Nevertheless, at least you will be guaranteed that every subsequent connection you ever make to that machine is going to the right place. You actually have no guarantee on this first encounter that you are really talking to the host you think it is. Another approach is that, rather than knowing the host keys before hand, SSH clients will save host keys at the moment of first connection.Once this done, every SSH client will know about every SSH host key before they even connect for the first time. A system admin writes a script that gathers up all the host public keys in an organization, creates an ssh_known_hosts listing them all, and places this file in the /etc/sshd directory on every system in the organization.Key distribution can happen on of the two following ways: One way to deal with identifying machines on the Internet is to deploy your own Public Key Infrastructure(PKI) but using public-key infrastructure would be quite a cumbersome process for something like SSH.Īn SSH server, when installed, creates its own random public-private key pair that is not signed by anybody. This is to make sure that you don’t reveal username or password an attacker who got hold of server’s address. Then, before the client is willing to divulge any further information, it demands proof of the remote server’s identity. When an SSH client first connects to a remote host, the two exchange temporary public keys that let them encrypt the rest of their conversation without revealing any information to any watching third parties. We’ll not delve into SSH protocol internals, we’ll only look at the connection flow. A port forward that intercepts TCP connections.īefore automating SSH connections, we’ll take a brief look at how SSH conections are established.A file transfer session letting you browse the remote filesystem.The individual execution of a single command.An interactive shell session, like that supported by Telnet.Once connected on SSH, you can create several kinds of channels: So using an SSH connection for as many operations justifies the high intitial expense of setting it up. It’s takes a few second of real time to setup an SSH connection. Multiplexing makes sense because the real expense of an SSH connection is setting it up. Every block of information SSH sends across its socket is labeled with a “channel” identifier so that several conversations can share the socket. SSH has a notion of ‘channels’, mutliple channels can run on same SSH socket. SSH is a sophisticated protocol that implements its own multiplexing. IP protocol has no clue about the different applications running at transport layer. UDP and TCP use the concept of port numbers, let’s several different applications run on a machine over single IP. SSH preserved all the great features of the early remote-shell protocol added wit hsecurity, encryption and efficient multiplexing.SSH is descended from the ‘r’-family of protocols(rlogin, rsh, and rcp).SSH protocol is one of the best-known examples of a secure, encrypted protocol.Socket.error, socket.gaierror, paramiko.SSHException Secure remote shell, file transfer, port forwarding
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