As a way of getting better acquainted with the ARM-based devices cluttering up my desk, I picked up this gem of a textbook at Amazon:
Reading through the interrupts section reveals an implementation of Inception on the ARM platform:
Back when I first started SSH (around the RedHat 4.x days), I’d occasionally be connected to another host via SSH when the host or the network connection would suddenly lock up. I’d end up trying to figure out which SSH process was the one that was frozen and kill -9ing it. That is, until someone showed me how to use SSH escape sequences. Occasionally I see people talking about killing frozen SSH sessions and it reminds me to pass on this tip.
If SSH is running on an interactive terminal, it listens for an escape character whenever it is listening for a the first character after a newline (or the first character in the stream). By default, this character is the tilde (~), but you can specify a different character using the -e argument.
You can get a list of escape sequences by typing “~?” after a newline:
Supported escape sequences:
~. - terminate connection (and any multiplexed sessions)
~B - send a BREAK to the remote system
~C - open a command line
~R - Request rekey (SSH protocol 2 only)
~^Z - suspend ssh
~# - list forwarded connections
~& - background ssh (when waiting for connections to terminate)
~? - this message
~~ - send the escape character by typing it twice
(Note that escapes are only recognized immediately after newline.)
The one I use most frequently is ~.. This one kills the SSH terminal, along with any of the port forwardings you might have started as part of the command-line or in your .ssh/config file. ~& is also pretty useful when using port forwarding: it closes the SSH terminal, backgrounds SSH and leaves the port forwardings alive until the last one terminates.
These escape sequences will work, even if the underlying TCP/IP connection is toast and SSH seems completely unresponsive. If SSH isn’t picking up your escape sequences, make sure that you’re hitting the enter key first. It won’t pick up escape sequences in the middle of a line.
Inside the box was the netbook, a set of instructions and the new set of Cr-48 decals. The decals are pretty flashy and look good, but I figured I’d wait a bit before putting them on (hey, this thing looks pretty good as-is).
The first thing you notice when starting the netbook up is that it’s fast. Pushing the power button to the firstboot or login screen is a matter of seconds. It’s the same while signing out or powering down. Oh, and the power button functions as a signout key as well. Hold it for a few seconds and it signs you out. Keep it held down a few more seconds and it powers down.
There aren’t a lot of surprises on this box. It’s basically a giant battery strapped to the Chrome browser. The battery is pretty amazing. Popping the power cord out yielded a runtime of just under eight hours when I first got the machine. A few discharge/charge cycles later and it’s sitting at more than eight hours.
Overall, the hardware is pretty decent. It’s an Atom N445 processor with 2GB RAM. It has 16GB of onboard solid-state storage. For comparison, the Dell Inspiron Mini 10 I just bought had a similar processor, but half the memory and way more storage (albeit spinning bits instead). The screen is really great and the keyboard is very comfortable to use.
I’ve heard bad things about the trackpad on the Cr-48. It seemed to be working well after I first started up the machine, but over time it’s clearly shaping up to be the weakest part of the system. The trackpad is unreliable at times. It gets stuck in a clicked state at time, where it thinks that you’re holding a finger down and moving a finger around starts selecting things. Other times it fails to recognize the two-finger right-click, making for a frustrating experience trying to copy and paste from one place to another.
Aside: I swear that when I first got this machine, the trackpad didn’t support the ability to click and drag by pushing down on the whole trackpad with one finger and dragging the other. This is working now and I can’t explain it. *shrug*
The Chrome browser runs fairly well on this hardware given the size of its CPU, but it’s definitely not as slick as Chrome on my Macbook. It can start to feel a bit sluggish when you end up with a number of tabs open. Sites that use position:fixed or background-attachment:fixed are terribly slow to scroll as well. I imagine that future versions of the OS will bring hardware-accelerated compositing to scrolling.
