So SteamOS has been released. While that's marginally interesting in and as of itself, there are two observations to be made:

1. Microsoft, Nintendo, and Sony will feel an impact. More functionality on cheaper hardware which can easily by upgraded; I bet quite a few managers are not happy, at the moment.
2. While the stand-alone Linux Steam client was initially targeted at Ubuntu, SteamOS is based on Debian Wheezy.

Actual Linux (not Android) for the end user The first one means more Linux installations. In the living room. On a machine that children are really focussed on and will want to play with, quite literally. The next logical step is for people who play games to install SteamOS on their other machines; desktops, laptops, everywhere they want to game. This could really be the tipping point where the average adolescent computer enthusiast does not need to reboot into Linux to fool around with, but the other way round: To need to boot to Windows for a few select legacy applications which don't run on the FLOSS variant of Wine like Office or Photoshop. And once this momentum starts to shift, other software vendors will follow the money trail. Could 2014 finally be.... the year of Linux on the desktop...? Debian vs Debian-based The latter one is also really interesting... Obviously, I don't know why Valve decided to go down this road, but there are several reasons which come to mind:

• No need for the extra bloat
• They wanted to avoid the tie-in with another for-profit entity
• Unhappiness with some technical decisions made by UbuntuCanonical
• Lack of faith in the long-term governance of Ubuntu

What we are left with is a major player entering the ring of Linux for end-users and choosing Debian over Ubuntu. Hopefully, improvements to the base system will be fed back upstream, enabling all Debian-based distributions to profit easily, not only Ubuntu-based ones. I am willing to bet that two years ago, SteamOS would have been based on Ubuntu, not Debian. Recently, there's been a lot of backlash over various decisions which Canonical forced onto Ubuntu and it will be interesting to see how this plays out in the long run... I will be interesting to see how much pain Linux Mint and Kubuntu will endure. Forecast Users All in all, we are looking at a massive influx of new users into the Debian ecosystem. How massive? 65 million registered users massive. 7 million concurrent users at once, 1.2 million users actively playing the top 100 games at the same time massive. This is huge. Contributors In time, a substantial part of that userbase will switch over one or more of their machines over to SteamOS. The tinkerers among them will realize they can install plain Debian and install Steam as a package. The hackers among those will start to improve upon their systems; and what better way to do that then to go upstream? If even a tiny fraction of users makes it this far, the count of actively involved contributors with Debian will skyrocket if we let them join. Raspbian and some other not-quite-ideal decisions come to mind. Vendors Commercial software vendors need to stay profitable. Thus, they are forced to support distributions which promise enough paying users. In the past, this meant mainly SuSE and Red Hat; they had commercial backers, went through certifications, etc. In the recent past, this also meant Ubuntu. All of a sudden, Debian stable has a potential market of tens of millions of average computer users and computer enthusiasts. A lot of whom will want to continue to use their OS of choice at work, as well. Oh boy...

Cleaning up X server warnings So I was sitting in the Narita airport with a couple of other free software developers merging X server patches. One of the developers was looking over my shoulder while the X server was building and casually commented on the number of warnings generated by the compiler. I felt like I had invited someone into my house without cleaning for months embarrassed and ashamed that we d let the code devolve into this state. Of course, we ve got excuses the X server code base is one of the oldest pieces of regularly used free software in existence. It was started before ANSI-C was codified. No function prototypes, no const , no void * , no enums or stdint.h. There may be a few developers out there who remember those days (fondly, of course), but I think most of us are glad that our favorite systems language has gained a lot of compile-time checking in the last 25 years. We ve spent time in the past adding function prototypes and cleaning up other warnings, but there was never a point at which the X server compiled without any warnings. More recently, we ve added a pile of new warning flags when compiling the X server which only served to increase the number of warnings dramatically. The current situation With the master branch of the X server and released versions of the dependencies, we generate 1047 warnings in the default build. -Wcast-qual considered chatty The GCC flag, -Wcast-qual, complains when you cast a pointer and change the const qualifier status. A very common thing for the X server to do is declare pointers as const to mark them as immutable once assigned. Often, the relevant data is actually constructed once at startup in allocated memory and stored to the data structure. During server reset, that needs to be freed, but free doesn t take a const pointer, so we cast to (void *), which -Wcast-qual then complains about. Loudly. Of the 1047 warnings, 380 of them are generated by this one warning flag. I ve gone ahead and just disabled it in util/macros for now. String constants are a pain The X server uses string constants to initialize defaults for font paths, configuration options, font names along with a host of other things. These end up getting stored in variables that can also take allocated storage. I ve gone ahead and declared the relevant objects as const and then fixed the code to suit. I don t have a count of the number of warnings these changes fixed; they were scattered across dozens of X server directories, and I was fixing one directory at a time, but probably more than half of the remaining warnings were of this form. And a host of other warnings Fixing the rest of the warnings was mostly a matter of stepping through them one at a time and actually adjusting the code. Shadowed declarations, unused values, redundant declarations and missing printf attributes were probably the bulk of them though. Changes to external modules Instead of just hacking the X server code, I ve created patches for other modules where necessary to fix the problems in the right place.

• proto/fontsproto. Declares FontPathElement names as const char *
• mesa/drm. Adds printf attribute to the debug_print function
• util/macros. Removes -Wcast-qual from the default warning set.

Getting the bits In case it wasn t clear, the X server build now generates zero warnings on my machine. I m hoping that this will also be true for other people. Patches are available at:

xserver - git://people.freedesktop.org/~keithp/xserver warning-fixes
fontsproto - git://people.freedesktop.org/~keithp/fontsproto fontsproto-next
mesa/drm - git://people.freedesktop.org/~keithp/drm warning-fixes
util/macros - already upstream on master

Keeping our house clean Of course, these patches are all waiting until 1.15 ships so that we don t accidentally break something important. However, once they re merged, I ll be bouncing any patches which generate warnings on my system, and if other people find warnings when they build, I ll expect them to send patches as well. Now to go collect the tea cups in my office and get them washed along with the breakfast dishes so I won t be embarrassed if some free software developers show up for lunch today.

