12 ms·

Using a Yubikey as smartcard for SSH public key authentication

317 points by sverige 8y ago

jwr 8y ago
If you are OK with using PGP keys, there is an excellent guide at https://github.com/drduh/YubiKey-Guide https://github.com/drduh/YubiKey-Guide — I've been using this kind of setup for almost a year now and it works really, really well. Highly recommended. Be sure to set the Yubikey to require touch. As a side note, the author writes: > GnuPG's user interface is a disaster Well, I'd say the procedure described in the article is a strong contender, too :-)
- donmcronald 8y ago
  That's a great guide.
- tanderson92 8y ago
  I used this too, it was great and works flawlessly. I found the author's reasoning unconvincing (and not really argued at all).
amaccuish 8y ago
I second using opensc over gpg. GPG was a nightmare with it's own particular way of doing things and general refusal to help other projects. Their scdaemon takes exclusive use of the card and when this has been brought up with the project, they said other projects should use their scdaemon to inferface with cards rather than PKCS11 and opensc.
- moreentropy 8y ago
  This was exactly my experience from two years ago. But to my surprise with recent gpg2 versions most of those issues are gone (plus EC ssh key files are supported, older gpg-agent could only do RSA) scdaemon used to crash all the time, that doesn't happen anymore. GPG doesn't lock the card so I have to stop scdaemon to use it w/ other apps. So for the last half year I've happily used gpg-agent/scdaemon also as SSH agent and it works really well without any issues. But setting this up (w/ Ubuntu+Gnome) is still a ridiculous task: - Ensure gnupg2, scdaemon, pinentry-gnome3 are installed - cp /etc/xdg/autostart/gnome-keyring-ssh.desktop ~/.config/autostart/ - edit ~/.config/autostart/gnome-keyring-ssh.desktop and add "X-GNOME-Autostart-enabled=false" - edit ~/.gnupg/gpg-agent.conf and add "enable-ssh-support" Gnome session startup will read both the "X-GNOME-Autostart-enabled=false" and the "enable-ssh-support" and set up and start gpg-agent as ssh agent in the session. There are other ways to disable a .desktop file, but the String "X-GNOME-Autostart-enabled=false" has to be there for this to work. When all this is set up usability is excellent. the system will even prompt to plug in the right yubikey when you ssh into something. No need to add/remove the card to/from the agent.
  - Tharre 8y ago
    And yet, scdaemon will still hang everytime you suspend on linux[0]. I've written a udev rule to somewhat mitigate this[1], but it's still really annoying that seemingly nobody cares enough to fix this issue. [0] https://wiki.gnupg.org/SmartCard#Known_problem_of_Yubikey https://wiki.gnupg.org/SmartCard#Known_problem_of_Yubikey [1] https://github.com/Tharre/pkgbuilds/blob/master/arch-system/etc-yubikey.rules https://github.com/Tharre/pkgbuilds/blob/master/arch-system/...
- ak217 8y ago
  I recommend using the winscard/pcsc interface directly. winscard is a standard library on Windows, PCSC.framework is standard on Mac OS, and libpcsclite is available on Linux by installing pcscd/pcsc-lite. I recently implemented a library (https://github.com/pyauth/exile https://github.com/pyauth/exile) to use Yubikeys to sign AWS API requests, which required writing Python ctypes bindings to call these libraries. It turned out to be fairly easy once I threw away the idea that I should rely on any of the intermediary libraries, and just started talking via the winscard/PCSC protocol directly.
convolvatron 8y ago
i bought a yubikey to do this. and after a while installing gpg and creating master keys and subkeys, and dealing with the usual 'there are 4 different verions of recipes to do this and none of them seem to work anymore', i gave up. this seems like such an overwhelmingly common use case I dont understand why yubico doesnt make this as frictionless as possible. i understand that the smart card spec is probably a hindrance, but still.. but its still on my (physical) keychain, looking forward to trying your non-gpg workflow. thanks for posting.
- naggie 8y ago
  I almost gave up too, but after (admittedly) a lot of battling I finally got GPG to work well with my yuibkeys, allowing a portable SSH/GPG identity using a single yubikey over several machines. I also got GPG agent forwarding to work transparently and with improved security by forwarding a dynamically created unix socket instead of a TCP socket. It allows me to do remote code signing, as well as chain through a bastion host. Aside from jamming up with ansible occasionally, the setup is reliable. I've documented the process for my own reference as much as I could here (yep, a fifth guide): https://github.com/naggie/dotfiles/blob/master/etc/yubikey.md https://github.com/naggie/dotfiles/blob/master/etc/yubikey.m... -- see functions.sh in the same repository for some mechanisms to automatically manage gpg-agent and the sockets without getting deadlocked. I hope someone finds this useful. I'll certainly be trying the opensc method here though, out of interest.
  - philsnow 8y ago
    You're talking about forwarding the GPG agent, so I was worried that you hadn't found the touch-to-sign setting, but indeed you had. Do you have a strong opinion on `on` vs `fixed` ? I tell myself that I should use fixed but haven't bitten the bullet yet.
    - StreakyCobra 8y ago
      I set it to `on`. I read somewhere on internet an argument why `fixed` is not really necessary: for setting it back to `off` you need the admin PIN, and you have only 3 tries (by default) for the password. So I am not really worried about someone managing to disable it. And that keep the possibility to change my mind later on open, without having to reset the key.
