Advanced SSH Key Authentication for Secure SFTP Access

Published {$created} by Carsten Blum

SSH key authentication is one of the most reliable and secure ways to access servers and cloud storage endpoints — and it’s the preferred method when working with SFTP, SCP, or managed cloud storage like ftpGrid.

In this tutorial, we’ll go beyond the basics of generating SSH keys and dive into advanced topics such as key management, rotation, multiple identity setups, and automation.

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Why SSH Keys Matter

SSH keys eliminate the need for passwords in secure file transfer scenarios. Instead of typing your password every time, your client authenticates using a cryptographic key pair — a private key (which stays on your machine) and a public key (which you upload to the server).

Using keys instead of passwords provides:

Stronger protection against brute-force attacks
Easier automation of backups, scripts, and uploads
Integration with CI/CD pipelines and IoT devices
Compatibility with SFTP, SCP, rsync, and cloud systems like ftpGrid

1. Choosing the Right Key Type

There are several SSH key algorithms available. The most common are:

Type	Description	Recommended
RSA	Traditional and widely supported	Still good for compatibility
ED25519	Modern, faster, smaller, and more secure	Recommended
ECDSA	Efficient but less portable	Use with caution

Generate a new ED25519 key:

ssh-keygen -t ed25519 -C "your_email@example.com" -f ~/.ssh/id_ed25519

Or generate an RSA key (for legacy systems):

ssh-keygen -t rsa -b 4096 -C "your_email@example.com" -f ~/.ssh/id_rsa

2. Securing Your Private Key

Your private key should never be shared. Keep it locked down with the correct permissions:

chmod 600 ~/.ssh/id_ed25519

You can also encrypt it with a passphrase for extra protection during login.To avoid typing it every time, use an SSH agent:

eval "$(ssh-agent -s)" ssh-add ~/.ssh/id_ed25519

Tip: The SSH agent keeps your key decrypted in memory, so scripts and SFTP sessions can use it securely without prompting for a password.

3. Managing Multiple Keys with `~/.ssh/config`

If you use different keys for different services, you can configure them in your SSH config file for easy access.

Edit or create ~/.ssh/config:

Host ftpgrid HostName edgeN.ftpgrid.com User PREFIX.demo IdentityFile ~/.ssh/id_ed25519_ftpgrid IdentitiesOnly yes

Now you can simply connect with:

sftp ftpgrid

This setup keeps things clean and avoids conflicts between personal, corporate, or test keys.

4. Using SSH Keys for Automated Transfers

SSH keys are perfect for automated uploads, nightly backups, or CI/CD deployment pipelines.Here’s a simple example using SFTP batch mode:

Create a batch file:

echo "put backup.sql /backups/" > batch.txt

Run automated upload:

sftp -b batch.txt ftpgrid

Or use SCP:

scp -i ~/.ssh/id_ed25519 ./backup.sql ftpgrid:/backups/

You can schedule it with cron for periodic uploads:

crontab -e

Example entry (daily at 03:00):

0 3 * * * scp -i ~/.ssh/id_ed25519 /data/backup.sql ftpgrid:/backups/

5. Rotating SSH Keys Safely

Security best practices suggest rotating SSH keys periodically — especially for production or shared environments.

Steps to rotate keys:

Generate a new key pair
Upload the new public key to ftpGrid (via web dashboard or API)
Test connection using the new key
Remove the old key from the authorized list

Always test before removing the old key to avoid losing access.

6. Using SSH Key Authentication with ftpGrid

ftpGrid supports full SSH key authentication for both SFTP and SCP.Once you have your public key, simply upload it in your ftpGrid dashboard under:

Storage accounts -> Create account

Then connect using your configured alias:

sftp ftpgrid

You’ll have instant access without typing a password, using secure encrypted authentication.

7. Key Takeaways

Use ED25519 keys for best performance and security
Protect your private keys with proper file permissions and passphrases
Automate secure transfers using batch scripts or cron jobs
Rotate SSH keys periodically
Use ~/.ssh/config for clean multi-key management
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