Written by Alex Taylor | 11/18/2023

SCP (Secure Copy Protocol)

Secure Copy Protocol (SCP) is a network protocol that supports file transfers between hosts on a network. SCP uses Secure Shell (SSH) for data transfer and utilizes the same mechanisms for authentication, thereby ensuring the confidentiality and security of the data during transit. It is a simple and efficient means to copy files from one host to another over a secure, encrypted connection.

SCP is typically used for copying files between a local and a remote host or between two remote hosts. It is a command-line tool, and its operation is similar to the older rcp command but with the added security provided by SSH.

Key Features of SCP:

  • Secure Transfer: SCP uses SSH for data transfer, which encrypts the session, making it more secure against network sniffing attacks.
  • Authentication: Like SFTP, SCP requires valid SSH credentials for authentication before file transfer can commence, which can include passwords or SSH keys.
  • Non-Interactive Batch Operations: SCP is often used in scripts and automated tasks because it does not require user interaction once authentication credentials are set.
  • Preservation of File Attributes: SCP can preserve file attributes like timestamps and permissions during the transfer process.

How SCP Works:

  1. A user initiates an SCP command and specifies the source file and the destination location, which can be on a local machine or a remote machine.
  2. The SCP client contacts the SCP server (which is typically an SSH server) on the remote host.
  3. The user authenticates using SSH credentials. If the credentials are accepted, the server initiates the file transfer.

The SCP command-line syntax for copying files is straightforward. To copy a file from a local to a remote system, the command would look like this:

scp /path/to/local/file username@remote:/path/to/remote/directory

To copy a file from a remote system to the local system, the command would be:

scp username@remote:/path/to/remote/file /path/to/local/directory

SCP does not have an interactive interface and lacks the more advanced file management features of SFTP. It is primarily designed for secure file transfer and not for remote file system navigation or file management. SCP is generally faster than SFTP at transferring files, especially when dealing with a large number of files, because it uses a more straightforward protocol.

However, SCP is considered less secure than SFTP for a few reasons:

  • It is susceptible to various attacks, such as man-in-the-middle, if strict host key checking is not enforced.
  • SCP protocol does not have a well-defined standard as SFTP does, which can lead to inconsistencies in implementation.

Despite its simplicity and speed, SCP is being gradually replaced by SFTP and rsync (for more advanced features like delta encoding) in many applications. This is due to their richer feature sets and more robust security models, which are crucial for modern secure file transfer requirements. Nevertheless, SCP remains a valuable tool for quick and secure file transfers in many administrative tasks and scripted operations.