420codebro 8y ago
Used this a few years ago, then got tired of the complexity. Now I just store my keyfile on my mac. I do have a few high-security things that I keep on the yubikeys still, but all my general-level security stuff is no longer on it. I wish I could just have the ssh private keys stored on a TPM device - either on the laptop itself, or even on my iPhone (keeping the key physically with me, even away from laptop).
equalunique 8y ago
This article was featured on BSD Now, a podcast that I would recommend to anyone interested in using any of the BSDs: https://www.freebsdnews.com/2019/03/21/bsd-now-episode-289-microkernel-failure/ https://www.freebsdnews.com/2019/03/21/bsd-now-episode-289-m...
- sverige 8y ago
  Thanks for this! I used to listen to this regularly but fell out of the habit a couple years ago.
bsder 8y ago
I really loathe the fact that I can't just enroll 3 Yubikeys (or the equivalent) for an employee (1 to be used, 1 for backup, and 1 extra in case the backup fails) and be done with security for everything. I'm not even requesting that I as the issuer be able to subordinate those keys. Just make them work without making me want to shoot anyone who mentions the word "security". The security folks whine that nobody does security, but they sure don't make it very easy to do so when someone wants to.
- jrockway 8y ago
  We had a very good system at Google and I think there are papers floating around about how it worked. You authenticated once per day per machine, and occasionally privileged operations would require human presence detection by pressing the security key. ssh, web... everything, all integrated. I wish we had the same system at my current job, but alas, much programming would be required. I believe Google sells a product, the "identity aware proxy", that is very much like what existed internally. I haven't used it, so am unsure. But it sounds great.
  - YawningAngel 8y ago
    We use both Google Cloud Platform and the Identity Aware Proxy, with Google as our sole identity provider. One login + hardware token gets you onto ssh, k8s and web endpoints, which is pretty great. There are a lot of rough edges that make it pretty janky to administer though.
    - bsder 8y ago
      > There are a lot of rough edges that make it pretty janky to administer though. That pretty much describes every security token system I have ever seen. Sadly.
  - cvwright 8y ago
    Sounds like you're talking about BeyondCorp? https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/44860.pdf https://static.googleusercontent.com/media/research.google.c...
jinnko 8y ago
I was frustrated with the complexity and automated the process. Unfortunately even automation doesn't protect you from the complexities of GPG, but it does help. This is the tooling: https://github.com/ixydo/gpg-smartcard-automation https://github.com/ixydo/gpg-smartcard-automation
platz 8y ago
What happens when I loose the yubikey
- opencl 8y ago
  You have a spare and revoke the ability to use the one you lost.
  - platz 8y ago
    Ah, makes sense. I bet most people only buy 1 though
    - Faaak 8y ago
      You keep a backup of your master key in a secure way (paper key + locker + passphrase)
- daniel_berg_ 8y ago
  Follow the guide and you will have a spare. You create the keys on a live distro, just to be sure nothing is written to disk. Then write the master keys to an encrypted usb drive that you hide in a safe. After that you write the keys (stripped) to the yubikey. When you lose the yubikey you import the master keys from the usb drive and all your access is there. Then you revoke the keys and start over.
atonse 8y ago
There seems to be an opportunity here for someone to create the "Algo VPN" version of Yubikey SSH. Or maybe the Teleport people can just make this as painless as possible. Or for keybase to make it painless. Don't try to support everything. Just start with only supporting Yubikeys. Then you can expand.
- phren0logy 8y ago
  I would love to see Keybase tackle this also. I expect it would be marginally less secure than the current nightmare but orders of magnitude more convenient.
- xur17 8y ago
  Whoever does this -> I would love for the ability to backup my ssh and gpg keys using backup words, similar to what cryptocurrency wallets use (24 words that are used to define the entropy).
megatraveller 8y ago
I love using the Yubikey Neo with NFC, having my GPG Keys on it and using it also for SSH connections, but mostly I love it for the OTP Feature. Mostly using it on my Nexus 5. It is great, because using it by NFC with Open Keychain and k9 I do not need to place my private key on the phone. Additionaly that works also great to use the Yubikey to unlock the Phone and also using it on the Yubico Authentificator for the OTPs. That keys are really great. Love them. The only other Tool I would recomend with similar features is the Nitrokey (https://www.nitrokey.com/ https://www.nitrokey.com/) but the Disadvantage is, that they really lack on some features. But maybe a good alternative for GPG and SSH. The advantage of the Nitrokeys are, that in compare to Yubico products they use open hardware. Hope this helps out some people. And, for everybody who is struggling on the usage, belive me, I spend over four years making everything work and some really frustrating time reseting stuff, building keys, fu*... up big and recover Accounts :D
- Boulth 8y ago
  > Mostly using it on my Nexus 5. It is great, because using it by NFC with Open Keychain and k9 I do not need to place my private key on the phone. And with TermBot you can use Yubikey to login via SSH. Can come in handy in trouble.
codys 8y ago
