Matt's Musings

July 12, 2014

GPG Key Management Rant

Filed under: Debian,Linux,WLUG / LinuxNZ — Matt Brown @ 12:17 pm NZST

2014 and it’s still annoyingly hard to find a reasonable GPG key management system for personal use… All I want is to keep the key material isolated from any Internet connected host, without requiring me to jump through major inconvenience every time I want to use the key.

An HSM/Smartcard of some sort is an obvious choice, but they all suck in their own ways:
* FSFE smartcard – it’s a smartcard, requires a reader, which are generally not particular portable compared to a USB stick.
* Yubikey Neo – restricted to 2048 bits, doesn’t allow imports of primary keys (only subkeys), so you either generate on device and have no backup, or maintain some off-device primary key with only subkeys on the Neo, negating the main benefits of it in the first place.
* Smartcard HSM – similar problems to the Neo, plus not really supported by GPG well (needs 2.0 with specific supporting module version requirements).
* Cryptostick – made by some Germans, sounds potentially great, but perpetually out of stock.

Which leaves basically only the “roll your own” dm-crypt+LUKS usb stick approach. It obviously works well, and is what I currently use, but it’s a bunch of effort to maintain, particularly if you decide, as I have, that the master key material can never touch a machine with a network connection. The implication is that you now need to keep an airgapped machine around, and maintain a set of subkeys that are OK for use on network connected machines to avoid going mad playing sneakernet for every package upload.

The ideal device would be a USB form factor, supporting import of 4096 bit keys, across all GPG capabilities, but with all crypto ops happening on-device, so the key material never leaves the stick once imported. Ideally also cheap enough (e.g. ~100ish currency units) that I can acquire two for redundancy.

As far as I can tell, such a device does not exist on this planet. It’s almost enough to make a man give up on Debian and go live a life of peace and solitude with the remaining 99.9% of the world who don’t know or care about this overly complicated mess of encryption we’ve wrought for ourselves.

end rant.

June 13, 2011

Using StartCom Free SSL certificates with Cyrus imapd

Filed under: Linux — @ 9:12 am NZST

A stumbled across Start Com a few months ago, an Israeli company that run a Certificate Authority (CA) called StartSSL with a root certificate in all the modern browsers and operating systems. Best of all they don’t participate in the cartel run by the rest of the SSL certificate industry and offer domain validated certificates at the price it costs them to issue them – nothing.

I had the first opportunity to use their services today when I needed an SSL cert to secure the IMAP server I run for my parents and I was very pleased with the experience. The web interface is a bit weird and you have to jump through some strange hoops, but to save paying more money to the SSL certificate cartel it seemed more than worthwhile.

Like most CAs these days the certificate which signs your server certificate is not the actual root certificate included in your operating system or browser, but an intermediate CA certificate which is in turn signed by the root certificate. This means that you have to ensure that your server includes the intermediate CA certificate alongside the server certificate so the client can validate the entire path back to the root.

Unlike Apache which explicitly allows you to specify a certificate chain file, the openssl methods used by Cyrus 2.2 only seem to recognise a single CA certificate in the file pointed to by tls_ca_file. All as not lost however, as the openssl libraries are actually quite smart and will automagically determine which intermediate certs they need to bundle into the handshake if you install them appropriately under /etc/ssl/certs (at least on Debian).

The trick is that you have to install the intermediate CA cert into a file named after the hash of the certificate, like so:

# wget -O /etc/ssl/certs/startcom-class1-intermediate.pem
# hash=$(openssl x509 -hash -noout -in /etc/ssl/certs/startcom-class1-intermediate.pem)
# ln -s ./startcom-class1-intermediate.pem /etc/ssl/certs/${hash}.0
# ls -l /etc/ssl/certs/${hash}.0
lrwxrwxrwx 1 root root 34 2011-06-13 07:43 /etc/ssl/certs/ea59305e.0 -> ./startcom-class1-intermediate.pem

Then in imapd.conf:

tls_cert_file: /etc/ssl/certs/your-server-cert.pem
tls_key_file: /etc/ssl/private/your-server-key.key
tls_ca_file: /etc/ssl/certs/startcom-ca.pem

Voila. Works everywhere I’ve tried so far.

