unable to use sealed key (TPM_RC_AUTH_FAIL (session 1): the authorization HMAC check failed and DA counter incremented")

[FLX-0x00]

I have not been able to use my sealed key for a few weeks now. I tried to generate a new key with ssh-tpm-keygen, but it does not work either (different error message - something with hmac, not very sure about it). The whole setup worked flawlessly until 4-5 weeks ago. Is there any help in troubleshooting this problem? I have absolutely no idea where to start.

Things I tried:

• Restart everything
• restart the agent
• generate a new key direktly with ssh-tpm-keygen
• importing my current key again
• switching the kernel to lts
• installing latest release from git with the 0c68627 commit latest
• checking errors with journalctl -k --grep=tpm
• check if tpm2_pcrread works

After try to use the key the ssh-tpm-agent.service logs level=INFO msg="agent 13: failed getting handle: TPM_RC_INTEGRITY (parameter 1): integrity check failed"

my current working kernel is 6.10.3-arch1-2 (Arch Linux) keytype is ecdsa-sha2-nistp256

Hoping for some input on this =)

[Foxboron]

Could you write out the commands from your terminal?

[FLX-0x00]

With a complete new key:

ム ssh-add -D
All identities removed.
ム ssh-add -L
The agent has no identities.
ム ssh-tpm-keygen
Generating a sealed public/private ecdsa key pair.
Enter file in which to save the key (/home/xxx/.ssh/id_ecdsa): 
/home/xxx/.ssh/id_ecdsa.tpm already exists.
Overwrite (y/n)? y
/home/xxx/.ssh/id_ecdsa.pub already exists.
Overwrite (y/n)? y
Enter pin (empty for no pin): 
Confirm pin: 
Your identification has been saved in /home/xxx/.ssh/id_ecdsa.tpm
Your public key has been saved in /home/xxx/.ssh/id_ecdsa.pub
The key fingerprint is:
SHA256:q8ZLwQvwx7ne2C/xxxxxxxxxxxx
The key's randomart image is the color of television, tuned to a dead channel.
ム ssh-add -L
The agent has no identities.
ム systemctl --user restart ssh-tpm-agent.service
ム ssh-add -L
ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBG1kcvbUpwS5vpn/xxxxxxxxxxxx
ム git pull
sign_and_send_pubkey: signing failed for ECDSA "/home/xxx/.ssh/id_ecdsa" from agent: agent refused operation
ム systemctl --user status ssh-tpm-agent.service
● ssh-tpm-agent.service - ssh-tpm-agent service
     Loaded: loaded (/home/xxx/.config/systemd/user/ssh-tpm-agent.service; indirect; preset: enabled)
     Active: active (running) since Thu 2024-08-08 00:22:36 CEST; 1min 46s ago
 Invocation: 37c20871df2147e79f878f837e6f593b
TriggeredBy: ● ssh-tpm-agent.socket
       Docs: man:ssh-agent(1)
             man:ssh-add(1)
             man:ssh(1)
   Main PID: 18718 (ssh-tpm-agent)
      Tasks: 7 (limit: 115482)
     Memory: 4.8M (peak: 6M)
        CPU: 179ms
     CGroup: /user.slice/user-1000.slice/user@1000.service/app.slice/ssh-tpm-agent.service
             └─18718 /usr/bin/ssh-tpm-agent -A /run/user/1000/ssh-agent.socket

Aug 08 00:22:36 xxx systemd[1641]: Started ssh-tpm-agent service.
Aug 08 00:22:36 xxx ssh-tpm-agent[18718]: time=2024-08-08T00:22:36.263+02:00 level=INFO msg="Activated agent by socket"
Aug 08 00:24:19 xxx ssh-tpm-agent[18718]: time=2024-08-08T00:24:19.566+02:00 level=INFO msg="agent 13: failed to sign: TPM_RC_AUTH_FAIL (session 1): the authorization HMAC check failed and DA counter incremented"

Edit 00:48: I will go to bed =) checking things in the next morning

[Foxboron]

I can't reproduce this.

Are you sure you are using the build from the git checkout for all your commands?

