🔐 Definition — SSH, or Secure Shell, is a network protocol that provides secure remote access to computers over unsecured networks, ensuring encrypted data communications and strong authentication.

🖥️ Usage — SSH is widely used by network administrators for secure remote management of systems, executing commands, and transferring files between computers over a network.

🔑 Authentication — SSH supports both password and public key authentication, with the latter being more secure. SSH keys consist of a public and a private key, where the public key is shared and the private key is kept secure.

🔒 Security — SSH uses encryption techniques like symmetric and asymmetric encryption, along with hashing, to secure data transmission and authenticate users and hosts.

🌐 Applications — SSH is used for secure remote access, managing routers, server hardware, virtualization platforms, and operating systems, as well as for secure file transfers and command execution.

How SSH Works

🔄 Client-Server Model — SSH operates on a client-server model where the client initiates a connection to the server, which listens for connections on a specific port, typically port 22.

🔑 Key Exchange — During the initial connection, SSH uses a key exchange algorithm to establish a secure channel, ensuring that both parties agree on encryption keys.

🔍 Host Authentication — The server presents its public key to the client, which checks it against known hosts to verify the server's identity.

🔐 Data Encryption — Once authenticated, all data exchanged between the client and server is encrypted, ensuring confidentiality and integrity.

🖥️ Remote Command Execution — SSH allows users to execute commands on a remote server as if they were physically present, providing a secure shell session.

SSH Key Management

🔑 Key Pair Generation — Users generate SSH key pairs using tools like ssh-keygen, which creates a public and a private key for secure authentication.

📂 Key Storage — The private key is stored securely on the user's local machine, while the public key is added to the server's authorized_keys file.

🔄 Key Rotation — Regularly rotating SSH keys enhances security by reducing the risk of key compromise.

🔒 Passphrase Protection — Adding a passphrase to the private key provides an additional layer of security, requiring the passphrase for key usage.

🛡️ Key Distribution — Public keys can be distributed freely, but private keys must be kept confidential to prevent unauthorized access.

SSH Security Practices

🔒 Disable Password Login — For enhanced security, disable password-based logins and rely on SSH key authentication.

🔍 Monitor Access — Regularly monitor SSH access logs for suspicious activity to detect potential security breaches.

🔄 Update Regularly — Keep SSH software up to date to protect against vulnerabilities and exploits.

🛡️ Limit Access — Restrict SSH access to trusted IP addresses and use firewalls to control incoming connections.

🔐 Use Strong Keys — Generate SSH keys with strong cryptographic algorithms like RSA or ED25519 to ensure robust security.

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