I've configured gpg to use keys from "smart cards" before, and didn't really fall in love. After the setup, things worked ok, but there were a few limitations that made me more happy with just having the key on my computer. The primary was that I had no way to validate that the key material was encrypted at rest, and no documentation even appeared to make claims about how the key material was stored. My setup used a fairly long PIN to replace what would have been a fairly long password for decrypting the key material stored on my computer. I wasn't really comfortable with using something simpler as a PIN. It may be the case that I could have leaned more on the hardware for security and told myself that the limit to the number of password attempts should allow for a shorter PIN to be used. But I was looking for something that I could add as another layer to my existing process, rather than something that replaced it. At the end of the day, using a smart card to store key material just made it harder for me to reason about the security of the key material itself due to the increased number of unknowns. And it was more inconvenient.
ak217 8y ago
I recently wrote a different application for YubiKeys - using the YKOATH functionality to sign AWS API requests with HMAC-SHA256 (https://github.com/pyauth/exile https://github.com/pyauth/exile). What I found is that Yubikey's protocol documentation is good, but their tools are pretty bad, and none of them should be used. Instead, I recommend talking to the smartcard interface through the lowest level library that's already bundled with the major OSs - winscard/pcsclite/PCSC.framework (three implementations all providing the same API). The app I wrote includes Python ctypes bindings for all three implementations (https://github.com/pyauth/exile/tree/master/exile/scard https://github.com/pyauth/exile/tree/master/exile/scard, and https://github.com/pyauth/exile/blob/master/exile/ykoath https://github.com/pyauth/exile/blob/master/exile/ykoath contains an example of how to use them). Hopefully these will be useful to others writing YubiKey-based applications. I should add, there are other YubiKey modes (like U2F) that use the USB HID protocol instead of the USB PCSC protocol. For those, someone at Google wrote this library: https://github.com/google/pyu2f https://github.com/google/pyu2f which provides similar capabilities for HID-based protocols. It similarly interfaces directly with the system-provided HID API using ctypes.
- Boulth 8y ago
  > Hopefully these will be useful to others writing Yubikey-based applications. Definitely! HMAC-SHA256 is nice and I was wondering if the TOTP feature of Yubikeys can be (ab)used for anything else that also uses HMAC-SHA256 (e.g. Macaroons). I'll take some time to digest your code, thanks!
- ecesena 8y ago
  Can you use pyu2f with ssh? It’d be great to have a ssh binding to fido2, with full support for new algos and resident keys, instead of gpg/pkcs11.
  - dfox 8y ago
    I don't think that there is existing solution for that, but it should not be too hard to implement one.
Boulth 8y ago
> Since nobody can get at the ssh key thats in the Yubikey, a short pin will be fine - at least that's what the system promises. Short pin is fine because after 3 tries the token is locked. On the other hand there are no limits with software keys.
munchbunny 8y ago
This is awesome. I've played with something similar and have been thinking about automating some of this process to give small startups a really lightweight way to on-board this kind of capability for physical + PIN multi-factor SSH access.
nickray 8y ago
As I'm currently working on possible options to expose on-device keys and cryptography for our open source FIDO2 key (SoloKeys) beyond the FIDO use case, I'd be curious about opinions on just exposing and using the PKCS#11 API (Cryptoki) [0] directly. Envisioned setup would entail: download (custom) `libsolo-pk11.so`, generate RSA or ECDSA key on the USB key, get public key via `ssh-keygen -D libsolo-pk11.so`, use via `ssh -I libsolo-pk11.so user@example.com`. The equivalent thing can be done for TPMs with simple-tpm-pk11 [1] today. Technically, I'd extend the FIDO2 CTAPHID transport with "vendor commands" [2] mapping the basic Cryptoki API, and call that from the custom PKCS#11 shared library, which is then just a simple shim/wrapper. No additional drivers needed (everyone has HID). Issues I can foresee: Users too attached to GPG workflow. Installation of custom shared library. No SSH support (via PKCS#11) for Ed25519 yet. SSH support for ECDSA only in about-to-be-released OpenSSH 8.0. Vanilla PuTTY on Windows has no PKCS#11 support. Bad rap of PKCS#11 due to existing vendors adding proprietary and closed source extensions. And the fact that SSH (currently) presents all keys to the host - I'd really like to be able to specify which key to use. Personally, I'm a bit allergic to the GPG/PCSC/PIV/CCID way of doing things... My itch-to-scratch is just having a few keys off my computers (in particular, portable), and perform (infrequent) signatures on the separate device. And do this via a (comparatively) sane, open standard. [0] http://docs.oasis-open.org/pkcs11/pkcs11-base/v2.40/os/pkcs11-base-v2.40-os.html http://docs.oasis-open.org/pkcs11/pkcs11-base/v2.40/os/pkcs1... [1] https://github.com/ThomasHabets/simple-tpm-pk11 https://github.com/ThomasHabets/simple-tpm-pk11 [2] https://fidoalliance.org/specs/fido-v2.0-rd-20180702/fido-client-to-authenticator-protocol-v2.0-rd-20180702.html#usb-vendor-specific-commands https://fidoalliance.org/specs/fido-v2.0-rd-20180702/fido-cl...
- velosol 8y ago
  Personally I'd prefer as open a standard as possible usable across the greatest swath possible (e.g. Chrome Windows/Mac, Chromium Linux, Firefox W/M/L, Android Chrome/Firefox). Someone else seems to second lower-level standards as the best way [1]. [1]: https://news.ycombinator.com/item?id=19567277 https://news.ycombinator.com/item?id=19567277