The netbook supports multiple users, but it can’t support more than one user logged in at a time. That’s likely to avoid having more than one user hogging the limited resources of the box. I’d really love to see something along the lines of tab hibernation used, instead of forcing one user to log out to let another log in. Once a user signs out, the state of their session should be persisted to disk locally and restored after they log in again.
I’ve been trying to get used to a world without any apps beyond the browser. It’s tough. I set up Guacamole to get access to a Linux desktop where I could run a bunch of applications that I need access to. As a developer, I can’t really live without a few desktop apps. If there were a way for me to get access to the applications on my desktop remotely, I’d be bringing this netbook everywhere instead of lugging around the much heavier Macbook Pro.
Overall, I’m really impressed with the ChromeOS netbook. It feels designed, not just made. I’m confident that a lot of the issues I’ve seen can be fixed in software updates. There are probably a lot of people that could make a switch full-time to this netbook. I’m not one of those right now, but I’d love to use something small like this for more of my computing needs.
This blog post was composed entirely on the Cr-48, including the awkward dance to download my previous Cr-48 pics from Twitpic and upload them into Wordpress.
Follow me on Twitter: @mmastrac.
(This was originally a response to a question asked of me on Quora, but I’ve copied it here to my blog so I can expand on it)
“Pivot” is a big catchphrase in the startup world these days. It has a glamorous feel to it: you picture the Twitter team dropping Odeo on the ground and moving on to the brand new idea without a moment’s thought. There’s more to it than that.
In May of 2010 we stopped spending all of our resources on DotSpots and started working on our new idea, Gri.pe. By our September launch at TechCrunch Disrupt, we were focusing all of our efforts on it and decided that we’d start the process of shutting down DotSpots.
Moving on from DotSpots was bittersweet. We spent a few years pouring our heart into the product, which we all honestly believed would revolutionize how people consumed news. Unfortunately we underestimated how difficult it would be to get publishers to sign on and missed the window overall for success.
Another thing that’s hard for me is having the great GWT-based infrastructure we built to pop up UI overtop of any webpage basically sitting idle. I’d love to open-source that one day, but it’s not pressing right now. Perhaps if the right project comes along, we might be able to hand off some of it to them.
We did manage to use some of the DotSpots technology to bootstrap our efforts at Gri.pe. The core web infrastructure for serving Gri.pe pages is basically what we were going to use for serving dotspots.com. I’ll be opening that up at some point in the future at http://stencilproject.net.
The great part about moving on is that you have a chance to let go of all the future plans that were weighing on your mind. After a few years at a startup, you’ve got stuff that you’ve always wanted to do but never had time for. Pivoting to a new idea lets you finally let go of those in your mind.
You also have a chance to make your core technology choices again. At DotSpots, we built everything in Java running Jetty on EC2. At Gri.pe, we’ve chosen to work on AppEngine, which opens up so many exciting possibilities with all of the technology Google is hooking up to it.
It’s also a great feeling to be working on an application that’s seeing significant traction in the market. We blew by the total lifetime number of users of DotSpots within a few months and continue to great press and a continuous stream of signups. It makes you feel good seeing numbers that show people are using the application and it’s making a positive impact on their lives. I would have loved for DotSpots to have a positive impact too, but it just never caught on.
In the end, it’s an awesome move for us. On the other hand it’s a bit sad - like moving from a house you’ve lived in for years and have built memories in.
Follow me on Twitter: @mmastrac.
This particular challenge piqued my curiosity. One of my hobbies is rooting Android phones and I enjoy all sorts reverse-engineering problems. More importantly, this one happened to match up with some downtime I had this afternoon.
I fired up Python and quickly got to work. At my day job, Gri.pe, we use Java. I love Java as a development language, but I find that Python’s interactive mode is best for quickly experimenting with data in unknown formats. There’s a great deal of power in the standard Python libraries and it’s well-suited for quick byte and bit manipulation.
