Notes

Here's an explanation of how SSH works.
A description of SSH
SSH is a remote administration protocol that allows users to manage their remote servers through the Internet. A secure alternative to unencrypted Telnet was created and uses cryptographic techniques to protect all communication to and from the remote server. This authentication mechanism allows the client to provide input to the host, and the host to relay this information back to the client.

Here is an example SSH window. A Linux or macOS user can connect to their remote server directly from a terminal window. SSH clients like Putty can be installed on Windows. The shell commands you issue when remote accessing the computer can be also executed as if you were using the computer physically.


An example of SSH connection to illustrate how it works
We will explore the basics of SSH, along with the underlying technologies used by the protocol to provide the opportunity for secure remote access. Online SSH Client Among other things, it will describe the different types of encryption and their purposes.

Workings of SSH
SSH can be used very easily when using Linux or Mac. You must use an SSH client on Windows in order to establish SSH connections. There is no doubt that PuTTY is the most popular SSH client. Find more details here.

Mac and Linux users should use their terminal programs to follow the steps outlined below:

There are three parts to SSH:

Log in as user@host
Your system will respond to an SSH key command by prompting it to open an encrypted Secure Shell connection. You are trying to access the user account of [user]. In that case, you could try accessing the root user, which is effectively equivalent to the system administrator, and has full authority to modify anything on the computer. You connect to the computer by typing [host]. IP addresses (e.g. 2319) ) (e.g. XYZ Domain).

If you press enter, you'll be asked for the requested account password. Your password will not be displayed on the screen but it is being transmitted. Press enter once more after you're finished typing. Upon entering a valid password, a remote terminal window will be displayed.

See more SSH commands here.

Understanding encryption techniques
Over its predecessors, SSH offers the advantage of using encryption to encrypt information transfers between the host and the client. Client and host are two terms that refer to the server and computer you are using to access the server. SSH uses three different encryption technologies:

Synchronous encryption
Using asymmetric encryption
Hashing.
An encryption technique called symmetric encryption
Using symmetric encryption means both the client and the host use an identical secret key for encrypting and decrypting a message. A key holder can decrypt the message effectively.

How to symmetrically encrypt files with SSH

Symmetrical encryption is also known as shared key or shared secret encryption. Usually, one key is used, or sometimes a pair of them where the first key can be calculated by using the second key.

SSH session encryption uses symmetric keys. It is agreed between the client and server how to derive the secret key, and that key is never disclosed to a third party. In symmetric key creation, a key exchange algorithm is used. A unique characteristic of this algorithm is that the key is never transmitted between the client and the server. Rather than simultaneously calculating the key, the two computers split public pieces of data and manipulate them independently. A machine that captures the publicly shared data will still not be able to compute the key since it doesn't know the key exchange algorithm.

A secret token must be noted, however, since it is generated before client authentication in each SSH session. As soon as the key is generated, all packets that travel between the two machines must be encrypted. A user's credentials are always protected from network packet sniffers, including the password he types into the console.

There are a variety of symmetrical encryption ciphers, including, but not limited to, AES (Advanced Encryption Standard), CAST128 Blowfish. Before establishing a secure connection, the client and the host decide the cipher to use, by listing supported ciphers in order of preference. A bidirectional cipher is selected from the clients supported ciphers that are present on the hosts list.

As an example, if two Ubuntu 1404 LTS machines are syncing over SSH, each will use aes128-ctr by default.

Encryption based on asymmetric principals
As opposed to symmetrical encryption, asymmetrical encryption uses two different keys for encryption and decryption. There are two types of keys, the public key and the private key. The public and private keys together form a pair.


Asymmetric Cryptography

According to its name, the public key is freely distributed and distributed among all parties. Though the public key is closely tied to the private key in terms of functionality, the private key cannot be calculated mathematically from the public key. The relationship between the two keys is highly complex: a message encrypted by a machine's public key can only be decrypted by that machine's private key. A one-way relationship means that neither the public key nor the private key can decrypt each other's messages.


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