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What specifically do you consider a gigantic pain in the ass about using SSH keys on a Yubikey? Also, how is keeping the private key ensconced in a (presumably)

What specifically do you consider a gigantic pain in the ass about using SSH keys on a Yubikey? Also, how is keeping the private key ensconced in a (presumably) secure HSM a 'bit of security theatre'? Genuinely interested, here.

tptacek 9y ago
The agent process is tricky to set up and persnickety, especially if you use the token for anything else besides SSH. At one point, before I tableflipped and switched back to software keys, I had to switch agent processes any time I used my Y4 to sign into a VPN. The theater is that you're protecting a key but not the account the key protects. Yes, you'll never lose the actual RSA key bits to an attacker. But that'll be cold comfort after an attacker uses a hijacked SSH process to compromise every account you log into. There's some value to the Y4 SSH key, don't get me wrong. It's just much less value than you'd expect from all the ceremony.
- rileytg 9y ago
  totally agreed on agent. also on provisioning the keys. my windows users eyes, even the more technical of the bunch, glaze over when teaching intro to your yubi key
- spilk 9y ago
  I switched my SSH keys on my Yubikey from using the OpenPGP applet and all the funkiness of gpg-agent over to using X.509 certificates with the PIV applet. Added bonus is that not only does it work with SSH, but you can use those certificates for TLS mutual authentication in web browsers. Works out of the box on Mac/Windows.
  - edutechnion 9y ago
    Can you provide a link or reference to this path? I can't find much with basic searches and have given up several times on the gpg-connect-agent path while using Windows or Ubuntu. The path on Mac seems okay but on other platforms is way too difficult.
- ryukafalz 9y ago
  >Yes, you'll never lose the actual RSA key bits to an attacker. But that'll be cold comfort after an attacker uses a hijacked SSH process to compromise every account you log into. But if you enable (and require) the touch feature, it'll be pretty obvious if someone's trying to use your agent to authenticate somewhere else, no? I'd certainly notice if I had to press the button twice while I'm logging into a machine that should only request auth once (i.e. I'm not proxying through another box).
  - derefr 9y ago
    They don't have to use your agent to authenticate again. They just feed commands to your SSH client binary that it then sends over the wire in your existing SSH session-context, with the SSH pty temporarily set to not echo input and discard output (or return it over the network to the attacker, but not render it in the local PTY character-buffer.) A hijacked SSH binary can even detect an elevation-requiring command you provided in the terminal and wrap it in a "sudo -c" along with a payload, such that the whole thing happens as one elevated "transaction", only hitting your agent once. Happily, this won't work if you only ever use SSH with a non-shell command, e.g. as a fancy encrypted netcat(1).
    - ryukafalz 9y ago
      Right, and that's still a problem, but not as much of a problem as if they were able to then use your key to authenticate to every other machine you have access to. The problem is at least contained to a single system at a time.
- plttn 9y ago
  FWIW, I never had that issue with my NEO on OSX/macOS. I was using my NEO for git signing, SSH, as well as U2F.
  - hdhzy 9y ago
    tptacek's VPN probably uses PIV applet instead of GPG one and you can't switch them easily (requires stopping and starting agents). If you stay in GPG+U2F land then you don't have these problems.
rileytg 9y ago
y4 is one more thing to worry about. to lose. to have stolen. to drop in the toilet. etc. i think part of the "theatre" is the whole convenience for safety thing. a few years ago it was gospel to change your passwords all the time. then some data started to point to this actually might be bad because it forced users into to using easy to remember things like sequences, or write them down (often in something like notes app or under keyboard on a sticky). while this may not be the good for military gov etc, it's probably a lot better for average joes. by making it easier to have pretty good security method, i can reasonably expect my users to stop doing stupid shit like keeping their keys on google drive (because "wernt you the guy who made us use drive because it's more secure than ftp?!"- yes many users are petty like that).
- ams6110 9y ago
  > y4 is one more thing to worry about. to lose. to have stolen. to drop in the toilet. etc. How is this different from your phone?
  - thedufer 9y ago
    Presumably most of the people in this thread already have a smartphone. So it isn't really one _more_ thing.
    - bigiain 9y ago
      Most of us have a keyring too - and losing that is a major pain in the ass. FOr me - I'd say my wallet/keys/phone are the objects I own that are "most secure".
      - rileytg 9y ago
        i'm keyless and loving it, true most aren't
        bigiain 9y ago
        So I have 4 motorcycles each with it's own key/keyring, my house keys, and my work keys. I've almost _always_ got three keyrings in my pocket.

