[1] The IETF Internet Draft states that, even though this protocol is described in the context of the SSH-2 protocol, it could be used in a number of different applications, such as secure file transfer over Transport Layer Security (TLS) and transfer of management information in VPN applications.
An SFTP client's extra capabilities include resuming interrupted transfers, directory listings, and remote file removal.
SFTP is not FTP run over SSH, but rather a new protocol designed from the ground up by the IETF SECSH working group.
The Internet Engineering Task Force (IETF) working group "Secsh" that was responsible for the development of the Secure Shell version 2 protocol (RFC 4251) also attempted to draft an extension of that standard for secure file transfer functionality.
[6] After a seven-year hiatus, in 2013 an attempt was made to restart work on SFTP using the version 3 draft as the baseline.
[7] Prior to the IETF's involvement, SFTP was a proprietary protocol of SSH Communications Security, designed by Tatu Ylönen with assistance from Sami Lehtinen in 1997.
The SFTP protocol supports a generic way of indicating extended commands, along with a method of including them in version negotiation.
An SSH-2 server which supports subsystems may be leveraged to keep a uniform SSH implementation while enhancing access controls with third party software, at the cost of fine-grained integration with connection details, and SSH-1 compatibility.
Examples of such a tool are Shell Control Box from Balabit[12] and CryptoAuditor from SSH Communications Security[13] (the original developer of the Secure Shell protocol) which provides functions such as SFTP transaction logging and logging of the actual data transmitted on the wire.