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I’m using Thunderbird and Enigmail on Kubuntu, signing all my email and encrypting correspondence whenever possible. Lately (probably due to an update) the password-entry window does not appear. In stead, it complains immediately about:

openpgpg alert - error bad passphrase

I have set the preferences to remember my password for several minutes, so I figured there’s some problem there. I am not using gpg-agent, so EnigMail should fall back to the default.

Checking OpenPGP > Debugging Options > View Console shows what Enigmail is doing. I type my message (signing option checked) and click Send. The console shows:

gpg: gpg-agent is not available in this session
gpg: can't query passphrase in batch mode

Which makes sense, I am not using gpg-agent. Finally, it complains:

gpg; [stdin]: clearsign failed: bad passphrase

And gives up. Googling around I find similar problems, but no solution. Then I noted the following line in the console:

gpg: NOTE: old default options file '~/.gnupg/options' ignored

The ‘options’ file has been obsoleted, gnupg uses gpg.conf now. I checked, indeed the contents of ‘options’ are also present in gpg.conf. Moving ‘options’ away and restarting Thunderbird solved the problem.

Moreover, it also solved my password problem, I now get the password prompt and can happily sign my email.

I am a long-time user of OpenPGP to digitally sign my email. I am aware of the fact that most mail clients do not support this by default (but installing the EnigMail addon in Thunderbird couldn’t be easier).

Most mail clients simply show the mail, with my signature as attachment. No hurt done, they can still read my email message. Now, microSoft Exchange Webmail 2010 has a new feature and gives the following error:

“This message has a digital signature. The digital signature couldn’t be validated because the S/MIME control isn’t available.”

And decides this is a reason to not show the contents of the email. PANIC!

But have no fear, there’s yet another typical microsoft feature here: click “Reply” and you’ll see the contents of the email as quoted text.

They never seize to amaze me.

Why sign email you wonder? Read this article.

Some time ago I wrote about building a NAS with Ubuntu Server on the Intel Atom platform. This nifty little processor, when combined with NVIDIA ION, can easily be used to build a full-fledged HTPC. Read the rest of this entry »

Compiler optimisation flags can be quite helpful in bringing the (sometimes huge) duration of your OMNeT++ simulations to an acceptable level. Using a compute cluster can help, but even then the execution of a single process can take many hours for large networks. So let’s look at how you compile your code; I got a speed-up of approximately 10 times on some of my simulations. Read the rest of this entry »

Post-backoff was introduced into IEEE 802.11 to make sure that a station could not claim the channel by noting that the channel was idle after its own transmission, and then immediately transmit again. The idea is quite simple; transmission over -> pull a backoff from the contention window and count down (respecting the same rules w.r.t. carrier sense and inter-frame spacing etc.) and finally end up in the idle state. If a new packet was handed down by the network layer during post-backoff, the countdown would continue and result in a transmission. This behaviour is also implemented in MiXiM’s Mac80211 (and prior to that in the Mobility Framework). However, there’s a bug. Read the rest of this entry »