- anilakar 8y ago
  I used TPM authentication with libsimple and recommended it to others with the assumption that I wouldn't need to back up any usespace data when when upgrading the system. Turned out this is not the case. Not only do you need the TPM password but also certain files from /var from the old install.
haberman 8y ago
I'm amazed this is so complicated. I recently used https://github.com/sekey/sekey https://github.com/sekey/sekey to set up SSH with TouchID on a mac, and was really surprised how simple it was.
- pisipisipisi 8y ago
  As a 10+ year smart card crypto specialist I absolutely LOVE sekey
everybodyknows 8y ago
Earler discussion on HN: https://news.ycombinator.com/item?id=19340638 https://news.ycombinator.com/item?id=19340638
teamspirit 8y ago
I have been doing this for a little over a year now. The most difficult/frustrating thing was using it on my phone. Luckily, TermBot [0] solved that, allowing me to choose an external agent for my key with OpenKeyChain [1]. A Yubikey 5 with NFC and I feel real futuristic tapping my phone to my pocket to gain access to remote computers. I get to do this with my password manager too [2]. [0] https://f-droid.org/en/packages/org.sufficientlysecure.termbot https://f-droid.org/en/packages/org.sufficientlysecure.termb... [1] https://f-droid.org/en/packages/org.sufficientlysecure.keychain https://f-droid.org/en/packages/org.sufficientlysecure.keych... [2] https://github.com/zeapo/Android-Password-Store https://github.com/zeapo/Android-Password-Store
- Steltek 8y ago
  I have been waiting for this for so long! Thank you so much for these links! I have Pass working but SSH was always a glaring missing piece of the puzzle. Now if only I can convince an SFTP client to do this, I'll be really sitting pretty.
jzig 8y ago
After using one for over a year now all I can say is it shouldn't be this hard :(
ejholmes 8y ago
If you have a newer MacBook with TouchID, you can get similar benefits using https://github.com/sekey/sekey https://github.com/sekey/sekey. Arguably better, because access is backed by biometrics (TouchID) so it's "something you are" (fingperint) + "something you have" (laptop) and quite a bit simpler than setting up GPG backend SSH keys.
- busterarm 8y ago
  Uh, what? You're just combining "something you have" + "something you have". Unlike with a Yubikey, your fingerprint will always be with you when you have your laptop. Biometric access is a terrible idea if you don't combine it with "something you know". Access to your laptop can now be coerced or compelled at any time. Every commercial biometrics system I've ever seen that's worth a damn at least combines it with a pinpad.
  - ejholmes 8y ago
    Obviously, depends on your threat model. I'd argue that being physically coerced ends up being a pretty low risk for most people. If you're just looking for something better than storing private key material on a hard disc, sekey is a pretty great alternative to using Yubikey + GPG.
1024core 8y ago
Speaking of Yubikeys: I found a Yubikey lying somewhere. I asked around, no takers. Is it safe to use such a Yubikey? It'd be a shame to waste it.
- TylerE 8y ago
  You have what appears to be a Yubikey. Many devious attacks involve dropping a device that LOOKS like a generic USB drive in a public location.
  - closeparen 8y ago
    If the device is U2F capable, you can check whether it is genuine [0]. Of course, if it is not genuine, it can own your machine the moment you plug it in. [0] https://www.yubico.com/genuine/ https://www.yubico.com/genuine/
jandeboevrie 8y ago
Remember to buy two devices and to swap usage every month. If one breaks you loose access since the keys shouldn't leave the device. Use two and always setup two keys . Oh and the yubikeys nowdays are closed source. If you want actual open source hardware and software, checkout the Nitrokey Start. It's cheaper and fully open source, hard and software. Its an openpgp token: https://raymii.org/s/articles/Nitrokey_Start_Getting_started_guide.html https://raymii.org/s/articles/Nitrokey_Start_Getting_started... If you want a smartcard, Nitrokey had Both the pro and the HSM. An openpgp smartcard and and smartcard-hsm (just pkcs#11).
jamesholden 8y ago
This is for OpenBSD. What about for us lowly Debian users? Anybody know how I can do something similar? :)
baud147258 8y ago
Funny, that's exactly what we're doing at work right now: we're adapting our JavaCard applet to use them with Yubikey, to be able to use the Yubikey like a smartcard, including public key authentication.
noliran 8y ago
In addition to using YubiKey's U2F capabilities, I've been using its HMAC-SHA1 challenge-response mode as my password manager (more precisely a password generator) for the past few months. It uses these 3 to consistently generate a password for websites: 1. A secret that I've pre-programmed in the YubiKey (+ 2 other backup YubiKeys) 2. A "pin code" (either provided by me, or in my case - protected by my TouchID) 3. The website's name If you want to take a peek, I always appreciate feedback. https://github.com/noliran/ykpass https://github.com/noliran/ykpass
ataturk 8y ago
My company forced Yubikeys on Mac users. They're trash. DO NOT USE.
coldacid 8y ago
I love my Yubikey for SSH auth, but it's a complete pain in the ass that gpg-agent and OpenSSH won't play together on Windows. I and others have tried to make broker apps that let them talk with each other but to no avail thanks to libassuan's Windows "workaround" for AF_UNIX sockets. In the end, I have to use gpg-agent's PuTTY support, which means no command-line SSH, only a separate PuTTY window when I want to do SSH sessions, and using plink for SSH auth for Git.

