Unix Domain Sockets

November 9th, 2010 by Ralf Schlatterbeck

I recently had to find a solution for a communication problem: An application running on a web-server should update configuration files that are only readable by a privileged user and these should not be directly writeable by the web-server user.
So the idea was to write an update-server running under the privileged account which receives update requests (and can perform additional checks) from the unprivileged web server user.
One of the checks I wanted to make was that only the web-server user (www-data on debian) should be able to send update requests. So I had to find out the user sending a request via the Unix-domain socket. Google found a nice socket howto on Henning Makholm’s blog which told me most of what I needed to know: “so I ended up just checking the EUID of the client process after the connection has been accept()ed. For your reference, the way to do this is getsockopt() with SO_PEERCRED for Linux”.
But one issue was remaining: I didn’t need a SOCK_STREAM socket but wanted to send datagrams to the other side (and didn’t want to fiddle with implementing my own datagram layer on top of a stream socket). With normal SOCK_DGRAM datagram sockets there is no connection — and therefore I can’t determine the user sending the datagram from the other side of the socket.
Looking further I discovered that Linux has connection-oriented datagram sockets for quite some time under the name SOCK_SEQPACKET. With this type of socket you first connect() to the other side and then you send a datagram. Since now there is a connection the trick with SO_PEERCRED as described above works, too.
Code for Server (python):

from socket import socket, SOCK_SEQPACKET, AF_UNIX, SOL_SOCKET
from struct import unpack
try :
    # Not implemented in python 2.6, maybe higher
    from socket import SO_PEERCRED
except ImportError :
    SO_PEERCRED = 17 # Linux
sock = socket (AF_UNIX, SOCK_SEQPACKET)
path = '/path/to/socket'
try :
    os.remove (path)
except OSError :
sock.bind (path)
conn, adr = self.sock.accept ()
ucred = conn.getsockopt (SOL_SOCKET, SO_PEERCRED, 12)
pid, uid, gid = unpack ('LLL', ucred)
if uid... check uid:
    conn.close ()

data = conn.recv (4096)

Code for client (python):

from socket import socket, SOCK_SEQPACKET, AF_UNIX
s.connect ('path/to/socket')
s.send (.....)
s.close ()

Skypes Flux Capacitor: UDP

October 6th, 2010 by Ralf Schlatterbeck

I recently wrote about the broken network obfuscation code (aka Flux Capacitor) of Skype published by Sean O’Neil. At the time I wasn’t able to decrypt UDP packets. Now I’ve looked a little more closely into the Vanilla Skype documentation — which also includes some code to decrypt Skype credentials on harddisk. This code contains a CRC implementation called CRC32. I had wrongly asumed that CRC32 of Skype would be the same as the crc32 implementation of pkzip, Ethernet, png, the POSIX cksum command etc. which is listed as “crc32″ in the CRC article on Wikipedia and which is standardized in e.g. IEEE 802.3.
The crc32 from the standards above inverts all the bits of the seed before using it (it uses an XOR mask of 0xFFFFFFFF) and does this again before returning the result of the CRC computation to the caller. But it uses the same polynomial as skype. So we can use an existing standard CRC implementation (e.g from the zlib library) as follows for computing the skype CRC:

def skype_crc (s, seed = 0xFFFFFFFF) :
    return (crc32 (s, seed ^ 0xFFFFFFFF)) ^ 0xFFFFFFFF

With this crc implementation I’m now able to also decrypt UDP (see updated code) packets. I’ve shown this some days ago at my talk @linuxwochenende, for slides see my events page.

Linuxwochenende 2010

September 21st, 2010 by Ralf Schlatterbeck

Dieses Wochenende ist wieder Linuxwochenende im metalab, ich werde einen Vortrag zu Skype und dem vor kurzem veröffentlichten Flux Capacitor code und einen zweiten zu Traffic Shaping unter Linux halten.

Skypes Flux Capacitor has been released

August 25th, 2010 by Ralf Schlatterbeck

Skype uses an obfuscation layer for making it harder for others to analyze the Skype network traffic. This obfuscation layer has been called “Flux Capacitor” by the authors of the 2006 publications “Silver Needle in the Skype” and “Vanilla Skype”, Philippe Biondi, Fabrice Desclaux, and Kostya Kortchinsky, see the Wikipedia article on Skype for references about their publications. They discovered this flux capacitor code when reverse engineering the Skype binary program but didn’t dare to publish it for fear of others attacking the Skype network. They hinted at all sorts of bad things that were possible when knowing the Skype prototocol, the least of which is scanning networks behind firewalls (Skype is well known to be able to connect to the internet even in the presence of firewalls).
Now this Flux Capacitor code has been released by a group called “Skype Reverse Engineering Team” in a blog post Skype’s Biggest Secret Revealed by Sean O’Neil claiming that the code was already leaked and used by spammers. But they didn’t tell us how to use that code and defer further information to the next Chaos Communication Congress 27C3.
I certainly hope that the security holes in Skype are not that bad as feared by others. Some good can come out of it: maybe we’ll see a free Skype client in the not-too-far future. A good plan now would be to write a Wireshark dissector for Skype so that we can analyze the network traffic. Unfortunately the authors didn’t tell us yet how to call that code to de-obfuscate Skype traffic. But there is plenty of information in the aforementioned publications. So I’ve written a Makefile to create a shared library from the now released code and a Python wrapper that decrypts a single packet from a Skype network dump called SkypeIRC.cap published on the Wireshark page. This at least proves that the code works — the first several bytes of a Skype TCP stream decrypt to a known value.
Maybe others want to use this as a starting point before more is released by the authors at the Chaos Communication Congress 27C3.