The first thing I did was to take a look at the individual bytes of the base64 decoded data:
>> min(s), max(s)
(32,90)
The range of 32 (‘ ‘) to 90 (‘Z’) suggested that the bytes had been coerced to a printable range from their natural, though binary-uncomfortable, base-59 representation. I worked from this part on assuming that this was true as it held for the challenge itself, as well as the various sample encodings:
>>> qbf
[1, 24, 38, 18, 30, 16, 43, 40, 15, 39, 35, 29, 28, 46, 48, 32, 33, 7, 19, 12, 45, 2, 1, 39, 4, 45, 45, 53, 23, 56, 41, 14, 47, 45, 23, 37, 47, 49, 34, 53, 43, 44, 13, 48, 54, 34, 30, 7, 22, 32, 52, 0, 27, 10, 13, 35, 51, 14, 21, 34, 5, 15, 27, 2, 44, 7, 47, 49, 31, 14, 6, 49, 3, 49, 24, 1, 25, 33, 15, 16, 55, 21, 46, 50, 20, 40, 6, 52, 19, 28, 32, 51, 20, 47, 14, 16, 12, 48, 15, 15, 42, 1, 21, 21, 17, 35, 21, 22, 7, 15, 22, 13, 49, 9, 23, 40, 9, 42, 27, 23, 20, 1, 25, 35, 57, 55, 34, 53, 16, 49, 55, 21, 17, 33, 55, 20, 18, 27, 13, 36, 7, 27, 47, 33, 40, 34, 29, 57, 55, 45, 38, 43, 46, 45, 23, 43, 22, 34, 30, 30, 30, 39, 0, 27, 42, 43, 54, 4, 41, 54, 20, 3, 42, 49, 29, 27, 56, 53, 6, 29, 11, 8, 57, 52, 32, 10, 7, 9, 11, 5, 2, 9, 2, 23, 12, 3, 39, 4, 56, 30, 18, 42, 52, 40, 2, 32, 1, 51, 12, 30, 53, 11, 52, 33, 54, 31, 22, 5, 9, 20, 54, 53, 18, 11, 28, 3, 9, 55, 18, 5, 29, 53, 49, 42, 40, 50, 23, 58, 34, 23, 43, 32, 31, 33, 19, 1, 2, 41, 14, 31, 42, 37, 17, 50, 42, 34, 12, 56, 5, 1, 38, 7, 31, 30, 44, 31, 29, 56, 56, 14, 7, 4, 50, 7, 56, 56, 2, 50, 8, 52, 33, 53, 14, 53, 16, 26, 23, 20, 26, 14, 2, 32, 25, 45, 25, 37, 47, 41, 39, 39, 26, 35, 25, 18, 31, 43, 58, 9, 34, 18, 57, 6, 30, 29, 55, 19, 42, 13, 42, 12, 6, 8, 53, 24, 7, 15, 40, 7, 23, 25, 58, 33, 53, 35, 53, 37, 28, 49, 32, 35, 43, 39, 24, 9, 56, 12, 25, 5, 28, 27, 31, 47, 48, 47, 43, 40, 51, 28, 16, 2, 58, 36, 33, 33, 53, 50, 25, 18, 1, 10, 28, 33, 39, 38, 45, 23, 10, 49, 23, 28, 12, 17, 50]
It didn’t appear to be a simple encoding as the number of bits wasn’t a nice, round number:
>>> len(qbf)/43.