Start Com – Highly Recommended. I’ll be using them for any future SSL certificate purchases (e.g. EV certs) that I need to make.

May 12, 2011

Linux ignores IPv6 router advertisements when forwarding is enabled

Filed under: Linux — @ 11:26 am NZST

IPv6 adoption is increasing, and along with it come a new set of behaviours and defaults that system administrators and users must learn and become familiar with. I was recently caught out by Linux’s handling of IPv6 router advertisements (RAs) when forwarding is also enabled on the interface. It took me a while to figure out and searching for obvious terms (such as those in the first half of the title of this post) didn’t immediately yield useful answers, so here is my attempt to help shed some light on the subject.

By default Linux will ignore IPv6 RAs if the interface is configured to forward traffic. This is in line with RFC2462 which states that a device should be either a Host or a Router. If you’re forwarding packets you’re a router and you’re therefore expected to be sending RAs, not receiving them. This policy does make a certain amount of sense but there are obviously situations where it can be useful to accept RAs and still forward packets over the interface[0]. The confusing part is that the Linux IPv6 stack allows the accept_ra sysctl to be set to 1 (enabled) at the same time as the forwarding sysctl is set to 1, yet all incoming RAs are ignored with no hint as to why. If you’re not aware that the default behaviour is to ignore RAs when forwarding is enabled it looks very much like autoconfiguration has simply broken.

The key piece of information is that makes everything as clear as mud is realising that the forwarding and accept_ra sysctl’s are not simple boolean enabled/disabled flags like many of their brethren. There are instead three possible values for each, all clearly documented in sysctl.txt, when you take the time to read it. Ironically the documentation states the type of the values as “BOOLEAN” even though they’re not… at least it helped me to feel better about my hasty assumption that the sysctl’s were boolean values.

accept_ra – BOOLEAN
Accept Router Advertisements; autoconfigure using them.

Possible values are:
0 Do not accept Router Advertisements.
1 Accept Router Advertisements if forwarding is disabled.
2 Overrule forwarding behaviour. Accept Router Advertisements
even if forwarding is enabled.

Functional default: enabled if local forwarding is disabled.
disabled if local forwarding is enabled.

The documentation for forwarding is similar, but much longer, so you can refer to the link above to see it.

Conclusion: If you want to autoconfigure IPv6 addresses on an interface that you’re also forwarding IPv6 traffic over, you need to set accept_ra to 2.

No doubt there are more IPv6 quirks and defaults like this waiting to trap me in the future ­čÖé

[0] Arguably you really don’t want to be autoconfiguring addresses on your router ever, but that’s a philosophical debate that isn’t really relevant to this post.

December 7, 2010

Under the cover of the Kindle 3

Filed under: Linux — @ 12:52 pm NZST

For my birthday back in October, my wonderful wife gave me a Kindle 3 from Amazon. I’d been considering other e-book readers for quite some time, but I had mostly ignored the Kindle due to the lack of EPUB support and a general dislike of Amazon’s DRM enforcement. In the end, the superior hardware and ecosystem of the Kindle overpowered those concerns and overall I’m very pleased with the purchase. The screen is amazing, literally just like reading off a piece of paper and the selection of books is OK. I’ve been buying almost all my books from Amazon to date since it’s so easy (the Whispernet is amazingly quick!) but it’s not terribly difficult to get EPUBs from elsewhere onto the device after a quick run through Calibre to turn them into a MOBI file, so I keep telling myself I’ve still got some flexibility.

Almost as much fun as reading on the device has been learning about how it works. The Mobile Read forums have lots of step by step posts on how to do specific tasks like replacing the screensaver image, but they don’t give much background detail on how the Kindle is actually operating which is what really interests me. Luckily among all the step by step posts I also found a “usbnetwork” package which also adds an SSH server to the Kindle,├é┬áso after installing that and then SSHing in to my Kindle I’ve been poking around.