[Foxboron]

It's also worth pointing out that the error from the terminal example is different from the initial error you reported

[FLX-0x00]

Jep. The error message is not the same. Error message in the title displays only when using my original key and not a new one. I am using the AUR git package. Not sure how to investigate further into this.

[FLX-0x00]

Anyway, thanks for your time and effort. I will set up a new arch linux environment and try to get this to work. If you cannot reproduce it - its definitely my system or config. What is confusing is the fact that the agent and key worked fine until last month.

[Foxboron]

If you could tell me which version the old key was created with i can try to bisect it.

[FLX-0x00]

The old key was created with ssh-keygen from arch linux on a air gapped system because I want to backup the private key. Then I imported / sealed it with ssh-tpm-keygen --import

[Foxboron]

Ah, lol.

I forgot I deprecated the format from the previous release :)

https://github.com/Foxboron/ssh-tpm-agent/releases/tag/v0.5.0

If the old key is made with the previous version please recreate it. If the issue is with the key you have ran --import on i can continue to look at it.

[FLX-0x00]

I dont think so - I have used the linux build in command to generate my own key - but maybe this is the point? I have read the notes with the breaking changes and thought, they do not effect me because I have not generated my key with ssh-tpm-keygen but if the import is also affected... I will git clone the repo and compile ssh-tpm-keygen for myself to be sure.

[Foxboron]

--import wraps the ssh key with the TSS keyfile format, so it's affected.

[Foxboron]

I'll be more clear in future announcements if you feel the previous one was unclear :)

[FLX-0x00]

Sorry for keeping you up on this, but I went all in as I saw this repo and used only the TPM sealed key for anything because the Yubikey GPG agent is quite pain in the ass ;)

So with the new binaries the old error is gone but the key does not work. The new error message appears now: time=2024-08-08T23:21:55.061+02:00 level=INFO msg="agent 13: failed to sign: TPM_RC_AUTH_FAIL (session 1): the authorization HMAC check failed and DA counter incremented"

[FLX-0x00]

What about the public key?

The tool asks:

Sealing an existing public/private key pair.
id_ecdsa.pub already exists.
Overwrite (y/n)? y

but the pub key is not modified. I the public key is removed the ssh-tpm-keygen will not continue. Maybe its totally confusing but thats only my observations.

But I have tested with new keys so this should not matter.

[Foxboron]

but the pub key is not modified. I the public key is removed the ssh-tpm-keygen will not continue. Maybe its totally confusing but thats only my observations.

I'm just mimicking ssh-keygen and don't check the content of the file as we have not created the key yet. It should not matter.

[Foxboron]

Sorry for keeping you up on this, but I went all in as I saw this repo and used only the TPM sealed key for anything because the Yubikey GPG agent is quite pain in the ass ;)

No worries!

[FLX-0x00]

Even with a complete new key I can not get this to work. Error message stays the same :/

Is there any chance to get deeper? jounalctl and systemd status has not much info for me. Encrypting and decrypting using gpg works fine btw. from TPM.

[Foxboron]

I suspect there is a regression from when I introduced wrapped keys. I don't have any test coverage for the key creation stuff so it's a bit hard to write proper tests for.

https://github.com/Foxboron/ssh-tpm-agent/commit/5334976e9a09040609b294de73a50b1ea97bdbc4

[FLX-0x00]

Sounds reasonable. Is there anything that I can help you?

[Foxboron]

I've tried two sets of P256 keys with no password, with a password, and imported them all to my ssh-tpm-agent and sshed to my NAS. I'm still unable to recreate the error you are seeeing.

λ ssh-tpm-agent master Ɇ » ssh-keygen -t ecdsa -b 256 -f ./testkey
λ ssh-tpm-agent master Ɇ » ./bin/ssh-tpm-keygen --import ./testkey
λ ssh-tpm-agent master Ɇ » ./bin/ssh-tpm-add ./testkey.tpm

Am I missing something?

[Foxboron]

Please make sure you do make and run the binaries from ./bin.

ssh-tpm-agent can be ran with debug mode enabled.