Fingerprints and Key IDsOpenPGPv4 fingerprints are made from an SHA-1 digest over the key's public key material, creation date, and some boilerplate. SHA-1 digests are 160 bits in length. The "long key ID" of a key is the last 64 bits of the key's fingerprint. The "short key ID" of a key is the last 32 bits of the key's fingerprint. You can see both of the key IDs as a hash in and of themselves, as "32-bit truncated SHA-1" is a sort of hash (albeit not a cryptographically secure one). I'm arguing here that short Key IDs and long Key IDs are actually useless, and we should stop using them entirely where we can do so. We certainly should not be exposing normal human users to them. (Note that I am not arguing that OpenPGP v4 fingerprints themselves are cryptographically insecure. I do not believe that there are any serious cryptographic risks currently associated with OpenPGP v4 fingerprints. This post is about Key IDs specifically, not fingerprints.)Key IDs have serious problemsAsheesh pointed out two years ago that OpenPGP short key IDs are bad because they are trivial to replicate. This is called a preimage attack against the short key ID (which is just a truncated fingerprint). Today, David Leon Gil demonstrated that a collision attack against the long key ID is also trivial. A collision attack differs from a preimage attack in that the attacker gets to generate two different things that both have the same digest. Collision attacks are easier than preimage attacks because of the birthday paradox. dlg's colliding keys are not a surprise, but hopefully the explicit demonstration can serve as a wakeup call to help us improve our infrastructure. So this is not a way to spoof a specific target's long key ID on its own. But it indicates that it's more of a worry than most people tend to think about or plan for. And remember that for a search space as small as 64-bits (the long key ID), if you want to find a pre-image against any one of 2k keys, your search is actually only in a (64-k)-bit space to find a single pre-image. The particularly bad news: gpg doesn't cope well with the two keys that have the same long key ID:

0 dkg@alice:~$ gpg --import x
gpg: key B8EBE1AF: public key "9E669861368BCA0BE42DAF7DDDA252EBB8EBE1AF" imported
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)
0 dkg@alice:~$ gpg --import y
gpg: key B8EBE1AF: doesn't match our copy
gpg: Total number processed: 1
2 dkg@alice:~$ 

This probably also means that caff (from the signing-party package) will also choke when trying to deal with these two keys. I'm sure there are other OpenPGP-related tools that will fail in the face of two keys with matching 64-bit key IDs. We should not use Key IDs I am more convinced than ever that key IDs (both short and long) are actively problematic to real-world use of OpenPGP. We want two things from a key management framework: unforgability, and human-intelligible handles. Key IDs fail at both.

• Fingerprints are unforgable (as much as SHA-1's preimage resistance, anyway -- that's a separate discussion), but they aren't human-intelligible.
• User IDs are human-intelligible, and they are unforgable if we can rely on a robust keysigning network.
• Key IDs (both short and long) are neither human-intelligible nor unforgable (regardless of existence of a keysigning network), so they are the worst of all possible worlds.

So reasonable tools should not expose either short or long key IDs to users, or use them internally if they can avoid them. They do not have any properties we want, and in the worst case, they actively mislead people or lead them into harm. What reasonable tool should do that? How to replace Key IDs If we're not going to use Key IDs, what should we do instead? For anything human-facing, we should be using human-intelligible things like user IDs and creation dates. These are trivial to forge, but people can relate to them. This is better than offering the user something that is also trivial to forge, but that people cannot relate to. The job of any key management UI should be to interpret the cryptographic assurances provided by the certifications and present that to the user in a comprehensible way. For anything not human-facing (e.g. key management data storage, etc), we should be using the full key itself. We'll also want to store the full fingerprint as an index, since that is used for communication and key exchange (e.g. on calling cards). There remain parts of the spec (e.g. PK-ESK, Issuer subpackets) that make some use of the long key ID in ways that provide some measure of convenience but no real cryptographic security. We should fix the spec to stop using those, and either remove them entirely, or replace them with the full fingerprints. These fixes are not as urgent as the user-facing changes or the critical internal indexing fixes, though. Key IDs are not useful. We should stop using them.Tags: collision, crypto, gpg, openpgp, pgp, security

Thanks to a corporate reward program, I just got a Pure Sensia digital and Internet radio receiver: basically, it is a device able to play streams from FM, DAB, HTTP and USB sticks. In overall, it works fine, and it has a remote controller, so it makes a nice addition to my home equipment, but it has what I consider a major flaw, which I suspect to have been designed on purpose.For playing streams from FM or DAB, the process is rather simple: you select a frequency and it plays, nothing else is involved. I did not try USB yet but it should be similar: you select a file or a playlist and it plays it. But for HTTP streams, it is quite different: you select a stream from a the Pure Connect directory which is a list of HTTP streaming services maintained by the manufacturer Pure. This raises three concerns:

1. If all HTTP stream access is made from that remote directory, it probably means Pure knows, and possibly logs, every stream you listen to. That is not acceptable.
2. What will happen when that service is shut down? Not if it is shut down, mind you, but when it is, because it will, since I never heard of any company keeping a service forever, or any company lasting forever itself actually. Well, here is what will happen: all these digital and Internet radio receivers will become digital but not Internet radio receiver. That is not acceptable: when you buy a radio receiver, you buy a device, not a service of indefinite term.
3. What do you do if you want to listen to an HTTP stream which is not listed on Pure's directory? Answer of Pure's support: you can add custom streams by URL to your Pure account's favourites. Well, good try, but that is not enough or rather, that is too much: requiring a Pure account to do that, is an artificial restriction, which suffers from exactly the same flaw as the Pure directory. And letting a single company know every Internet stream you listen to is not acceptable either.

Considering that flaw, here is my overall comment about that radio receiver: it is based on a good idea, and it has a good overall design, but it implements it in a precarious way. If you buy one of these things, you should know that you are not buying a complete digital and Internet radio receiver but only a digital radio receiver with some Internet features with privacy concerns, which will work for a time and one day stop working on Pure's decision.

I am happy to announce that OASIS v0.4.0 has just been released. OASIS is a tool to help OCaml developers to integrate configure, build and install systems in their projects. It should help to create standard entry points in the source code build system, allowing external tools to analyse projects easily. This tool is freely inspired by Cabal which is the same kind of tool for Haskell. You can find the new release here and the changelog here. More information about OASIS in general on the OASIS website. I have recently resumed my work on OASIS and this will be hopefully the new version that will lead to quicker iteration in the development of OASIS. The development process was slowdown by the fact, that I feared introducing new fields in _oasis or regression. This was a pain and I decided to change my development model. Features The most important step is the introduction of AlphaFeatures and BetaFeatures fields. They allow to introduce pieces of code that will only be activated if certain features are listed in those fields. It should help to be always ready to release. The features also cover other aspect like flag_tests and flag_docs which has been introduced in OASIS v0.3.0. In fact the features API is now used to introduce all enhancement while keeping backward compatibility with regard to OASISFormat. Rather than defining a ~since_version:0.3 for fields we use a feature that handle the maturity level of the feature. When I feel a specific feature is ready to ship, I just change the InDev Alpha to InDev Beta and then SinceVersion 0.4. On the long term, when we won't support anymore a version of OASIS that existed before the SinceVersion, the feature will always be true and I will fully integrate it in the code. The only constraint around features is: if you use AlphaFeatures or BetaFeatures field, you must use the latest OASISFormat... Features section in the manual. Example of features available:

• section_object: allow to create object (.cmo/.cmx) in _oasis
• pure_interface: an OCamlbuild feature that allows to handle .mli without a .ml file

Automate Another topic is automation of testing releases. For OASIS v0.3.0, I ran tests on all platforms manually, late in the development of v0.3.0 and it was painful to fix. So I have decided to setup a Jenkins instance that automate testing on Linux. On the long term, I plan to also setup a Mac OS X builder and start looking at Windows as well. This should help me catch errors early and be able to fix them quickly. However, for v0.4.0 I have decided to just release what I have and which has mainly be tested on Linux. The point here is to quickly release and iterate, rather than wait for perfection. Hopefully end user testing will allow to quickly discover new bugs. Time boxed release In the coming months, I will try to do time boxed releases. I will try to release version of OASIS every 15th of the month. The point here is to try to iterate faster and avoid long delay between release. See you in 1 month for the next release.

