One of the main features of the SSH protocol is that almost the entire communication between the client and the server is encrypted - including the authentication of the user. (Naturally, the negotiation of the encryption method to be used is in plain text). During the initialization of the session server authentication is performed and parameters for encryption, data compression and integrity verification of the data transferred are negotiated. The protocol enforces user authentication and is capable of authenticating the user via various methods: password, RSA key, Challenge/Response schemes like S/Key and OPIE, etc.
The typical uses of SSH include the following:
- Remote shell
Remotely administer a computer via an interactive terminal console. This is one of the most widespread uses of SSH.
- Remote command execution
Execute commands on the remote machine. Remote command execution can also result in significant data transfer, for example when performing scheduled or manual tasks such as file copying (scp), data or file synchronization (rsync), creating archive backups (tar), etc.
- TCP IP forwarding (also known as port forwarding)
It is possible to tunnel any TCP/IP connection from the client or from the server into the encrypted SSH channel. It can also be used to forward communication otherwise not allowed, such as the access of ports banned by the security policy. This allows to secure any - normally unencrypted - data transfer and is frequently used as an easy way to secure connections between the hosts without the need to set up full VPN connections.
- File transfer
Securely transfer files using SFTP.
- X11 forwarding
Applications running on the server and requiring graphical interface (X Window) appear on the client's monitor, but run on the server in all other respect, thus it is possible to work with them remotely.
- Agent forwarding:
Transfer authentication requests to the client machine.
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