File: rfc3080.txt

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Network Working Group                                            M. Rose
Request For Comments: 3080                        Invisible Worlds, Inc.
Category: Standards Track                                     March 2001


              The Blocks Extensible Exchange Protocol Core

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This memo describes a generic application protocol kernel for
   connection-oriented, asynchronous interactions called the BEEP
   (Blocks Extensible Exchange Protocol) core.  BEEP permits
   simultaneous and independent exchanges within the context of a single
   application user-identity, supporting both textual and binary
   messages.
























Rose                        Standards Track                     [Page 1]

RFC 3080                     The BEEP Core                    March 2001


Table of Contents

   1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  4
   2.      The BEEP Core  . . . . . . . . . . . . . . . . . . . . . .  5
   2.1     Roles  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   2.1.1   Exchange Styles  . . . . . . . . . . . . . . . . . . . . .  6
   2.2     Messages and Frames  . . . . . . . . . . . . . . . . . . .  7
   2.2.1   Frame Syntax . . . . . . . . . . . . . . . . . . . . . . .  8
   2.2.1.1 Frame Header . . . . . . . . . . . . . . . . . . . . . . .  9
   2.2.1.2 Frame Payload  . . . . . . . . . . . . . . . . . . . . . . 12
   2.2.1.3 Frame Trailer  . . . . . . . . . . . . . . . . . . . . . . 13
   2.2.2   Frame Semantics  . . . . . . . . . . . . . . . . . . . . . 14
   2.2.2.1 Poorly-formed Messages . . . . . . . . . . . . . . . . . . 14
   2.3     Channel Management . . . . . . . . . . . . . . . . . . . . 15
   2.3.1   Message Semantics  . . . . . . . . . . . . . . . . . . . . 16
   2.3.1.1 The Greeting Message . . . . . . . . . . . . . . . . . . . 16
   2.3.1.2 The Start Message  . . . . . . . . . . . . . . . . . . . . 17
   2.3.1.3 The Close Message  . . . . . . . . . . . . . . . . . . . . 20
   2.3.1.4 The OK Message . . . . . . . . . . . . . . . . . . . . . . 23
   2.3.1.5 The Error Message  . . . . . . . . . . . . . . . . . . . . 23
   2.4     Session Establishment and Release  . . . . . . . . . . . . 25
   2.5     Transport Mappings . . . . . . . . . . . . . . . . . . . . 27
   2.5.1   Session Management . . . . . . . . . . . . . . . . . . . . 27
   2.5.2   Message Exchange . . . . . . . . . . . . . . . . . . . . . 27
   2.6     Asynchrony . . . . . . . . . . . . . . . . . . . . . . . . 28
   2.6.1   Within a Single Channel  . . . . . . . . . . . . . . . . . 28
   2.6.2   Between Different Channels . . . . . . . . . . . . . . . . 28
   2.6.3   Pre-emptive Replies  . . . . . . . . . . . . . . . . . . . 29
   2.6.4   Interference . . . . . . . . . . . . . . . . . . . . . . . 29
   2.7     Peer-to-Peer Behavior  . . . . . . . . . . . . . . . . . . 30
   3.      Transport Security . . . . . . . . . . . . . . . . . . . . 31
   3.1     The TLS Transport Security Profile . . . . . . . . . . . . 34
   3.1.1   Profile Identification and Initialization  . . . . . . . . 34
   3.1.2   Message Syntax . . . . . . . . . . . . . . . . . . . . . . 35
   3.1.3   Message Semantics  . . . . . . . . . . . . . . . . . . . . 36
   3.1.3.1 The Ready Message  . . . . . . . . . . . . . . . . . . . . 36
   3.1.3.2 The Proceed Message  . . . . . . . . . . . . . . . . . . . 36
   4.      User Authentication  . . . . . . . . . . . . . . . . . . . 37
   4.1     The SASL Family of Profiles  . . . . . . . . . . . . . . . 38
   4.1.1   Profile Identification and Initialization  . . . . . . . . 39
   4.1.2   Message Syntax . . . . . . . . . . . . . . . . . . . . . . 42
   4.1.3   Message Semantics  . . . . . . . . . . . . . . . . . . . . 43
   5.      Registration Templates . . . . . . . . . . . . . . . . . . 44
   5.1     Profile Registration Template  . . . . . . . . . . . . . . 44
   5.2     Feature Registration Template  . . . . . . . . . . . . . . 44
   6.      Initial Registrations  . . . . . . . . . . . . . . . . . . 45
   6.1     Registration: BEEP Channel Management  . . . . . . . . . . 45
   6.2     Registration: TLS Transport Security Profile . . . . . . . 45



Rose                        Standards Track                     [Page 2]

RFC 3080                     The BEEP Core                    March 2001


   6.3     Registration: SASL Family of Profiles  . . . . . . . . . . 46
   6.4     Registration: application/beep+xml . . . . . . . . . . . . 47
   7.      DTDs . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
   7.1     BEEP Channel Management DTD  . . . . . . . . . . . . . . . 48
   7.2     TLS Transport Security Profile DTD . . . . . . . . . . . . 50
   7.3     SASL Family of Profiles DTD  . . . . . . . . . . . . . . . 51
   8.      Reply Codes  . . . . . . . . . . . . . . . . . . . . . . . 52
   9.      Security Considerations  . . . . . . . . . . . . . . . . . 53
           References . . . . . . . . . . . . . . . . . . . . . . . . 54
           Author's Address . . . . . . . . . . . . . . . . . . . . . 55
   A.      Acknowledgements . . . . . . . . . . . . . . . . . . . . . 56
   B.      IANA Considerations  . . . . . . . . . . . . . . . . . . . 57
           Full Copyright Statement . . . . . . . . . . . . . . . . . 58






































Rose                        Standards Track                     [Page 3]

RFC 3080                     The BEEP Core                    March 2001


1. Introduction

   This memo describes a generic application protocol kernel for
   connection-oriented, asynchronous interactions called BEEP.

   At BEEP's core is a framing mechanism that permits simultaneous and
   independent exchanges of messages between peers.  Messages are
   arbitrary MIME [1] content, but are usually textual (structured using
   XML [2]).

   All exchanges occur in the context of a channel -- a binding to a
   well-defined aspect of the application, such as transport security,
   user authentication, or data exchange.

   Each channel has an associated "profile" that defines the syntax and
   semantics of the messages exchanged.  Implicit in the operation of
   BEEP is the notion of channel management.  In addition to defining
   BEEP's channel management profile, this document defines:

   o  the TLS [3] transport security profile; and,

   o  the SASL [4] family of profiles.

   Other profiles, such as those used for data exchange, are defined by
   an application protocol designer.


























Rose                        Standards Track                     [Page 4]

RFC 3080                     The BEEP Core                    March 2001


2. The BEEP Core

   A BEEP session is mapped onto an underlying transport service.  A
   separate series of documents describe how a particular transport
   service realizes a BEEP session.  For example, [5] describes how a
   BEEP session is mapped onto a single TCP [6] connection.

   When a session is established, each BEEP peer advertises the profiles
   it supports.  Later on, during the creation of a channel, the client
   supplies one or more proposed profiles for that channel.  If the
   server creates the channel, it selects one of the profiles and sends
   it in a reply; otherwise, it may indicate that none of the profiles
   are acceptable, and decline creation of the channel.

   Channel usage falls into one of two categories:

   initial tuning: these are used by profiles that perform
      initialization once the BEEP session is established (e.g.,
      negotiating the use of transport security); although several
      exchanges may be required to perform the initialization, these
      channels become inactive early in the BEEP session and remain so
      for the duration.

   continuous: these are used by profiles that support data exchange;
      typically, these channels are created after the initial tuning
      channels have gone quiet.