Today, here in the UK, the date is 11/12/13. Today, here in Edinburgh, I we became married.

I've already promised I will make no more than two jokes, ever, about "owning a wife". I will save them for suitable occasions.

For the fifth year in a row the fearless WebKitGTK+ hackers have gathered in A Coru a to bring GNOME and the web closer. Igalia has organized and hosted it as usual, welcoming a record 30 people to its office. The GNOME foundation has sponsored my trip allowing me to fly the cool 18 seats propeller airplane from Lisbon to A Coru a, which is a nice adventure, and have pulpo a feira for dinner, which I simply love! That in addition to enjoying the company of so many great hackers. The goals for the hackfest have been ambitious, as usual, but we made good headway on them. Web the browser (AKA Epiphany) has seen a ton of little improvements, with Carlos splitting the shell search provider to a separate binary, which allowed us to remove some hacks from the session management code from the browser. It also makes testing changes to Web more convenient again. Jon McCan has been pounding at Web s UI making it more sleek, with tabs that expand to make better use of available horizontal space in the tab bar, new dialogs for preferences, cookies and password handling. I have made my tiny contribution by making it not keep tabs that were created just for what turned out to be a download around. For this last day of hackfest I plan to also fix an issue with text encoding detection and help track down a hang that happens upon page load. Martin Robinson and myself have as usual dived into the more disgusting and wide-reaching maintainership tasks that we have lots of trouble pushing forward on our day-to-day lives. Porting our build system to CMake has been one of these long-term goals, not because we love CMake (we don t) or because we hate autotools (we do), but because it should make people s lives easier when adding new files to the build, and should also make our build less hacky and quicker it is sad to see how slow our build can be when compared to something like Chromium, and we think a big part of the problem lies on how complex and dumb autotools and make can be. We have picked up a few of our old branches, brought them up-to-date and landed, which now lets us build the main WebKit2GTK+ library through cmake in trunk. This is an important first step, but there s plenty to do. Under the hood, Dan Winship has been pushing HTTP2 support for libsoup forward, with a dead-tree version of the spec by his side. He is refactoring libsoup internals to accomodate the new code paths. Still on the HTTP front, I have been updating soup s MIME type sniffing support to match the newest living specification, which includes specification for several new types and a new security feature introduced by Internet Explorer and later adopted by other browsers. The huge task of preparing the ground for a one process per tab (or other kinds of process separation, this will still be topic for discussion for a while) has been pushed forward by several hackers, with Carlos Garcia and Andy Wingo leading the charge. Other than that I have been putting in some more work on improving the integration of the new Web Inspector with WebKitGTK+. Carlos has reviewed the patch to allow attaching the inspector to the right side of the window, but we have decided to split it in two, one providing the functionality and one the API that will allow browsers to customize how that is done. There s a lot of work to be done here, I plan to land at least this first patch durign the hackfest. I have also fought one more battle in the never-ending User-Agent sniffing war, in which we cannot win, it looks like. I am very happy to be here for the fifth year in a row, and I hope we will be meeting here for many more years to come! Thanks a lot to Igalia for sponsoring and hosting the hackfest, and to the GNOME foundation for making it possible for me to attend! See you in 2014!

A nice set of recent posts have done a great job detailing the remaining ways that a root user can get at kernel memory. Part of this is driven by the ideas behind UEFI Secure Boot, but they come from the same goal: making sure that the root user cannot directly subvert the running kernel. My perspective on this is toward making sure that an attacker who has gained access and then gained root privileges can t continue to elevate their access and install invisible kernel rootkits. An outline for possible attack vectors is spelled out by Matthew Gerrett s continuing useful kernel lockdown patch series. The set of attacks was examined by Tyler Borland in Bypassing modules_disabled security . His post describes each vector in detail, and he ultimately chooses MSR writing as the way to write kernel memory (and shows an example of how to re-enable module loading). One thing not mentioned is that many distros have MSR access as a module, and it s rarely loaded. If modules_disabled is already set, an attacker won t be able to load the MSR module to begin with. However, the other general-purpose vector, kexec, is still available. To prove out this method, Matthew wrote a proof-of-concept for changing kernel memory via kexec. Chrome OS is several steps ahead here, since it has hibernation disabled, MSR writing disabled, kexec disabled, modules verified, root filesystem read-only and verified, kernel verified, and firmware verified. But since not all my machines are Chrome OS, I wanted to look at some additional protections against kexec on general-purpose distro kernels that have CONFIG_KEXEC enabled, especially those without UEFI Secure Boot and Matthew s lockdown patch series. My goal was to disable kexec without needing to rebuild my entire kernel. For future kernels, I have proposed adding /proc/sys/kernel/kexec_disabled, a partner to the existing modules_disabled, that will one-way toggle kexec off. For existing kernels, things got more ugly. What options do I have for patching a running kernel? First I looked back at what I d done in the past with fixing vulnerabilities with systemtap. This ends up being a rather heavy-duty way to go about things, since you need all the distro kernel debug symbols, etc. It does work, but has a significant problem: since it uses kprobes, a root user can just turn off the probes, reverting the changes. So that s not going to work. Next I looked at ksplice. The original upstream has gone away, but there is still some work being done by Jiri Slaby. However, even with his updates which fixed various build problems, there were still more, even when building a 3.2 kernel (Ubuntu 12.04 LTS). So that s out too, which is too bad, since ksplice does exactly what I want: modifies the running kernel s functions via a module. So, finally, I decided to just do it by hand, and wrote a friendly kernel rootkit. Instead of dealing with flipping page table permissions on the normally-unwritable kernel code memory, I borrowed from PaX s KERNEXEC feature, and just turn off write protect checking on the CPU briefly to make the changes. The return values for functions on x86_64 are stored in RAX, so I just need to stuff the kexec_load syscall with mov -1, %rax; ret (-1 is EPERM):

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
static unsigned long long_target;
static char *target;
module_param_named(syscall, long_target, ulong, 0644);
MODULE_PARM_DESC(syscall, "Address of syscall");
/* mov $-1, %rax; ret */
unsigned const char bytes[] =   0x48, 0xc7, 0xc0, 0xff, 0xff, 0xff, 0xff,
                                0xc3  ;
unsigned char *orig;
/* Borrowed from PaX KERNEXEC */
static inline void disable_wp(void)
 
        unsigned long cr0;
        preempt_disable();
        barrier();
        cr0 = read_cr0();
        cr0 &= ~X86_CR0_WP;
        write_cr0(cr0);
 
static inline void enable_wp(void)
 
        unsigned long cr0;
        cr0 = read_cr0();
        cr0  = X86_CR0_WP;
        write_cr0(cr0);
        barrier();
        preempt_enable_no_resched();
 
static int __init syscall_eperm_init(void)
 
        int i;
        target = (char *)long_target;
        if (target == NULL)
                return -EINVAL;
        /* save original */
        orig = kmalloc(sizeof(bytes), GFP_KERNEL);
        if (!orig)
                return -ENOMEM;
        for (i = 0; i < sizeof(bytes); i++)  
                orig[i] = target[i];
         
        pr_info("writing %lu bytes at %p\n", sizeof(bytes), target);
        disable_wp();
        for (i = 0; i < sizeof(bytes); i++)  
                target[i] = bytes[i];
         
        enable_wp();
        return 0;
 
module_init(syscall_eperm_init);
static void __exit syscall_eperm_exit(void)
 
        int i;
        pr_info("restoring %lu bytes at %p\n", sizeof(bytes), target);
        disable_wp();
        for (i = 0; i < sizeof(bytes); i++)  
                target[i] = orig[i];
         
        enable_wp();
        kfree(orig);
 
module_exit(syscall_eperm_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Kees Cook <kees@outflux.net>");
MODULE_DESCRIPTION("makes target syscall always return EPERM");

