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SSH (Secure Shell) is a network protocol used to securely connect to remote machines over an unsecured network. It ensures confidentiality, integrity, and authentication for remote access, file transfers, and command execution, protecting data from eavesdropping and tampering.
Here’s a breakdown of the main events that occur during an SSH connection:
1) Key Exchange
SSH begins with a key exchange process, typically using the Diffie-Hellman algorithm. The client and server exchange public components to derive a shared secret, creating a secure session key for encrypted communication without transmitting sensitive private keys.
2) Server Verification
The client validates the server’s identity by checking its public key against a locally stored `known_hosts` file. This prevents man-in-the-middle (MITM) attacks, ensuring the connection is established only with a trusted server.
3) Session Key & Encryption Setup
After establishing the shared secret, SSH derives a symmetric session key. This key encrypts all subsequent communication, providing both confidentiality (data remains private) and integrity (modifications are detected).
4) Client Authentication
The client proves its identity through authentication methods, such as public key authentication. The client signs a server-provided challenge with its private key, and the server verifies it using the client’s public key.
You Should Know:
SSH Commands & Practical Usage
Basic SSH Connection
ssh username@remote_host
Using a Specific Port
ssh -p 2222 username@remote_host
Generating SSH Keys
ssh-keygen -t rsa -b 4096
Copying Public Key to Remote Server
ssh-copy-id username@remote_host
SSH Config File (~/.ssh/config)
Host myserver HostName server.example.com User myuser Port 2222 IdentityFile ~/.ssh/my_private_key
Checking SSH Fingerprint (Server Verification)
ssh-keygen -lf /etc/ssh/ssh_host_rsa_key.pub
Forcing SSH to Use a Specific Key
ssh -i ~/.ssh/custom_key username@remote_host
Tunneling with SSH (Port Forwarding)
ssh -L 8080:localhost:80 username@remote_host Local forwarding ssh -R 9000:localhost:3000 username@remote_host Remote forwarding
Disabling Password Authentication (Hardening SSH)
Edit `/etc/ssh/sshd_config`:
PasswordAuthentication no PermitRootLogin no
Then restart SSH:
sudo systemctl restart sshd
Debugging SSH Connection Issues
ssh -vvv username@remote_host
What Undercode Say:
SSH is a fundamental tool for secure remote administration, but many users only scratch the surface of its capabilities. Beyond basic logins, SSH enables:
– Secure file transfers (scp, sftp)
– Tunneling (bypassing firewalls securely)
– Agent forwarding (managing keys securely)
– Automated scripts (using `sshpass` or `expect` carefully)
For advanced hardening:
- Use ed25519 keys (
ssh-keygen -t ed25519) - Enforce 2FA via SSH (Google Authenticator PAM module)
- Rotate keys frequently and use certificate-based auth
Expected Output:
A secure, encrypted, and authenticated remote session with full control over remote systems while preventing eavesdropping and MITM attacks.
Further Reading:
References:
Reported By: Nikkisiapno How – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
