Packaging for the Yubikey NEO, a frustrating adventure

I have already posted a howto on how to set up the YubiKey NEO and YubiKey NEO-n for U2F, and I promised I would write a bit more on the adventure to get the software packaged in Gentoo.

You have to realize at first that my relationship with Yubico has not always being straightforward. I have at least once decided against working on the Yubico set of libraries in Gentoo because I could not get a hold of a device as I wanted to use it. But luckily now I was able to place an order with them (for some two thousands euro) and I have my devices.

But Yubico’s code is usually quite well written, and designed to be packaged much more easily than most other device-specific middleware, so I cannot complain too much. Indeed, they split and release separately different libraries with different goals, so that you don’t need to wait for enough magnitude to be pulled for them to make a new release. They also actively maintain their code in GitHub, and then push proper make dist releases on their website. They are in many ways a packager’s dream company.

But let’s get back to the devices themselves. The NEO and NEO-n come with three different interfaces: OTP (old-style YubiKey, just much longer keys), CCID (Smartcard interface) and U2F. By default the devices are configured as OTP only, which I find a bit strange to be honest. It is also the case that at the moment you cannot enable both U2F and OTP modes, I assume because there is a conflict on how the “touch” interaction behaves, indeed there is a touch-based interaction on the CCID mode that gets entirely disabled once enabling either of U2F or OTP, but the two can’t share.

What is not obvious from the website is that to enable U2F (or CCID) modes, you need to use yubikey-neo-manager, an open-source app that can reconfigure the basics of the Yubico device. So I had to package the app for Gentoo of course, together with its dependencies, which turned out to be two libraries (okay actually three, but the third one sys-auth/ykpers was already packaged in Gentoo — and actually originally committed by me with Brant proxy-maintaining it, the world is small, sometimes). It was not too bad but there were a few things that might be worth noting down.

First of all, I had to deal with dev-libs/hidapi that allows programmatic access to raw HID USB devices: the ebuild failed for me, both because it was not depending on udev, and because it was unable to find the libusb headers — turned out to be caused by bashisms in the configure.ac file, which became obvious as I moved to dash. I have now fixed the ebuild and sent a pull request upstream.

This was the only real hard part at first, since the rest of the ebuilds, for app-crypt/libykneomgr and app-crypt/yubikey-neo-manager were mostly straightforward — only I had to figure out how to install a Python package as I never did so before. It’s actually fun how distutils will error out with a violation of install paths if easy_install tries to bring in a non-installed package such as nose, way before the Portage sandbox triggers.

The problems started when trying to use the programs, doubly so because I don’t keep a copy of the Gentoo tree on the laptop, so I wrote the ebuilds on the headless server and then tried to run them on the actual hardware. First of all, you need to have access to the devices to be able to set them up; the libu2f-host package will install udev rules to allow the plugdev group access to the hidraw devices — but it also needed a pull request to fix them. I also added an alternative version of the rules for systemd users that does not rely on the group but rather uses the ACL support (I was surprised, I essentially suggested the same approach to replace pam_console years ago!)

Unfortunately that only works once the device is already set in U2F mode, which does not work when you’re setting up the NEO for the first time, so I originally set it up using kdesu. I have since decided that the better way is to use the udev rules I posted in my howto post.

After this, I switched off OTP, and enabled U2F and CCID interfaces on the device — and I couldn’t make it stick, the manager would keep telling me that the CCID interface was disabled, even though the USB descriptor properly called it “Yubikey NEO U2F+CCID”. It took me a while to figure out that the problem was in the app-crypt/ccid driver, and indeed the change log for the latest version points out support for specifically the U2F+CCID device.

I have updated the ebuilds afterwards, not only to depend on the right version of the CCID driver – the README for libykneomgr does tell you to install pcsc-lite but not about the CCID driver you need – but also to check for the HIDRAW kernel driver, as otherwise you won’t be able to either configure or use the U2F device for non-Google domains.

Now there is one more part of the story that needs to be told, but in a different post: getting GnuPG to work with the OpenPGP applet on the NEO-n. It was not as straightforward as it could have been and it did lead to disappointment. I’ll be a good post for next week.

