How do I add my Windows public key to an existing Linux account?

1. Transfer the public key

An existing authorised login method must already work. This upload does not expose the private key.

scp "$env:USERPROFILE\.ssh\server_ed25519.pub" adminuser@203.0.113.10:server_ed25519.pub

The destination is the account’s home directory. Confirm that the chosen temporary public-key filename will not overwrite another file.

2. Verify the public fingerprint before enrolment

In the existing remote session, confirm that the transferred file contains only the expected public key. Match its fingerprint to your locally generated key, and ensure it is not already enrolled.

ssh-keygen -lf "$HOME/server_ed25519.pub"

This read-only check must show the expected public fingerprint before you run the following enrolment block.

install -d -m 700 "$HOME/.ssh"
printf "\n" >> "$HOME/.ssh/authorized_keys"
cat "$HOME/server_ed25519.pub" >> "$HOME/.ssh/authorized_keys"
printf "\n" >> "$HOME/.ssh/authorized_keys"
chmod 600 "$HOME/.ssh/authorized_keys"

Run as the intended account. Leading and trailing newlines keep the new key separate even if an existing final line lacked a newline. Blank lines are harmless; existing keys remain in place.

3. Test a second connection

From a new Windows terminal, choose the corresponding private key explicitly.

ssh -o IdentitiesOnly=yes -i "$env:USERPROFILE\.ssh\server_ed25519" adminuser@203.0.113.10

Confirm successful login before ending the original session.