Under the cover the Kindle reveals a fairly standard Linux installation. While the hardware and IO devices are obviously unique, compared to something like an Android phone, the Kindle is refreshingly “normal”.


  • ├»┬╗┬┐Freescale MX35 ARMv6 based CPU with Java specific instruction support.
  • 256MB RAM
  • 4GB of internal flash presented as an SDHC device with four partitions. A ~700MB root partition, a ~30MB /var/local partition, another roughly 30MB kernel partition and then the rest (~3.1G) as the writeable “user” partition where your books and other content are stored. The root and /var/local partitions are ext3! (not jffs or some other more traditional flash based file system) while the user partition is vfat for easy use with Windows, etc.
  • The board is code-named ‘luigi’ and there are lots of references to ‘mario’ and ‘fiona’ scattered around the device, and even in some URLs on Amazon’s website. Someone was obviously a Super Mario fan.
  • The wireless chipset is Atheros based using the ar6000 drivers.
  • The WAN (3G) modem presents itself as a USB serial device and is controlled via a custom daemon named ‘wand’ which uses the standard Linux pppd package to establish IP connections over a private APN Amazon (provided by Vodafone here in Ireland).
  • The EInk display shows up as some special files under /proc rather than as a device. With a bit of digging I found some simple constants that when written to the proc files cause the screen to display the standard boot/progress/upgrading images. I haven’t deciphered how to make more complex updates to the display yet.


  • The kernel is based on Linux 2.6.26, with a bunch of hardware specific patches and drivers from, an Amazon subsidiary who appear to be responsible for much of the low-level driver and device development.
  • Lots of familiar open source projects are present, e.g. syslog-ng, DBus, busybox, pppd, wpa_supplicant, gstreamer, pango, openssl and the list goes on. You can download all the sources from Amazon’s website. I haven’t spent any time to see what if anything has been modified.
  • There were a few unexpected finds as well such as GDB and powertop! No doubt useful for the developers, but highly unlikely to actually be used on a shipping Kindle.
  • Boot-up is controlled by a set of sysv style init scripts which setup the filesystems and then start a handful of daemons to look after the low-level subsystems (network, power, sound) as well as the standard syslog and cron daemons you’d expect to see on any Linux box.
  • Once the basic system is up and running the init scripts kick off the “framework” which lives under /opt/amazon/ebook and consists of lots of Java classes. The system uses the cvm Java environment from Sun/Oracle which is specialised for embedded low-memory devices like this. The framework appears to take over most of the co-ordination, management and interaction tasks once it has started up.

The application/framework code is heavily obfuscated apparently using the Allatori Java Obfuscator. The jrename and jd-gui utilities have proven very handy in helping to untangle the puzzle, although they still only leave you with a pile of Java source code with mostly single letter alphabetic variable and class names! I’ve been using IntelliJ’s support for refactoring/renaming Java code to slowly work through it (thanks in large part to error/log messages and string constants found through the code which can’t be obfuscated easily and help to explain what is going on), and I’m slowly beginning to piece together how the book reading functionality works. I’ll maybe write more on this in a future post.

In one of my initial tweets about the Kindle I mentioned that it seemed to be regularly uploading syslog data to Amazon based on some sendlogs scripts I’d noticed and a few syslog lines containing GPS co-ordinates that had been pasted on the Mobile Read forums. I can’t find any trace of GPS co-ordinates in any syslog messages I’ve seen on my device, but there is definitely information about the cell sites that my Kindle can see, the books that I’m opening and where I’m up to in them:

