What Is Secure Shell (SSH)

What Is Secure Shell (SSH)

What Is Secure Shell (SSH)?

Secure Shell (SSH) is a computer program and a protocol for secure communication. The connection protocol requires an exchange of encryption keys at the beginning of the connection. Thereafter all the frames are encrypted. It becomes impossible to use a sniffer to see what the user. SSH was designed with the aim of replacing the various programs rlogin, telnet and rsh.

The SSH protocol

SSH comes in two major versions: the version 1.0 and version 2.0. The first version can connect remotely to a computer to get a shell or command line. This version still suffers from security problems in verifying the integrity of data sent or received, making it vulnerable to active attacks. In addition, this version implements a system of transmission of summary files, and port tunneling.

SSH protocol version 2, that was state of the draft until January 2006 is already widely used throughout the world. This version is much more cryptographically secure, and has an additional protocol file transfer complete.

Usually SSH uses port 22. It is used to open a shell (console) on a remote computer. Little use on the Windows (with PuTTY, OpenSSH, or cygwin), SSH refers to remote access on the Linux and Unix.

SSH can also be used for “Forward” TCP ports from one machine to another, creating a tunnel. This method is commonly used to secure a connection that is not (eg POP3 email protocol) as being transferred through the encrypted SSH tunnel.


OpenSSH (OpenBSD Secure Shell) is a set of free tools to secure communications over a computer network using the SSH protocol.

Created as an alternative open source software suite offered by the SSH Communications Security, OpenSSH is developed by the OpenBSD team, led by its founder, Theo de Raadt, and released under BSD license.
SSH file transfer protocol
In the context of secure shell (SSH), SFTP describes these two things here:

* A communication protocol running over SSH to transfer and manage files remotely;
* A command line program that implements the client part of this communication protocol, such as that provided by OpenSSH.

Compared to the previous protocol SCP, SFTP protocol supports many more operations on remote files. It behaves more like a protocol for file system. It is supposed to be more independent of the platform to use, eg with scp, extension wildcards (*) specified by the customer are charged to the server, which makes what he wants, then the architecture of STP avoids these problems.

The SFTP program provides an interface similar to FTP program. The SFTP protocol is not FTP over SSH or SSL (secure FTP visit) is a new protocol designed entirely by the IETF working group SECSH.

Some implementations of the program makes use scp protocol to SFTP protocol instead of SCP.

SFTP is often associated with the protocol (and program) SSH-2, because they were conceived together by the same group. However, it is possible to operate on SSH-1, and some implementations do.
Secure File Transfer Protocol or Secure File Transfer

Secure File Transfer Protocol (Secure File Transfer) is a variant of FTP which tunnel the session through a secure connection for the secure shell.

Since FTP uses multiple TCP connections (which is an exception in the list of TCP / IP), it is particularly difficult to achieve tunneling.

The name Secure FTP is not to be confused with other methods of securing FTP, such as FTPS.

~  Study: thanks to Wikipedia


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