Ning eliminates free networks

April 19th, 2010 by Ralf Schlatterbeck

That Ning now no longer supports free networks has been compared to blackmailing by some.
I also think so. But to be blackmailed there are two factors:

  • somebody who wants to blackmail others
  • a willing victim to go into the trap

You have the choice: Only use a service which at least provides a way to get your data out. (To be fair, it seems Ning will be offering this according to the blog entry cited above, but the details are still unclear)
But: The data alone is nothing without the software. So you need a service where you can export the data and have open source software available to do something with the extracted data. But the first part is the crucial one: If you have only the data, software can be written…
I’ve written earlier in this blog (and talked @Manchester) about the problem of vendor lock-in in “cloud computing” which is almost the same as “web 2.0 services”, namely software as a service (SAAS). Ning falls into that category as do other social network services like facebook or Xing.
This boils down to what the open cloud initiative has defined as cloud computing openness: For open content you ideally want to go for a free cloud with open APIs, open formats, open source (software), and open data.
Note that facebook is no alternative to ning: People have been thrown off facebook for retrieving their data, cited in these two entries on Henry Story’s blog.
But the choice has to be made by customers (or non-paying users) of these services: Don’t use something where you lock in your data. Or your data might be at risk, or locked in, or dead.
Doc Searls, co-Author of Cluetrain Manifesto and Editor of Linux Journal has written about this in a blog entry called Silos End: “These problems cannot be solved by the companies themselves. Companies make silos. It’s as simple as that. Left to their own devices, that’s what they do. Over and over and over again.”
Ideally there would be a standardized service and hosters agree to use the same software (maybe customized in the appearance) to host services for users. A hosting standard for collaboration software. Starting with the services Facebook, Xing, etc. are offering today. We want an interchange format that everybody can use, export, import.
I think a standard for these types of services will leave us with a network of hosters. This — in comparison to the status quo today — will be a distributed system, maybe a peer-to-peer system, not some big players locking in users. A common standard will hopefully keep the players honest.
To get there: Lets try to evaluate replacement software for Ning. Work on interchange formats. A suitable format for contact information is the Friend of a Friend (FOAF) format endorsed by the W3C, this is part of the semantic web effort.
One software that comes close to this goal might be elgg — I’ve not tried it myself, but there is already a group of Elgg Service Providers which comes close to the goal of a support infrastructure built around an open source project.
I’ve two points of critique, one of them being more personal taste, the other related to the license. The first is that the software is in PHP. The license is the GNU General Public License which offers no protection against a service provider making own modifications to the hosted software and not releasing these modifications as open source software. Details are in my earlier article on the subject. So far, the team of elgg seems to play the game very open. The Source code with (yet) unrelease modifications to the software is freely accessible as a subversion software repository. Furthermore they offer nightly builds for download.
There are many other good points, too: It offers syndication with RSS and JSON, and has an API to interconnect with software running elsewhere — which are the basic ingredients for a distributed system. The API is Representational State Transfer (REST) that happens to be the same mechanism on which the semantic web can be built.
So lets take some steps in the direction of a system built on standardized components where no vendor can lock us in.
When we get there, we’ve left Web 2.0 behind. The future is a distributed system, lets call it Web 3.0.


February 17th, 2010 by Ralf Schlatterbeck

Two weeks ago I’ve finally — wanted to do this forever — passed the ham exam and got a callsign for austria. I had done some SWL (short wave listening) quite some time ago — including digital modes like RTTY. Now I can explore the sending side, too…Thanks to the Metafunk group @Metalab and to Mike, OE3MZC and Gerhard, OE3GSU for supporting our joint preparation.

Vor zwei Wochen habe ich endlich die Amateurfunkprüfung gemacht — ich wollte das eigentlich schon immer tun — und habe jetzt ein Rufzeichen für Österreich. Schon früher habe ich ein bisschen SWL (Kurzwellen-Hören) betrieben, inklusive digitaler Modi wie RTTY (Funkfernschreiben). Jetzt kann ich auch die Sendeseite ausprobieren… Danke an die Metafunk Gruppe im Metalab und an Mike, OE3MZC und Gerhard, OE3GSU für die Unterstützung unserer gemeinsame Vorbereitung.