317 points by sverige 8y ago

jwr 8y ago

If you are OK with using PGP keys, there is an excellent guide at https://github.com/drduh/YubiKey-Guide https://github.com/drduh/YubiKey-Guide — I've been using this kind of setup for almost a year now and it works really, really well. Highly recommended. Be sure to set the Yubikey to require touch. As a side note, the author writes: > GnuPG's user interface is a disaster Well, I'd say the procedure described in the article is a strong contender, too :-)

donmcronald 8y ago
That's a great guide.
tanderson92 8y ago
I used this too, it was great and works flawlessly. I found the author's reasoning unconvincing (and not really argued at all).

amaccuish 8y ago

I second using opensc over gpg. GPG was a nightmare with it's own particular way of doing things and general refusal to help other projects. Their scdaemon takes exclusive use of the card and when this has been brought up with the project, they said other projects should use their scdaemon to inferface with cards rather than PKCS11 and opensc.

moreentropy 8y ago
This was exactly my experience from two years ago. But to my surprise with recent gpg2 versions most of those issues are gone (plus EC ssh key files are supported, older gpg-agent could only do RSA) scdaemon used to crash all the time, that doesn't happen anymore. GPG doesn't lock the card so I have to stop scdaemon to use it w/ other apps. So for the last half year I've happily used gpg-agent/scdaemon also as SSH agent and it works really well without any issues. But setting this up (w/ Ubuntu+Gnome) is still a ridiculous task: - Ensure gnupg2, scdaemon, pinentry-gnome3 are installed - cp /etc/xdg/autostart/gnome-keyring-ssh.desktop ~/.config/autostart/ - edit ~/.config/autostart/gnome-keyring-ssh.desktop and add "X-GNOME-Autostart-enabled=false" - edit ~/.gnupg/gpg-agent.conf and add "enable-ssh-support" Gnome session startup will read both the "X-GNOME-Autostart-enabled=false" and the "enable-ssh-support" and set up and start gpg-agent as ssh agent in the session. There are other ways to disable a .desktop file, but the String "X-GNOME-Autostart-enabled=false" has to be there for this to work. When all this is set up usability is excellent. the system will even prompt to plug in the right yubikey when you ssh into something. No need to add/remove the card to/from the agent.
- Tharre 8y ago
  And yet, scdaemon will still hang everytime you suspend on linux[0]. I've written a udev rule to somewhat mitigate this[1], but it's still really annoying that seemingly nobody cares enough to fix this issue. [0] https://wiki.gnupg.org/SmartCard#Known_problem_of_Yubikey https://wiki.gnupg.org/SmartCard#Known_problem_of_Yubikey [1] https://github.com/Tharre/pkgbuilds/blob/master/arch-system/etc-yubikey.rules https://github.com/Tharre/pkgbuilds/blob/master/arch-system/...
ak217 8y ago
I recommend using the winscard/pcsc interface directly. winscard is a standard library on Windows, PCSC.framework is standard on Mac OS, and libpcsclite is available on Linux by installing pcscd/pcsc-lite. I recently implemented a library (https://github.com/pyauth/exile https://github.com/pyauth/exile) to use Yubikeys to sign AWS API requests, which required writing Python ctypes bindings to call these libraries. It turned out to be fairly easy once I threw away the idea that I should rely on any of the intermediary libraries, and just started talking via the winscard/PCSC protocol directly.

convolvatron 8y ago

i bought a yubikey to do this. and after a while installing gpg and creating master keys and subkeys, and dealing with the usual 'there are 4 different verions of recipes to do this and none of them seem to work anymore', i gave up. this seems like such an overwhelmingly common use case I dont understand why yubico doesnt make this as frictionless as possible. i understand that the smart card spec is probably a hindrance, but still.. but its still on my (physical) keychain, looking forward to trying your non-gpg workflow. thanks for posting.

naggie 8y ago
I almost gave up too, but after (admittedly) a lot of battling I finally got GPG to work well with my yuibkeys, allowing a portable SSH/GPG identity using a single yubikey over several machines. I also got GPG agent forwarding to work transparently and with improved security by forwarding a dynamically created unix socket instead of a TCP socket. It allows me to do remote code signing, as well as chain through a bastion host. Aside from jamming up with ansible occasionally, the setup is reliable. I've documented the process for my own reference as much as I could here (yep, a fifth guide): https://github.com/naggie/dotfiles/blob/master/etc/yubikey.md https://github.com/naggie/dotfiles/blob/master/etc/yubikey.m... -- see functions.sh in the same repository for some mechanisms to automatically manage gpg-agent and the sockets without getting deadlocked. I hope someone finds this useful. I'll certainly be trying the opensc method here though, out of interest.
- philsnow 8y ago
  You're talking about forwarding the GPG agent, so I was worried that you hadn't found the touch-to-sign setting, but indeed you had. Do you have a strong opinion on `on` vs `fixed` ? I tell myself that I should use fixed but haven't bitten the bullet yet.
  - StreakyCobra 8y ago
    I set it to `on`. I read somewhere on internet an argument why `fixed` is not really necessary: for setting it back to `off` you need the admin PIN, and you have only 3 tries (by default) for the password. So I am not really worried about someone managing to disable it. And that keep the possibility to change my mind later on open, without having to reset the key.

