SSH - Secure Shell

calendarMay 6, 2025 · 2 min read · Info

SSH (Secure Shell) is a cryptographic network(encryption and decryption) protocol that allows secure communication between a client and a server over an unsecured network. It encrypts all data sent between your computer and the remote machine, keeping passwords, commands, and files safe from hackers.

Why SSH?

SSH is required because older protocols like Telnet, FTP, and rlogin transmit data — including usernames and passwords — in plain text, making them vulnerable to eavesdropping and attacks.

🔒 Why SSH is better:

  • Encryption: Unlike Telnet or FTP, SSH encrypts all communication.
  • Authentication: SSH uses secure methods like public-key authentication.
  • Integrity: It ensures that data isn't altered during transmission.
  • All-in-One: SSH can replace multiple insecure tools (e.g., Telnet, FTP, rsh) with a single secure solution.

SSH uses three main types of encryption to secure communication:

  • Symetric Encryption.
  • Asymmetric Encryption.
  • Hashing.

Symmetric Encryption.

  • Both client and server use the same secret key to encrypt and decrypt data.
  • Key is securely exchanged during the handshake.
  • It's fast and used for the actual data transfer.
  • Example: AES, ChaCha20 (Algorithms used.)

Symmetrical encryption is often called shared key or shared secret encryption.

Asymmetric Encryption.

  • Uses a key pair: a public key and a private key.
  • Helps in secure login and key exchange.
  • server has the public key, and client has the private key.
  • Example: RSA, Ed25519.(Algorithms used.)

Hashing (MAC – Message Authentication Code).

  • Ensures data integrity — checks if the data was changed in transit.
  • Example: HMAC-SHA256(Algorithms used.)

Generating SSH Key:

1ssh-keygen -t ed25519 -C "your_email@example.com"

If you are using a legacy system that doesn't support the Ed25519 algorithm, use:

1ssh-keygen -t rsa -b 4096 -C "your_email@example.com"

For example let's create a ssh key for my system:

1ssh-keygen -t rsa -b 4096 -C "your_email@example.com"

then you'll get these:

1Enter file in which to save the key (/home/you/.ssh/id_algorithm):[enter]
2Enter passphrase (empty for no passphrase): [Type a passphrase] or [enter].
3Enter same passphrase again: [Type passphrase again]or [enter].

then you'll get your public/private key.

just type : ls -al, go to .ssh folder, then cat id_rsa to get private key, and cat id_rsa.pub to get public key. Then you can share this public key with the server, you want to connect with.