101206:235431 wand[2515]: I dtp:diag: t=4cfd77b7,MCC MNC=272 01,Channel=10762,Band=WCDMA I IMT 2000,Cell ID=1362209,LAC=3021,RAC=1
,Network Time=0000/00/00 00.00.00,Local Time Offset=Not provided,Selection Mode=Automatic,Test Mode=0,Bars=4,Roaming=1,RSSI=-88,Tx
Power=6,System Mode=WCDMA,Data Service Mode=HSDPA,Service Status=Service,Reg Status=Success,Call Status=Conversation,MM Attach St
ate=Attach accept,MM LU State=LU update,GMM Attach State=Attach accept,GMM State=Registered,GMM RAU State=Not available,PDP State=
Active,Network Mode=CS PS separate attach mode,PMM Mode=Connected,SIM Status=Valid; PIN okay; R3,MM Attach Error=No error,MM LU Er
ror=No error,GMM Attach Error=No error,GMM RAU Error=Not available,PDP Rej Reason=No error,Active/Monitored Sets=0;39;-11 1;180;-1
5,RSCP=-111,DRX=64,HSDPA Status=Active,HSDPA Indication=HSDPA HSUPA unsupp,Neighbor Cells=,Best 6 Cells=,Pathloss=,MFRM=,EGPRS Ind
ication=,HPLMN=,RPLMN=272;01 ,FPLMN=234;33 234;30 234;20 272;05 ,n=1:

101206:235758 cvm[3426]: I Reader:BOOK INFO:book asin=B003IWZZ3Y,file size=233168,file last mod date=2010-11-27 19.18.22 +0000,con
tent type=ebook,length=MobiPosition_ 465747,access=2010-12-06 09.44.32 +0000,last read position=MobiPosition_ 464387,isEncrypted=f

101206:233416 udhcpc[5639]: Offer from server received
101206:233416 udhcpc[5639]: Sending select for

Interestingly you can see from the last two lines, that Amazon has taken some care to preserve privacy by not including the full IP address given to the device by my local Wifi network, so in light of that I find it interesting that they decided not to obfuscate the Cell and Book IDs in those respective log messages too. Seems rather inconsistent.

As to how and when these logs are sent to Amazon, the picture is a little bit murky. Every 15 minutes tinyrot runs out of cron and rotates /var/log/messages if it is greater than 256k in size. Rotated logs are stored into /var/local/log under filenames like messages_00000044_20101207000006.gz and alongside the log files are a set of state files named nexttosendfile, messages_oldest, messages_youngest. Something regularly sweeps through this directory to update the state and remove the old logs (after sending them up to Amazon I assume). I suspect that something is buried in the Java application code mentioned above.

On the whole the Kindle is a fascinating piece of technology. It delivers a wonderful reading experience on top of a familiar Linux system and is going to provide me with many more hours of entertainment as I unpack all the tricks and techniques that have gone into this device. I would recommended it as a present for geeks everywhere.

February 18, 2009

Blacked Out – no “Guilt Upon Accusation”

Filed under: General,Linux,WLUG / LinuxNZ — @ 1:37 pm NZST

If you’re reading this post via the website rather than a feed/planet then you will notice that the site has gone completely black in support of the Creative Freedom Foundation’s campaign against S92A of the NZ Copyright Amendment Act which is due to come into effect on 28th February 2009. I’ve also joined the wave of people blacking out their “avatar” on Facebook/Jabber/MSN, etc.

S92A introduces “Guilt Upon Accusation” whereby if you are accused of copyright infringement (downloading music and movies, etc) “repeatedly” (likely 3 or more times) you are at risk of being disconnected from the Internet by your ISP. The law does not require any proof or substantiation of the accusations and the entire process would occur outside of the courts and the established legal system. Not only does it place every user at risk, the wording is very unclear on exactly what type of organisation is considered an ISP and there is significant concern that schools, businesses, libraries and hospitals will be placed in the difficult position of determining whether their users have broken the law and require disconnection.

Opposition to the law is not an attack on copyright, or a statement that we should be free to download all the movies and music that we desire. Those sorts of activities are clearly wrong, and I don’t have any issue with copyright holders wanting to enforce their rights when their content is illegally copied. However, disconnecting people upon accusation, with no proof or formal legal process to prove guilt is not the right way to go about it.

