SSH File Transfer Protocol

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In computing, the SSH File Transfer Protocol or SFTP is a network protocol that provides file transfer and manipulation functionality over any reliable data stream. It is typically used with the SSH-2 protocol (TCP port 22) to provide secure file transfer, but is intended to be usable with other protocols as well.

Capabilities

Compared to the earlier, deprecated, SCP protocol, which allows only file transfers, the SFTP protocol allows for a range of operations on remote files – it is more like a remote file system protocol. An SFTP client's extra capabilities compared to an SCP client include resuming interrupted transfers, directory listings, and remote file removal. For the same reason it is reasonable to implement a GUI SFTP client, but not a GUI SCP client.

SFTP attempts to be more platform-independent than SCP; for instance, with SCP, the expansion of wildcards specified by the client was up to the server, whereas SFTP's design avoids this problem. While SCP was most frequently implemented on Unix platforms, there exist SFTP servers for most platforms.

A common misconception is that SFTP is simply FTP run over SSH; in fact it is a new protocol designed from the ground up by the IETF SECSH working group. It is sometimes confused with Simple File Transfer Protocol.

The protocol itself does not provide authentication and security; it expects the underlying protocol to secure this. SFTP is most often used as subsystem of SSH protocol version 2 implementations, having been designed by the same working group. However, it is possible to run it over SSH-1 (and some implementations support this) or other data streams. Running SFTP server over SSH-1 is not platform independent as SSH-1 does not support the concept of subsystems. An SFTP client willing to connect to an SSH-1 server needs to know the path to the SFTP server binary on the server side.

The Secure Internet Live Conferencing (SILC) protocol defines the SFTP as its default file transfer protocol. In SILC the SFTP data is not protected with SSH but SILC's secure packet protocol is used to encapsulate the SFTP data into SILC packet and to deliver it peer-to-peer. This is possible as SFTP is designed protocol independent.

For uploads, the transferred files may be associated with their basic attributes, such as timestamps. This is an advantage over the common FTP protocol, which does not have provision for uploads to include the original date/timestamp attribute.

Standardization

The protocol is not yet an Internet standard. The latest specification is an expired Internet Draft, which defines version 6 of the protocol. Currently the most widely used version is 3, implemented by the popular OpenSSH SFTP server. Many Microsoft Windows-based SFTP implementations use version 4 of the protocol, which lessened its ties with the Unix platform.

The Internet Engineering Task Force (IETF) "Secsh Status Pages" search tool contains links to all versions of the Internet draft-ietf-secsh-filexfer which describes this protocol.

SFTP client

The term SFTP can also refer to Secure file transfer program, a command-line program that implements the client part of this protocol, such as that supplied with OpenSSH.

The sftp program provides an interactive interface similar to that of traditional FTP clients.

Some implementations of the scp program actually use the SFTP protocol to perform file transfers; however, some such implementations are still able to fallback to the SCP protocol if the server does not provide SFTP service.

References

See also

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