[byjpr]

Closes #12

Changes

• Verify first. just install scans the stock image's ed25519 host key, shows its fingerprint, and requires you to paste the matching fingerprint from the provider's web console before anything is uploaded.
  • The console shows it in cloud-init's "SSH HOST KEY FINGERPRINTS" boot output, or via ssh-keygen -lf … after logging in there.
  • INSTALL_HOST_FINGERPRINT=SHA256:… skips the prompt.
  • Typing trust skips verification explicitly, with a warning.
• Pin it. The verified key is pinned for:
  • detect-machine.sh, which no longer uses accept-new;
  • nixos-anywhere. It always passes -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no, and OpenSSH uses the first value given for an option, so --ssh-option can't override it. An ssh wrapper placed first on PATH puts the pinned options in front. nixos-anywhere's Nix wrapper appends its own openssh last on PATH, so the wrapper is the one used.
• The nixos-anywhere kexec installer keeps the stock image's host keys (nixos-anywhere relies on this), so the pin holds through the installer phase too. The server's private host key, which also decrypts all secrets, is only ever sent to the verified machine.

Testing

I ran a local sshd and called the wrapper with nixos-anywhere's exact options appended:

Pinned key	Result
correct key	connected
a different key	Host key verification failed.

All 5 provider example systems build. nixfmt, shellcheck and tofu validate pass.

🤖 Generated with Claude Code

https://claude.ai/code/session_01G22o7QQ17GRtkCqpJNFr9B

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