8.9069767441860463
I explored the possibility that it was a base-59 encoded version of something as well, but nothing seemed to pop out (none of the base-59 numbers had promising base-2, 10 or 16 representations):
>>> reduce(lambda x,y: x*59+y, qbf)
41407517501859586326197566364505794272099644350300252534189551267025735776717090113531360628479958032951680470965566919981633022692412690504948993859533954300510015897257502231588804493684836579000834698632035250601929666970976653754473920192216650558365260965365239849090933529931468815659914090640650939870573055692803806368452144490717915923609157169530794000213060205251901007965316849847932159686920362166230161797107467060590682186205774757385089316643047935984486008508524050103003822235196827448543677268467374714192183904155940695587335521537764755681737258468452222357818887460237021822605843003409567903505844564024546249528549309875903061566053488229272080782809344L
>>> hex(reduce(lambda x,y: x*59+y, qbf))
'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'
>>> bin(reduce(lambda x,y: x*59+y, qbf))
'0b1100110000011111000111110110101100111011110000000010111111111111100100100111001111001101000001111011101111000001111100111110000001011000100110011000101010111001001110000101010010100111100111101011001010001001100000011011101101101101001100011111010000000101111001101100010111010011100011000010010110111101000100110100011001001010010101000011111010110111100000011101011100110101111011000111001011110000011100000000001110011100100110111111110001001011110000110111010100111110110010100011010110100011110011010010100000101010010000111011111110010110100110001001111111111101000001100110011010000010011110010110011011110100011000001111001110101110111001111101011111000100001000001011011111000111000110111101110100000010110111110100111100101101101101101100100101100110000000011100011001001001110011111101111100100111110100110001111011011101100000000010101010101001100110001001101001011011100110111010100011111101101110010110001001111000110110010101101101111011000000001010110000110001111100100100110111000111111111110010110001000010010100101000101010100001100010100101111000010010010011101101110010010110100111101100001011001011010010000010000110111101010101001100110111000010101101111000110111001010110101111110011100110000001001101001110010011000001101011110111101000100011000010111110100101100010010101100011110001110010011010010011110001100010000110001110001110110101111101100110111101100111110100101010010010110010100011100101100101111011100011011101101000111000111100011111011100101001110001001111110111011101001100011011011100110110101110101111100011011101111000010110001100011001100000000011011110100011110111100100010011010010110001111110100100010110011010001010001001100001100111001101011110011001110010110010111101100111110101000101000111011110101100001011101011100111100010010100010110010000001101111110010101011000001100001100111110110011111111101001111011111000010100110011010001100000100000000111011100100000100100100101100110111000101111010000000101100010100111011001011000101011101000111010100111000001110110000010010100111011110000010001011110100001111001110000100101101100011011101101111111110010101111111001100011000010101100110110100011111010111000100000001111010110100010010010110011000001011010101011101001111101110010101100100000000'
I also used numpy’s histogram function to see if there were signs of a simple substitution. While there were spikes of various values, nothing seemed to be significant when you compared the histograms of the various encodings of “THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG”.
The fact that more than eight output positions on average represented a single input position strongly suggested that there was some sort of reduction involved in decoding. I tried a number of different approaches with bit counting and different groupings, but none yielded any promising results.
The breakthrough came about a minute after Erik posted his last hint:
If you base64 decode this
IThGMj4wS0gvR0M9PE5QQEEnMyxNIiFHJE1NVTdYSS5PTTdFT1FCVUtMLVBW Qj4nNkBUIDsqLUNTLjVCJS87IkwnT1E/LiZRI1E4ITlBLzBXNU5SNEgmVDM8 QFM0Ty4wLFAvL0ohNTUxQzU2Jy82LVEpN0gpSjs3NCE5Q1lXQlUwUVc1MUFX NDI7LUQnO09BSEI9WVdNRktOTTdLNkI+Pj5HIDtKS1YkSVY0I0pRPTtYVSY9 KyhZVEAqJykrJSIpIjcsI0ckWD4ySlRIIkAhUyw+VStUQVY/NiUpNFZVMis8 IylXMiU9VVFKSFI3WkI3S0A/QTMhIkkuP0pFMVJKQixYJSFGJz8+TD89WFgu JyRSJ1hYIlIoVEFVLlUwOjc0Oi4iQDlNOUVPSUdHOkM5Mj9LWilCMlkmPj1X M0otSiwmKFU4Jy9IJzc5WkFVQ1VFPFFAQ0tHOClYLDklPDs/T1BPS0hTPDAi WkRBQVVSOTIhKjxBR0ZNNypRNzwsMVI=The first 5 characters are “!8F2>”
Those 5 characters represent the first “T”. Another “T” won’t necessarily result in the same code. Actually, the odds of ever seeing that code again for a “T” is low.