If I didn t want to leave an obvious indication that the kernel had been manipulated, the module could be changed to:

• not announce what it s doing
• remove the exit route to not restore the changes on module unload
• error out at the end of the init function instead of staying resident

And with this in place, it s just a matter of loading it with the address of sys_kexec_load (found via /proc/kallsyms) before I disable module loading via modprobe. Here s my upstart script:

# modules-disable - disable modules after rc scripts are done
#
description "disable loading modules"
start on stopped module-init-tools and stopped rc
task
script
        cd /root/modules/syscall_eperm
        make clean
        make
        insmod ./syscall_eperm.ko \
                syscall=0x$(egrep ' T sys_kexec_load$' /proc/kallsyms   cut -d" " -f1)
        modprobe disable
end script

And now I m safe from kexec before I have a kernel that contains /proc/sys/kernel/kexec_disabled.

2013, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.

A new Armadillo release 3.930 came out a few days ago, with a very nice set of changes (see below). I rolled this into RcppArmadillo 0.3.930.0. However, one of these changes revealed that R shipped only the standard SVD for complex-valued matrices, and not the more performant divide-and-conquer approach. So in R builds using the default built-in Lapack, at least one CRAN package no longer built. After some back and forth, Conrad put some branching in the library to fall back to the standard SVD, and I added a built-time configuration test for an appropriate preprocessor directive used by the fallback code. This is now on which is now on CRAN and in Debian as RcppArmadillorelease 0.3.930.1, and Conrad will probably update the Armadillo page as well (though the fix is only needed with R's builtin Rlapack). Also of note is that R Core already added the missing Fortran routine zgesdd to R 3.1.0 (aka "R-devel") so this issue goes away with the next release. Also of note, I wrote up a short Rcpp Gallery post illustrating the performance gains available from divide-and-conquer SVD. The complete list of changes is below.

Changes in RcppArmadillo version 0.3.930.1 (2013-12-09)

• Upgraded to Armadillo release Version 3.930.1
  • Armadillo falls back to standard complex svd if the more performant divide-and-conquer variant is unavailable
• Added detection for Lapack library and distinguish between R's own version (withhout zgesdd) and system Lapack; a preprocessor define is set accordingly

Changes in RcppArmadillo version 0.3.930.0 (2013-12-06)

• Upgraded to Armadillo release Version 3.930 ("Dragon's Back")
  • added divide-and-conquer variant of svd_econ(), for faster SVD
  • added divide-and-conquer variant of pinv(), for faster pseudo-inverse
  • added element-wise variants of min() and max()
  • added size() based specifications of submatrix view sizes
  • added randi() for generating matrices with random integer values
  • added more intuitive specification of sort direction in sort() and sort_index()
  • added more intuitive specification of method in det(), .i(), inv() and solve()
  • added more precise timer for the wall_clock class when using C++11
• New unit tests for complex matrices and vectors

Courtesy of CRANberries, there is also a diffstat report for the most recent release As always, more detailed information is on the RcppArmadillo page. Questions, comments etc should go to the rcpp-devel mailing list off the R-Forge page.

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. Please report excessive re-aggregation in third-party for-profit settings.

krb5-sync is the software we run at Stanford to synchronize principal information from a central Heimdal realm to Active Directory, allowing users to use either a Linux-based Kerberos environment or Active Directory with the same account and password. The original intent of this release was to add a new feature to allow a subsidiary instance of an account in the MIT or Heimdal realm to be synchronized with the instance-less account in Active Directory. This allows, for example, an rra/windows instance to be used to set and maintain the password for an rra principal in Active Directory. In the process of implementing that, though, I ended up doing a significant overall of the code, since the plugin architecture was quite awkward and dated. The code now uses the MIT Kerberos data structures in a more natural and native way, since MIT Kerberos has now added direct support for plugins of this sort. Kerberos contexts and Kerberos error codes are used uniformly throughout the plugin, which provides consistent and more robust error handling and reporting. I also significantly enhanced the test suite, although it still needs more work to test the core functionality that has complex external dependencies. This release also drops support for all versions of MIT Kerberos prior to 1.9, which required an external patch; to run krb5-sync 3.0, you should upgrade to a recent version of MIT Kerberos. This allowed me to drop support for the legacy API. There are a couple of major backward-incompatible changes in this release (and both unfortunately are not handled automatically by the Debian package upgrade, since it's hard to find and safely modify KDC configuration). First, the ad_ldap_base configuration option is now mandatory when synchronizing account status and its meaning has changed. Previously, dc elements for the realm were appended to a provided partial base. Now, the complete DN of the root of the Active Directory tree should be provided. This is more flexible and more useful with a wider variety of Active Directory setups. Second, I took advantage of the backward-incompatibilities to change the module name to sync.so from krb5_sync.so, since the latter sounded weirdly redundant and verbose when installed in the Kerberos plugin directory. This will require a configuration change to the plugin configuration for the KDC or kadmin server. Also in this release are a couple of new options: ad_queue_only, which forces all changes to be queued for later processing instead of processed in real time, and syslog, which can be used to turn off the internal syslog logging of non-errors from the module. (This is mostly useful for test suites.) Now, password changes are queued on any Active Directory failure, not just a few oddly-distinguished ones. The previous behavior was rather specific to Stanford's needs, and queuing all password changes shouldn't pose any problems. Finally, the krb5-sync-backend utility program for manipulating the queued changes has been completely rewritten and is much cleaner. It now uses the Net::Remctl::Backend Perl module for command and option handling, so that module (provided with remctl 3.4 or later) must be installed. It also requires IPC::Run, which is available from CPAN. It uniformly supports a -d option to specify the queue location, and skips event files during processing that no longer exist. You can get the latest release from krb5-sync distribution page.

Once more, I m going to FOSDEM 2014, the largest Free/Libre/Open Source Software event in Europe (5,000 attendants every year). As usual, I will be in charge of the Desktops DevRoom, together with our friends from Gnome (Christophe Fergeau), Unity (Didier Roche), Enlightenment (Philippe Caseiro) and others. See you in Brussels 1-2 February 2014! BTW, have you already submitted your talk proposal for the Desktops DevRoom? The deadline (15th December) is very close! Do not wait any more!!! See the details here: FOSDEM 2014 Desktops DevRoom Call for Talks

I ve come up with some new favorites this season. The boys and Laura were around for all three, and I am happy to report there were many kitchen smiles over these! From-Scratch Hot Chocolate There s something about hot chocolate made from scratch, with chocolate melted into milk, instead of a powder stirred in. It takes quite a bit more time, and probably has more calories, but it is quite delicious. The key to a delicious result where milk is concerned is to take things slow and keep stirring. You don t want the chocolate to scorch at the bottom of the pan. Heating up the milk before the chocolate should help things mix in more easily as well.

