Public key authentication

How it works

SSH checks a signature against an authorized public key. The file protocol runs after that. The private key is the secret. A shared password on the same server is a second, weaker door if you leave it open.

A nightly SFTP job uses key billing-push. Password login is disabled. A leaked password from an old runbook does nothing. A leaked private key does. They rotate the key and remove the old public key the same hour.

How it differs

This is not mutual TLS. The channel is SSH. The idea, prove a key, is similar.

A key with no passphrase on a laptop is one theft away from the partner folder.

Passphrase the key or keep it on a host you control.

On the ticket

• The practical close is a log line: time, actor, byte count, result.
• Without that line the transfer is a story.
• With it, the next person can see whether this door did what the ticket claimed.
• If the path is shared, say so in the partner profile so a later change does not silently pick a different limit, key, or region.
• On a real ticket, write down the door, the byte count, and the clock.
• For public key authentication, that means naming the host or bucket, the expected size, and the time the other side must have a complete file.
• A progress bar is not that record.
• A 200 response that arrives before the complete call is not that record.
• If a retry is allowed, say how many and whether it resumes.
• If a person must approve the send, name the person.
• Partners who receive public key authentication files should match on hash or size before they import.
• A same-length corrupt file passes a size check and fails a hash.
• Keep the published hash off the only channel an attacker can edit, or treat it as a corruption check rather than a substitution check.
• When the path changes, new key, new region, new cap, update the profile the same day so the next run does not use a stale limit.