The fact that the law does not require proof of guilt is only the tip of the iceberg in terms of problems with it. For further background on the problems it causes for ISPs by placing them as the middle-man in copyright disputes you should refer to the following posts:

Finally, I think it is worth pointing out that S92A was removed from the proposed Amendment at the select committee stage, but was later reintroduced by Judith Tizard during the final reading of the bill. Mark Harris has an excellent post on the history of the amendment which includes facts such as the official report on the amendment also recommended removing S92A as it was unecessary given existing ISP terms and conditions which forbid illegal activity. The fact that the select committee (based on public submissions) recognised the problems with S92A and removed it, only to have it added back in again at the last stage when we no longer had any say on it really hacks me off and I cant’ help but feel the influence of the “big money” American media companies pressuring our politicians to pass a law that they don’t really understand the full consequences of.

So what is to be done? The Blacked Out campaign, being run by the Creative Freedom Foundation is gathering steam and international attention. Peter Dunne of United Future (who originally voted for the amendment) has declared that the amendment is wrong, and doesn’t do what they thought they were voting to do, we need to convince National and the rest of the house of the same. Time is running out for this to happen before the amendment comes into effect on Feb 28th, but there is still time to write to your local MP and sign the petition against S92A “Guilt Upon Accusation”. The Creative Freedom Foundation site has a nice easy list of what you can do to register your protest.

September 9, 2008

New Gadgets

Filed under: Debian,General,Linux — @ 10:11 am NZST

It’s been a while since I last acquired new gadgets but I think I’ve made up for lost time with my last weeks purchases.

You may remember that I’ve had my eye on the Openmoko phones since early 2007, but in between shifting across the world and starting a new job I never got around to purchasing one of the first versions. The second version, the “Freerunner”, was released in June this year and I placed an order with Pulster, a local distributor, shortly after. The phones have been in hot demand, so I only received my phone last week, a wait of of almost 2 months, and it turned up missing one of the cables that was meant to come with it. Still some distribution kinks to be worked out.

Distribution kinks are the least of Openmoko’s worries at the moment though. As advertised, the phone is definitely not ready for primetime distribution yet. I’ve tried three different software images on it: the original “stable” 2007.2 image, the current “devel” 2008.8 image and the latest completely rebuilt SHR release which is the most promising yet. With the SHR image I’ve been able to send and receive calls and text messages, although the interface is somewhat arcane. I’m most interested in the GPS which looks to be working reasonably well at this stage.

After almost a week with the phone I’m glad I purchased it, and I’m having fun hacking on it, but there is a huge way to go before I’ll be able to use it as my primary phone. So that’s gadget #1.

The second gadget is a new Digital SLR camera. I’ve been thinking about getting back into photography for a while (I last took photos seriously in high school) and when I saw how affordable digital SLRs had become I couldn’t resist. There isn’t much between Canon and Nikon when comparing mid-range SLRs these days, so after about a week of deliberation I decided on the Canon 450D, primarily because most of my workmates also have Canon SLRs!

I only got the camera on Friday, and spent half the weekend playing with the GPS on the phone (I want to set them up so I can geo tag all my photos), so I haven’t had quite as much time to play with it yet. I expect to spend plenty of quality time with it on our holiday in Malta next week. First impressions are favourable, although I’m fast discovering camera viewfinders were not really designed for people who wear glasses. I may have to consider wearing contacts again.

Once we get back from Malta I’d like to find a local (or online) photography club with some good weekly assignments to fire my creativity and motivate me to get the most out of my new toy.

July 14, 2008

Ubuntu versions numbers on crack

Filed under: Debian,Linux,WLUG / LinuxNZ — @ 3:56 am NZST

On hardy after the latest round of updates:

matt@krypton:~$ dpkg -s flashplugin-nonfree | grep Version

Granted this package is in hardy-backports not hardy proper, but still, what on earth?!?!

April 13, 2008

The Australian Open Source Industry & Community Report

Filed under: Linux,WLUG / LinuxNZ — @ 4:34 am NZST

I highly recommend making some time to read the The Australian Open Source Industry & Community Report. Based on a census of the Australian Open Source community conducted at the end of last year, it presents a range statistics about the state of the Open Source community and industry in Australia.