420codebro 8y ago

Used this a few years ago, then got tired of the complexity. Now I just store my keyfile on my mac. I do have a few high-security things that I keep on the yubikeys still, but all my general-level security stuff is no longer on it. I wish I could just have the ssh private keys stored on a TPM device - either on the laptop itself, or even on my iPhone (keeping the key physically with me, even away from laptop).

equalunique 8y ago

This article was featured on BSD Now, a podcast that I would recommend to anyone interested in using any of the BSDs: https://www.freebsdnews.com/2019/03/21/bsd-now-episode-289-microkernel-failure/ https://www.freebsdnews.com/2019/03/21/bsd-now-episode-289-m...

sverige 8y ago
Thanks for this! I used to listen to this regularly but fell out of the habit a couple years ago.

bsder 8y ago

I really loathe the fact that I can't just enroll 3 Yubikeys (or the equivalent) for an employee (1 to be used, 1 for backup, and 1 extra in case the backup fails) and be done with security for everything. I'm not even requesting that I as the issuer be able to subordinate those keys. Just make them work without making me want to shoot anyone who mentions the word "security". The security folks whine that nobody does security, but they sure don't make it very easy to do so when someone wants to.

jrockway 8y ago
We had a very good system at Google and I think there are papers floating around about how it worked. You authenticated once per day per machine, and occasionally privileged operations would require human presence detection by pressing the security key. ssh, web... everything, all integrated. I wish we had the same system at my current job, but alas, much programming would be required. I believe Google sells a product, the "identity aware proxy", that is very much like what existed internally. I haven't used it, so am unsure. But it sounds great.
- YawningAngel 8y ago
  We use both Google Cloud Platform and the Identity Aware Proxy, with Google as our sole identity provider. One login + hardware token gets you onto ssh, k8s and web endpoints, which is pretty great. There are a lot of rough edges that make it pretty janky to administer though.
  - bsder 8y ago
    > There are a lot of rough edges that make it pretty janky to administer though. That pretty much describes every security token system I have ever seen. Sadly.
- cvwright 8y ago
  Sounds like you're talking about BeyondCorp? https://static.googleusercontent.com/media/research.google.com/en//pubs/archive/44860.pdf https://static.googleusercontent.com/media/research.google.c...

jinnko 8y ago

I was frustrated with the complexity and automated the process. Unfortunately even automation doesn't protect you from the complexities of GPG, but it does help. This is the tooling: https://github.com/ixydo/gpg-smartcard-automation https://github.com/ixydo/gpg-smartcard-automation

platz 8y ago

What happens when I loose the yubikey

opencl 8y ago
You have a spare and revoke the ability to use the one you lost.
- platz 8y ago
  Ah, makes sense. I bet most people only buy 1 though
  - Faaak 8y ago
    You keep a backup of your master key in a secure way (paper key + locker + passphrase)
daniel_berg_ 8y ago
Follow the guide and you will have a spare. You create the keys on a live distro, just to be sure nothing is written to disk. Then write the master keys to an encrypted usb drive that you hide in a safe. After that you write the keys (stripped) to the yubikey. When you lose the yubikey you import the master keys from the usb drive and all your access is there. Then you revoke the keys and start over.

atonse 8y ago

There seems to be an opportunity here for someone to create the "Algo VPN" version of Yubikey SSH. Or maybe the Teleport people can just make this as painless as possible. Or for keybase to make it painless. Don't try to support everything. Just start with only supporting Yubikeys. Then you can expand.

phren0logy 8y ago
I would love to see Keybase tackle this also. I expect it would be marginally less secure than the current nightmare but orders of magnitude more convenient.
xur17 8y ago
Whoever does this -> I would love for the ability to backup my ssh and gpg keys using backup words, similar to what cryptocurrency wallets use (24 words that are used to define the entropy).

megatraveller 8y ago

I love using the Yubikey Neo with NFC, having my GPG Keys on it and using it also for SSH connections, but mostly I love it for the OTP Feature. Mostly using it on my Nexus 5. It is great, because using it by NFC with Open Keychain and k9 I do not need to place my private key on the phone. Additionaly that works also great to use the Yubikey to unlock the Phone and also using it on the Yubico Authentificator for the OTPs. That keys are really great. Love them. The only other Tool I would recomend with similar features is the Nitrokey (https://www.nitrokey.com/ https://www.nitrokey.com/) but the Disadvantage is, that they really lack on some features. But maybe a good alternative for GPG and SSH. The advantage of the Nitrokeys are, that in compare to Yubico products they use open hardware. Hope this helps out some people. And, for everybody who is struggling on the usage, belive me, I spend over four years making everything work and some really frustrating time reseting stuff, building keys, fu*... up big and recover Accounts :D

Boulth 8y ago
> Mostly using it on my Nexus 5. It is great, because using it by NFC with Open Keychain and k9 I do not need to place my private key on the phone. And with TermBot you can use Yubikey to login via SSH. Can come in handy in trouble.