   Note that because of their special nature, only one tuning channel
   may be established at any given time; in contrast, BEEP allows
   multiple data exchange channels to be simultaneously in use.





















Rose                        Standards Track                     [Page 5]

RFC 3080                     The BEEP Core                    March 2001


2.1 Roles

   Although BEEP is peer-to-peer, it is convenient to label each peer in
   the context of the role it is performing at a given time:

   o  When a BEEP session is established, the peer that awaits new
      connections is acting in the listening role, and the other peer,
      which establishes a connection to the listener, is acting in the
      initiating role.  In the examples which follow, these are referred
      to as "L:" and "I:", respectively.

   o  A BEEP peer starting an exchange is termed the client; similarly,
      the other BEEP peer is termed the server.  In the examples which
      follow, these are referred to as "C:" and "S:", respectively.

   Typically, a BEEP peer acting in the server role is also acting in a
   listening role.  However, because BEEP is peer-to-peer in nature, no
   such requirement exists.

2.1.1 Exchange Styles

   BEEP allows three styles of exchange:

   MSG/RPY: the client sends a "MSG" message asking the server to
      perform some task, the server performs the task and replies with a
      "RPY" message (termed a positive reply).

   MSG/ERR: the client sends a "MSG" message, the server does not
      perform any task and replies with an "ERR" message (termed a
      negative reply).

   MSG/ANS: the client sends a "MSG" message, the server, during the
      course of performing some task, replies with zero or more "ANS"
      messages, and, upon completion of the task, sends a "NUL" message,
      which signifies the end of the reply.

   The first two styles are termed one-to-one exchanges, whilst the
   third style is termed a one-to-many exchange.













Rose                        Standards Track                     [Page 6]

RFC 3080                     The BEEP Core                    March 2001


2.2 Messages and Frames

   A message is structured according to the rules of MIME.  Accordingly,
   each message may begin with "entity-headers" (c.f., MIME's Section 3
   [1]).  If none, or only some, of the "entity-headers" are present:

   o  the default "Content-Type" is "application/octet-stream"; and,

   o  the default "Content-Transfer-Encoding" is "binary".

   Normally, a message is sent in a single frame.  However, it may be
   convenient or necessary to segment a message into multiple frames
   (e.g., if only part of a message is ready to be sent).

   Each frame consists of a header, the payload, and a trailer.  The
   header and trailer are each represented using printable ASCII
   characters and are terminated with a CRLF pair.  Between the header
   and the trailer is the payload, consisting of zero or more octets.

   For example, here is a message contained in a single frame that
   contains a payload of 120 octets spread over 5 lines (each line is
   terminated with a CRLF pair):

       C: MSG 0 1 . 52 120
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/SASL/OTP' />
       C: </start>
       C: END

   In this example, note that the entire message is represented in a
   single frame.


















Rose                        Standards Track                     [Page 7]

RFC 3080                     The BEEP Core                    March 2001


2.2.1 Frame Syntax

   The ABNF [7] for a frame is:

   frame      = data / mapping

   data       = header payload trailer

   header     = msg / rpy / err / ans / nul

   msg        = "MSG" SP common          CR LF
   rpy        = "RPY" SP common          CR LF
   ans        = "ANS" SP common SP ansno CR LF
   err        = "ERR" SP common          CR LF
   nul        = "NUL" SP common          CR LF

   common     = channel SP msgno SP more SP seqno SP size
   channel    = 0..2147483647
   msgno      = 0..2147483647
   more       = "." / "*"
   seqno      = 0..4294967295
   size       = 0..2147483647
   ansno      = 0..2147483647

   payload    = *OCTET

   trailer    = "END" CR LF

   mapping    = ;; each transport mapping may define additional frames






















Rose                        Standards Track                     [Page 8]

RFC 3080                     The BEEP Core                    March 2001


2.2.1.1 Frame Header

   The frame header consists of a three-character keyword (one of:
   "MSG", "RPY", "ERR", "ANS", or "NUL"), followed by zero or more
   parameters.  A single space character (decimal code 32, " ")
   separates each component.  The header is terminated with a CRLF pair.

   The channel number ("channel") must be a non-negative integer (in the
   range 0..2147483647).

   The message number ("msgno") must be a non-negative integer (in the
   range 0..2147483647) and have a different value than all other "MSG"
   messages on the same channel for which a reply has not been
   completely received.

   The continuation indicator ("more", one of: decimal code 42, "*", or
   decimal code 46, ".") specifies whether this is the final frame of
   the message:

      intermediate ("*"): at least one other frame follows for the
      message; or,

      complete ("."): this frame completes the message.

   The sequence number ("seqno") must be a non-negative integer (in the
   range 0..4294967295) and specifies the sequence number of the first
   octet in the payload, for the associated channel (c.f., Section
   2.2.1.2).

   The payload size ("size") must be a non-negative integer (in the
   range 0..2147483647) and specifies the exact number of octets in the
   payload.  (This does not include either the header or trailer.)

   Note that a frame may have an empty payload, e.g.,

       S: RPY 0 1 * 287 20
       S:     ...
       S:     ...
       S: END
       S: RPY 0 1 . 307 0
       S: END

   The answer number ("ansno") must be a non-negative integer (in the
   range 0..4294967295) and must have a different value than all other
   answers in progress for the message being replied to.






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   There are two kinds of frames: data and mapping.  Each transport
   mapping (c.f., Section 2.5) may define its own frames.  For example,
   [5] defines the SEQ frame.  The remainder of this section discusses
   data frames.

   When a message is segmented and sent as several frames, those frames
   must be sent sequentially, without any intervening frames from other
   messages on the same channel.  However, there are two exceptions:
   first, no restriction is made with respect to the interleaving of
   frames for other channels; and, second, in a one-to-many exchange,
   multiple answers may be simultaneously in progress.  Accordingly,
   frames for "ANS" messages may be interleaved on the same channel --
   the answer number is used for collation, e.g.,

       S: ANS 1 0 * 0 20 0
       S:     ...
       S:     ...
       S: END
       S: ANS 1 0 * 20 20 1
       S:     ...
       S:     ...
       S: END
       S: ANS 1 0 . 40 10 0
       S:     ...
       S: END

   which shows two "ANS" messages interleaved on channel 1 as part of a
   reply to message number 0.  Note that the sequence number is advanced
   for each frame sent on the channel, and is independent of the
   messages sent in those frames.





















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   There are several rules for identifying poorly-formed frames:

   o  if the header doesn't start with "MSG", "RPY", "ERR", "ANS", or
      "NUL";

   o  if any of the parameters in the header cannot be determined or are
      invalid (i.e., syntactically incorrect);

   o  if the value of the channel number doesn't refer to an existing
      channel;

   o  if the header starts with "MSG", and the message number refers to
      a "MSG" message that has been completely received but for which a
      reply has not been completely sent;

   o  if the header doesn't start with "MSG", and refers to a message
      number for which a reply has already been completely received;

   o  if the header doesn't start with "MSG", and refers to a message
      number that has never been sent (except during session
      establishment, c.f., Section 2.3.1.1);

   o  if the header starts with "MSG", "RPY", "ERR", or "ANS", and
      refers to a message number for which at least one other frame has
      been received, and the three-character keyword starting this frame
      and the immediately-previous received frame for this message
      number are not identical;

   o  if the header starts with "NUL", and refers to a message number
      for which at least one other frame has been received, and the
      keyword of of the immediately-previous received frame for this
      reply isn't "ANS";

   o  if the continuation indicator of the previous frame received on
      the same channel was intermediate ("*"), and its message number
      isn't identical to this frame's message number;

   o  if the value of the sequence number doesn't correspond to the
      expected value for the associated channel (c.f., Section 2.2.1.2);
      or,

   o  if the header starts with "NUL", and the continuation indicator is
      intermediate ("*") or the payload size is non-zero.

