be defeated just as easily as any other, the default encryption key for these routers is trivial and can be determined just by spotting it in a regular AP (Access Point) scan of the area.

The encryption key can be discovered in seconds, without the need for conventional wireless cracking tools such as the aircrack-ng suite. These routers effectively have no security whatsoever, as even the most tech-challenged of computer users can break into them.  From there, the users of the network are vulnerable to all kinds of harm, ranging from innocent piggy-backing to malware and identity theft.

In under a minute, one can find the key using only the router's wireless network name (SSID) and its wireless MAC address (BSSID).  These routers stick out like a sore thumb because their SSIDs are simply 4 hex characters (e.g. 'D78A') and their MAC addresses typically begin with 00:26:F3, 00:22:2D, or 78:CD:8E (OUI). 

Here's how:

In this example, let's assume we see a router whose SSID is '4B5F' and whose wireless MAC address is 00:26:F3:73:4B:52. The WEP key is generated in this format:

[first 10 characters of MAC] + [last two characters of SSID] + 14 0's

Following this format, we take the first 10 hex digits (or first 5 octets) of the MAC address, which we can easily find when performing a normal everyday wireless scan in Windows or OS X: "00:26:F3:73:4B", append the last two digits of the SSID: "5F", and tack on 14 0's to form the router's 128-bit encryption key:

00:26:F3:73:4B:5F:00:00:00:00:00:00:00

Knowing this, any joe-shmo can "hack" into an Road Runner SMC-Networks router with just a smartphone and optionally a pen and paper.  I would highly recommend that either SMC Networks or Road Runner move on to WPA2 encryption in their new routers and attempt to update these routers to use WPA2.  New Verizon FiOS Actiontec routers come factory default with WPA2 enabled with a randomly generated 32 character string and WPS disabled; they could learn something from Verizon!

EDIT: Apparently, the insecurity of these routers was already covered in an article from 2009; it's sad to see nothing has been done about it since then!  

"However, the Time Warner devices come pre-configured and locked, with URL blocking being the only feature available to the customer through the web administration interface."

According to the article, the router's web administration is locked and the home user cannot change the encryption scheme nor the encryption key, even if he or she wanted to.  This is definitely a huge issue.  

Python: Calculating the average color of an area of an image (PIL)

Here's a snippet of code I whipped up in Python to calculate the the average color of a square shaped area of an image.  I used the Python Imaging Library (PIL) to load the image, so be sure to have it available if you're using this.

import Image

def get_average_color((x,y), n, image):
    """ Returns a 3-tuple containing the RGB value of the average color of the
    given square bounded area of length = n whose origin (top left corner) 
    is (x, y) in the given image"""

    r, g, b = 0, 0, 0
    count = 0
    for s in range(x, x+n+1):
        for t in range(y, y+n+1):
            pixlr, pixlg, pixlb = image[s, t]
            r += pixlr
            g += pixlg
            b += pixlb
            count += 1
    return ((r/count), (g/count), (b/count))

image = Image.open('test.png').load()
r, g, b = get_average_color((24,290), 50, image)
print r,g,b

This is great for detecting the color of an area of an animated and constantly changing game screen, where finding the color of a single pixel may not be accurate enough for your needs.