One of these, PBSZ, appears to be redundant and is probably included only to satisfying the RFC specification. Three commands are used, AUTH, PBSZ, and PROT. After the switch, all FTP commands are encrypted, but importantly, data is not encrypted unless further commands are provided. To do so, the client issues an AUTH command, upon which the client and the server negotiate a secure connection. These commands tell the server whether or not subsequent data-channels should be secure.Ĭlients can connect to FTPS servers in unencrypted mode, and then switch to secure mode upon request. Data- channels are not secured until PBSZ and PROT commands are issued. The AUTH command only secures the control-channel. Only one control-channel is used in each session, but several data-channels may be used – one for each data transfer. ![]() Securing Control and Data ChannelsįTP sessions use two channels: control and data. Unless implicit mode is required it is best to have the implicit mode FTPS protocol disabled in CompleteFTP. Implicit FTPS clients can still be found, but explicit mode is always preferred. FTPS protocol clients send the AUTH command prior to logging in so that credentials are secured. This meant that unencrypted FTP clients can connect on the same port as FTPS protocol clients - the unencrypted clients simply never send an AUTH command and the session remains unencrypted. Typically, the implicit FTPS protocol uses port 990 rather than the standard FTP port 21.Įxplicit FTPS fixed this by requiring the AUTH command to be sent by the client prior to securing the connection. If FTP and FTPS (implicit) are to be supported on the same server, they require different port numbers. This is a problem for unencrypted FTP clients - they will no longer be able to connect on a server port that requires securing the connection immediately. Upon connecting, implicit FTPS protocol clients automatically start securing the connection using SSL/TLS. Implicit FTPS and Explicit FTPSĪn early version of the FTPS protocol is now known as implicit FTPS Protocol. The FTPS protocol was designed to fix this by encrypting communications using the SSL/TLS protocol, which is specifically designed for securing network connections.įTPS is an IETF standard as described in RFC 4217. This means eavesdroppers sniffing the network will have little trouble obtaining credentials and copies of the transferred files. ![]() This article explains the FTPS protocol and how FTPS server software such as CompleteFTP can be used to securely transfer files.įTPS (FTP Secure) is FTP over SSL connections.Ī significant problem with "plain" FTP is that it is not secure - usernames, passwords and data are sent across the network in the clear.
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