codys 8y ago

I've configured gpg to use keys from "smart cards" before, and didn't really fall in love. After the setup, things worked ok, but there were a few limitations that made me more happy with just having the key on my computer. The primary was that I had no way to validate that the key material was encrypted at rest, and no documentation even appeared to make claims about how the key material was stored. My setup used a fairly long PIN to replace what would have been a fairly long password for decrypting the key material stored on my computer. I wasn't really comfortable with using something simpler as a PIN. It may be the case that I could have leaned more on the hardware for security and told myself that the limit to the number of password attempts should allow for a shorter PIN to be used. But I was looking for something that I could add as another layer to my existing process, rather than something that replaced it. At the end of the day, using a smart card to store key material just made it harder for me to reason about the security of the key material itself due to the increased number of unknowns. And it was more inconvenient.

ak217 8y ago

I recently wrote a different application for YubiKeys - using the YKOATH functionality to sign AWS API requests with HMAC-SHA256 (https://github.com/pyauth/exile https://github.com/pyauth/exile). What I found is that Yubikey's protocol documentation is good, but their tools are pretty bad, and none of them should be used. Instead, I recommend talking to the smartcard interface through the lowest level library that's already bundled with the major OSs - winscard/pcsclite/PCSC.framework (three implementations all providing the same API). The app I wrote includes Python ctypes bindings for all three implementations (https://github.com/pyauth/exile/tree/master/exile/scard https://github.com/pyauth/exile/tree/master/exile/scard, and https://github.com/pyauth/exile/blob/master/exile/ykoath https://github.com/pyauth/exile/blob/master/exile/ykoath contains an example of how to use them). Hopefully these will be useful to others writing YubiKey-based applications. I should add, there are other YubiKey modes (like U2F) that use the USB HID protocol instead of the USB PCSC protocol. For those, someone at Google wrote this library: https://github.com/google/pyu2f https://github.com/google/pyu2f which provides similar capabilities for HID-based protocols. It similarly interfaces directly with the system-provided HID API using ctypes.

Boulth 8y ago
> Hopefully these will be useful to others writing Yubikey-based applications. Definitely! HMAC-SHA256 is nice and I was wondering if the TOTP feature of Yubikeys can be (ab)used for anything else that also uses HMAC-SHA256 (e.g. Macaroons). I'll take some time to digest your code, thanks!
ecesena 8y ago
Can you use pyu2f with ssh? It’d be great to have a ssh binding to fido2, with full support for new algos and resident keys, instead of gpg/pkcs11.
- dfox 8y ago
  I don't think that there is existing solution for that, but it should not be too hard to implement one.

Boulth 8y ago

> Since nobody can get at the ssh key thats in the Yubikey, a short pin will be fine - at least that's what the system promises. Short pin is fine because after 3 tries the token is locked. On the other hand there are no limits with software keys.

munchbunny 8y ago

This is awesome. I've played with something similar and have been thinking about automating some of this process to give small startups a really lightweight way to on-board this kind of capability for physical + PIN multi-factor SSH access.

nickray 8y ago

As I'm currently working on possible options to expose on-device keys and cryptography for our open source FIDO2 key (SoloKeys) beyond the FIDO use case, I'd be curious about opinions on just exposing and using the PKCS#11 API (Cryptoki) [0] directly. Envisioned setup would entail: download (custom) `libsolo-pk11.so`, generate RSA or ECDSA key on the USB key, get public key via `ssh-keygen -D libsolo-pk11.so`, use via `ssh -I libsolo-pk11.so user@example.com`. The equivalent thing can be done for TPMs with simple-tpm-pk11 [1] today. Technically, I'd extend the FIDO2 CTAPHID transport with "vendor commands" [2] mapping the basic Cryptoki API, and call that from the custom PKCS#11 shared library, which is then just a simple shim/wrapper. No additional drivers needed (everyone has HID). Issues I can foresee: Users too attached to GPG workflow. Installation of custom shared library. No SSH support (via PKCS#11) for Ed25519 yet. SSH support for ECDSA only in about-to-be-released OpenSSH 8.0. Vanilla PuTTY on Windows has no PKCS#11 support. Bad rap of PKCS#11 due to existing vendors adding proprietary and closed source extensions. And the fact that SSH (currently) presents all keys to the host - I'd really like to be able to specify which key to use. Personally, I'm a bit allergic to the GPG/PCSC/PIV/CCID way of doing things... My itch-to-scratch is just having a few keys off my computers (in particular, portable), and perform (infrequent) signatures on the separate device. And do this via a (comparatively) sane, open standard. [0] http://docs.oasis-open.org/pkcs11/pkcs11-base/v2.40/os/pkcs11-base-v2.40-os.html http://docs.oasis-open.org/pkcs11/pkcs11-base/v2.40/os/pkcs1... [1] https://github.com/ThomasHabets/simple-tpm-pk11 https://github.com/ThomasHabets/simple-tpm-pk11 [2] https://fidoalliance.org/specs/fido-v2.0-rd-20180702/fido-client-to-authenticator-protocol-v2.0-rd-20180702.html#usb-vendor-specific-commands https://fidoalliance.org/specs/fido-v2.0-rd-20180702/fido-cl...

velosol 8y ago
Personally I'd prefer as open a standard as possible usable across the greatest swath possible (e.g. Chrome Windows/Mac, Chromium Linux, Firefox W/M/L, Android Chrome/Firefox). Someone else seems to second lower-level standards as the best way [1]. [1]: https://news.ycombinator.com/item?id=19567277 https://news.ycombinator.com/item?id=19567277
anilakar 8y ago
I used TPM authentication with libsimple and recommended it to others with the assumption that I wouldn't need to back up any usespace data when when upgrading the system. Turned out this is not the case. Not only do you need the TPM password but also certain files from /var from the old install.

