Older blog entries for elwell (starting at number 99)

Alice and Bob go hashing

Alice wants to share some files with Bob over a public medium. Alice's computer is presumed 'secure'

she can easily generate a nice long 'passprase' by generating a cryptographic hash of the plaintext (say sha256sum) and use this as a key for a symmetrical crypt

ie

alice$> echo "hello world" > plaintext # generate sample input file
alice$> sha256sum plaintext # a948904f2f0f479b8f8197694b30184b0d2ed1c1cd2a1ec0fb85d299a192a447

and then crypt the file


alice$> openssl aes-256-cbc -in plaintext -out ciphertext
enter aes-256-cbc encryption password: [SHA256SUM GENERATED ABOVE]
Verifying - enter aes-256-cbc encryption password: [ditto]
alice$> ls -l plaintext ciphertext
-rw-rw-r--. 1 alice alice 32 Nov  7 16:01 ciphertext
-rw-rw-r--. 1 alice alice 12 Nov  7 16:00 plaintext

Syndicated 2012-11-07 15:10:00 (Updated 2012-11-07 15:10:28) from Andrew Elwell

Metering Musings

I've been intermittently trying to get our smart metering datafeed out to to a server for better logging, but I don't want to run a 300W PC to tell me my baseload in the house is 300+N W. There are several clamp meter / arduino designs thanks to the folks like OpenEnergyMonitor and Nanode, but things should be easier as there's a nice serial out already documented by ERDF (there's also the upcoming 'linky' interface but we're still on old-school)

Syndicated 2012-09-23 19:14:00 (Updated 2012-09-23 19:15:34) from Andrew Elwell

Aaaand we're back

Yay. I now have shiny broadband again thanks to <a href="http://www.k-net.fr/">k-net</a>. One difference between now and last time is that I also have an ipv6 prefix off them, so my home machines are accessible withoit needing port forwarding. Well, would be if I could get the RA working better on the router.

I have a linksys E3000, but that doesn't sipport ipv6 by default, so instead I have one of the TomatoUSB variants installed that does. I'd rather not use stateless config, but pre-assign IP addresses in advance so I can keep say kids machienes in a separate subnet. Overall - seems to work faiely well and the 'sam knows' box seems to have noticed too:

Syndicated 2012-09-19 20:45:00 (Updated 2012-09-19 20:45:57) from Andrew Elwell

Radio Scrobbling via MQTT

Since I often listen to the most excellent Soma FM during the day (go support them, it's worth it!) I often wish that I could go and stash some similar tunes to listen to when I'm not online. To do this, I sell my soul to CBS and use last.fm to generate similar / listened to by others recommendations.

Sadly Rhythmnbox doesn't scrobble radio stations (even though the scrobble API has a flag for this
track.scrobble(chosenByUser=0) to indicate that its been chosen by a radio service), despite it updating my 'now listening' status on IM. So, in a geeky overkill solution I decided to save time in the long run and use a pub/sub system with MQTT. Oh, and use some python and twitter along the way...

The design is that I have an MQTT publisher that uses the tritter streaming api (via tweepy) and filters for all the somafm twitter streams that Rusty pushes with BigUrl. This gives me near realtime announcements of the start of the track being played (after some trivial split / strip manipulation)

ie

justcovers       Pat Boone - Enter Sandman  (2012-06-25 07:20:30)
digitalis        Zephyrs - Stand Round Hold Hands (Ulrich  (2012-06-25 07:20:37)
secretagentsoma  Eat Static - Love Truncheon  (2012-06-25 07:21:02)
beatblender      Kerry Chandler (Lazy Dog Ben W - Isis  (2012-06-25 07:21:29)
sonicuniverse    In The Country - Only The Birds Can See Us  (2012-06-25 07:21:29)

Syndicated 2012-06-25 07:29:00 (Updated 2012-06-25 07:29:19) from Elwell

Temp / Humidity update

Since yesterdays posting, I plugged the FTDI outpur from the nanode into my bifferboard (needed to install kmod-usb-serial-ftdi) and have knocked up a simple python script to read the output and post to pachube^Wcosm

and lo:
https://cosm.com/feeds/60594

Syndicated 2012-05-22 09:25:00 (Updated 2012-05-22 09:25:33) from Elwell

DHT22 + Arduino

I recently purchased a DHT22 (Also known as RHT03 on Sparkfun) from Proto-Pic temp and humidity sensor with the aim of using it as an outdoor sensor in the garden. Although there are several DHT22 libraries on github I couldn't get the nethoncho one (or the patched forks) to return anything other than checksum error.

However the combined dht11/22 one I found linked on arduino.cc seems to work just fine. Need to test with -ve temps next but an overnight plot on the bench seems reasonable

Despite many forums saying that it needs 5v I've managed to get it working OK with the 3.3v pin on my nanode, next step is to test on a jeenode and send the output via RF. Oh, and then get a solar panel to run the thing...

Syndicated 2012-05-21 06:32:00 (Updated 2012-05-21 06:33:38) from Elwell

Prowling round Android

One of the apps I miss from my iphone days is Prowl - This also allowed me to receive IRC messages when away (screen detactched) - Since then I've discovered Notify My Android which does the same thing to android devices, and lo, a quick patch of my script is available

as normal, on github (https://github.com/Elwell/irssi-prowlnotify)

Syndicated 2012-03-08 11:06:00 (Updated 2012-03-08 11:23:46) from Elwell

Yubico / Yubikeys

I'm impressed.

I have small keyring with a USB memory stick, 2 yubikeys and a cofee machine cashless RFID key on. Stupidly I left said key in the vending machine. The system operators at work collected it and set about finding the owner. 1st up, they discovered that they can't read any files off yubikeys (heh) but googled the image and found the manufacturers website and said they had found serial #.... and #.....

Having spend the last 2 days rummaging in car / home looking for it, I got an email from yubico saying that <email> had found my key, based on the serial no of the one I purchased. Work also got an email for the other serial no, which they traced to me.

I'm *very* impressed by this level of attention at yubico, and it means when distributing keys within the business it pays to keep track of the serial no (printed under the 2d barcode).

It does raise the question of how (if) one should notify yubico if they're passed on - especially if I overwrite the yubi profile (as I have done) to prove that I am the rightful owner of the key.

Things to consider with revocation / blocking, especially with a distributed architecture like Fedora....

Syndicated 2012-02-27 19:12:00 (Updated 2012-02-27 19:12:28) from Elwell

apcupsd via Python to Pachube

In python, the 'default' URL accessing toolkit (urllib2) doesn't support PUT, however I've discovered requests which a) does and b) is in Fedora. So one apt-get install python-requests.noarch and you're off.

So - one trivial script (reusing much of the code for my MQTT variant) you get https://gist.github.com/1903259. The only minor niggle was working out how to prepend the minimum extra json content (version and datastreams) as I'd not used the json libs before.