• Begin with 3 cups milk and 1 cup heavy whipping cream. Heat slowly over moderate to low heat, stirring periodically. Once you see bubbles start to form around the edges, it is plenty hot (or even a bit more hot than it needs to be).
• Add one cup of semisweet chocolate chips, 1 teaspoon sugar, and 1/2 tsp vanilla extract.
• Stir constantly until all the chocolate is melted and well mixed. There will still be some small bits of chocolate within, but if it is all done slowly like this, the chocolate should be pretty well melted.

The basis for this recipe was here, and it called for 2 cups milk and 2 cups half-and-half. I trust my heavy whipping cream was fine! <grin> There are also some other variations on that site. This nearly made my little cast iron kettle overflow, so next time I made a 3/4 recipe. Hot Spiced Cider We put up a Christmas tree yesterday, so I thought hot spiced cider would be perfect for the occasion. I went searching for recipes, and many of them called for cloves (which have to be sifted out later or put in a spice bag). I wasn t going to have time to delay two boys from setting up a Christmas tree long enough for that, so I found this basic recipe to work well. However, I, as usual, made some modifications ;-)

• Warm 4 cups apple cider (not juice, as the recipe suggests) in a pot.
• Add 1/2 tsp cinnamon
• Add 1/4 tsp nutmeg or allspice (I used allspice because I was mysteriously out of nutmeg, but will probably use nutmeg next time)
• Add 1 tbsp brown sugar
• Stir constantly until sufficiently dissolved. Pour immediately before drinking, as the contents will tend to separate.

Mmmmm . yum . Turkey or Chicken Noodle Soup The annual what to do with all that leftover turkey quest strikes again. I like chicken noodle soup, so why not a turkey noodle soup done the same way? Here s what I used, roughly, in my large 6-quart cast iron cooking pot (aka Dutch oven ):

• 9 cups chicken/turkey broth. Your own if you have it, or the canned variety works. Or make your own with boullion if you have it.
• 2 chopped yellow onions. (I added half a chopped red onion as well because I had it sitting around. Nobody complained, but 2.5 onions was a little much.)
• 4 tsp fresh basil or 1 tsp dried basil
• 4 tsp fresh oregano or 1 tsp dried oregano
• 1/2 tsp pepper
• 1/2 tsp salt
• 1 tsp beef bouillon
• 2 bay leaves
• 20 oz frozen mixed vegetables (I d probably add more than that next year; this wasn t quite enough)
• Plenty of wide egg noodles. The recipe I used called for 1 cup, which was laughably inadequate. I just dumped until it looked right, and then the package was almost empty so I dumped the rest in too.
• 4 cups cooked turkey or chicken, cubed (a kitchen scissors makes quick work of that)
• Two 14.5-oz cans diced tomatoes (do not drain)

Start with the broth, onion, basil, oregano, pepper, and bay leaf. Heat up the mixture and add the vegetables. Bring it to boiling, then add the uncooked noodles. Return to boiling, then reduce heat, cover, and simmer for 8 minutes. Add the turkey or chicken and diced tomatoes, and simmer until hot enough to serve. The nice thing about soups is that they freeze well and make great winter leftovers. This recipe makes quite a lot of soup; you may wish to halve it. This recipe was adapted from one in a Better Homes & Gardens cookbook.

There has been a lot of discussion recently about the concept of a Basic Income (Wikipedia), largely due to the efforts to change the Swiss constitution to provide a Basic Income [1]. The concept of a Basic Income is that residents get a fixed payment without having to be sick, disabled, looking for work, or eligible for other forms of social security. A Basic Income wouldn t replace all other forms of social security, one of the most obvious examples is that sick people will often need money for medical care in additional to living expenses. Also I believe that it shouldn t be means tested in any way. I think that one of the problems with current payment schemes is that there are complex eligibility criteria which require effort for the applicant and for government agencies to prevent accidental or fraudulent over-payment. The tax rates could be raised slightly to make it revenue neutral. Newstart In Australia the main form of social security for unemployed people at the moment is called Newstart [2]. Currently Newstart payments range from a maximum of $501 per fortnight for a single person ($13,026 per annum), to a maximum of $699.90 per fortnight for someone who is a carer. The Newstart payments start to decrease if the recipient earns more than $62 per fortnight. The minimum wage in Australia is $16.37 per hour for permanent work or $20.30 for casual work [3]. So if someone works for more than 3 hours at a casual rate (and I can t imagine 4 hours a fortnight being anything other than casual) then their Newstart payments will decrease. The payment decreases are fairly significant, for every dollar that is earned about 50 cents will be deducted from the payments. That s a great incentive to either avoid opportunities to do part-time work or to do cash-only work that s outside the tax system. The most obvious way of implementing a Basic Income would be to replace Newstart. Then anyone who is in that situation would be free to just not get a job which would be OK IMHO as people who don t want to work probably wouldn t do a good job if the government forced them to get a job. People who are unemployed who want to work could work as much as they want and scale up according to what their employer asks and how much money they need. Currently the full-time minimum wage is $622.20 per week (I m not sure exactly how they get that from $16.37). That s almost 2.5* the Newstart allowance for a single person (but less than twice the Newstart allowance for a carer). While Newstart (and the other forms of social security) don t provide a great income, it seems that the difference between Newstart and the minimum wage isn t that great particularly when you consider that working involves some expenses for travel etc. There doesn t seem to be a great financial incentive for someone to leave Newstart and get a minimum wage job. People Who Want Social Security Some people think it s great to get government payments while others find it embarrassing to need such payments and won t necessarily apply if they are eligible. I think that the current system of forcing people to apply for social security is a way of discouraging people who find themselves unexpectedly in a difficult situation but doesn t discourage people who are happy not to work. This seems to effectively reduce the incidence of payments to the people who most tax-payers would regard as the most worthy recipients. Economics Charles Stross wrote about some ideas related to this [4]. He suggests that as the workforce participation has been steadily reducing due to technology we should move to a social model that isn t based around working to live but working to buy luxuries that aren t covered by the Basic Income. One of the many economic changes related to a Basic Income is that the minimum wage could be smaller than it might otherwise be. For example if the minimum wage was decreased by the same amount that the Basic Income provided then the minimum income would remain the same while employers would pay less, this would affect the viability of certain types of contract work web sites if they were subject to minimum wage laws (currently they just ignore the minimum wage laws by paying based on job completion instead of hours worked). I don t think that the minimum wage should decrease that much though, currently employers are able to run viable businesses with the minimum wage laws and I don t think that a Basic Income should be used as a way of helping corporations avoid paying their employees. If we had a Basic Income then there s many ways that it could be used to stabilise the economy. If people could pay their rent even if they lost their job then a down-turn in one area of the economy wouldn t immediately affect other areas. Also if rent payments were deducted automatically from an account used to receive the Basic Income then landlords would be more likely to rent to poor people as they could be guaranteed to receive rent payments (it would be easy to have a contractual agreement for rent to take priority and have bank computers enforce that). The Implementation Problem I don t think that my idea would have any significant negative effects. It wouldn t decrease government revenues if tax was adjusted accordingly. It wouldn t make people stop working as people who don t want to work already avoid it. It would help people who are out of work to get work by reducing the barriers to entry in terms of paperwork and of unreasonable cuts to Newstart making it bad value to take part time work. I think that the big problem with implementing it is people who want to prevent poor people from having opportunities. They want to reduce social security and minimum wages even though such changes will in the long run only give less tax revenue and greater expense in law enforcement. It seems rather ironic that such hostility often comes from people at the low end of the middle class whos jobs are most likely to be at risk from new technology. As on-going technological development reduces the number of workers that are required to keep things running we need to have some form of payment to the people who aren t doing enough work to survive. A decent Basic Income is a much better option than giving Newstart payments and forcing a significant portion of the population into a degrading search for jobs that don t exist. As that s the inevitable future I think we should make political changes to deal with it sooner rather than later. However a Basic Income might be implemented now it s surely going to be a lot better than what might happen if we wait until the majority of the population are unemployed before doing something about it.

