this post was submitted on 16 Jul 2023
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How do you handle secrets in home automation? (sh.itjust.works)
submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/selfhosted
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Say you have a script or something that gets run in cron/task scheduler and it needs a password.. say to ssh to a raspberry pi elsewhere in your house.

How do you save that password in a way that automation can access it?

Some ideas:

  • Plaintext file. Not a fan because its sitting unencrypted on the box somewhere.
  • Environment variable. Not a fan because its still unencrypted somewhere to someone on the box (albeit likely the same user or an admin).
  • A secrets manager. If I use something locally like hashicorp vault or infisical, I can get to a point where a cli/api call gets the password. Though in this case I still need a vault password/secret to get my password. So I fall back to needing one of the above to get this to work.

If the secrets manager is easily available, the secret to get into the secrets manager is available as well leading to a feeling of security by obscurity.

If someone breaks into my system via SSH/etc. then they can get the passwords either way.

.. How do people normally do this? I'm not sure I actually get anything out of a secrets manager if its local and I have the disk itself encrypted before login.

What actually makes sense at a personal/home scale?

(Edit: I know using SSH key probably is better for getting to the raspberry pi, but still the question is the same idea).

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[–] [email protected] 26 points 1 year ago* (last edited 1 year ago) (1 children)

If you want to get fancy: systemd credentials. It can store the secrets encrypted on disk and seal the encryption key with the TPM chip. The encrypted secret is decrypted (non-interactively) and made available only to a specific systemd service. The process itself does not need special systemd integration--it just sees a plain text file containing the secret, backed by a tmpfs that's not visible to other processes.

Depending on which TPM PCRs you bind to, you can choose how secure you want it to be. A reasonable/usable configuration would be something like binding to PCRs 7 and 14. With that setup, the TPM will not unseal the key if the system is booted into any other OS (i.e. anything signed with a different UEFI Secure Boot key). But if you really want to lock things down, you can bind to additional PCRs and make it so changing any hardware, boot order, BIOS setting, etc. will prevent the TPM from unsealing the key.

[–] [email protected] 6 points 1 year ago

TIL, thanks!