How to Enable RSA Encryption Algorithm Key in OpenSSH 8.8: Step-by-Step Guide for Secure SSH Connections

💡 Pro Tip: Always use the latest secure algorithms when possible. Only re-enable RSA for legacy compatibility!

🎯 Why Was RSA Disabled in OpenSSH 8.8?

OpenSSH 8.8+ disables RSA/SHA-1 by default due to security and obsolescence concerns. However, some legacy systems (e.g., old Git servers) still require RSA keys for authentication.

Key Points:

• ✅ RSA/SHA-1 is considered weak
• ✅ OpenSSH prefers modern algorithms (ED25519, ECDSA)
• ✅ Legacy servers may only support RSA

🚀 Step-by-Step: Re-Enabling RSA in OpenSSH 8.8+

1. Prepare Your Environment

• Use Docker or a VM for safe testing
• Ensure you have OpenSSH 8.8+ and a legacy server (e.g., GitLab)

2. Generate an RSA Key

ssh-keygen -t rsa -b 4096 -C "your_email@example.com"
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_rsa

3. Upload Public Key to Server

cat ~/.ssh/id_rsa.pub
# Copy to your Git server's SSH settings

4. Test SSH Connection

ssh -T -v git@x.x.x.x
# If you see: send_pubkey_test: no mutual signature algorithm
# It means RSA is disabled by default

🔧 How to Re-Enable RSA/SHA-1 in OpenSSH

Edit your ~/.ssh/config:

Host x.x.x.x
  HostkeyAlgorithms +ssh-rsa
  PubkeyAcceptedAlgorithms +ssh-rsa

Save and retry your SSH connection:

ssh -T -v git@x.x.x.x
# You should now connect successfully

📈 OpenSSH 8.8+ vs Previous Versions

🚨 Security Best Practices

• Use ED25519 or ECDSA keys for new systems
• Only re-enable RSA for legacy compatibility
• Regularly update OpenSSH and monitor security advisories
• Restrict RSA usage to specific hosts in your SSH config
• Never share your private key

🔗 Related Articles

• How to Use Multiple GitHub Accounts with SSH
• Jenkins Server Setup with SSH Keys
• P2P Technology Fundamentals: IPv4 and NAT
• STUN, TURN, and ICE Protocols

✅ Conclusion

Re-enabling RSA in OpenSSH 8.8+ is sometimes necessary for legacy compatibility, but always prefer modern, secure algorithms when possible.

Key Takeaways:

• 🎯 RSA/SHA-1 is deprecated for security
• 🛡️ Use only for legacy systems
• 🔧 Configure SSH client for compatibility
• 📈 Prefer ED25519/ECDSA for new deployments

💡 Pro Tip: Regularly audit your SSH keys and configurations to maintain strong security!