   If a frame is poorly-formed, then the session is terminated without
   generating a response, and it is recommended that a diagnostic entry
   be logged.




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2.2.1.2 Frame Payload

   The frame payload consists of zero or more octets.

   Every payload octet sent in each direction on a channel has an
   associated sequence number.  Numbering of payload octets within a
   frame is such that the first payload octet is the lowest numbered,
   and the following payload octets are numbered consecutively.  (When a
   channel is created, the sequence number associated with the first
   payload octet of the first frame is 0.)

   The actual sequence number space is finite, though very large,
   ranging from 0..4294967295 (2**32 - 1).  Since the space is finite,
   all arithmetic dealing with sequence numbers is performed modulo
   2**32.  This unsigned arithmetic preserves the relationship of
   sequence numbers as they cycle from 2**32 - 1 to 0 again.  Consult
   Sections 2 through 5 of [8] for a discussion of the arithmetic
   properties of sequence numbers.

   When receiving a frame, the sum of its sequence number and payload
   size, modulo 4294967296 (2**32), gives the expected sequence number
   associated with the first payload octet of the next frame received.
   Accordingly, when receiving a frame if the sequence number isn't the
   expected value for this channel, then the BEEP peers have lost
   synchronization, then the session is terminated without generating a
   response, and it is recommended that a diagnostic entry be logged.

























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2.2.1.3 Frame Trailer

   The frame trailer consists of "END" followed by a CRLF pair.

   When receiving a frame, if the characters immediately following the
   payload don't correspond to a trailer, then the session is terminated
   without generating a response, and it is recommended that a
   diagnostic entry be logged.











































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2.2.2 Frame Semantics

   The semantics of each message is channel-specific.  Accordingly, the
   profile associated with a channel must define:

   o  the initialization messages, if any, exchanged during channel
      creation;

   o  the messages that may be exchanged in the payload of the channel;
      and,

   o  the semantics of these messages.

   A profile registration template (Section 5.1) organizes this
   information.

2.2.2.1 Poorly-formed Messages

   When defining the behavior of the profile, the template must specify
   how poorly-formed "MSG" messages are replied to.  For example, the
   channel management profile sends a negative reply containing an error
   message (c.f., Section 2.3.1.5).

   If a poorly-formed reply is received on channel zero, the session is
   terminated without generating a response, and it is recommended that
   a diagnostic entry be logged.

   If a poorly-formed reply is received on another channel, then the
   channel must be closed using the procedure in Section 2.3.1.3.






















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2.3 Channel Management

   When a BEEP session starts, only channel number zero is defined,
   which is used for channel management.  Section 6.1 contains the
   profile registration for BEEP channel management.

   Channel management allows each BEEP peer to advertise the profiles
   that it supports (c.f., Section 2.3.1.1), bind an instance of one of
   those profiles to a channel (c.f., Section 2.3.1.2), and then later
   close any channels or release the BEEP session (c.f., Section
   2.3.1.3).

   A BEEP peer should support at least 257 concurrent channels.






































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2.3.1 Message Semantics

2.3.1.1 The Greeting Message

   When a BEEP session is established, each BEEP peer signifies its
   availability by immediately sending a positive reply with a message
   number of zero that contains a "greeting" element, e.g.,

       L: <wait for incoming connection>
       I: <open connection>
       L: RPY 0 0 . 0 110
       L: Content-Type: application/beep+xml
       L:
       L: <greeting>
       L:    <profile uri='http://iana.org/beep/TLS' />
       L: </greeting>
       L: END
       I: RPY 0 0 . 0 52
       I: Content-Type: application/beep+xml
       I:
       I: <greeting />
       I: END

   Note that this example implies that the BEEP peer in the initiating
   role waits until the BEEP peer in the listening role sends its
   greeting -- this is an artifact of the presentation; in fact, both
   BEEP peers send their replies independently.

   The "greeting" element has two optional attributes ("features" and
   "localize") and zero or more "profile" elements, one for each profile
   supported by the BEEP peer acting in a server role:

   o  the "features" attribute, if present, contains one or more feature
      tokens, each indicating an optional feature of the channel
      management profile supported by the BEEP peer;

   o  the "localize" attribute, if present, contains one or more
      language tokens (defined in [9]), each identifying a desirable
      language tag to be used by the remote BEEP peer when generating
      textual diagnostics for the "close" and "error" elements (the
      tokens are ordered from most to least desirable); and,

   o  each "profile" element contained within the "greeting" element
      identifies a profile, and unlike the "profile" elements that occur
      within the "start" element, the content of each "profile" element
      may not contain an optional initialization message.

   Section 5.2 defines a registration template for optional features.



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2.3.1.2 The Start Message

   When a BEEP peer wants to create a channel, it sends a "start"
   element on channel zero, e.g.,

       C: MSG 0 1 . 52 120
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/SASL/OTP' />
       C: </start>
       C: END

   The "start" element has a "number" attribute, an optional
   "serverName" attribute, and one or more "profile" elements:

   o  the "number" attribute indicates the channel number (in the range
      1..2147483647) used to identify the channel in future messages;

   o  the "serverName" attribute, an arbitrary string, indicates the
      desired server name for this BEEP session; and,

   o  each "profile" element contained with the "start" element has a
      "uri" attribute, an optional "encoding" attribute, and arbitrary
      character data as content:

      *  the "uri" attribute authoritatively identifies the profile;

      *  the "encoding" attribute, if present, specifies whether the
         content of the "profile" element is represented as a base64-
         encoded string; and,

      *  the content of the "profile" element, if present, must be no
         longer than 4K octets in length and specifies an initialization
         message given to the channel as soon as it is created.

   To avoid conflict in assigning channel numbers when requesting the
   creation of a channel, BEEP peers acting in the initiating role use
   only positive integers that are odd-numbered; similarly, BEEP peers
   acting in the listening role use only positive integers that are
   even-numbered.

   The "serverName" attribute for the first successful "start" element
   received by a BEEP peer is meaningful for the duration of the BEEP
   session.  If present, the BEEP peer decides whether to operate as the
   indicated "serverName"; if not, an "error" element is sent in a
   negative reply.




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   When a BEEP peer receives a "start" element on channel zero, it
   examines each of the proposed profiles, and decides whether to use
   one of them to create the channel.  If so, the appropriate "profile"
   element is sent in a positive reply; otherwise, an "error" element is
   sent in a negative reply.

   When creating the channel, the value of the "serverName" attribute
   from the first successful "start" element is consulted to provide
   configuration information, e.g., the desired server-side certificate
   when starting the TLS transport security profile (Section 3.1).

