rfc1312.txt

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RFC 1312                Message Send Protocol 2               April 1992




             +--------+---------+---------+---------+
           0 |    B   |    c    |    h    |    r    |
             +--------+---------+---------+---------+
           4 |    i   |    s    |  <NULL> |  <NULL> |
             +--------+---------+---------+---------+
           8 |    H   |    i    |   <CR>  |   <LF>  |
             +--------+---------+---------+---------+
          12 |    H   |    o    |    w    |         |
             +--------+---------+---------+---------+
          16 |    a   |    b    |    o    |    u    |
             +--------+---------+---------+---------+
          20 |    t   |         |    l    |    u    |
             +--------+---------+---------+---------+
          24 |    n   |    c    |    h    |    ?    |
             +--------+---------+---------+---------+
          28 |  <NULL>|    s    |    a    |    n    |
             +--------+---------+---------+---------+
          32 |    d   |    y    |  <NULL> |    c    |
             +--------+---------+---------+---------+
          36 |    o   |    n    |    s    |    o    |
             +--------+---------+---------+---------+
          40 |    l   |    e    |  <NULL> |    9    |
             +--------+---------+---------+---------+
          44 |    1   |    0    |    8    |    0    |
             +--------+---------+---------+---------+
          48 |    6   |    1    |    2    |    1    |
             +--------+---------+---------+---------+
          52 |    3   |    2    |    5    |  <NULL> |
             +--------+---------+---------+---------+
          56 | <NULL> |
             +--------+


   Note that the RECIP-TERM  and SIGNATURE parts are empty. The COOKIE
   is the string "910806121325", which in this implementation indicates
   that the message was sent at 12:13:25 on the 6th of August, 1991.
   The identity if the sending and receiving systems is not included in
   the message; the server must obtain this information from the
   transport service.

   Advisories

   Client and server implementations must follow the character set
   restrictions noted in the MESSAGE part description. Failure to do so
   may have undesirable effects on the operation of the receiver's
   terminal; more seriously, it may open up a significant security



Nelson & Arnold                                                 [Page 5]

RFC 1312                Message Send Protocol 2               April 1992


   "hole". The checks must be made on any part of the message which may
   be displayed, including the sender's name and terminal.  This is one
   case where the admonition to "be liberal in what you accept" is not
   applicable. A server may chose to apply additional checks to an
   incoming message, and to reject any message which may pose a security
   risk. For example, a system using a PostScript-based display may
   reject a message which might be interpreted as an executable
   PostScript program.

   The underlying transport, whether TCP or UDP, is expected to provide
   checksums for the message and any response.

   The semantics of the various RECIPIENT and RECIP-TERM combinations
   may be confusing. The introduction of the "*" wildcard designation in
   the RECIP-TERM part makes it possible to send a message to all
   terminals on the designated system (if RECIPIENT is empty), or to all
   terminals at which a particular recipient has logged in.

   A positive acknowledgement may indicate only that the Message Send
   server was able to successfully invoke a local message delivery
   service. It may not be possible for true end-to-end semantics to be
   inferred.

   For example, a Message Send server may employ a local delivery
   mechanism which calls upon the services of a window system to display
   the message in a pop-up window. This process may take some
   significant time to complete, and it is unclear whether it is useful
   for the server to wait for an indeterminate period before returning
   an acknowledgement.  Therefore, this specification does not prescribe
   whether the acknowledgement is associated with delivery of the
   message to the local service, the display of the message, or
   confirmation by the user that the message has been read by, e.g.,
   dismissing the pop-up window.

Security Considerations

   Those who plan to implement this service must ensure that the
   following issues are reflected in the documentation of their
   products, and that their implementations include sufficient
   configuration controls to allow systems and network administrators to
   achieve the appropriate levels of usability and security.

   First, this service may allow someone to write on a user's terminal
   without the user giving his or her permission.  Where possible, users
   should be provided with a mechanism for disabling this.

   Second, it is extremely important for implementors to observe the
   rules for filtering message text as discussed under Message Syntax



Nelson & Arnold                                                 [Page 6]

RFC 1312                Message Send Protocol 2               April 1992


   above. Failure to do this may introduce major security holes.

   The third issue concerns the verification of the sender's identity.
   If the recipient is fooled into believing that a message is from a
   particular user, various security issues may arise. For example, the
   recipient may send a reply containing confidential material.

   This service is primarily intended for "open" environments:
   controlled local area networks used by reasonably trusted
   participants, in which security considerations may be relaxed in the
   interests of ease of use and administration. In such an environment
   it is appropriate to trust the user name and source IP address as
   identifying the actual sender of the message.

   Within more security-conscious environments, this assumption is
   probably unacceptable. As has been widely noted, there is no way
   within the current Internet architecture to ensure that the source
   address of an IP datagram is correct. Hence it is entirely possible
   for someone to spoof the IP address.

   The obvious, and simplest, answer is to disallow the use of this
   protocol in such situations.  However a more constructive approach is
   to incorporate within the protocol some mechanism by which a server
   can reliably identify the sender.

   In this version of the protocol specification, we define a SIGNATURE
   part within a message. If this part is empty, the identity of the
   sender cannot be verified, and the server implementation may elect to
   reject all such requests.  If the part is not empty, it is treated as
   a case-insensitive text encoding of some security token. This RFC
   does not define the encoding or interpretation of this token. We
   expect that such matters will form part of future RFCs on security
   and privacy issues; at an appropriate time, this RFC will be re-
   issued to include references to these RFCs.

Acknowledgements

   PostScript is a trademark of Adobe Systems, Inc.













Nelson & Arnold                                                 [Page 7]

RFC 1312                Message Send Protocol 2               April 1992


Authors' Addresses

   Russell Nelson
   Crynwr Software
   11 Grant St.
   Potsdam, NY 13676

   Phone:  [phone]
   EMail:  [e-mail]


   Geoff Arnold
   Sun Microsystems, Inc.
   2 Federal Street
   Billerica, MA 01821

   Phone:  [phone]
   EMail:  [e-mail]

































Nelson & Arnold                                                 [Page 8]