SCP, or Secure Copy Protocol, is a method based on (Secure Shell) SSH for safely transferring computer files between a local host and a remote host, or between two remote hosts. The protocol is a “secure” implementation of the RCP (Remote Copy Protocol)—a protocol for transferring files across a network.
SCP combines RCP’s file transfer capabilities with SSH’s authentication and encryption features, creating a hybrid protocol. This ensures the confidentiality of the data in transit, effectively thwarting packet sniffers from gleaning sensitive information from the data packets. Additionally, SCP leverages SSH’s advantages by preserving file permissions and timestamps during uploads.
SCP operates over the SSH protocol, offering an authentication mechanism that ensures both the authenticity and confidentiality of files during transfer, like how SSH secures the obsolete and less secure Telnet protocol. With SCP’s authentication system between hosts and encryption during data transfer, it guarantees the integrity and security of the data being moved.
When users employ applications to transfer files between a server and a client, or in the opposite direction, the SCP protocol typically facilitates these transfers unless the SFTP protocol has been set as the default. SCP enables rapid file transfers through command line use, which is often quicker and more straightforward than using a graphical client interface. Additionally, the command line utility of SCP is advantageous for automating the transfer of batch files and scripts.
How does SCP Protocol work?
Secure Copy requires authentication from the participating hosts. Before initiating a transfer via this protocol, an SSH connection must be established between the local host and the designated remote host. This process involves entering the authorized key as part of the public key authentication procedure.
Once the SSH connection is established between the two hosts, the SCP client can initiate the secure copy operation in either source mode or sink mode. To activate source mode, which reads files from the remote host to send to the client, the SCP client typically uses the -f flag. Conversely, to enable sink mode for transferring data to the remote host, the -t flag is used. In source mode, the SCP client requests and retrieves files from the distant host. In sink mode, the client signals the remote host to prepare for receiving and writing incoming data.
Typically, the syntax of an SCP program is like the syntax of cp (copy). If you wish to copy a local file to a remote host, then you should type in the following command:
scp LocalSourceFile user@remotehost:directory/TargetFile
If you would like to copy a file from remote host or copy a folder from remote host (with -r switch), the following commands apply respectively:
scp user@remotehost:directory/SourceFile LocalTargetFile
scp -r user@host:directory/SourceFolder LocalTargetFolder
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