   For example, a successful channel creation might look like this:

       C: MSG 0 1 . 52 178
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/SASL/OTP' />
       C:    <profile uri='http://iana.org/beep/SASL/ANONYMOUS' />
       C: </start>
       C: END
       S: RPY 0 1 . 221 87
       S: Content-Type: application/beep+xml
       S:
       S: <profile uri='http://iana.org/beep/SASL/OTP' />
       S: END

   Similarly, an unsuccessful channel creation might look like this:

       C: MSG 0 1 . 52 120
       C: Content-Type: application/beep+xml
       C:
       C: <start number='2'>
       C:    <profile uri='http://iana.org/beep/SASL/OTP' />
       C: </start>
       C: END
       S: ERR 0 1 . 221 127
       S: Content-Type: application/beep+xml
       S:
       S: <error code='501'>number attribute
       S: in &lt;start&gt; element must be odd-valued</error>
       S: END









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   Finally, here's an example in which an initialization element is
   exchanged during channel creation:

       C: MSG 0 1 . 52 158
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/TLS'>
       C:        <![CDATA[<ready />]]>
       C:    </profile>
       C: </start>
       C: END
       S: RPY 0 1 . 110 121
       S: Content-Type: application/beep+xml
       S:
       S: <profile uri='http://iana.org/beep/TLS'>
       S:     <![CDATA[<proceed />]]>
       S: </profile>
       S: END
































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2.3.1.3 The Close Message

   When a BEEP peer wants to close a channel, it sends a "close" element
   on channel zero, e.g.,

       C: MSG 0 2 . 235 71
       C: Content-Type: application/beep+xml
       C:
       C: <close number='1' code='200' />
       C: END

   The "close" element has a "number" attribute, a "code" attribute, an
   optional "xml:lang" attribute, and an optional textual diagnostic as
   its content:

   o  the "number" attribute indicates the channel number;

   o  the "code" attribute is a three-digit reply code meaningful to
      programs (c.f., Section 8);

   o  the "xml:lang" attribute identifies the language that the
      element's content is written in (the value is suggested, but not
      mandated, by the "localize" attribute of the "greeting" element
      sent by the remote BEEP peer); and,

   o  the textual diagnostic (which may be multiline) is meaningful to
      implementers, perhaps administrators, and possibly even users, but
      never programs.

   Note that if the textual diagnostic is present, then the "xml:lang"
   attribute is absent only if the language indicated as the remote BEEP
   peer's first choice is used.

   If the value of the "number" attribute is zero, then the BEEP peer
   wants to release the BEEP session (c.f., Section 2.4) -- otherwise
   the value of the "number" attribute refers to an existing channel,
   and the remainder of this section applies.

   A BEEP peer may send a "close" message for a channel whenever all
   "MSG" messages it has sent on that channel have been acknowledged.
   (Acknowledgement consists of the first frame of a reply being
   received by the BEEP peer that sent the MSG "message".)

   After sending the "close" message, that BEEP peer must not send any
   more "MSG" messages on that channel being closed until the reply to
   the "close" message has been received (either by an "error" message
   rejecting the request to close the channel, or by an "ok" message
   subsequently followed by the channel being successfully started).



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   NOTE WELL: until a positive reply to the request to close the channel
   is received, the BEEP peer must be prepared to process any "MSG"
   messages that it receives on that channel.

   When a BEEP peer receives a "close" message for a channel, it may, at
   any time, reject the request to close the channel by sending an
   "error" message in a negative reply.

   Otherwise, before accepting the request to close the channel, and
   sending an "ok" message in a positive reply, it must:

   o  finish sending any queued "MSG" messages on that channel of its
      own;

   o  await complete replies to any outstanding "MSG" messages it has
      sent on that channel; and,

   o  finish sending complete replies to any outstanding "MSG" messages
      it has received on that channel, and ensure that the final frames
      of those replies have been successfully delivered, i.e.,

      *  for transport mappings that guarantee inter-channel ordering of
         messages, the replies must be sent prior to sending the "ok"
         message in a positive reply; otherwise,

      *  the replies must be sent and subsequently acknowledged by the
         underlying transport service prior to sending the "ok" message
         in a positive reply.























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   Briefly, a successful channel close might look like this:

       C: MSG 0 2 . 235 71
       C: Content-Type: application/beep+xml
       C:
       C: <close number='1' code='200' />
       C: END
       S: RPY 0 2 . 392 46
       S: Content-Type: application/beep+xml
       S:
       S: <ok />
       S: END

   Similarly, an unsuccessful channel close might look like this:

       C: MSG 0 2 . 235 71
       C: Content-Type: application/beep+xml
       C:
       C: <close number='1' code='200' />
       C: END
       S: ERR 0 2 . 392 79
       S: Content-Type: application/beep+xml
       S:
       S: <error code='550'>still working</error>
       S: END


























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2.3.1.4 The OK Message

   When a BEEP peer agrees to close a channel (or release the BEEP
   session), it sends an "ok" element in a positive reply.

   The "ok" element has no attributes and no content.

2.3.1.5 The Error Message

   When a BEEP peer declines the creation of a channel, it sends an
   "error" element in a negative reply, e.g.,

       I: MSG 0 1 . 52 115
       I: Content-Type: application/beep+xml
       I:
       I: <start number='2'>
       I:    <profile uri='http://iana.org/beep/FOO' />
       I: </start>
       I: END
       L: ERR 0 1 . 221 105
       L: Content-Type: application/beep+xml
       L:
       L: <error code='550'>all requested profiles are
       L: unsupported</error>
       L: END

   The "error" element has a "code" attribute, an optional "xml:lang"
   attribute, and an optional textual diagnostic as its content:

   o  the "code" attribute is a three-digit reply code meaningful to
      programs (c.f., Section 8);

   o  the "xml:lang" attribute identifies the language that the
      element's content is written in (the value is suggested, but not
      mandated, by the "localize" attribute of the "greeting" element
      sent by the remote BEEP peer); and,

   o  the textual diagnostic (which may be multiline) is meaningful to
      implementers, perhaps administrators, and possibly even users, but
      never programs.

   Note that if the textual diagnostic is present, then the "xml:lang"
   attribute is absent only if the language indicated as the remote BEEP
   peer's first choice is used.







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   In addition, a BEEP peer sends an "error" element whenever:

   o  it receives a "MSG" message containing a poorly-formed or
      unexpected element;

   o  it receives a "MSG" message asking to close a channel (or release
      the BEEP session) and it declines to do so; or

   o  a BEEP session is established, the BEEP peer is acting in the
      listening role, and that BEEP peer is unavailable (in this case,
      the BEEP acting in the listening role does not send a "greeting"
      element).

   In the final case, both BEEP peers terminate the session, and it is
   recommended that a diagnostic entry be logged by both BEEP peers.




































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2.4 Session Establishment and Release

   When a BEEP session is established, each BEEP peer signifies its
   availability by immediately sending a positive reply with a message
   number of zero on channel zero that contains a "greeting" element,
   e.g.,

       L: <wait for incoming connection>
       I: <open connection>
       L: RPY 0 0 . 0 110
       L: Content-Type: application/beep+xml
       L:
       L: <greeting>
       L:    <profile uri='http://iana.org/beep/TLS' />
       L: </greeting>
       L: END
       I: RPY 0 0 . 0 52
       I: Content-Type: application/beep+xml
       I:
       I: <greeting />
       I: END

   Alternatively, if the BEEP peer acting in the listening role is
   unavailable, it sends a negative reply, e.g.,

       L: <wait for incoming connection>
       I: <open connection>
       L: ERR 0 0 . 0 60
       L: Content-Type: application/beep+xml
       L:
       L: <error code='421' />
       L: END
       I: RPY 0 0 . 0 52
       I: Content-Type: application/beep+xml
       I:
       I: <greeting />
       I: END
       I: <close connection>
       L: <close connection>
       L: <wait for next connection>

   and the "greeting" element sent by the BEEP peer acting in the
   initiating role is ignored.  It is recommended that a diagnostic
   entry be logged by both BEEP peers.







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   Note that both of these examples imply that the BEEP peer in the
   initiating role waits until the BEEP peer in the listening role sends
   its greeting -- this is an artifact of the presentation; in fact,
   both BEEP peers send their replies independently.

