How To Use SCP (Safe Copy) With SSH Key Authentication

Anybody who administers Linux machines seemingly is aware of safe shell. With out this device, administering these servers remotely can be fairly difficult. It could additionally change into tougher to maneuver information forwards and backwards, at the least with a modicum of safety. That’s the place safe copy comes into play. With the SCP command, you may copy information to and from a distant Linux server by way of an encrypted SSH tunnel.

SEE: The way to View Your SSH Keys in Linux, macOS, and Home windows

Nonetheless, with the assistance of SSH key authentication, you may make that much more safe. I need to present you ways you should utilize safe key authentication and SCP so you may relaxation assured your information are being moved forwards and backwards securely. I’ll exhibit on an Elementary OS shopper and Ubuntu 16.04.1 server and assume you have got a safe shell put in and dealing.

SSH keys

The very first thing that have to be achieved is to create an SSH key pair. To do that, open up a terminal window and subject the command:

ssh-keygen -t rsa

You can be requested to call the file (use the default) and provides the keypair a passphrase.

As soon as the important thing’s randomart prints, your key is able to go.

The following step is to repeat the important thing to the distant server. That is achieved with the command:

ssh-copy-id USER@SERVER

The place USER is the username of the distant server, and SERVER is the tackle of the distant server.

You can be prompted for the distant person password. When you efficiently authenticate, the general public key will likely be copied to the server. You’re able to go.

SEE: Securing Linux coverage (Tech Professional Analysis)

Utilizing SCP together with your key

Now that our keys are in all the appropriate locations, let’s see how we are able to use them by way of SCP. Assuming you accepted the default title on your SSH key upon creation, the command to ship a file to your distant server utilizing your SSH key’s:

scp -i ~/.ssh/id_rsa.pub FILENAME USER@SERVER:/residence/USER/FILENAME

The place FILENAME is the title of the file, USER is the username on the distant machine, and SERVER is the tackle of the distant server.

You ought to be prompted for the SSH key password (not the person password). As soon as authenticated, the file will likely be transferred.

The identical holds true if it’s essential pull a file from the distant server. The construction of that command can be:

scp -i ~/.ssh/id_rsa.pub USER@SERVER:/residence/USER/FILENAME /residence/USER/FILENAME

Once more, you can be requested on your SSH key password, and the file will likely be pulled from the server and copied to the native machine.

SEE: The way to Add an SSH Fingerprint to Your known_hosts File in Linux

Neglect that password

Let’s say you might be about to bear an extended session of copying information to your server. Certain, you may tar all of them up into one greater file. However say they should all be positioned in numerous directories. That’s a whole lot of typing. You may make this barely extra environment friendly through the use of the ssh-agent and ssh-add instructions.

That’s proper, utilizing the mixture of SCP, SSH key authentication, and ssh-agent works effectively. This may preserve you from having to kind that SSH key password each time you subject the SCP command. The one caveat is that you have to bear in mind the PID of the agent session and kill it whenever you’re achieved.

Right here’s what it’s important to do.

1. Earlier than issuing the SCP command subject eval ssh-agent to begin the session.
2. Make an observation of the Course of ID you might be given when the session begins.
3. Add your SSH key to the session with the command ssh-add.
4. Begin utilizing SCP to repeat your information.

That’s all there’s to it. While you’re achieved with the session, guarantee to subject the command kill PID (the place PID is the precise quantity given to you whenever you began the ssh-agent session with eval).

SEE: 20 fast tricks to make Linux networking simpler (free PDF) (TechRepublic)

Is SCP nonetheless safe?

Somebody asking if SCP is safe has seemingly learn the 2019 launch announcement for OpenSSH 8.0, which acknowledged that the SCP protocol is “outdated, rigid and never readily mounted” and really helpful SFTP and Rsync as options for file switch.

Earlier than OpenSSH 8.0, SCP couldn’t confirm file integrity throughout transfers, leaving customers uncovered to unauthorized overwrites and injection assaults if their server was compromised (CVE-2019-611). Nonetheless, the replace launched stricter filename checking because the default for the SCP command, making it safer, and moved its earlier non-checking conduct to the command scp -T.

Then, in OpenSSH 9.0, launched in 2022, SFTP was adopted because the default backend for SCP as a substitute of the legacy SCP/RCP protocol, that means that transfers are actually encrypted and authenticated with the SSH protocol. Whereas broadly considered safe, customers ought to nonetheless be cautious of different dangers like misconfigured servers or outdated software program variations.

What can I take advantage of as a substitute of SCP?

• SFTP: Whereas SCP defaults to utilizing the SFTP protocol, you may think about using native SFTP shoppers for superior file administration because it permits for extra operations, similar to viewing directories and file deletion.
• Rsync: Ultimate for synchronizing information and directories, particularly for incremental backups and huge datasets. See TechRepublic’s information on tips on how to again up a community utilizing Rsync.
• FTPS: A safe possibility for conventional FTP transfers with SSL/TLS encryption, however it may be advanced to configure.
• HTTPS-based instruments: Resembling curl or wget, for safe downloads over HTTPS. That is nice for automation, however they don’t present full listing administration like SFTP.

Fiona Jackson up to date this text in January 2025.