I ran through a few quick tests and discovered the first part of the solution: the sum of the first five characters, modulo 59, equalled the first character of the output!
>>> sum(qbf[:5])
111
>>> sum(qbf[:5])%59
52
>>> ord('T')-32
52
I went though the other versions of the sample encoding and saw that the same held for the first five digits. I checked the next five and didn’t see the correlation there. It also didn’t hold for the next six. The pattern *did* hold for the next seven. Even more tantalizing was that the challenge itself appeared to follow the same pattern:
>>> chr(sum(orig[:5])%59+32)
'D'
>>> chr(sum(orig[5:12])%59+32)
'O'
At this point I figured that I’d write a quick program to brute force the rest of the string.
#!/usr/bin/python
from base64 import *
qbf = [ord(x)-32 for x in b64decode("""IThGMj4wS0gvR0M9PE5QQEEnMyxNIiFHJE1NVTdYSS5PTTdFT1FCVUtMLVBW Qj4nNkBUIDsqLUNTLjVCJS87IkwnT1E/LiZRI1E4ITlBLzBXNU5SNEgmVDM8 QFM0Ty4wLFAvL0ohNTUxQzU2Jy82LVEpN0gpSjs3NCE5Q1lXQlUwUVc1MUFX
NDI7LUQnO09BSEI9WVdNRktOTTdLNkI+Pj5HIDtKS1YkSVY0I0pRPTtYVSY9 KyhZVEAqJykrJSIpIjcsI0ckWD4ySlRIIkAhUyw+VStUQVY/NiUpNFZVMis8 IylXMiU9VVFKSFI3WkI3S0A/QTMhIkkuP0pFMVJKQixYJSFGJz8+TD89WFgu
JyRSJ1hYIlIoVEFVLlUwOjc0Oi4iQDlNOUVPSUdHOkM5Mj9LWilCMlkmPj1X M0otSiwmKFU4Jy9IJzc5WkFVQ1VFPFFAQ0tHOClYLDklPDs/T1BPS0hTPDAi WkRBQVVSOTIhKjxBR0ZNNypRNzwsMVI=""")]
orig = [ord(x)-32 for x in b64decode("""QCgyPSghK1kwTlRJO0MrVTtZLUxWLCg3MypEUCNQJjNGTlMuIyU8TzwpSDNP ND0tRFg7RkUoJjotJzQwIz8pJUFCODtQI0AyPCFaTkNTUyQ/PUgqN0VKLCEi VUxWRjo2SUYnSiAiMkdGVCpGSCw+NDAqVyhUIEAtWTVMRiQzMi8jIiMuPyFP
V0k0MjlVOyQyTFM4VkgvQStRWkY3SEkwKDsqIzlFSjxHJS0+P0xTPDZIRSZW NVkvO0kuM1REJUkqMk8/Sz4tPy1JR04/WjM4V0ggVD8tU0JURDFBMCovMldO MzVVSjFDTjY0Lz00Ojc5UkZBSkMyUyxAOy05MCA5KyJXJVQ6KTZJTFJJL0pC
JyIkRCUiLkhOSTZJKyRDKC4qV0EuOz4qTVg/OypMUztAMTFLLzI8RU8+VVct OzQ+NEdIRUwm""")]
text = "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG"
output = ""
i = 0
start = 0
text_i = 0
while True:
c = chr(sum(qbf[start:i])%59+32)
print sum(qbf[start:i]), c, text[text_i]
if c == text[text_i]:
print "Found at %d-%d %d" % (start,i,i-start)
output += chr(sum(orig[start:i])%59+32)
start = i
i = i + 4
text_i = text_i + 1
print output
i = i + 1
The output from this test program yielded most of the solution:
0 T
1 ! T
25 9 T
63 $ T
81 6 T
111 T T
Found at 0-5 5
D
153 C H
188 + H
217 H H
Found at 5-12 7
DO
187 * E
194 1 E
213 D E
225 P E
270 B E
272 D E
273 E E
Found at 12-23 11
DON
... [a few dozen lines snipped] ...