Setting up Yubikey NEO and U2F on Gentoo (and Linux in general)

When the Google Online Security blog announced earlier this week the general availability of Security Key, everybody at the office was thrilled, as we’ve been waiting for the day for a while. I’ve been using this for a while already, and my hope is for it to be easy enough for my mother and my sister, as well as my friends, to start using it.

While the promise is for a hassle-free second factor authenticator, it turns out it might not be as simple as originally intended, at least on Linux, at least right now.

Let’s start with the hardware, as there are four different options of hardware that you can choose from:

Yubico FIDO U2F which is a simple option only supporting the U2F protocol, no configuration needed;
Plug-up FIDO U2F which is a cheaper alternative for the same features — I have not witnessed whether it is as sturdy as the Yubico one, so I can’t vouch for it;
Yubikey NEO which provides multiple interface, including OTP (not usable together with U2F), OpenPGP and NFC;
Yubikey NEO-n the same as above, without NFC, and in a very tiny form factor designed to be left semi-permanently in a computer or laptop.

I got the NEO, but mostly to be used with LastPass – the NFC support allows you to have 2FA on the phone without having to type it back from a computer – and a NEO-n to leave installed on one of my computers. I already had a NEO from work to use as well. The NEO requires configuration, so I’ll get back at it in a moment.

The U2F devices are accessible via hidraw, a driverless access protocol for USB devices, originally intended for devices such as keyboards and mice but also leveraged by UPSes. What happen though is that you need access to the device, that the Linux kernel will make by default accessible only by root, for good reasons.

To make the device accessible to you, the user actually at the keyboard of the computer, you have to use udev rules, and those are, as always, not straightforward. My personal hacky choice is to make all the Yubico devices accessible — the main reason being that I don’t know all of the compatible USB Product IDs, as some of them are not really available to buy but come from instance from developer mode devices that I may or may not end up using.

If you’re using systemd with device ACLs (in Gentoo, that would be sys-apps/systemd with acl USE flag enabled), you can do it with a file as follows:

# /etc/udev/rules.d/90-u2f-securitykey.rules
ATTRS{idVendor}=="1050", TAG+="uaccess"
ATTRS{idVendor}=="2581", ATTRS{idProduct}=="f1d0", TAG+="uaccess"

If you’re not using systemd or ACLs, you can use the plugdev group and instead do it this way:

# /etc/udev/rules.d/90-u2f-securitykey.rules
ATTRS{idVendor}=="1050", GROUP="plugdev", MODE="0660"
ATTRS{idVendor}=="2581", ATTRS{idProduct}=="f1d0", GROUP="plugdev", MODE="0660"

-These rules do not include support for the Plug-up because I have no idea what their VID/PID pairs are, I asked Janne who got one so I can amend this later.- Edit: added the rules for the Plug-up device. Cute their use of f1d0 as device id.

Also note that there are properly less hacky solutions to get the ownership of the devices right, but I’ll leave it to the systemd devs to figure out how to include in the default ruleset.

These rules will not only allow your user to access /dev/hidraw0 but also to the /dev/bus/usb/* devices. This is intentional: Chrome (and Chromium, the open-source version works as well) use the U2F devices in two different modes: one is through a built-in extension that works with Google assets, and it accesses the low-level device as /dev/bus/usb/*, the other is through a Chrome extension which uses /dev/hidraw* and is meant to be used by all websites. The latter is the actually standardized specification and how you’re supposed to use it right now. I don’t know if the former workflow is going to be deprecated at some point, but I wouldn’t be surprised.

For those like me who bought the NEO devices, you’ll have to enable the U2F mode — while Yubico provides the linked step-by-step guide, it was not really completely correct for me on Gentoo, but it should be less complicated now: I packaged the app-crypt/yubikey-neo-manager app, which already brings in all the necessary software, including the latest version of app-crypt/ccid required to use the CCID interface on U2F-enabled NEOs. And if you already created the udev rules file as I noted above, it’ll work without you using root privileges. Just remember that if you are interested in the OpenPGP support you’ll need the pcscd service (it should auto-start with both OpenRC and systemd anyway).