   When a BEEP peer wants to release the BEEP session, it sends a
   "close" element with a zero-valued "number" attribute on channel
   zero.  The other BEEP peer indicates its willingness by sending an
   "ok" element in a positive reply, e.g.,

       C: MSG 0 1 . 52 60
       C: Content-Type: application/beep+xml
       C:
       C: <close code='200' />
       C: END
       S: RPY 0 1 . 264 46
       S: Content-Type: application/beep+xml
       S:
       S: <ok />
       S: END
       I: <close connection>
       L: <close connection>
       L: <wait for next connection>

   Alternatively, if the other BEEP doesn't want to release the BEEP
   session, the exchange might look like this:

       C: MSG 0 1 . 52 60
       C: Content-Type: application/beep+xml
       C:
       C: <close code='200' />
       C: END
       S: ERR 0 1 . 264 79
       S: Content-Type: application/beep+xml
       S:
       S: <error code='550'>still working</error>
       S: END

   If session release is declined, the BEEP session should not be
   terminated, if possible.











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2.5 Transport Mappings

   All transport interactions occur in the context of a session -- a
   mapping onto a particular transport service.  Accordingly, this memo
   defines the requirements that must be satisfied by any document
   describing how a particular transport service realizes a BEEP
   session.

2.5.1 Session Management

   A BEEP session is connection-oriented.  A mapping document must
   define:

   o  how a BEEP session is established;

   o  how a BEEP peer is identified as acting in the listening role;

   o  how a BEEP peer is identified as acting in the initiating role;

   o  how a BEEP session is released; and,

   o  how a BEEP session is terminated.


2.5.2 Message Exchange

   A BEEP session is message-oriented.  A mapping document must define:

   o  how messages are reliably sent and received;

   o  how messages on the same channel are received in the same order as
      they were sent; and,

   o  how messages on different channels are sent without ordering
      constraint.
















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2.6 Asynchrony

   BEEP accommodates asynchronous interactions, both within a single
   channel and between separate channels.  This feature allows
   pipelining (intra-channel) and parallelism (inter-channel).

2.6.1 Within a Single Channel

   A BEEP peer acting in the client role may send multiple "MSG"
   messages on the same channel without waiting to receive the
   corresponding replies.  This provides pipelining within a single
   channel.

   A BEEP peer acting in the server role must process all "MSG" messages
   for a given channel in the same order as they are received.  As a
   consequence, the BEEP peer must generate replies in the same order as
   the corresponding "MSG" messages are received on a given channel.

   Note that in one-to-many exchanges (c.f., Section 2.1.1), the reply
   to the "MSG" message consists of zero or more "ANS" messages followed
   by a "NUL" message.  In this style of exchange, the "ANS" messages
   comprising the reply may be interleaved.  When the BEEP peer acting
   in the server role signifies the end of the reply by generating the
   "NUL" message, it may then process the next "MSG" message received
   for that channel.

2.6.2 Between Different Channels

   A BEEP peer acting in the client role may send multiple "MSG"
   messages on different channels without waiting to receive the
   corresponding replies.  The channels operate independently, in
   parallel.

   A BEEP peer acting in the server role may process "MSG" messages
   received on different channels in any order it chooses.  As a
   consequence, although the replies for a given channel appear to be
   generated in the same order in which the corresponding "MSG" messages
   are received, there is no ordering constraint for replies on
   different channels.












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2.6.3 Pre-emptive Replies

   A BEEP peer acting in the server role may send a negative reply
   before it receives the final "MSG" frame of a message.  If it does
   so, that BEEP peer is obliged to ignore any subsequent "MSG" frames
   for that message, up to and including the final "MSG" frame.

   If a BEEP peer acting in the client role receives a negative reply
   before it sends the final "MSG" frame for a message, then it is
   required to send a "MSG" frame with a continuation status of complete
   (".") and having a zero-length payload.

2.6.4 Interference

   If the processing of a particular message has sequencing impacts on
   other messages (either intra-channel or inter-channel), then the
   corresponding profile should define this behavior, e.g., a profile
   whose messages alter the underlying transport mapping.

































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2.7 Peer-to-Peer Behavior

   BEEP is peer-to-peer -- as such both peers must be prepared to
   receive all messages defined in this memo.  Accordingly, an
   initiating BEEP peer capable of acting only in the client role must
   behave gracefully if it receives a "MSG" message.  Accordingly, all
   profiles must provide an appropriate error message for replying to
   unexpected "MSG" messages.

   As a consequence of the peer-to-peer nature of BEEP, message numbers
   are unidirectionally-significant.  That is, the message numbers in
   "MSG" messages sent by a BEEP peer acting in the initiating role are
   unrelated to the message numbers in "MSG" messages sent by a BEEP
   peer acting in the listening role.

   For example, these two messages

       I: MSG 0 1 . 52 120
       I: Content-Type: application/beep+xml
       I:
       I: <start number='1'>
       I:    <profile uri='http://iana.org/beep/SASL/OTP' />
       I: </start>
       I: END
       L: MSG 0 1 . 221 116
       L: Content-Type: application/beep+xml
       L:
       L: <start number='2'>
       L:    <profile uri='http://iana.org/beep/APEX' />
       L: </start>
       L: END

   refer to different messages sent on channel zero.


















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RFC 3080                     The BEEP Core                    March 2001


3. Transport Security

   When a BEEP session is established, plaintext transfer, without
   privacy, is provided.  Accordingly, transport security in BEEP is
   achieved using an initial tuning profile.

   This document defines one profile:

   o  the TLS transport security profile, based on TLS version one [3].

   Other profiles may be defined and deployed on a bilateral basis.
   Note that because of their intimate relationship with the transport
   service, a given transport security profile tends to be relevant to a
   single transport mapping (c.f., Section 2.5).

   When a channel associated with transport security begins the
   underlying negotiation process, all channels (including channel zero)
   are closed on the BEEP session.  Accordingly, upon completion of the
   negotiation process, regardless of its outcome, a new greeting is
   issued by both BEEP peers.  (If the negotiation process fails, then
   either BEEP peer may instead terminate the session, and it is
   recommended that a diagnostic entry be logged.)

   A BEEP peer may choose to issue different greetings based on whether
   privacy is in use, e.g.,

       L: <wait for incoming connection>
       I: <open connection>
       L: RPY 0 0 . 0 110
       L: Content-Type: application/beep+xml
       L:
       L: <greeting>
       L:    <profile uri='http://iana.org/beep/TLS' />
       L: </greeting>
       L: END
       I: RPY 0 0 . 0 52
       I: Content-Type: application/beep+xml
       I:
       I: <greeting />
       I: END
       I: MSG 0 1 . 52 158
       I: Content-Type: application/beep+xml
       I:








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       I: <start number='1'>
       I:    <profile uri='http://iana.org/beep/TLS'>
       I:        <![CDATA[<ready />]]>
       I:    </profile>
       I: </start>
       I: END
       L: RPY 0 1 . 110 121
       L: Content-Type: application/beep+xml
       L:
       L: <profile uri='http://iana.org/beep/TLS'>
       L:     <![CDATA[<proceed />]]>
       L: </profile>
       L: END

           ... successful transport security negotiation ...

       L: RPY 0 0 . 0 221
       L: Content-Type: application/beep+xml
       L:
       L: <greeting>
       L:    <profile uri='http://iana.org/beep/SASL/ANONYMOUS' />
       L:    <profile uri='http://iana.org/beep/SASL/OTP' />
       L:    <profile uri='http://iana.org/beep/APEX' />
       L: </greeting>
       L: END
       I: RPY 0 0 . 0 52
       I: Content-Type: application/beep+xml
       I:
       I: <greeting />
       I: END

   Of course, not all BEEP peers need be as single-minded:

       L: <wait for incoming connection>
       I: <open connection>
       L: RPY 0 0 . 0 268
       L: Content-Type: application/beep+xml
       L:
       L: <greeting>
       L:    <profile uri='http://iana.org/beep/SASL/ANONYMOUS' />
       L:    <profile uri='http://iana.org/beep/SASL/OTP' />
       L:    <profile uri='http://iana.org/beep/APEX' />
       L:    <profile uri='http://iana.org/beep/TLS' />
       L: </greeting>
       L: END
       I: RPY 0 0 . 0 52
       I: Content-Type: application/beep+xml
       I:



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       I: <greeting />
       I: END
       I: MSG 0 1 . 52 158
       I: Content-Type: application/beep+xml
       I:
       I: <start number='1'>
       I:    <profile uri='http://iana.org/beep/TLS'>
       I:        <![CDATA[<ready />]]>
       I:    </profile>
       I: </start>
       I: END
       L: RPY 0 1 . 268 121
       L: Content-Type: application/beep+xml
       L:
       L: <profile uri='http://iana.org/beep/TLS'>
       L:     <![CDATA[<proceed />]]>
       L: </profile>
       L: END

           ... failed transport security negotiation ...

