rfc913.txt

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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


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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














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   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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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.

            +Send account

               Password ok but you haven't specified the account.

            -Wrong password, try again


































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   You cannot specify any of the following commands until you receive a
   '!' response from the remote system.

      TYPE { A | B | C }

         The mapping of the stored file to the transmission byte stream
         is controlled by the type.  The default is binary if the type
         is not specified.

         A - ASCII

            The ASCII bytes are taken from the file in the source
            system, transmitted over the connection, and stored in the
            file in the destination system.

            The data is the 7-bit ASCII codes, transmitted in the
            low-order 7 bits of 8-bit bytes.  The high-order bit of the
            transmission byte must be zero, and need not be stored in
            the file.

            The data is "NETASCII" and is to follow the same rules as
            data sent on Telnet connections.  The key requirement here
            is that the local end of line is to be converted to the pair
            of ASCII characters CR and LF when transmitted on the
            connection.

            For example, TOPS-20 machines have 36-bit words.  On TOPS-20
            machines, The standard way of labeling the bits is 0 through
            35 from high-order to low-order.  On TOPS-20 the normal way
            of storing ASCII data is to use 5 7-bit bytes per word.  In
            ASCII mode, the bytes transmitted would be [0-6], [7-13],
            [14-20], [21-27], [28-34], (bit 35 would not be
            transmitted), each of these 7-bit quantities would be
            transmitted as the low-order 7 bits of an 8-bit byte (with
            the high-order bit zero).

            For example, one disk page of a TOPS-20 file is 512 36-bit
            words.  But using only 35 bits per word for 7-bit bytes, a
            page is 17920 bits or 2560 bytes.










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         B - BINARY

            The 8-bit bytes are taken from the file in the source
            system, transmitted over the connection, and stored in the
            file in the destination system.

            The data is in 8-bit units.  In systems with word sizes
            which are not a multiple of 8, some bits of the word will
            not be transmitted.

            For example, TOPS-20 machines have 36-bit words.  In binary
            mode, the bytes transmitted would be [0-7], [8-15], [16-23],
            [24-31], (bits 32-35 would not be transmitted).

            For example, one disk page of a TOPS-20 file is 512 36-bit
            words.  But using only 32 bits per word for 8-bit bytes, a
            page is 16384 bits or 2048 bytes.

         C - CONTINUOUS

            The bits are taken from the file in the source system
            continuously, ignoring word boundaries, and sent over the
            connection packed into 8-bit bytes.  The destination system
            stores the bits received into the file continuously,
            ignoring word boundaries.

            For systems on machines with a word size that is a multiple
            of 8 bits, the implementation of binary and continuous modes
            should be identical.

            For example, TOPS-20 machines have 36-bit words.  In
            continuous mode, the bytes transmitted would be [first word,
            bits 0-7], [first word, bits 8-15], [first word, bits
            16-23], [first word, bits 24-31], [first word, bits 32-35 +
            second word, bits 0-3], [second word, bits 4-11], [second
            word, bits 12-19], [second word, bits 20-27], [second word,
            bits 28-35], then the pattern repeats.

            For example, one disk page of a TOPS-20 file is 512 36-bit
            words.  This is 18432 bits or 2304 8-bit bytes.

         Replies are:

            +Using { Ascii | Binary | Continuous } mode

            -Type not valid



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      LIST { F | V } directory-path

         A null directory-path will return the current connected
         directory listing.

         F specifies a standard formatted directory listing.

            An error reply should be a '-' followed by the error message
            from the remote systems directory command.  A directory
            listing is a '+' followed immediately by the current
            directory path specification and a <CRLF>.  Following the
            directory path is a single line for each file in the
            directory.  Each line is just the file name followed by
            <CRLF>.  The listing is terminated with a <NULL> after the
            last <CRLF>.

         V specifies a verbose directory listing.

            An error returns '-' as above.  A verbose directory listing
            is a '+' followed immediately by the current directory path
            specification and a <CRLF>.  It is then followed by one line
            per file in the directory (a line ending in <CRLF>).  The
            line returned for each file can be of any format.  Possible
            information to return would be the file name, size,
            protection, last write date, and name of last writer.
























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RFC 913                                                   September 1984
Simple File Transfer Protocol


      CDIR new-directory

         This will change the current working directory on the remote
         host to the argument passed.

         Replies are:

            !Changed working dir to <new-directory>

            -Can't connect to directory because: (reason)

            +directory ok, send account/password

         If the server replies with '+' you should then send an ACCT or
         PASS command.  The server will wait for ACCT or PASS commands
         until it returns a '-' or '!' response.

            Replies to ACCT could be:

               !Changed working dir to <new-directory>

               +account ok, send password