• [1] http://tinyurl.com/mwemen5
  
• [2] http://www.humanservices.gov.au/customer/services/centrelink/newstart-allowance
• [3] http://www.fairwork.gov.au/PAY/NATIONAL-MINIMUM-WAGE/pages/default.aspx
• [4] http://tinyurl.com/mjq3dwl

I previously wrote about the financial value of a university degree [1], my general conclusion is that the value is decreasing for most fields of employment that don t have a legal requirement for a degree. In the past I wrote about some ideas for a home university [2], basically extending the home-schooling concept to a university level. I recently read John Scalzi s post about being poor [3], many of the comments address the difficulty of getting to college and how it impacts career possibilities. From reading that it seems that my ideas about a home university are mostly based around what middle-class people can afford. Also getting a job afterwards will probably be a lot easier for someone who was born into the middle classes. It seems to me that a large part of the problem with the university system is the expectation that they will both provide for academic research and train people for jobs. Dr. David Helfand has some great ideas for running a university to give the higher education that a university is supposed to provide rather than the work training that most universities actually provide [4]. His ideas aren t theoretical, they have been implemented and proven to work. Note that Dr Helfand s talk starts slowly, the second half is the best (for those of you with short attention spans). The fact that most people think of a university degree in terms of getting a job seems to be a failure of the university system to fulfill it s original aim. If Dr Helfand s ideas take off then it would really address the problem of universities not educating people. But that still leaves the issue of job training. Is a Degree Mandatory? I think that to some degree people expect that a university degree is necessary job training even when it isn t. I wonder what would happen if it was generally agreed that the right thing to do was to search for a job between the end of high school and the start of university, then anyone who got a suitable offer could defer their university course and see what career success they could achieve without it. When I was at school the general idea was that after completing year 12 everyone just had a holiday until the start of university as the entire point of school was to get into university. While hiring managers prefer candidates who have degrees they also prefer to hire people who will accept a lower salary, so hiring an 18yo with no degree may give better value than a 21yo who has a degree. I believe that making university degrees more accessible has reduced inequality which is a good thing. But making degrees mandatory (which is widely believed by high school students and thus is the situation that they have to deal with) contributes to greater inequality. While university doesn t cost much by middle-class standards it is still expensive for poor people. If a university degree wasn t considered to be mandatory then the number of people employed to teach at a university level would be smaller. This would hopefully mean that the average skill of university lecturers would increase (I hope that the least skillful lecturers would be the ones to find work elsewhere).

• [1] http://etbe.coker.com.au/2012/06/14/financial-value-degree/
• [2] http://etbe.coker.com.au/2007/10/04/ideas-for-a-home-university/
• [3] http://whatever.scalzi.com/2005/09/03/being-poor/
• [4] http://tedxtalks.ted.com/video/Designing-a-university-for-the

The recent news that openSUSE considers btrfs safe for users prompted me to consider using it. And indeed I did. I was already familiar with zfs, so considered this a good opportunity to experiment with btrfs. btrfs makes an intriguing filesystem for all sorts of workloads. The benefits of btrfs and zfs are well-documented elsewhere. There are a number of features btrfs has that zfs lacks. For instance:

• The ability to shrink a device that s a member of a filesystem/pool
• The ability to remove a device from a filesystem/pool entirely, assuming enough free space exists elsewhere for its data to be moved over.
• Asynchronous deduplication that imposes neither a synchronous performance hit nor a heavy RAM burden
• Copy-on-write copies down to the individual file level with cp --reflink
• Live conversion of data between different profiles (single, dup, RAID0, RAID1, etc)
• Live conversion between on-the-fly compression methods, including none at all
• Numerous SSD optimizations, including alignment and both synchronous and asynchronous TRIM options
• Proper integration with the VM subsystem
• Proper support across the many Linux architectures, including 32-bit ones (zfs is currently only flagged stable on amd64)
• Does not require excessive amounts of RAM

The feature set of ZFS that btrfs lacks is well-documented elsewhere, but there are a few odd btrfs missteps:

• There is no way to see how much space subvolume/filesystem is using without turning on quotas. Even then, it is cumbersome and not reported with df like it should be.
• When a maxmium size for a subvolume is set via a quota, it is not reported via df; applications have no idea when they are about to hit the maximum size of a filesystem.

btrfs would be fine if it worked reliably. I should say at the outset that I have never lost any data due to it, but it has caused enough kernel panics that I ve lost count. I several times had a file that produced a panic when I tried to delete it, several times when it took more than 12 hours to unmount a btrfs filesystem, behaviors where hardlink-heavy workloads take days longer to complete than on zfs or ext4, and that s just the ones I wrote about. I tried to use btrfs balance to change the metadata allocation on the filesystem, and never did get it to complete; it seemed to go into an endless I/O pattern after the first 1GB of metadata and never got past that. I didn t bother trying the live migration of data from one disk to another on this filesystem. I wanted btrfs to work. I really, really did. But I just can t see it working. I tried it on my laptop, but had to turn of CoW on my virtual machine s disk because of the rm bug. I tried it on my backup devices, but it was unusable there due to being so slow. (Also, the hardlink behavior is broken by default and requires btrfstune -r. Yipe.) At this point, I don t think it is really all that worth bothering with. I think the SuSE decision is misguided and ill-informed. btrfs will be an awesome filesystem. I am quite sure it will, and will in time probably displace zfs as the most advanced filesystem out there. But that time is not yet here. In the meantime, I m going to build a Debian Live Rescue CD with zfsonlinux on it. Because I don t ever set up a system I can t repair.