How to get smartcards or crypto-tokens running on Debian Linux and Windows

December 5th, 2009 by Ralf Schlatterbeck

This is a step-by-step Howto on installation and usage of the necessary commands to get smartcards or crypto-tokens working on Linux — and on Windows.
Smart card software on Linux consists of a driver for the card reader also called card terminal and a driver for the smartcard or token. There are two projects, OpenSC and MUSCLE. Both projects produce drivers for card terminals (for OpenSC this sub-project is called OpenCT) and for various cards. There are configuration options to make one project see the drivers of the other and vice versa.
I’m using OpenCT (card terminal) and OpenSC (smart card) software because these have worked better for me — except for the pcscd daemon from the MUSCLE project that might be needed for some applications. If you’re using software that depends on a PC/SC interface, you’ll also need to install the pcscd daemon (comes as a debian package).
Manufacturers are continuously improving their smartcards and the applications that run on the card. Up to now this has created an ever-changing pile of middleware to talk to these cards. An idea to improve the situation was a programmable card: Put a Java interpreter on the card and provide applets (so-called “cardlets”) for applications. The idea claims this would improve the situation for middleware on the host. Unfortunately this isn’t quite true: The Java virtual machine on smartcards is subject to change. So we have cards with a recent JVM and old cards with an ancient (1.1 from 2001) JVM. This means the applet needed to make the card work has to be cross-compiled to an older JVM depending on the card used. And there are still a number of host configuration issues.
The situation is worsened by the fact that many manufacturers of smartcards provide cards with their proprietary cardlet in the ROM of the card. This means these cards cannot be used with the applet that matches your middleware. And we’re back to the start and have to write a driver for the proprietary (this time java) middleware as before.
If you’re using Java-based smartcards you need to get a card that can accept a new applet and has the necessary developer keys published. Usually these cards are called “developer version” or similar. You then can use the MCardApplet from the MUSCLE plugins project. I recommend to build the applet yourself — after all this is a security application where your security depends on the software running on the card. There is a section below for preparing a java card with the appropriate applet.
I got the eToken PRO 32k (4.2B) working with OpenSC but not the eToken PRO 72k (Java). The first uses Siemens CardOS, the number in parentheses denotes the version number. Unfortunately these old CardOS based tokens will be discontinued, and Siemens seems to have announced end of life status for its CardOS.
The 72k eToken from Aladdin uses Java and needs a Java applet. The OpenSC project claims that the Java token works with OpenSC, but it didn’t for me. Maybe the token wasn’t a developer version that can accept an applet. The token also didn’t work under windows (although it worked with the Aladdin software there, i.e., I could initialize it) and I had a recent OpenSC binary release for windows from October 2009.
From the OpenSC documentation: “For programmable java cards: the support is for the card with the specific applet – if you have a different applet on your card, it might not be supported.”
First steps for non-Java cards or Java-cards with MCardApplet installed (for installation of the applet, see below):
Install smartcard software and card terminal framework:

apt-get install pcscd opensc libengine-pkcs11-openssl
The following NEW packages will be installed:
  libengine-pkcs11-openssl libp11-0

If your smartcard reader is not supported by pcscd, you should install the openct package in addition to the packages above. You can then run pcscd on top of openct.
After installing these programs, we need to configure pcscd to correctly use our reader. Configure /etc/opensc/opensc.conf to use the pcscd method, search for reader_drivers inside the app default stanza of the config file and modify this to:

reader_drivers = pcsc;

For CCID compatible readers without openct installed, the reader should be visible after plugging in the reader into the USB port:

Readers known about:
Nr.    Driver     Name
0      pcsc       Gemplus GemPC Key 00 00

If the card reader is not directly supported by pcscd (but is supported by openct) we need to configure /etc/reader.conf.d/openct, a config file of pcscd, to use OpenCT as the input method, for this the file should contain:

DEVICENAME       /dev/null
LIBPATH          /usr/lib/openct-ifd.so
CHANNELID        0

after modifying this file on Debian (on non-Debian systems you’ll probably have to modify /etc/reader.conf directly) we have to run:


which creates a new /etc/reader.conf. Now stop and restart openct and pcscd in the following order:

/etc/init.d/pcscd stop
/etc/init.d/openct restart
/etc/init.d/pcscd start

When everything went OK, you should see a pcscd based reader using opensc-tool:

opensc-tool -l
Readers known about:
Nr.    Driver     Name
0      pcsc       OpenCT 00 00

Add user to “scard” group in /etc/group and log in again to have the permissions to access the card. This is necessary if you want to use a reader provided by openct without going through pcscd.
If all else fails, you can still use openct without pcscd and set reader_drivers in /etc/opensc/opensc.conf to:

reader_drivers = openct;

Then a reader should be visible like this:

opensc-tool -l
Readers known about:
Nr.    Driver     Name
0      openct     Aladdin eToken PRO 64k
1      openct     OpenCT reader (detached)
2      openct     OpenCT reader (detached)
3      openct     OpenCT reader (detached)
4      openct     OpenCT reader (detached)

Now we should be able to read the card, if there is only one token in the USB port and no other smartcard readers are installed, we can leave out the -r option (for specifying the reader to use):

Info : CardOS V4.2B (C) Siemens AG 1994-2005
Chip type: 123
Serial number: 27 37 c0 09 2b 18
Full prom dump:
33 66 00 45 CB CB CB CB 7B FF 27 37 C0 09 2B 18 3f.E....{.'7..+.
00 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 ................
OS Version: 200.9 (that's CardOS M4.2b)
Current life cycle: 32 (administration)
Security Status of current DF:
Free memory : 1024
ATR Status: 0x0 ROM-ATR
Packages installed:
Ram size: 4, Eeprom size: 32, cpu type: 66, chip config: 63
Free eeprom memory: 27686
System keys: PackageLoadKey (version 0xfe, retries 10)
System keys: StartKey (version 0xff, retries 10)
Path to current DF:

1.   Using Java-based Smartcards
Java-based smartcards need some preparation to work with OpenSC. First you should make sure that you have a card that permits you to upload your own applet (cardlet) to the card. This usually means you need a so-called developer version. Avoid cards that have a proprietary manufacturer applet in read-only memory! You also usually need some development keys to upload a cardlet to the card.
For the following instructions I’ve used the Gemalto TOP IM FIPS CY2 (Cyberflex Access 64k v2) which is an old card that has a Java virtual machine version 1.1 from 2001 (!) but the card is well established and will probably be available for some time.
For the card reader I’ve used the Gemalto USB Shell V2 (GemPC Key), a CCID compatible reader. When buying a new reader, you should use one that follows the CCID specification from the PC/SC Workgroup, this ensures that OpenCT will support it. The card reader I’m using can read ID-000 format cards, also called SIM cards. These are small form-factor cards that are nice for authentication purposes. The Cyberflex card I’m using is available in ID-000. If a card isn’t available in ID-000, chances are you can make it fit using a service similar to this SIM cutting service.
Preparing the card for use with OpenSC is a two-step process. The first step is to obtain the necessary applet for the card. The second is to upload the applet to the card and initialize the card with a default PIN. Note that 2048 bit keys may not work with MCardApplet with the current software versions, see Some notes on key sizes.

1.1.   Obtaining the MCardApplet for your card
I recommend building your own version of the applet from source. Get the source code from svn://svn.debian.org/muscleplugins/trunk/MCardApplet using the source code control tool subversion:

svn co svn://svn.debian.org/muscleplugins/trunk/MCardApplet

I had to make several changes to use Java 1.6 for cross-building for the ancient Java VM that runs on the card. My Cflex.properties looks like this:


In particular, I’m using the native java environment installed on debian lenny. This lives in /usr. Otherwise you should follow the excellent building instructions in the file INSTALL. Then I’ve modified the javac in the target named compile in the common.xml ant build file as follows:

<target depends="precompile" name="compile">
    <mkdir dir="${OUTPUT_DIR}"/>
    <javac debug="on"
            <pathelement location="${BOOTCLASSPATH}"/>
            <pathelement location="${API_JAR}"/>
            <pathelement location="."/>
            <pathelement path="${java.class.path}"/>

I’ve added the target and source options. These refer to the specific java virtual machine version we’re cross-building for. I’ve also added the bootclasspath to get the classes that are VM specific from the old java development package.
This allows me to cross-build the applet for an old version of the java virtual machine without running the old java development environment which does no longer run on recent versions of Linux due to library incompatibilities.
I also had to change all the backslashes in common.xml to forward slashes. It looks like the java compiler can handle the backslashes in path names, but the other tools cannot.
Before building you should also look through CflexCapabilities.properties for any capabilities you want to enable which are not enabled in the default configuration. I had to enable -DWITH_RSA_2048 and -DWITH_SIGN for example.
For the impatiant I’m offering a pre-compiled version of the applet. I’ll update this text with the build instructions soon.

1.2.   Uploading the applet to the card
As a preparation for this step, you should install the pcsc daemon and the pcsclite development packages on debian:

apt-get install pcscd libpcsclite-dev

For uploading the applet to the card, I recommend using gpshell, a tool from the globalplatform project which depends on the globalplatform library. Unfortunately these are not yet packaged as Debian packages, so obtain the sourcecode to both, gpshell and the globalplatform library . Unpack these packages and build using the normal process:

make install

For the globalplatform library you need the development libraries for libpcsclite, available as the Debian package libpcsclite-dev which should be installed before the ./configure step above.
If you installed the globalplatform library without root privileges, you have to run ldconfig as root to make the new library available in the shared library cache.
Check that your smartcard services are running (see above for how to do that) and verify that you see your card reader (or token) using:

opensc-tool -l

The gpshell tool interfaces to the card via pcscd, so you should see something similar to the following:

Readers known about:
Nr.    Driver     Name
0      pcsc       Gemplus GemPC Key 00 00

Now we can proceed to upload the applet using gpshell. We need the following applet upload gpshell script, put this into the file applet_install.gpshell, note that lines terminated with “” need to be concatenated, gpshell currently doesn’t understand continuation lines:

select -AID a000000003000000
open_sc -security 1 -keyind 0 -keyver 0 
   -mac_key 404142434445464748494a4b4c4d4e4f 
   -enc_key 404142434445464748494a4b4c4d4e4f
delete -AID a00000000101
delete -AID a000000001
delete -AID a0000003230101
delete -AID a00000032301
install_for_load -pkgAID a000000001 -nvCodeLimit 16000 
   -sdAID a000000003000000
load -file CardEdgeCflex.ijc
install_for_install -instParam 00 -priv 02 -AID a00000000101 
   -pkgAID a000000001 -instAID a00000000101 -nvDataLimit 32000

and run the script with gpshell:

gpshell applet_install.gpshell

Finally we will have to set a default PIN for the card using opensc-tool:

opensc-tool -s 00:A4:04:00:06:A0:00:00:00:01:01 -s 

This sets the PIN to eight zeros, “00000000”. After this procedure the card can be used like a normal PKCS#15 based card with OpenSC.