I’ll recount separately the issues with packaging the software. In the mean time make sure you keep your accounts safe, and let’s all hope that more sites will start protecting your accounts with U2F — I’ll also write a separate opinion piece on why U2F is important and why it is better than OTP, this is just meant as documentation, howto set up the U2F devices on your Linux systems.

OpenSSH 6.2 adds support for two-factor authentication

OpenSSH releases are always interesting, they never go without at least introducing one feature that makes ~~paranoid~~ security conscious people and no exception is OpenSSH 6.2 which was just released. In particular in this case I was very happy to read:

sshd(8): Added support for multiple required authentication in SSH
protocol 2 via an AuthenticationMethods option. This option lists
one or more comma-separated lists of authentication method names.
Successful completion of all the methods in any list is required for
authentication to complete. This allows, for example, requiring a
user having to authenticate via public key or GSSAPI before they
are offered password authentication.

What’s going on is not extremely obvious, but basically it means that you can now chain, instead of replace, the authentication method. Okay, step back. Have you ever noticed that when ah SSH connection fail, often enough you have a message saying public-key,keyboard-interactive? That means that it tried, in sequence, the two options, and when they failed, it refused the connection. Any of the two would have been enough for a successful connection. This is akin to the sufficient option in PAM, which means that a single positive result is enough to produce a valid login. The new option in this version of OpenSSH is equivalent to PAM’s requisite option, so if any of the configured login methods fails, the connection is dropped.

So why is this important? Well, this allows two-factor – or actually multi-factor – authentication, as now just having access to your laptop with an unprotected SSH key might not be enough to enter your critical servers. In my case, that would become at least a three-factor authentication as I could make it pass through my SmartCard (which requires the physical card and knowledge of its PIN), and then ask me the password itself.

Since the second factor can be PAM itself, there is no reason why you cannot add more than one factor there. In particular you might remember that just last year I looked into two-factor authentication options and in particular I looked into DuoSecurity — unfortunately, using DuoSecurity as is with PAM is a bit of a mess. I did send a patchset to upstream to make the PAM module more useful, and reliable – among other things making it feasible to use with sudo, so that get asked the second factor only when executing commands as root – but upstream does not care. It doesn’t fit their marketing and their main consulting target, so they basically left me dangling there with a patchset that is now probably to forwardport.

If you’re interested in getting a version of duo_unix with my patchset apply available in Portage (and available in source form for other distributions), i suggest you poke Jon and Doug at DuoSecurity, and ask them about it. If they were to ask me I would be glad to forwardport the patches, and change them as needed if they don’t like the precise way I wrote them. But I reached out enough myself, trying to help them with the packaging, – including proposing to just chat on the phone about what they want to do with it while I was in the US – at this point it’s their turn.

Alternatively, I’m pretty sure you can use YubiKey but I never ended up having one of them in my hands.

Securing logins, Duo Security experience

In January, I’ve ranted about not being able to get a Yubikey so that I could test some kind of OTP token for logging in to the FTP of one of my servers, so that my friend who is maintaining the WordPress install could work even from his office (where SSH does not work).

In the comments of that post Dug Song pointed me to his company, Duo Security which actually seemed like a good idea for what I had in mind. It provides support for both software and hardware token generators, has a clear API, and has a few integrations already available. Unfortunately now we’re in April, and you’ve seen nothing from me discussing it before. Why?

Well, mostly it feels like there’s a problem with timing. When I ranted about Yubikey, it was the week before leaving for FOSDEM, so I was finishing up job stuff and I couldn’t look at it until I came back from my combined trip (after FOSDEM I came here to Los Angeles). So when I started looking into it, I was at first only able to provide them with some build system changes.

When I then decided to spend some more time on it since the need to set up FTP increased, I started fighting with vsftpd to get it to accept using their PAM integration to use log in. The end result has been … a lot of time spent. Unfortunately the original design of their PAM implementation only works with a normal challenge-response authentication method (so it wouldn’t work with “safe” sshd PAM configurations), and more to the point, it would require asking two passwords, which an FTP client can’t.

While I first hacked it around, I was able to implement while here in LA last month a more complete patchset that implements a proper way to use it as a “single factor” authentication, or as a secondary push authentication. Unfortunately, I haven’t yet received a response about this patchset, which is why you won’t find duo_unix in Gentoo as it is.