λ ssh-tpm-agent master Ɇ » export SSH_AUTH_SOCK="/run/user/$(id -u)/ssh-tpm-agent.sock"
λ ssh-tpm-agent master Ɇ » ./bin/ssh-tpm-agent -d

Client

λ ssh-tpm-agent master Ɇ » export SSH_AUTH_SOCK="/run/user/$(id -u)/ssh-tpm-agent.sock"
λ ssh-tpm-agent master Ɇ » ssh-keygen -t ecdsa -b 256 -f ./testkey
λ ssh-tpm-agent master Ɇ » ./bin/ssh-tpm-keygen --import ./testkey
λ ssh-tpm-agent master Ɇ » ./bin/ssh-tpm-add ./testkey.tpm

[FLX-0x00]

Hm. Maybe the ssh-tpm-add is the thing...for adding I always restarted the service. the ssh-tpm-add do not work in zsh or bash for my system O.o first parameter is not recognized

[Foxboron]

Lol, sorry. I pushed a commit now fixing it :) The CA stuff had faulty logic.

EDIT: Even more funny I had the fix locally while writing. I just forgot it would affect you as well while debugging this!

[FLX-0x00]

hehe :D nice - love the bleeding edge!

even with debugging agent (service and socket stopped)

time=2024-08-09T00:08:14.956+02:00 level=DEBUG msg="called extensions"
time=2024-08-09T00:08:14.956+02:00 level=DEBUG msg="called list"
time=2024-08-09T00:08:14.967+02:00 level=DEBUG msg="called signwithflags"
time=2024-08-09T00:08:15.709+02:00 level=INFO msg="agent 13: failed to sign: TPM_RC_AUTH_FAIL (session 1): the authorization HMAC check failed and DA counter incremented"
time=2024-08-09T00:08:15.721+02:00 level=DEBUG msg="called signwithflags"
time=2024-08-09T00:08:16.465+02:00 level=INFO msg="agent 13: failed to sign: TPM_RC_AUTH_FAIL (session 1): the authorization HMAC check failed and DA counter incremented"

[Foxboron]

Is this with or without a password?

[FLX-0x00]

with pin. will try without a pin

[Foxboron]

with pin.

Do you have an ssh askpass package installed :)?

[Foxboron]

I'm betting you don't.

I have for some reason implemented this in a way where we never actually check if an askpass binary is available before we continue. So your pin is never added to the TPM object which fails the AUTH check.

https://github.com/Foxboron/ssh-tpm-agent/blob/master/cmd/ssh-tpm-agent/main.go#L220

I'll try and rework this tomorrow and provide a clear error, but in the meantime you can install x11-ssh-askpass.

[FLX-0x00]

I just bury myself

[Foxboron]

I just bury myself

Nah, it's my fault. There should be a clear error somewhere instead of silently continuing.

[FLX-0x00]

Yes. Before this requirement it was using the casual arch linux default dialog that works for gpg

[FLX-0x00]

I never looked into new dependancies...now it worked but the interface for the pin looks like Windows 95 or earlier :D

[Foxboron]

Pinentry depends on gnupg so it's a bit awkward to have with an ssh-agent. I'll fix this tomorrow and sorry for the issue :)

I never looked into new dependancies...now it worked but the interface for the pin looks like Windows 95 or earlier :D

Yes, there are some kde versions and stuff. I was contemplating writing some GUI thing for this and bundle it with this agent but havent had time to look at it.

[FLX-0x00]

Oh man thanks for this incredible debug session :D what a damn issue. Yeah I am on XFCE so that was never a thing before

[FLX-0x00]

My ssh directory totally messed up. Time to check btrfs snapshots :D

Thanks for taking time into this and the whole project! Awesome

[Foxboron]

No worries. Thanks for not loosing faith in me :)

[FLX-0x00]

Maybe its time for a new release. I was using the official arch package and as well the git package. I am not sure if the binaries were up to date, especially now with the ./ssh-tpm-add fixes and maybe the pinentry workaround.

[Foxboron]

I'll do a release after fixing the askpass error stuff.