Author Archives: Rainer Müller

Tinkering with ATtiny9

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In June 2013 I attended a workshop on SMD soldering at the Gulaschprogrammiernacht 2013 (GPN13), a German hacker event organized by the regional CCC group in Karlsruhe. The result of a workshop organized by DrLuke was this small board with an ATtiny9 microcontroller and a 74HCT595 shift register.

Result of the SMD soldering workshop at #gpn13
(Originally published at https://twitter.com/raimue/statuses/340191330959519745)

The image shows my finished board with pin headers soldered. Later I changed the pin header for the 8 output pins again to make them point to the bottom. Now the board can easily be used on a breadboard for prototyping.

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Checking expiry dates of local and remote SSL certificates

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A few years ago I already covered how to check the expiry date of a SSL certificate using OpenSSL. When the recent global outage of Windows Azure was caused by an expired SSL certificate, this got me thinking about this topic once again.

In my previous post, I presented a mechanism to check the remaining lifetime of an SSL certificate using the PEM certificate file locally on disk. However, in the case with Azure recently, customers were dependent on the actions by Microsoft and had no access to the actual file. Thus, there might be a need to check remote certificates of services you use, e.g. your off-site backup provider. As you want to ensure you can always use this service, why not check this for expiring certificates once in a while? Maybe it’s your notification to the sysadmins who saves yourself and all other customers from being locked out.

Here is the updated script ssl-cert-check that now not only handles x509 certificate files, but also remote addresses for various forms and protocols. For simplicity, here are the usage instruction from inside this script:

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tmux update-environment

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tmux is one of the tools I use everyday. But one thing always annoyed me: even though I am using X11 forwarding and ssh-agent forwarding when re-attaching to a session, the DISPLAY and SSH_AUTH_SOCK environment variables are often wrong. Environment variables are initialized only once when the window was created. tmux is able to update some environment variables for new windows and panes based on the update-environment setting, however, existing shell windows cannot be updated.

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The mysterious stalled scp connections

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Lately, I had some problems with stalling transfers when using scp, the file transfer tool for the SSH protocol and part of the OpenSSH suite. Here is a report on what happened, how I found the cause and how I applied the solution. Actually, this is a pretty lame story, but I just wanted to write it down anyway.

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