haberman 8y ago

I'm amazed this is so complicated. I recently used https://github.com/sekey/sekey https://github.com/sekey/sekey to set up SSH with TouchID on a mac, and was really surprised how simple it was.

pisipisipisi 8y ago
As a 10+ year smart card crypto specialist I absolutely LOVE sekey

everybodyknows 8y ago

Earler discussion on HN: https://news.ycombinator.com/item?id=19340638 https://news.ycombinator.com/item?id=19340638

teamspirit 8y ago

I have been doing this for a little over a year now. The most difficult/frustrating thing was using it on my phone. Luckily, TermBot [0] solved that, allowing me to choose an external agent for my key with OpenKeyChain [1]. A Yubikey 5 with NFC and I feel real futuristic tapping my phone to my pocket to gain access to remote computers. I get to do this with my password manager too [2]. [0] https://f-droid.org/en/packages/org.sufficientlysecure.termbot https://f-droid.org/en/packages/org.sufficientlysecure.termb... [1] https://f-droid.org/en/packages/org.sufficientlysecure.keychain https://f-droid.org/en/packages/org.sufficientlysecure.keych... [2] https://github.com/zeapo/Android-Password-Store https://github.com/zeapo/Android-Password-Store

Steltek 8y ago
I have been waiting for this for so long! Thank you so much for these links! I have Pass working but SSH was always a glaring missing piece of the puzzle. Now if only I can convince an SFTP client to do this, I'll be really sitting pretty.

jzig 8y ago

After using one for over a year now all I can say is it shouldn't be this hard :(

ejholmes 8y ago

If you have a newer MacBook with TouchID, you can get similar benefits using https://github.com/sekey/sekey https://github.com/sekey/sekey. Arguably better, because access is backed by biometrics (TouchID) so it's "something you are" (fingperint) + "something you have" (laptop) and quite a bit simpler than setting up GPG backend SSH keys.

busterarm 8y ago
Uh, what? You're just combining "something you have" + "something you have". Unlike with a Yubikey, your fingerprint will always be with you when you have your laptop. Biometric access is a terrible idea if you don't combine it with "something you know". Access to your laptop can now be coerced or compelled at any time. Every commercial biometrics system I've ever seen that's worth a damn at least combines it with a pinpad.
- ejholmes 8y ago
  Obviously, depends on your threat model. I'd argue that being physically coerced ends up being a pretty low risk for most people. If you're just looking for something better than storing private key material on a hard disc, sekey is a pretty great alternative to using Yubikey + GPG.

1024core 8y ago

Speaking of Yubikeys: I found a Yubikey lying somewhere. I asked around, no takers. Is it safe to use such a Yubikey? It'd be a shame to waste it.

TylerE 8y ago
You have what appears to be a Yubikey. Many devious attacks involve dropping a device that LOOKS like a generic USB drive in a public location.
- closeparen 8y ago
  If the device is U2F capable, you can check whether it is genuine [0]. Of course, if it is not genuine, it can own your machine the moment you plug it in. [0] https://www.yubico.com/genuine/ https://www.yubico.com/genuine/

jandeboevrie 8y ago

Remember to buy two devices and to swap usage every month. If one breaks you loose access since the keys shouldn't leave the device. Use two and always setup two keys . Oh and the yubikeys nowdays are closed source. If you want actual open source hardware and software, checkout the Nitrokey Start. It's cheaper and fully open source, hard and software. Its an openpgp token: https://raymii.org/s/articles/Nitrokey_Start_Getting_started_guide.html https://raymii.org/s/articles/Nitrokey_Start_Getting_started... If you want a smartcard, Nitrokey had Both the pro and the HSM. An openpgp smartcard and and smartcard-hsm (just pkcs#11).

jamesholden 8y ago

This is for OpenBSD. What about for us lowly Debian users? Anybody know how I can do something similar? :)

baud147258 8y ago

Funny, that's exactly what we're doing at work right now: we're adapting our JavaCard applet to use them with Yubikey, to be able to use the Yubikey like a smartcard, including public key authentication.

noliran 8y ago

In addition to using YubiKey's U2F capabilities, I've been using its HMAC-SHA1 challenge-response mode as my password manager (more precisely a password generator) for the past few months. It uses these 3 to consistently generate a password for websites: 1. A secret that I've pre-programmed in the YubiKey (+ 2 other backup YubiKeys) 2. A "pin code" (either provided by me, or in my case - protected by my TouchID) 3. The website's name If you want to take a peek, I always appreciate feedback. https://github.com/noliran/ykpass https://github.com/noliran/ykpass

ataturk 8y ago

My company forced Yubikeys on Mac users. They're trash. DO NOT USE.

coldacid 8y ago

I love my Yubikey for SSH auth, but it's a complete pain in the ass that gpg-agent and OpenSSH won't play together on Windows. I and others have tried to make broker apps that let them talk with each other but to no avail thanks to libassuan's Windows "workaround" for AF_UNIX sockets. In the end, I have to use gpg-agent's PuTTY support, which means no command-line SSH, only a separate PuTTY window when I want to do SSH sessions, and using plink for SSH auth for Git.