1.2.1.   Some notes on using the gpshell script with other cards
Many of the magic numbers in the gpshell script depend on the card in use and on the applet that is uploaded. An AID is an applet-ID. The open_sc command has nothing to do with OpenSC, but opens a secure channel to the card. The parameters are the developer keys of the card. In our example, the key is used twice and the hex-bytes denote the string:


The AID used for the secure channel is different for other brands of cards. I was able to find out this AID using the following AID gpshell script:

open_sc -security 1 -keyind 0 -keyver 0 
   -mac_key 404142434445464748494a4b4c4d4e4f 
   -enc_key 404142434445464748494a4b4c4d4e4f
get_status -element 80

This displays for the Gemalto TOP IM FIPS CY2:

List of applets (AID state privileges)
a000000003000000        7       0

The delete commands remove older versions of the applet — there also was a version that had another applet ID — from the card before uploading the new version. Think of the applet living in a package named a000000001 and the applet named a00000000101. The install_for_load command establishes the package inside the a000000003000000 package. Then the install_for_install command installs the applet into non volatile memory after upload.
Note that these numbers are hard-coded into the applet that is being uploaded. This is defined during compile-time and for the MCardApplet this can be configured in the common.xml ant-file. When packaging the compiled java classes, the build process generates .cap files which contain the applet ID in binary format, notably the Applet.cap file contains the AID of the applet.
So if these numbers are changed when building a custom applet, be sure to adapt the upload commands, too. A warning here: All tools that depend on the MCardApplet expect the given AID, so changing the AID would incur a change of all tools or at least their configuration.

2.   OpenVPN Preparation: Step by step process with high-level tool
This section describes how to initialize a token, create a user key and certificate using tools that come with OpenVPN. This was only tested on Linux since the certificate handling scripts for OpenVPN are more advanced on Linux.
I had to patch the pkitool of OpenVPN to use the pkcs15-init command instead of the pkcs11-tool command for initializing the token and creating keys. The reason is that Aladdin limits their tokens to use one key for only one purpose (encryption or signing). The pkcs15-init command allows the specification of the key purpose while the pkcs11-tool command does not.
In the following we assume you are in the easy-rsa directory of OpenVPN, and you have initialized the configuration by reading the configuration in vars. It’s also always a good idea to have a backup of all the OpenVPN keys before starting.
Initializing the token for first use (or re-using an already formatted token) THIS DESTROYS ALL DATA ON THE TOKEN:

./pkitool --pkcs15-init 0 "Thomas Mustermann"
New User PIN.
Please enter User PIN:
Please type again to verify:
Unblock Code for New User PIN (Optional - press return for no PIN).
Please enter User unblocking PIN (PUK):
Please type again to verify:

If the token was already initialized, the procedure would also ask for the old password.
Now we can check that everything worked, by looking at the PINs:

pkcs15-tool --list-pins

Now we can proceed to generate a key pair and a certificate, this takes a long time:

./pkitool --pkcs15 /usr/lib/opensc-pkcs11.so 0 45 "user cert" client27

When everything went OK, we should be able to display keys, public keys, and certificates on the token:

pkcs15-tool --list-keys
pkcs15-tool --list-public-keys
pkcs15-tool --list-certificates

3.   What is needed for Windows
I’ve first installed the latest OpenVPN installer, only this package has the necessary TAP network driver for Linux. Only the TAP driver needs to be installed.
I’ve used a compiled version of OpenVPN that comes bundled with OpenSC from the binary windows repository, I’ve used the latest


files (from Oct 2009). For 64bit Windows (AMD64) the


files should be used. Everything unpacked from these files should be installed to


I’ve also created a configuration directory under that directory called config. In config there are the necessary certificates (root ca) and hash keys and the client.ovpn configuration file.
When using my OpenVPN admin script, Python for windows from python.org and the Python WIN32 package are needed. In addition my rsclib library needs to be installed. For installing rsclib, unpack the .zip file and run:

setup.py install

from a command prompt. The admin script in pyovpn.zip has the same installation procedure.
After installing everything, basic working of the smart card can be verified with the OpenSC tools:

opensc-tool -l
pkcs15-tool --list-certificates

3.1.   Aladdin Token
For using the Aladdin eToken with Windows, the smart card tools of the manufacturer have to be installed — these include the driver for accessing the tokens. I’ve used:



eToken PKI Client 5.0 SP1 Windowsx32.zip

3.2.   Gemalto USB Shell Token V2
The driver for the Gemalto USB Shell Token reader can be downloaded free of charge from the Gemalto website.

4.   Using OpenVPN with SmartCard
OpenVPN uses a PKCS#11 provider library, on Debian this is /usr/lib/opensc-pkcs11.so, to access the smart card. We can show which certificates are on the card by issuing:

openvpn --show-pkcs11-ids /usr/lib/opensc-pkcs11.so
The following objects are available for use.
Each object shown below may be used as parameter to
--pkcs11-id option please remember to use single quote mark.