       L: RPY 0 0 . 0 268
       L: Content-Type: application/beep+xml
       L:
       L: <greeting>
       L:    <profile uri='http://iana.org/beep/SASL/ANONYMOUS' />
       L:    <profile uri='http://iana.org/beep/SASL/OTP' />
       L:    <profile uri='http://iana.org/beep/APEX' />
       L:    <profile uri='http://iana.org/beep/TLS' />
       L: </greeting>
       L: END
       I: RPY 0 0 . 0 52
       I: Content-Type: application/beep+xml
       I:
       I: <greeting />
       I: END















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RFC 3080                     The BEEP Core                    March 2001


3.1 The TLS Transport Security Profile

   Section 6.2 contains the registration for this profile.

3.1.1 Profile Identification and Initialization

   The TLS transport security profile is identified as:

       http://iana.org/beep/TLS

   in the BEEP "profile" element during channel creation.

   During channel creation, the corresponding "profile" element in the
   BEEP "start" element may contain a "ready" element.  If channel
   creation is successful, then before sending the corresponding reply,
   the BEEP peer processes the "ready" element and includes the
   resulting response in the reply, e.g.,

       C: MSG 0 1 . 52 158
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/TLS'>
       C:        <![CDATA[<ready />]]>
       C:    </profile>
       C: </start>
       C: END
       S: RPY 0 1 . 110 121
       S: Content-Type: application/beep+xml
       S:
       S: <profile uri='http://iana.org/beep/TLS'>
       S:     <![CDATA[<proceed />]]>
       S: </profile>
       S: END

















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   Note that it is possible for the channel to be created, but for the
   encapsulated operation to fail, e.g.,

       C: MSG 0 1 . 52 173
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/TLS'>
       C:        <![CDATA[<ready version="oops" />]]>
       C:    </profile>
       C: </start>
       C: END
       S: RPY 0 1 . 110 193
       S: Content-Type: application/beep+xml
       S:
       S: <profile uri='http://iana.org/beep/TLS'>
       S:     <![CDATA[<error code='501'>version attribute
       S: poorly formed in &lt;ready&gt; element</error>]]>
       S: </profile>
       S: END

   In this case, a positive reply is sent (as channel creation
   succeeded), but the encapsulated response contains an indication as
   to why the operation failed.

3.1.2 Message Syntax

   Section 7.2 defines the messages that are used in the TLS transport
   security profile.






















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3.1.3 Message Semantics

3.1.3.1 The Ready Message

   The "ready" element has an optional "version" attribute and no
   content:

   o  the "version" element defines the earliest version of TLS
      acceptable for use.

   When a BEEP peer sends the "ready" element, it must not send any
   further traffic on the underlying transport service until a
   corresponding reply ("proceed" or "error") is received; similarly,
   the receiving BEEP peer must wait until any pending replies have been
   generated and sent before it processes a "ready" element.

3.1.3.2 The Proceed Message

   The "proceed" element has no attributes and no content.  It is sent
   as a reply to the "ready" element.

   When a BEEP peer receives the "ready" element, it must not send any
   further traffic on the underlying transport service until it
   generates a corresponding reply.  If the BEEP peer decides to allow
   transport security negotiation, it implicitly closes all channels
   (including channel zero), and sends the "proceed" element, and awaits
   the underlying negotiation process for transport security.

   When a BEEP peer receives a "proceed" element in reply to its "ready"
   message, it implicitly closes all channels (including channel zero),
   and immediately begins the underlying negotiation process for
   transport security.



















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4. User Authentication

   When a BEEP session is established, anonymous access, without trace
   information, is provided.  Accordingly, user authentication in BEEP
   is achieved using an initial tuning profile.

   This document defines a family of profiles based on SASL mechanisms:

   o  each mechanism in the IANA SASL registry [15] has an associated
      profile.

   Other profiles may be defined and deployed on a bilateral basis.

   Whenever a successful authentication occurs, on any channel, the
   authenticated identity is updated for all existing and future
   channels on the BEEP session; further, no additional attempts at
   authentication are allowed.

   Note that regardless of transport security and user authentication,
   authorization is an internal matter for each BEEP peer.  As such,
   each peer may choose to restrict the operations it allows based on
   the authentication credentials provided (i.e., unauthorized
   operations might be rejected with error code 530).




























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4.1 The SASL Family of Profiles

   Section 6.3 contains the registration for this profile.

   Note that SASL may provide both user authentication and transport
   security.  Once transport security is successfully negotiated for a
   BEEP session, then a SASL security layer must not be negotiated;
   similarly, once any SASL negotiation is successful, a transport
   security profile must not begin its underlying negotiation process.

   Section 4 of the SASL specification [4] requires the following
   information be supplied by a protocol definition:

   service name: "beep"

   initiation sequence: Creating a channel using a BEEP profile
      corresponding to a SASL mechanism starts the exchange.  An
      optional parameter corresponding to the "initial response" sent by
      the client is carried within a "blob" element during channel
      creation.

   exchange sequence: "Challenges" and "responses" are carried in
      exchanges of the "blob" element.  The "status" attribute of the
      "blob" element is used both by a server indicating a successful
      completion of the exchange, and a client aborting the exchange,
      The server indicates failure of the exchange by sending an "error"
      element.

   security layer negotiation: When a security layer starts negotiation,
      all channels (including channel zero) are closed on the BEEP
      session.  Accordingly, upon completion of the negotiation process,
      regardless of its outcome, a new greeting is issued by both BEEP
      peers.

      If a security layer is successfully negotiated, it takes effect
      immediately following the message that concludes the server's
      successful completion reply.

   use of the authorization identity: This is made available to all
      channels for the duration of the BEEP session.











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4.1.1 Profile Identification and Initialization

   Each SASL mechanism registered with the IANA is identified as:

       http://iana.org/beep/SASL/mechanism

   where "MECHANISM" is the token assigned to that mechanism by the
   IANA.

   Note that during channel creation, a BEEP peer may provide multiple
   profiles to the remote peer, e.g.,

       C: MSG 0 1 . 52 178
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/SASL/ANONYMOUS' />
       C:    <profile uri='http://iana.org/beep/SASL/OTP' />
       C: </start>
       C: END
       S: RPY 0 1 . 221 87
       S: Content-Type: application/beep+xml
       S:
       S: <profile uri='http://iana.org/beep/SASL/OTP' />
       S: END


























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   During channel creation, the corresponding "profile" element in the
   BEEP "start" element may contain a "blob" element.  Note that it is
   possible for the channel to be created, but for the encapsulated
   operation to fail, e.g.,

       C: MSG 0 1 . 52 183
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/SASL/OTP'>
       C:        <![CDATA[<blob>AGJsb2NrbWFzdGVy</blob>]]>
       C:    </profile>
       C: </start>
       C: END
       S: RPY 0 1 . 221 178
       S: Content-Type: application/beep+xml
       S:
       S: <profile uri='http://iana.org/beep/SASL/OTP'>
       S:     <![CDATA[<error code='534'>authentication mechanism is
       S: too weak</error>]]>
       S: </profile>
       S: END

   In this case, a positive reply is sent (as channel creation
   succeeded), but the encapsulated response contains an indication as
   to why the operation failed.