(Yes, yes... Maybe I should post in Spanish.. But hey, gotta keep consistecy in my blog!) General, public, open invitation Are you in Mexico City, or do you plan to be next Wednesday (December 11)? Are you interested in video edition? In Free Software? I will have the pleasure to host at home the great Chema Serralde, a good friend, and a multifacetic guru both in the technical and musical areas. He will present a workshop: Video editing from the command line. I asked Chema for an outline of his talk, but given he is a busy guy, I will basically translate the introduction he prepared for this same material in FSL Vallarta, held two weeks ago.

With the help of the commandline, you can become a multimedia guru. We will edit a video using just a terminal. This skill will surprise your friends and your couple. But the most important is that this knowledge is just an excuse to understand step by step what does a video CODEC mean, what is a FORMAT, and how video and audio editors work; by using this knowledge, you will be able to set the basis for multimedia editing, without the promises and secrets of propietary editors. How much does my file weigh and why? How to improve a video file's quality? Why cannot I read my camera's information from GNU/Linux? By the end of this workshop, we well see how some libraries help you develop your first audio and video application, what are their main APIs and uses.

Logistics Everybody is welcome to come for free, no questions asked, no fees collected. I can offer coffee for all, but if you want anything else to eat/drink, you are welcome to bring it. We do require you to reserve and confirm your place (mail me to my usual mail address). We have limited space, and I must set an absolute quota of 10 participants. Some people hide their address... Mine is quite publicly known: Av. Copilco 233, just by Parque Hugo Margain, on the Northern edge of UNAM (Metro Copilco). The course starts at 16:00, and lasts... As long as we make it last ;-) So, that said... See you there! :-D [update]: Chema sent me the list of topics he plans to cover. Copy/pasting from his mail, in Spanish:

TALLER REL MPAGO DE EDICI N AUDIOVISUAL EN L NEA DE COMANDO
Jos Mar a Serralde Ruiz, facilitador

1. Editando como cavern cola.
   1. Manipulaci n b sica de archivos multimedia en entornos POSIX.
   2. S un Bash VJ (videojockey)
   3. Vaciando y entubando
2. Editando como cient fico.
   1. Encabezados y fourcc
   2. 3 familias de CODECS de v deo y sus patentes
   3. 3 famlias de CODECS de audio y sus patentes
   4. Muxers, demuxers y muxes.
3. Editando como artista.
   1. Cajas de herramientas en software libre para procesamiento de v deo.
   2. Procesamiento en tiempo real de v deo (el que se crea artista pierde)
   3. Derritiendo v deo, audio con calcetines MELT + SOX

Software necesario (sistemas operativos POSIX, windouseros acercarse con el af n de repensar sus vidas): mplayer, avconv/ffmpeg (libavcodec), melt, sox, imagemagick

This Monday, I attended a workshop on Multi-party Off the Record Messaging and Deniability hosted by the Calyx Institute. The discussion was a combination of legal and technical people, looking at how the characteristics of this particular technology affect (or do not affect) the law. This is a report-back, since I know other people wanted to attend. I'm not a lawyer, but I develop software to improve communications security, I care about these questions, and I want other people to be aware of the discussion. I hope I did not misrepresent anything below. I'd be happy if anyone wants to offer corrections. BackgroundOff the Record Messaging (OTR) is a way to secure instant messaging (e.g. jabber/XMPP, gChat, AIM). The two most common characteristics people want from a secure instant messaging program are:

Authentication

Each participant should be able to know specifically who the other parties are on the chat.

Confidentiality

The content of the messages should only be intelligible to the parties involved with the chat; it should appear opaque or encrypted to anyone else listening in. Note that confidentiality effectively depends on authentication -- if you don't know who you're talking to, you can't make sensible assertions about confidentiality.

As with many other modern networked encryption schemes, OTR relies on each user maintaining a long-lived "secret key", and publishing a corresponding "public key" for their peers to examine. These keys are critical for providing authentication (and by extension, for confidentiality). But OTR offers several interesting characteristics beyond the common two. Its most commonly cited characteristics are "forward secrecy" and "deniability".

Forward secrecy

Assuming the parties communicating are operating in good faith, forward secrecy offers protection against a special kind of adversary: one who logs the encrypted chat, and subsequently steals either party's long-term secret key. Without forward secrecy, such an adversary would be able to discover the content of the messages, violating the confidentiality characteristic. With forward secrecy, this adversary is be stymied and the messages remain confidential.

Deniability

Deniability only comes into play when one of the parties is no longer operating in good faith (e.g. their computer is compromised, or they are collaborating with an adversary). In this context, if Alice is chatting with Bob, she does not want Bob to be able to cryptographically prove to anyone else that she made any of the specific statements in the conversation. This is the focus of Monday's discussion. To be clear, this kind of deniability means Alice can correctly say "you have no cryptographic proof I said X", but it does not let her assert "here is cryptographic proof that I did not say X" (I can't think of any protocol that offers the latter assertion). The opposite of deniability is a cryptographic proof of origin, which usually runs something like "only someone with access to Alice's secret key could have said X."

The traditional two-party OTR protocol has offered both forward secrecy and deniability for years. But deniability in particular is a challenging characteristic to provide for group chat which is the domain of Multi-Party OTR (mpOTR). You can read some past discussion about the challenges of deniability in mpOTR (and why it's harder when there are more than two people chatting) from the otr-users mailing list. If you're not doing anything wrong... The discussion was well-anchored by a comment from another participant who cheekily asked "If you're not doing anything wrong, why do you need to hide your chat at all, let alone be able to deny it?" The general sense of the room was that we'd all heard this question many times, from many people. There are lots of problems with the ideas behind the question from many perspectives. But just from a legal perspective, there are at least two problems with the way this question is posed:

• laws themselves are not always just (e.g. consider chat communications between an interracial couple in the USA before 1967, if instant messaging had existed at the time), and
• law enforcement (or a legal adversary in civil litigation) may have a different understanding or interpretation of the law than you do (e.g. consider chat communications between a corporate or government whistleblower and a journalist).