      DN:             /C=AT/ST=AT/L=Weidling/ ...
      Serial:         03
      Serialized id:  OpenSCx20Project/PKCSx20 ...

Now OpenVPN can be started with the smartcard. I’m using the following additional config entries for OpenVPN — pkcs11-providers is set to the path of the PKCS#11 provider library:

pkcs11-providers "/usr/lib/opensc-pkcs11.so"
management 4711

For Windows the provider library becomes (assuming the OpenSC tools where installed to C:ProgramsOpenVPNbin):

pkcs11-providers "C:\Programs\OpenVPN\bin\opensc-pkcs11.dll"

The other parameters are the same as for other operating systems.
Note also that the askpass option of OpenVPN does not work for querying the token password. In my experiment I had to give the token password to OpenVPN via the management interface using the config option management-query-passwords.
This configuration tells OpenVPN to open the management interface on Port 4711 of localhost. It will ask for the passphrase of the Aladdin token on that port. Additionally we wait (management-hold) until a management program has opened the management interface and told OpenVPN to proceed.
The pkcs11-id-management tells OpenVPN to accept the pkcs11-id to use via the management interface. With a little intelligence in the management interface we can avoid having the pkcs11-id in the configuration file (which would then be different for each user).
OpenVPN can be asked via the management interface about a listing of all pkcs11-ids. If there is only one certificate on the card, we feed the id of the only certificate back to OpenVPN when it asks about the pkcs11-id. This can be done without user intervention.
Unfortunately the feature that OpenVPN can ask the smartcard for all the certificates depends on the Token being present when OpenVPN is started. An alternative is to specify the pkcs11-id` directly in the configuration file. If this is specified, the management interface will ask for the token if it isn’t present when starting OpenVPN. The parameter to the pkcs11-id config parameter is the Serialized id from the command output above.
Since I have not found any graphical user interface programs for OpenVPN that can deal with asking the user for the token passphrase, I’ve written a little command-line python script which can be run on both, Windows and Linux, and will ask the user to insert the token and specify the token passphrase.
OpenVPN can be started with the script by issuing the command:


in a command prompt window. The command will start openvpn and proceed to ask for necessary token passwords.

4.1.   Low-level usage of the management interface
With the management-query-passwords option, OpenVPN will ask the password from the management interface. After starting the OpenVPN daemon and connnecting to the managment interface on the defined port (e.g., using telnet) we see the following message:

>INFO:OpenVPN Management Interface Version 1 -- type 'help' for more info
>PASSWORD:Need 'OpenSC Card (New User) token' password

The password can then be entered using the password command of the managment interface:

password 'OpenSC Card (New User) token' sehrgeheimespasswort

OpenVPN answers with:

SUCCESS: 'OpenSC Card (New User) token' password entered, but not yet verified

5.   Key Revocation
Revoke a certificate:

openssl ca  -config $KEY_CONFIG -revoke keys/02.pem

(re-) generate key revocation list (CRL):

openssl ca  -config $KEY_CONFIG -gencrl -out keys/crl.pem

6.   OpenVPN Preparation: Step by step process with low-level tools
This section describes the low-level tools as used by the patched pkitool from OpenVPN. It does not create a certificate with OpenSSL. This is for documentation purposes only (to understand what goes on behind the scenes) and was my first approach to getting started with OpenSC.

  • Erase the card — if you already have a Security Officer PIN installed, you need this for erasing the card:
    pkcs15-init -E
  • Create PKCS#15 structure (option –no-so-pin specified not to create security officer PIN and user PUK) on the card — note that the keys need to be between 6 and 8 characters long and should be numeric if you intend to use a keypad for key-entry (which applies mostly to smartcards not to USB tokens). Also note that if you omit –no-so-pin you should keep the Security Officer PIN secure — only with it can the token be re-formatted:
    pkcs15-init --create-pkcs15 --no-so-pin
    New Security Officer PIN (Optional - press return for no PIN).
    Please enter Security Officer PIN:
    Please type again to verify:
    Unblock Code for New User PIN (Optional - press return for no PIN).
    Please enter User unblocking PIN (PUK):
    Please type again to verify:
  • The steps above can be rolled into one command:
    pkcs15-init -E --create-pkcs15 --no-so-pin
  • Add an authentication (user) ID to the token with corresponding PIN and PUK:
    pkcs15-init --store-pin --auth-id 01 --label "User Name"
    New User PIN.
    Please enter User PIN:
    Please type again to verify:
    Unblock Code for New User PIN (Optional - press return for no PIN).
    Please enter User unblocking PIN (PUK):
    Please type again to verify:
  • Check that everything worked, by looking at the PINs:
    pkcs15-tool --list-pins
    PIN [Security Officer PIN]
        Com. Flags: 0x3
        ID        : ff
        Flags     : [0xB2], local, initialized, needs-padding, soPin
        Length    : min_len:6, max_len:8, stored_len:8
        Pad char  : 0x00
        Reference : 1
        Type      : ascii-numeric
        Path      : 3f005015
    PIN [User Name]
        Com. Flags: 0x3
        ID        : 01
        Flags     : [0x32], local, initialized, needs-padding
        Length    : min_len:4, max_len:8, stored_len:8
        Pad char  : 0x00
        Reference : 3
        Type      : ascii-numeric
        Path      : 3f005015
  • Now we can generate an RSA key on the card. Note that we could also import a PKCS-12 key onto the card, but the more secure option is to let the card generate the key (so the key will never be available outside the card). The split-key option actually generates two key-pairs, one for encryption and one for signing. There are some labelling options to attach names to the generated keys but these aren’t needed if you want only one key. You could specify an application profile with the –id option, if this isn’t given the default ID 45 (authentication purposes) is used. The command will ask for the Security officer PIN, then for the User PIN, then again for the Security officer PIN (!):
    pkcs15-init --generate-key rsa/2048 --auth-id 01 --split-key