The report seems to be aimed at demonstrating to Government and Businesses that Open Source has become a very viable business strategy in Australia and in particular how increased adoption of Open Source would reduce the Australian trade deficit. You don’t need to worry about being put to sleep. The report is relatively casual in tone and easy to read with lots of bright graphs to present the key statistics and findings. Including:

  • The Australian Open Source industry generates around AUD$500M in annual revenue. A small proportion of the AUD$54.4B total revenue for the Australian ICT Industry in 2004-2005. Lots of growth potential!
  • 70-80% of the industry is based on the traditional development, customisation, support and maintenance business model.
  • Most of the individuals making up the Australian Open Source community are working professionals, over half the community are in a relationship and a third of the community have children.

It would be fascinating to see a similar study of the New Zealand industry. I suspect that we would find that Open Source businesses are spread across the country similar to Australia. Obviously our community and financial figures would be smaller in absolute terms but would our proportion of Open Source based businesses be similar?

Maybe a good task for the current NZOSS committee would be to round up some of the larger Open Source businesses in New Zealand, along with the Ministry of Economic Development to sponsor a similar study for New Zealand!

July 9, 2007

POSIX/NFSv4 ACL Inheritance Problems

Filed under: Linux,WLUG / LinuxNZ — @ 4:23 am NZST

I (as root) have a directory hierarchy that I want a particular group to always have write access to. The files and folders inside the hierarchy are owned and manipulated by a wide variety of diffrent users.

Essentially I want to delegate ‘root’ access for a portion of the filesystem to a particular group.

My first attempt at implementing this was to use the standard POSIX ACLs that are available for almost every filesystem Linux supports.

I recursively set an ACL on the top-level directory to give the group write access to all files and directories that currently exist and then I recursively set a default ACL to give the group write access on all the directories. This default ACL should be inherited by any new files that are created ensuring that the group keeps write access to everything.

Problem solved? Unfortunately not.

The intricacies of complying with POSIX means that ACLs are implemented as an ACL plus a mask. To gain access to a particular file or directory the user or group must match an appropriate ACL granting the access and the mask for that file or directory must also allow the requested permission to be granted.

When you add an ACL to a file or directory, the ‘group’ bits of the standard Unix permissions magically switch from controlling group access to controlling the mask portion of the ACL, effectively providing an upper bound on the permissions that an ACL entry can grant. This prevents legacy POSIX applications that do not understand ACLs from unintentionally granting excessive permissions – arguably a good thing.

Unfortunately this also makes it very hard to preserve the ACL granting write access to the ‘root’ group which I legitimately intended to have in place on this portion of the filesystem.

Newly created files under the hierarchy generally inherit the ACL as intended, as most applications attempt to create files with as many permissions as possible, leaving it up to the umask to remove undesired permissions.

However any file that is copied into the hierarchy without the ‘group’ write bit set, or any file that has the ‘group’ write bit removed via chmod will actually remove the write bit from the ACL mask invalidating the ACL and leaving me back at square one!

After a bit of Googling I thought that NFSv4 ACLs might be the answer to this problem, as they are marketed as “very similar to Windows ACLs” and I’m sure that I vaugely recall Windows being able to properly inherit ACLs from parent directories. Unfortunately after downloading the NFSv4 ACL patches and trying all the various mount options I cannot find any combination that will offer the functionality I need. The implementation conforms to POSIX, so it still has a mask parameter and the same problems as the standard POSIX ACLs. The only benefit from using NFSv4 ACLs that I can see is that you have more permissions to grant.

So once again, I’m back to square one. I’m hoping that there is some fundamental point that I’m missing as this seems like a very common use-case that I would have thought would be well supported.

If a command-line example is clearer to you look at:

My current solution is to run a cronjob every X minutes to recursively ‘chmod -R g+w /dir’, however that’s far from optimal as it exposes all sorts of race conditions and just seems ugly!

Any suggestions or solutions will be gratefully received.

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