In these situations, people confront real risk from the law. If we care about these people, we need to figure out if we can build systems to help them reduce that legal risk (of course we also need to fix broken laws, and the legal environment in general, but those approaches were out of scope for this discussion). The Legal Utility of Deniability Monday's meeting was called specifically because it wasn't clear how much real-world usefulness there is in the "deniability" characteristic, and whether this feature is worth the development effort and implementation tradeoffs required. In particular, the group was interested in deniability's utility in legal contexts; many (most?) people in the room were lawyers, and it's also not clear that deniability has much utility outside of a formal legal setting. If your adversary isn't constrained by some rule of law, they probably won't care at all whether there is a cryptographic proof or not that you wrote a particular message (In retrospect, one possible exception is exposure in the media, but we did not discuss that scenario). Places of possible usefulness So where might deniability come in handy during civil litigation or a criminal trial? Presumably the circumstance is that a piece of a chat log is offered as incriminating evidence, and the defendant is trying to deny something that they appear to have said in the log. This denial could take place in two rather different contexts: during rules over admissibility of evidence, or (once admitted) in front of a jury. In legal wrangling over admissibility, apparently a lot of horse-trading can go on -- each side concedes some things in exchange for the other side conceding other things. It appears that cryptographic proof of origin (that is, a lack of deniability) on the chat logs themselves might reduce the amount of leverage a defense lawyer can get from conceding or arguing strongly over that piece of evidence. For example, if the chain of custody of a chat transcript is fuzzy (i.e. the transcript could have been mishandled or modified somehow before reaching trial), then a cryptographic proof of origin would make it much harder for the defense to contest the chat transcript on the grounds of tampering. Deniability would give the defense more bargaining power. In arguing about already-admitted evidence before a jury, deniability in this sense seems like a job for expert witnesses, who would need to convince the jury of their interpretation of the data. There was a lot of skepticism in the room over this, both around the possibility of most jurors really understanding what OTR's claim of deniability actually means, and on jurors' ability to distinguish this argument from a bogus argument presented by an opposing expert witness who is willing to lie about the nature of the protocol (or who misunderstands it and passes on their misunderstanding to the jury). The complexity of the tech systems involved in a data-heavy prosecution or civil litigation are themselves opportunities for lawyers to argue (and experts to weigh in) on the general reliability of these systems. Sifting through the quantities of data available and ensuring that the appropriate evidence is actually findable, relevant, and suitably preserved for the jury's inspection is a hard and complicated job, with room for error. OTR's deniability might be one more element in a multi-pronged attack on these data systems. These are the most compelling arguments for the legal utility of deniability that I took away from the discussion. I confess that they don't seem particularly strong to me, though some level of "avoiding a weaker position when horse-trading" resonates with me. What about the arguments against its utility? Limitations The most basic argument against OTR's deniability is that courts don't care about cryptographic proof for digital evidence. People are convicted or lose civil cases based on unsigned electronic communications (e.g. normal e-mail, plain chat logs) all the time. OTR's deniability doesn't provide any legal cover stronger than trying to claim you didn't write a given e-mail that appears to have originated from your account. As someone who understands the forgeability of e-mail, i find this overall situation troubling, but it seems to be where we are. Worse, OTR's deniability doesn't cover whether you had a conversation, just what you said in that conversation. That is, Bob can still cryptographically prove to an adversary (or before a judge or jury) that he had a communication with someone controlling Alice's secret key (which is probably Alice); he just can't prove that Alice herself said any particular part of the conversation he produces. Additionally, there are runtime tradeoffs depending on how the protocol manages to achieve these features. For example, forward secrecy itself requires an additional round trip or two when compared to authenticated, encrypted communications without forward secrecy (a "round trip" is a message from Alice to Bob followed by a message back from Bob to Alice). Getting proper deniability into the mpOTR spec might incur extra latency (imagine having to wait 60 seconds after everyone joins before starting a group chat, or a pause in the chat of 15 seconds when a new member joins) or extra computational power (meaning that they might not work well on slower/older devices) or an order of magnitude more bandwidth (meaning that chat might not work at all on a weak connection). There could also simply be complexity that makes it harder to correctly implement a protocol with deniability than an alternate protocol without deniability. Incorrectly-implemented software can put its users at risk. I don't know enough about the current state of mpOTR to know what the specific tradeoffs are for the deniability feature, but it's clear there will be some. Who decides whether the tradeoffs are worth the feature? Other kinds of deniability Further weakening the case for the legal utility of OTR's deniability, there seem to be other ways to get deniability in a legal context over a chat transcript. There are deniability arguments that can be made from outside the protocol. For example, you can always claim someone else took control of your computer while you were asleep or using the bathroom or eating dinner, or you can claim that your computer had a virus that exported your secret key and it must have been used by someone else. If you're desperate enough to sacrifice your digital identity, you could arrange to have your secret key published, at which point anyone can make signed statements with it. Having forward secrecy makes it possible to expose your secret key without exposing the content of your past communications to any listener who happened to log them. Conclusion My takeaway from the discussion is that the legal utility of OTR's deniability is non-zero, but quite low; and that development energy focused on deniability is probably only justified if there are very few costs associated with it. Several folks pointed out that most communications-security tools are too complicated or inconvenient to use for normal people. If we have limited development energy to spend on securing instant messaging, usability and ubiquity would be a better focus than this form of deniability. Secure chat systems that take too long to make, that are too complex, or that are too cumbersome are not going to be adopted. But this doesn't mean people won't chat at all -- they'll just use cleartext chat, or maybe they'll use supposedly "secure" protocols with even worse properties: for example, without proper end-to-end authentication (permitting spoofing or impersonation by the server operator or potentially by anyone else); with encryption that is reversible by the chatroom operator or flawed enough to be reversed by any listener with a powerful computer; without forward secrecy; or so on. As a demonstration of this, we heard some lawyers in the room admit to using Skype to talk with their clients even though they know it's not a safe communications channel because their clients' adversaries might have access to the skype messaging system itself. My conclusion from the meeting is that there are a few particular situations where deniability could be useful legally, but that overall, it is not where we as a community should be spending our development energy. Perhaps in some future world where all communications are already authenticated, encrypted, and forward-secret by default, we can look into improving our protocols to provide this characteristic, but for now, we really need to work on usability, popularization, and wide deployment. Thanks Many thanks to Nick Merrill for organizing the discussion, to Shayana Kadidal and Stanley Cohen for providing a wealth of legal insight and legal experience, to Tom Ritter for an excellent presentation of the technical details, and to everyone in the group who participated in the interesting and lively discussion. Tags: chat, deniability, otr, security

Today I should have been heading down to York, to attend the Bytemark Christmas party. Instead I'm here in Edinburgh, because wind/storms basically shutdown the rail network in Scotland for the morning. Technically I could have probably made it, but only belatedly and only at a huge cost to my sanity. The train-station was insane with stranded people, and there seemed no guarantee the recently-revived service would continue. So instead I'm sulking at home. I had a lot of other things scheduled to do in York/London today/tomorrow, for reasons that will become apparent next week, so to say I'm annoyed is an understatement. In happier news I'm not dead.

Walking to work this morning was horrific, there was so much wind 70-100mph, that I counldn't actually cross a bridge, on Ocean Drive, because I just kept getting blown into the road. (Yeah, that's a road that is very close to the coast. Driving wind. Horrible rain. Storming sea. Fun.)

I ended up retracing my steps, and taking a detour. (PS. My boots leaked.) Not a good day. Enjoy some software instead - a trivial HTTP / XMPP bridge.

Whatever you do with translations, consider translation management issues. For example, you are developing a multilingual web site. All kinds of labels and buttons and form fields are nicely translatable with trans template tag and ugettext. You have po files that follow your code from dev to stage to production environment.
Now you add a CMS into the mix. And suddenly - you translations are in more than one place, in more than one format and follow different routes to production.
Now imagine that you need to add Chinese language to your entire site. The translator is an off-site contractor. What files would you send to him to translate? How would you generate them? How will you integrate them?
If someone adds or changes a page on production in English: how will your developers see that change? how will you know that an updated translation for Chinese is needed? how will you manage the update of the translation?
If you make a CMS and don't have at least the export_po_file and import_po_file management commands, then you are not really multilingual. It is either that or figuring out your own answer for the above questions.
I have finally found a Django-based CMS that has those - http://pythonhosted.org/django-page-cms/ . Have not really tried it yet, but I am hopeful.