   Otherwise, the server sends a challenge (or signifies success), e.g.,

       C: MSG 0 1 . 52 183
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/SASL/OTP'>
       C:        <![CDATA[<blob>AGJsb2NrbWFzdGVy</blob>]]>
       C:    </profile>
       C: </start>
       C: END
       S: RPY 0 1 . 221 171
       S: Content-Type: application/beep+xml
       S:
       S: <profile uri='http://iana.org/beep/SASL/OTP'>
       S:    <![CDATA[<blob>b3RwLXNoYTEgOTk5NyBwaXh5bWlzYXM4NTgwNSBleHQ=
                                                              </blob>]]>
       S: </profile>
       S: END





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   Note that this example implies that the "blob" element in the
   server's reply appears on two lines -- this is an artifact of the
   presentation; in fact, only one line is used.

   If a challenge is received, then the client responds and awaits
   another reply, e.g.,

       C: MSG 1 0 . 0 97
       C: Content-Type: application/beep+xml
       C:
       C: <blob>d29yZDpmZXJuIGhhbmcgYnJvdyBib25nIGhlcmQgdG9n</blob>
       C: END
       S: RPY 1 0 . 0 66
       S: Content-Type: application/beep+xml
       S:
       S: <blob status='complete' />
       S: END

   Of course, the client could abort the authentication process by
   sending "<blob status='abort' />" instead.

   Alternatively, the server might reject the response with an error:
   e.g.,

       C: MSG 1 0 . 0 97
       C: Content-Type: application/beep+xml
       C:
       C: <blob>d29yZDpmZXJuIGhhbmcgYnJvdyBib25nIGhlcmQgdG9n</blob>
       C: END
       S: ERR 1 0 . 0 60
       S: Content-Type: application/beep+xml
       S:
       S: <error code='535' />
       S: END

















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   Finally, depending on the SASL mechanism, an initialization element
   may be exchanged unidirectionally during channel creation, e.g.,

       C: MSG 0 1 . 52 125
       C: Content-Type: application/beep+xml
       C:
       C: <start number='1'>
       C:    <profile uri='http://iana.org/beep/SASL/CRAM-MD5' />
       C: </start>
       C: END
       S: RPY 0 1 . 221 185
       S: Content-Type: application/beep+xml
       S:
       S: <profile uri='http://iana.org/beep/SASL/CRAM-MD5'>
       S: <![CDATA[<blob>PDE4OTYuNjk3MTcwOTUyQHBvc3RvZmZpY2UucmVzdG9uLm1
                                                     jaS5uZXQ+</blob>]]>
       S: </profile>
       S: END

   Note that this example implies that the "blob" element in the
   server's reply appears on two lines -- this is an artifact of the
   presentation; in fact, only one line is used.

4.1.2 Message Syntax

   Section 7.3 defines the messages that are used for each profile in
   the SASL family.

   Note that because many SASL mechanisms exchange binary data, the
   content of the "blob" element is always a base64-encoded string.





















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4.1.3 Message Semantics

   The "blob" element has an optional "status" attribute, and arbitrary
   octets as its content:

   o  the "status" attribute, if present, takes one of three values:

      abort: used by a client to indicate that it is aborting the
         authentication process;

      complete: used by a server to indicate that the exchange is
         complete and successful; or,

      continue: used by either a client or server, otherwise.

   Finally, note that SASL's EXTERNAL mechanism works with an "external
   authentication" service, which is provided by one of:

   o  a transport security profile, capable of providing authentication
      information (e.g., Section 3.1), being active on the connection;

   o  a network service, capable of providing strong authentication
      (e.g., IPSec [12]), underlying the connection; or,

   o  a locally-defined security service.

   For authentication to succeed, two conditions must hold:

   o  an external authentication service must be active; and,

   o  if present, the authentication identity must be consistent with
      the credentials provided by the external authentication service
      (if the authentication identity is empty, then an authorization
      identity is automatically derived from the credentials provided by
      the external authentication service).
















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5. Registration Templates

5.1 Profile Registration Template

   When a profile is registered, the following information is supplied:

   Profile Identification: specify a URI [10] that authoritatively
      identifies this profile.

   Message Exchanged during Channel Creation: specify the datatypes that
      may be exchanged during channel creation.

   Messages starting one-to-one exchanges: specify the datatypes that
      may be present when an exchange starts.

   Messages in positive replies: specify the datatypes that may be
      present in a positive reply.

   Messages in negative replies: specify the datatypes that may be
      present in a negative reply.

   Messages in one-to-many exchanges: specify the datatypes that may be
      present in a one-to-many exchange.

   Message Syntax: specify the syntax of the datatypes exchanged by the
      profile.

   Message Semantics: specify the semantics of the datatypes exchanged
      by the profile.

   Contact Information: specify the postal and electronic contact
      information for the author of the profile.

5.2 Feature Registration Template

   When a feature for the channel management profile is registered, the
   following information is supplied:

   Feature Identification: specify a string that identifies this
      feature.  Unless the feature is registered with the IANA, the
      feature's identification must start with "x-".

   Feature Semantics: specify the semantics of the feature.

   Contact Information: specify the postal and electronic contact
      information for the author of the feature.





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6. Initial Registrations

6.1 Registration: BEEP Channel Management

   Profile Identification: not applicable

   Messages exchanged during Channel Creation: not applicable

   Messages starting one-to-one exchanges: "start" or "close"

   Messages in positive replies: "greeting", "profile", or "ok"

   Messages in negative replies: "error"

   Messages in one-to-many exchanges: none

   Message Syntax: c.f., Section 7.1

   Message Semantics: c.f., Section 2.3.1

   Contact Information: c.f., the "Author's Address" section of this
      memo

6.2 Registration: TLS Transport Security Profile

   Profile Identification: http://iana.org/beep/TLS

   Messages exchanged during Channel Creation: "ready"

   Messages starting one-to-one exchanges: "ready"

   Messages in positive replies: "proceed"

   Messages in negative replies: "error"

   Messages in one-to-many exchanges: none

   Message Syntax: c.f., Section 7.2

   Message Semantics: c.f., Section 3.1.3

   Contact Information: c.f., the "Author's Address" section of this
      memo








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6.3 Registration: SASL Family of Profiles

   Profile Identification: http://iana.org/beep/SASL/mechanism, where
      "mechanism" is a token registered with the IANA

   Messages exchanged during Channel Creation: "blob"

   Messages starting one-to-one exchanges: "blob"

   Messages in positive replies: "blob"

   Messages in negative replies: "error"

   Messages in one-to-many exchanges: none

   Message Syntax: c.f., Section 7.3

   Message Semantics: c.f., Section 4.1.3

   Contact Information: c.f., the "Author's Address" section of this
      memo






























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6.4 Registration: application/beep+xml

   MIME media type name: application

   MIME subtype name: beep+xml

   Required parameters: none

   Optional parameters: charset (defaults to "UTF-8" [13])

   Encoding considerations: This media type may contain binary content;
      accordingly, when used over a transport that does not permit
      binary transfer, an appropriate encoding must be applied

   Security considerations: none, per se; however, any BEEP profile
      which uses this media type must describe its relevant security
      considerations

   Interoperability considerations: n/a

   Published specification: This media type is a proper subset of the
      the XML 1.0 specification [2].  Two restrictions are made.

