14.7. Overview of Supported File Transfer Protocols

14.7.1. Introduction

For those not familiar with the supported file transfer protocols, this page serves as an introduction to the protocols.

Not all protocols are available for both server-side and client-side implementations.

14.7.2. FTP

Protocol supported on both Server-side and Client-side

Shortform for File Transfer Protocol, the objectives of FTP are 1) to promote sharing of files (computer programs and/or data), 2) to encourage indirect or implicit (via programs) use of remote computers, 3) to shield a user from variations in file storage systems among hosts, and 4) to transfer data reliably and efficiently. FTP, though usable directly by a user at a terminal, is designed mainly for use by programs. Source from RFC 959.

Even though FTP is offered, it is highly recommended that a secure protocol be used. Please read on for other recommendations.

14.7.3. Explicit FTPS / FTPES (over TLS)

Protocol supported on both Server-side and Client-side

Explicit FTPS / FTPES is a security extension of FTP.

In explicit mode, an FTPS client must "explicitly request" security from an FTPS server and then step up to a mutually agreed encryption method. If a client does not request security, the FTPS server can either allow the client to continue in insecure mode or refuse the connection. Source from FTPS wiki.

Please note that the "implementation of this protocol extension does not ensure that each and every session and data transfer is secure, it merely provides the tools that allow a client and/or server to negotiate an acceptable or required level of security for that given session or data transfer." Source from RFC 4217

14.7.4. Implicit FTPS / FTPIS (over SSL)

Protocol supported on Server-side

Implicit FTPS / FTPIS is a security extension of FTP.

In implicit mode, an FTPS client is expected to "immediately expected to challenge the FTPS server with a TLS ClientHello message. If such a message is not received by the FTPS server, the server should drop the connection."

This protocol extension is considered to be a deprecated SSL negotiation mechanism (Source from IETF Appendix A Auth FTP SSL) and unlike Explicit FTPS is not defined in RFC 4217.

14.7.5. SFTP (over SSH version 2)

Protocol supported on both Server-side and Client-side

SFTP, shortform of SSH File Transfer Protocol and also Secure File Transfer Protocol, is a network protocol that allows for file access, transfer and management capabilities over the SSH (Secure Shell) protocol channel. It is thus considered one of the secure protocols to implement.

SFTP is designed to be used to implement a secure remote file system service and also a secure file transfer service.

SFTP should run over a secure channel, SSH, so that the server has already authenticated the client. The identity of the client user should also be available to the protocol.

The SFTP protocol follows a simple request-response model.

Each request and response contains a sequence number and multiple requests may be pending simultaneously. There are a relatively large number of different request messages, but a small number of possible response messages. Each request has one or more response messages that may be returned in result (e.g., a read either returns data or reports error status). Source from IETF Secure Shell Working Group Internet Draft 13.

It is worth nothing that SFTPPlus is only an SFTP/SCP server and does not support certain mechanisms of an SSH server such as virtual terminal or remote execution.

14.7.6. SCP (over SSH version 2)

Protocol supported only on Server-side

SCP, shortform of Secure Copy Protocol, is another network protocol with file transfer capabilities over the SSH (Secure Shell) protocol channel. The implementation of SCP within SFTPPlus is limited. SCP is a simple, non-standard protocol, with no official public specification. SFTPPlus is only an SFTP/SCP server and does not execute external 'scp' applications. It only supports file upload and download, without support for file management operations such as rename, delete, etc. Only remote execution of the 'scp' command is allowed. Support for recursive operations is not yet implemented.

Unlike SFTP, this protocol has some limited capabilities, such as in file management. We recommend that SFTP be used instead.

14.7.7. HTTP

Protocol supported only on Server-side

HTTP, shortform for Hypertext Transfer Protocol, is an application-level protocol for distributed, collaborative, hypermedia information systems. It is a generic, stateless, protocol which can be used for many tasks. Source from RFC 2616. While HTTP is available, it is highly recommended the HTTPS be implemented.

14.7.8. HTTPS

Protocol supported only on Server-side

HTTPS, shortform for HTTP over TLS, provides security measures in using HTTP via SSL and its successor, TLS.

The HTTPS service can be invoked by starting SFTPPlus and accessing the service via the URL on a web browser. Once accessed, you will be able to see the graphical interface designed to work in any web browser.

For those wishing to use a web browser option with their file transfer needs, HTTPS is recommended.

14.7.9. WebDAV over HTTPS

Protocol supported only on Client-side

Shortform for Web Distributed Authoring and Versioning, WebDAV is the extension to the HTTP protocol allowing clients to perform remote web content authoring operations. Source from RFC 2518.

The SFTPPlus implementation will be utilizing the HTTPS extension on client-side only with the authentication mechanism based on the claim-based method from Office 365 SharePoint Online service.

14.7.10. Azure Files over HTTPS

Protocol supported only on Client-side

SFTPPlus can exchange files with the Azure Files service provided by the Azure Storage account.

The communication is done over HTTPS. HTTP access is not supported.