Posts Tagged Linux

Enigmail password trouble with OpenPGP

Posted by on Thursday, 12 April, 2012

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.

Building a HTPC with Intel Atom and NVIDIA ION

Posted by on Saturday, 14 January, 2012

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 »

Speeding up OMNeT++/MiXiM simulations

Posted by on Wednesday, 21 December, 2011

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 »

Bug in Mac80211 in MiXiM post-backoff

Posted by on Friday, 16 December, 2011

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 »

Bug in Mac80211 in MiXiM backoff when channel busy

Posted by on Thursday, 15 December, 2011

This post describes a bug in MiXiM’s Mac80211 which seems to be a fundamental error: when the MAC gets a packet from the Netw and the channel is busy, it schedules a senseChannelWhileIdle(currentIFS + remainingBackoff) after the ongoing transmission ends. Unfortunately, remainingBackoff is often 0 as post-backoff is likely to have completed. The result? Many synchronised collisions one IFS after the ongoing transmission. Read the rest of this entry »