The situation is getting more complex now: from one side I’m going to cut down most of my contract work in Italy as that’s not making me any money (seriously I think that even with all my ranting Flattr and Google AdSense are making me more money than website hosting), so I don’t foresee the need to provide users with some kind of strong authentication on the long term. From the other, while the firmware I’m working on doesn’t really care about this kind of strong authentication, the organization for which I’m working could use something like this. Of course, if the upstream for the package is not responding, that’s bad enough not to consider this.

I’m honestly not sure what to say since Dug and Jon seemed like friendly and helpful guys, maybe they are just too swamped with other requests and they can’t process mine as well, but whatever the reason, the issue I’m afraid is going to be a lapsed sale for them. Guys if you’re reading this, please let me know something, okay?

How not to sell me something — Why I won’t be maintaining Yubikey software directly in Gentoo

You probably remember my previous notes about WordPress, FTP and the problem with security. At the end after a (boring) set up session I was able to get vsftpd provide FTPS service, which should be usable both by WordPress and by Dreamweaver, so that my friend the webmaster can upload through it directly.

This is important because as it happens I have another prospective customer who’s going to run WordPress, and FTPS now start to look more interesting than SSH, as it doesn’t require me to give shell access to the server either.

Unfortunately I’m a bit worried (maybe more than I should be) for the use of standard passwords rather than certificates or keypairs for authentication. Which meant I went tried to think of other alternatives.. of which there are mostly two: Google Authenticator and YubiKey .

The latter I knew by name already because I proxy-maintain the required software for Brant, and I know it’s outdated already and would require a new maintainer who can deal with those packages – I already posted about hardware-related maintenance for what it’s worth – so it was my first choice: while it meant I had to spend some money, it would have solved my problem and improved Gentoo, even if just for a tiny bit. The price for YubiKey devices is also low enough that, if I felt like providing more FTPS access to customers, I could simply bill it to them without many complaints.

So I went on the manufacturer’s (Yubico’s) website and tried to buy two of them (one for me to test and set up, and one to give my friend to access the server); despite publishing the prices in dollars, they sell through Sweden and UK, which means they are part of EU’s VAT area, and me being a registered business within EU, I should receive a reverse-charge invoice by stating my own VAT ID… never had much of a problem with it, as many of my suppliers are sparse through Europe, I registered for the “foreign-enabled” registry right when I opened business — don’t ask me why Italian (and Spanish as far as I can tell) business owners are not enabled by default to have intra-union suppliers.

Now trouble starts: since, as I just noted, not all VAT IDs are valid to use for intra-union trade, there has to be a way to ensure you’re dealing with an acceptable party. This is implemented through VIES the VAT Information Exchange System which, for what concerns Italian businesses, only tells you a boolean result of valid/invalid (and not the full registration data that most other states seem to provide). I knew VIES from a previous business agreement, but I never cared much. Turns out though that most e-Shops I encountered validate the VAT ID after order completed — or in the case of Amazon it seems like they check their internal database as well as VIES.

Yubico instead validates the request through VIES at the time of registration:

VAT Number could not be validated with VIES at this time. This typically happens when the service is under maintenance. Please retry after some time. For urgent orders, please contact order@yubico.com

Considering that the VIES website has a long disclaimer (which I can’t quote here for reasons that will be clear in a moment) stating that they do not guarantee the availability of the service at any time, and only seem to guarantee the validity of the data to the extent that the law ask them to (which probably means “as long as the states’ own databases are correct”), relying on such a service for registration is .. bad.

The VIES website is indeed down since at least 11am today (over four hours ago as I write this); for a moment they also gave me an interesting page (which I forgot to save), telling me that there were too many requests’ failures from “my IP address” … listing an IP address in the ²¹²⁄₈ range — my actual IP address is in the ⁹⁴⁄₈ range.

What’s the end result here? I’ll probably waste some more time trying to get Google Authenticator; Yubico basically lost a customer and a (possible) contributor by trying and failing to be smarter and won’t have a dedicated maintainer in Gentoo in the near future. It’s sad, because it seems to be easily the most cost- and time-effective solution out there (Google Authenticator is free, but it requires a greater investment of time, and time is money as we all should know).