    Note that with Java smartcards the keysize 2048 might not work with the current version of the tools, see Some notes on key sizes.

  • Now we can verify that the key was actually stored on the card:
    pkcs15-tool --list-keys
    Private RSA Key [Private Key]
        Com. Flags  : 3
        Usage       : [0x4], sign
        Access Flags: [0x1D], sensitive, alwaysSensitive, neverExtract, local
        ModLength   : 2048
        Key ref     : 16
        Native      : yes
        Path        : 3f005015
        Auth ID     : 01
        ID          : 45
  • List public keys:
    pkcs15-tool --list-public-keys
    Public RSA Key [Public Key]
        Com. Flags  : 2
        Usage       : [0x4], sign
        Access Flags: [0x0]
        ModLength   : 2048
        Key ref     : 0
        Native      : no
        Path        : 3f0050153048
        Auth ID     :
        ID          : 45
  • For the following steps we will need a minimum openssl config file:
    openssl_conf            = openssl_init
    [ openssl_init ]
    engines                 = engine_section
    [ req ]
    default_bits            = 2048
    default_keyfile         = privkey.pem
    distinguished_name      = req_distinguished_name
    [ req_distinguished_name ]
    countryName                     = Country Name (2 letter code)
    countryName_default             = AT
    countryName_min                 = 2
    countryName_max                 = 2
    stateOrProvinceName             = State or Province Name (full name)
    stateOrProvinceName_default     = Austria
    localityName                    = Locality Name (eg, city)
    localityName_default            = Vienna
    0.organizationName              = Organization Name (eg, company)
    0.organizationName_default      = example.com
    organizationalUnitName          = Organizational Unit Name (eg, section)
    organizationalUnitName_default  = IT-Department
    commonName                      = Common Name (eg, server's hostname)
    commonName_max                  = 64
    emailAddress                    = Email Address
    emailAddress_max                = 40
    [ engine_section ]
    pkcs11 = pkcs11_section
    [ pkcs11_section ]
    engine_id = pkcs11
    dynamic_path = /usr/lib/engines/engine_pkcs11.so
    MODULE_PATH = /usr/lib/opensc-pkcs11.so
    init = 0
  • Generate a certificate request (CSR) from this key using openssl:
    openssl req -days 3650 -new -out $CLIENT.csr -config openssl.cnf 
      -engine pkcs11 -keyform engine -key 0:45 -sha1

    This will ask for all the certificate parameters. Alternatively these can be specified using the -subj option of openssl (this is broken into several lines but should be assembled into one line) with the following parameter:

  • You can view the contents of the CSR using:
    openssl req -in $CLIENT.csr -noout -text
  • Now sign the certificate request with whatever tools you are using. With the pkitool of OpenVPN this would become (after having copied the certificate request newclient.csr to the keys directory):
    pkitool --sign newclient

    The message about not being able to access newclient.key can be ignored.

  • You may want to delete old certificates from the token:
    pkcs15-init --delete-objects cert --id=45
  • Then import the new certificate onto the token:
    pkcs15-init --store-certificate newclient.crt --id=45
  • Reading a certificate from the token and output with openssl:
    pkcs15-tool --read-certificate 45 | openssl x509 -noout -text

6.1.   Some notes on key sizes
Using 2048 bit keys should generally be possible with newer cards. I had some problems with these key sizes using my Java smartcard, though.
After uploading the applet to the card, it is possible to create a key with either 1024 or 2048 bit. This indicates that the card is able to handle the large keysize. When trying to generate a CSR using openssl the command failed with:

[opensc-pkcs11] iso7816.c:99:iso7816_check_sw: No precise diagnosis
[opensc-pkcs11] muscle.c:745:msc_compute_crypt_process: returning with:
                Card command failed
[opensc-pkcs11] muscle.c:840:msc_compute_crypt: returning with:
                Card command failed
[opensc-pkcs11] card-muscle.c:749:muscle_compute_signature:
                Card signature failed: Card command failed
[opensc-pkcs11] sec.c:53:sc_compute_signature: returning with:
                Card command failed
[opensc-pkcs11] pkcs15-sec.c:273:sc_pkcs15_compute_signature:
                sc_compute_signature() failed: Card command failed
20808:error:0E06D06C:configuration file routines:NCONF_get_string:no value:
conf_lib.c:329:group=req_attributes name=unstructuredName_min
20808:error:0E06D06C:configuration file routines:NCONF_get_string:no value:
conf_lib.c:329:group=req_attributes name=unstructuredName_max
20808:error:8000A005:Vendor defined:PKCS11_rsa_sign:General Error:
20808:error:0D0C3006:asn1 encoding routines:ASN1_item_sign:EVP lib:

Worse, after reinitializing the card in this state with:

pkcs15-init -E --create-pkcs15 --no-so-pin
pkcs15-init --store-pin --auth-id 01 --label "User Name"

and trying to generate a smaller key, this fails with:

pkcs15-init --generate-key rsa/1024 --auth-id 01 --split-key
[pkcs15-init] iso7816.c:102:iso7816_check_sw: Unknown SWs; SW1=9C, SW2=03
[pkcs15-init] muscle.c:557:msc_generate_keypair: returning with:
              Card command failed
[pkcs15-init] card.c:678:sc_card_ctl: returning with:
              Card command failed
[pkcs15-init] pkcs15-muscle.c:272:muscle_generate_key:
              Unable to generate key
[pkcs15-init] pkcs15-muscle.c:273:muscle_generate_key: returning with:
              Card command failed
Failed to generate key: Card command failed

I was able to fix this by re-downloading the applet onto the card. This also happens the other way round, when generating a 1024 bit key first and trying — after reinitializing the card with pkcs15-init — to generate a 2048 bit key.
So I recommend to stick with 1024 bit keys with the current software versions (debian lenny).

Media Ecologies Conference

November 3rd, 2009 by Ralf Schlatterbeck

I’m currently at the media ecologies conference in manchester, UK. I was just talking about what tools and interfaces we need for collaboration tools (on the web). This also rehashes some of the ideas in my blog entry on cloud computing and the problems with (lack of) openness of cloud applications. The slides of my talk can be downloaded from my website.

Did Ronja Fail?

October 27th, 2009 by Ralf Schlatterbeck

Ronja, the optical data link device, is often cited as a failed open source hardware project — the last one mentioning it I just read is Lawrence Kincheloe’s excellent essay Musings Upon the Nature of Open Source Hardware as a Business at the end of his project visit summary at Factor e Farm.
Roja did fail (in the sense that it isn’t very widespread today not in the sense of being a cool open source project). One of the research studies I know of is the presentation “Ronja — Darknet of Lights” by Johan Söderberg at the 4th Oekonux conference for which Audio is available. The study is very interesting although I don’t agree with the conclusions. So why did Ronja “fail”?
Ronja’s main application was cheap internet access. At the time of its design in 2001 wireless LAN (Wifi) wasn’t yet available cheaply. And in the Czech Republic DSL wasn’t available at the time.
Now consider the technical characteristics of Ronja:

  • Up to 10MBit/s
  • Up to 1.4 km range
  • Light: Doesn’t work in fog, or other bad weather (snow)
  • Light: Hard to get the beam to the destination (direction)
  • Light: Interference with daylight
  • For full-duplex communication we need two (receiver + transmitter) devices
  • sold for around 700$ at the time (the LED alone cost 120$ you get these for .75$ now)
  • needed “a hell of a lot of time to build one” according to Söderberg

And compare these with WLAN:

  • Up to 54MBit/s
  • With good antennas several km range (I’ve built a link with 5.5km)
  • Antennas are cheap and can even be built at home, e.g., a Cantenna — you can build a cantenna in an evening
  • Works in fog and bad weather
  • we need only one antenna at sender and one at receiver
  • WLAN is very cheap nowadays, it became available (with new frequencies) in 2005 in cz.

So I think that Ronja “failed” because it was replaced by something better and cheaper that was readily available. It isn’t an example of a failed open source business model for hardware and shouldn’t be used as an example. This doesn’t mean that we already know how a business model for open source hardware should look like, though.
The idea behind Ronja — according to the Wikipedia article on Ronja “User Controlled Technology” is (mostly) achieved with WLAN technology today: We can use cheap devices and modify them (using open source firmware and homegrown antennas) to suit our needs. And there are large wireless communities now like Funkfeuer in Vienna who do their own Internet communication.

PGAPy: Genetische Algorithmen mit Python

October 25th, 2009 by Ralf Schlatterbeck

[Dies ist der Abstract meines Vortrags am Linuxwochenende im Metalab, die alte Version des Abstracts ist inzwischen von der Linuxwochen Homepage verschwunden…]

PGAPy ist ein Python-Wrapper für PGAPack, eine der vollständigsten Bibliotheken für genetischen Algorithmen. Die Python-Bibliothek eignet sich für eigene Experimente mit genetischen Algorithmen, aber auch für die Implementierung von kompletten Anwendungen.

Der Vortrag gibt eine kurze Einführung in genetischen Algorithmen mit Beispielen in Python. Vorgestellt wird u.a. ein Programm zum automatischen Erzeugen der bekannten Sudoku Zahlenrätsel. Dabei wird schrittweise die Bewertungsfunktion für ein Sudoku entwickelt.