Found at 347-360 13
DON'T FORGET TO DRINK Y<-R OVALTIN9-
213 D D
Found at 360-365 5
DON'T FORGET TO DRINK Y<-R OVALTIN9-
104 M O
132 . O
165 O O
The solution wasn’t perfect at this point, but when you look at the output, the pattern becomes pretty clear:
Found at 0-5 5
Found at 5-12 7
Found at 12-23 11
Found at 23-36 13
Found at 36-41 5
Found at 41-48 7
Found at 48-59 11
Found at 59-72 13
Found at 72-77 5
Found at 77-84 7
Found at 84-95 11
Found at 95-108 13
From the pattern, I quickly whipped up a solution. It’s not the most elegant bit of Python, but the results are the most important part:
#!/usr/bin/python
from base64 import *
qbf = """IThGMj4wS0gvR0M9PE5QQEEnMyxNIiFHJE1NVTdYSS5PTTdFT1FCVUtMLVBW Qj4nNkBUIDsqLUNTLjVCJS87IkwnT1E/LiZRI1E4ITlBLzBXNU5SNEgmVDM8 QFM0Ty4wLFAvL0ohNTUxQzU2Jy82LVEpN0gpSjs3NCE5Q1lXQlUwUVc1MUFX
NDI7LUQnO09BSEI9WVdNRktOTTdLNkI+Pj5HIDtKS1YkSVY0I0pRPTtYVSY9 KyhZVEAqJykrJSIpIjcsI0ckWD4ySlRIIkAhUyw+VStUQVY/NiUpNFZVMis8 IylXMiU9VVFKSFI3WkI3S0A/QTMhIkkuP0pFMVJKQixYJSFGJz8+TD89WFgu
JyRSJ1hYIlIoVEFVLlUwOjc0Oi4iQDlNOUVPSUdHOkM5Mj9LWilCMlkmPj1X M0otSiwmKFU4Jy9IJzc5WkFVQ1VFPFFAQ0tHOClYLDklPDs/T1BPS0hTPDAi WkRBQVVSOTIhKjxBR0ZNNypRNzwsMVI="""
orig = """QCgyPSghK1kwTlRJO0MrVTtZLUxWLCg3MypEUCNQJjNGTlMuIyU8TzwpSDNP ND0tRFg7RkUoJjotJzQwIz8pJUFCODtQI0AyPCFaTkNTUyQ/PUgqN0VKLCEi VUxWRjo2SUYnSiAiMkdGVCpGSCw+NDAqVyhUIEAtWTVMRiQzMi8jIiMuPyFP
V0k0MjlVOyQyTFM4VkgvQStRWkY3SEkwKDsqIzlFSjxHJS0+P0xTPDZIRSZW NVkvO0kuM1REJUkqMk8/Sz4tPy1JR04/WjM4V0ggVD8tU0JURDFBMCovMldO MzVVSjFDTjY0Lz00Ojc5UkZBSkMyUyxAOy05MCA5KyJXJVQ6KTZJTFJJL0pC
JyIkRCUiLkhOSTZJKyRDKC4qV0EuOz4qTVg/OypMUztAMTFLLzI8RU8+VVct OzQ+NEdIRUwm"""
def decode(code):
values = [ord(a)-32 for a in b64decode(code)]
offsets = [5,7,11,13]*len(code) # note: won't need all of these, but guaranteed more than enough
decoded = ""
while len(values):
decoded += chr(sum(values[:offsets[0]])%59+32)
values = values[offsets[0]:]
offsets = offsets[1:]
return decoded
print decode(qbf)
print decode(orig)
The output, which I posted quickly to the blog and the HN story:
THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG
DON'T FORGET TO DRINK YOUR OVALTINE!