tptacek 9y ago

The agent process is tricky to set up and persnickety, especially if you use the token for anything else besides SSH. At one point, before I tableflipped and switched back to software keys, I had to switch agent processes any time I used my Y4 to sign into a VPN. The theater is that you're protecting a key but not the account the key protects. Yes, you'll never lose the actual RSA key bits to an attacker. But that'll be cold comfort after an attacker uses a hijacked SSH process to compromise every account you log into. There's some value to the Y4 SSH key, don't get me wrong. It's just much less value than you'd expect from all the ceremony.

rileytg 9y ago
totally agreed on agent. also on provisioning the keys. my windows users eyes, even the more technical of the bunch, glaze over when teaching intro to your yubi key
spilk 9y ago
I switched my SSH keys on my Yubikey from using the OpenPGP applet and all the funkiness of gpg-agent over to using X.509 certificates with the PIV applet. Added bonus is that not only does it work with SSH, but you can use those certificates for TLS mutual authentication in web browsers. Works out of the box on Mac/Windows.
- edutechnion 9y ago
  Can you provide a link or reference to this path? I can't find much with basic searches and have given up several times on the gpg-connect-agent path while using Windows or Ubuntu. The path on Mac seems okay but on other platforms is way too difficult.
ryukafalz 9y ago
>Yes, you'll never lose the actual RSA key bits to an attacker. But that'll be cold comfort after an attacker uses a hijacked SSH process to compromise every account you log into. But if you enable (and require) the touch feature, it'll be pretty obvious if someone's trying to use your agent to authenticate somewhere else, no? I'd certainly notice if I had to press the button twice while I'm logging into a machine that should only request auth once (i.e. I'm not proxying through another box).
- derefr 9y ago
  They don't have to use your agent to authenticate again. They just feed commands to your SSH client binary that it then sends over the wire in your existing SSH session-context, with the SSH pty temporarily set to not echo input and discard output (or return it over the network to the attacker, but not render it in the local PTY character-buffer.) A hijacked SSH binary can even detect an elevation-requiring command you provided in the terminal and wrap it in a "sudo -c" along with a payload, such that the whole thing happens as one elevated "transaction", only hitting your agent once. Happily, this won't work if you only ever use SSH with a non-shell command, e.g. as a fancy encrypted netcat(1).
  - ryukafalz 9y ago
    Right, and that's still a problem, but not as much of a problem as if they were able to then use your key to authenticate to every other machine you have access to. The problem is at least contained to a single system at a time.
plttn 9y ago
FWIW, I never had that issue with my NEO on OSX/macOS. I was using my NEO for git signing, SSH, as well as U2F.
- hdhzy 9y ago
  tptacek's VPN probably uses PIV applet instead of GPG one and you can't switch them easily (requires stopping and starting agents). If you stay in GPG+U2F land then you don't have these problems.

rileytg 9y ago

y4 is one more thing to worry about. to lose. to have stolen. to drop in the toilet. etc. i think part of the "theatre" is the whole convenience for safety thing. a few years ago it was gospel to change your passwords all the time. then some data started to point to this actually might be bad because it forced users into to using easy to remember things like sequences, or write them down (often in something like notes app or under keyboard on a sticky). while this may not be the good for military gov etc, it's probably a lot better for average joes. by making it easier to have pretty good security method, i can reasonably expect my users to stop doing stupid shit like keeping their keys on google drive (because "wernt you the guy who made us use drive because it's more secure than ftp?!"- yes many users are petty like that).

ams6110 9y ago
> y4 is one more thing to worry about. to lose. to have stolen. to drop in the toilet. etc. How is this different from your phone?
- thedufer 9y ago
  Presumably most of the people in this thread already have a smartphone. So it isn't really one _more_ thing.
  - bigiain 9y ago
    Most of us have a keyring too - and losing that is a major pain in the ass. FOr me - I'd say my wallet/keys/phone are the objects I own that are "most secure".
    - rileytg 9y ago
      i'm keyless and loving it, true most aren't
      - bigiain 9y ago
        So I have 4 motorcycles each with it's own key/keyring, my house keys, and my work keys. I've almost _always_ got three keyrings in my pocket.