SFTP

SFTP, or the SSH File Transfer Protocol, is a network protocol that provides secure file access, transfer, and management over a secure channel established by the SSH protocol. It is designed to securely replace older file transfer methods such as FTP and FTPS and typically operates over SSH-2 on port 22. All commands and data are transmitted through the SSH connection, offering encryption, integrity, and authenticity.

SFTP runs as a subsystem of SSH. After authentication, the client starts the SFTP subsystem, and the server exposes a set of operations such as open, close, read, write, delete, rename, and directory listings. Transfers are conducted through a binary protocol that carries file attributes and permissions, and supports symbolic links and resuming operations.

SFTP is standardized as part of the SSH File Transfer Protocol and is widely implemented. It relies on SSH for authentication, typically using passwords, public keys, or other SSH methods. It usually listens on port 22 but can be configured to operate on different ports when used with SSH.

Common implementations include OpenSSH's sftp and the sftp-server component, PuTTY's pscp/sftp, and GUI clients such as FileZilla and WinSCP. Software libraries such as libssh and Paramiko provide programmatic SFTP access. SFTP is widely used for secure remote administration, automated backups, and software deployment.

Compared with FTP and FTPS, SFTP tends to be simpler to firewall and configure because it uses a single encrypted channel rather than separate control and data connections. However, performance and compatibility considerations depend on the SSH server configuration and client support.