Simple File Transfer Protocol
RFC 913
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RFC - Historic
(September 1984; No errata)
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2013-03-02
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RFC 913 (Historic)
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Network Working Group Mark K. Lottor
Request for Comments: 913 MIT
September 1984
Simple File Transfer Protocol
STATUS OF THIS MEMO
This RFC suggests a proposed protocol for the ARPA-Internet
community, and requests discussion and suggestions for improvements.
Distribution of this memo is unlimited.
INTRODUCTION
SFTP is a simple file transfer protocol. It fills the need of people
wanting a protocol that is more useful than TFTP but easier to
implement (and less powerful) than FTP. SFTP supports user access
control, file transfers, directory listing, directory changing, file
renaming and deleting.
SFTP can be implemented with any reliable 8-bit byte stream oriented
protocol, this document describes its TCP specification. SFTP uses
only one TCP connection; whereas TFTP implements a connection over
UDP, and FTP uses two TCP connections (one using the TELNET
protocol).
THE PROTOCOL
SFTP is used by opening a TCP connection to the remote hosts' SFTP
port (115 decimal). You then send SFTP commands and wait for
replies. SFTP commands sent to the remote server are always 4 ASCII
letters (of any case) followed by a space, the argument(s), and a
<NULL>. The argument can sometimes be null in which case the command
is just 4 characters followed by <NULL>. Replies from the server are
always a response character followed immediately by an ASCII message
string terminated by a <NULL>. A reply can also be just a response
character and a <NULL>.
<command> : = <cmd> [<SPACE> <args>] <NULL>
<cmd> : = USER ! ACCT ! PASS ! TYPE ! LIST ! CDIR
KILL ! NAME ! DONE ! RETR ! STOR
<response> : = <response-code> [<message>] <NULL>
<response-code> : = + | - | | !
<message> can contain <CRLF>
Commands that can be sent to the server are listed below. The server
Lottor [Page 1]
RFC 913 September 1984
Simple File Transfer Protocol
replies to each command with one of the possible response codes
listed under each message. Along with the response, the server
should optionally return a message explaining the error in more
detail. Example message texts are listed but do not have to be
followed. All characters used in messages are ASCII 7-bit with the
high-order bit zero, in an 8 bit field.
The response codes and their meanings:
+ Success.
- Error.
An error occurred while processing your command.
Number.
The number-sign is followed immediately by ASCII digits
representing a decimal number.
! Logged in.
You have sent enough information to be able to log yourself in.
This is also used to mean you have sent enough information to
connect to a directory.
To use SFTP you first open a connection to the remote SFTP server.
The server replies by sending either a positive or negative greeting,
such as:
+MIT-XX SFTP Service
(the first word should be the host name)
-MIT-XX Out to Lunch
Lottor [Page 2]
RFC 913 September 1984
Simple File Transfer Protocol
If the server send back a '-' response it will also close the
connection, otherwise you must now send a USER command.
USER user-id
Your userid on the remote system.
The reply to this command will be one of:
!<user-id> logged in
Meaning you don't need an account or password or you
specified a user-id not needing them.
+User-id valid, send account and password
-Invalid user-id, try again
If the remote system does not have user-id's then you should
send an identification such as your personal name or host name
as the argument, and the remote system would reply with '+'.
ACCT account
The account you want to use (usually used for billing) on the
remote system.
Valid replies are:
! Account valid, logged-in
Account was ok or not needed. Skip the password.
+Account valid, send password
Account ok or not needed. Send your password next.
-Invalid account, try again
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RFC 913 September 1984
Simple File Transfer Protocol
PASS password
Your password on the remote system.
Valid replies are:
! Logged in
Password is ok and you can begin file transfers.
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