      First, no entity references other than the five predefined general
      entities references ("&amp;", "&lt;", "&gt;", "&apos;", and
      "&quot;") and numeric entity references may be present.

      Second, neither the "XML" declaration (e.g., <?xml version="1.0"
      ?>) nor the "DOCTYPE" declaration (e.g., <!DOCTYPE ...>) may be
      present.  (Accordingly, if another character set other than UTF-8
      is desired, then the "charset" parameter must be present.)

      All other XML 1.0 instructions (e.g., CDATA blocks, processing
      instructions, and so on) are allowed.

   Applications which use this media type: any BEEP profile wishing to
      make use of this XML 1.0 subset

   Additional Information: none

   Contact for further information: c.f., the "Author's Address" section
      of this memo

   Intended usage: limited use

   Author/Change controller: the IESG





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7. DTDs

7.1 BEEP Channel Management DTD

   <!--
     DTD for BEEP Channel Management, as of 2000-10-29


     Refer to this DTD as:

       <!ENTITY % BEEP PUBLIC "-//IETF//DTD BEEP//EN"
                  "http://xml.resource.org/profiles/BEEP/beep.dtd">
       %BEEP;
     -->


   <!--
     DTD data types:

           entity        syntax/reference     example
           ======        ================     =======
       a channel number
           CHAN          1..2147483647        1

       authoritative profile identification
           URI          c.f., [RFC-2396]      http://invisible.net/

       one or more feature tokens, separated by space
           FTRS         NMTOKENS              "magic"

       a language tag
           LANG         c.f., [RFC-1766]      "en", "en-US", etc.

       zero or more language tags
           LOCS         NMTOKENS              "en-US"

       a 3-digit reply code
           XYZ           [1-5][0-9][0-9]      500
   -->


   <!ENTITY % CHAN       "CDATA">
   <!ENTITY % URI        "CDATA">
   <!ENTITY % FTRS       "NMTOKENS">
   <!ENTITY % LANG       "NMTOKEN">
   <!ENTITY % LOCS       "NMTOKEN">
   <!ENTITY % XYZ        "CDATA">




Rose                        Standards Track                    [Page 48]

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   <!--
     BEEP messages, exchanged as application/beep+xml

        role       MSG         RPY         ERR
       =======     ===         ===         ===
       I and L                 greeting    error

       I or L      start       profile     error

       I or L      close       ok          error
     -->


   <!ELEMENT greeting    (profile)*>
   <!ATTLIST greeting
             features    %FTRS;            #IMPLIED
             localize    %LOCS;            "i-default">

   <!ELEMENT start       (profile)+>
   <!ATTLIST start
             number      %CHAN;             #REQUIRED
             serverName  CDATA              #IMPLIED>

   <!-- profile element is empty if contained in a greeting -->
   <!ELEMENT profile     (#PCDATA)>
   <!ATTLIST profile
             uri         %URI;              #REQUIRED
             encoding    (none|base64)      "none">

   <!ELEMENT close       (#PCDATA)>
   <!ATTLIST close
             number      %CHAN;             "0"
             code        %XYZ;              #REQUIRED
             xml:lang    %LANG;             #IMPLIED>

   <!ELEMENT ok          EMPTY>

   <!ELEMENT error       (#PCDATA)>
   <!ATTLIST error
             code        %XYZ;              #REQUIRED
             xml:lang    %LANG;             #IMPLIED>










Rose                        Standards Track                    [Page 49]

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7.2 TLS Transport Security Profile DTD

   <!--
     DTD for the TLS Transport Security Profile, as of 2000-09-04


     Refer to this DTD as:

       <!ENTITY % TLS PUBLIC "-//IETF//DTD TLS//EN"
                  "http://xml.resource.org/profiles/TLS/tls.dtd">
       %TLS;
     -->


   <!--
     TLS messages, exchanged as application/beep+xml

        role       MSG         RPY         ERR
       ======      ===         ===         ===
       I or L      ready       proceed     error
     -->


   <!ELEMENT ready       EMPTY>
   <!ATTLIST ready
             version     CDATA              "1">

   <!ELEMENT proceed     EMPTY>























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7.3 SASL Family of Profiles DTD

   <!--
     DTD for the SASL Family of Profiles, as of 2000-09-04


     Refer to this DTD as:

       <!ENTITY % SASL PUBLIC "-//IETF//DTD SASL//EN"
                  "http://xml.resource.org/profiles/sasl/sasl.dtd">
       %SASL;
     -->


   <!--
     SASL messages, exchanged as application/beep+xml

        role       MSG         RPY         ERR
       ======      ===         ===         ===
       I or L      blob        blob        error
     -->


   <!ELEMENT blob        (#PCDATA)>
   <!ATTLIST blob
             xml:space   (default|preserve)
                                           "preserve"
             status      (abort|complete|continue)
                                            "continue">






















Rose                        Standards Track                    [Page 51]

RFC 3080                     The BEEP Core                    March 2001


8. Reply Codes

   code    meaning
   ====    =======
   200     success

   421     service not available

   450     requested action not taken
           (e.g., lock already in use)

   451     requested action aborted
           (e.g., local error in processing)

   454     temporary authentication failure

   500     general syntax error
           (e.g., poorly-formed XML)

   501     syntax error in parameters
           (e.g., non-valid XML)

   504     parameter not implemented

   530     authentication required

   534     authentication mechanism insufficient
           (e.g., too weak, sequence exhausted, etc.)

   535     authentication failure

   537     action not authorized for user

   538     authentication mechanism requires encryption

   550     requested action not taken
           (e.g., no requested profiles are acceptable)

   553     parameter invalid

   554     transaction failed
           (e.g., policy violation)









Rose                        Standards Track                    [Page 52]

RFC 3080                     The BEEP Core                    March 2001


9. Security Considerations

   The BEEP framing mechanism, per se, provides no protection against
   attack; however, judicious use of initial tuning profiles provides
   varying degrees of assurance:

   1.  If one of the profiles from the SASL family is used, refer to
       [4]'s Section 9 for a discussion of security considerations.

   2.  If the TLS transport security profile is used (or if a SASL
       security layer is negotiated), then:

       1.  A man-in-the-middle may remove the security-related profiles
           from the BEEP greeting or generate a negative reply to the
           "ready" element of the TLS transport security profile.  A
           BEEP peer may be configurable to refuse to proceed without an
           acceptable level of privacy.

       2.  A man-in-the-middle may cause a down-negotiation to the
           weakest cipher suite available. A BEEP peer should be
           configurable to refuse weak cipher suites.

       3.  A man-in-the-middle may modify any protocol exchanges prior
           to a successful negotiation.  Upon completing the
           negotiation, a BEEP peer must discard previously cached
           information about the BEEP session.

       As different TLS ciphersuites provide varying levels of security,
       administrators should carefully choose which ciphersuites are
       provisioned.

   As BEEP is peer-to-peer in nature, before performing any task
   associated with a message, each channel should apply the appropriate
   access control based on the authenticated identity and privacy level
   associated with the BEEP session.
















Rose                        Standards Track                    [Page 53]

RFC 3080                     The BEEP Core                    March 2001


References

   [1]   Freed, N. and N. Borenstein, "Multipurpose Internet Mail
         Extensions (MIME) Part One: Format of Internet Message Bodies",
         RFC 2045, November 1996.

   [2]   World Wide Web Consortium, "Extensible Markup Language (XML)
         1.0", W3C XML, February 1998, <http://www.w3.org/TR/1998/REC-
         xml-19980210>.

   [3]   Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and
         P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January
         1999.

   [4]   Myers, J., "Simple Authentication and Security Layer (SASL)",
         RFC 2222, October 1997.

   [5]   Rose, M., "Mapping the BEEP Core onto TCP", RFC 3081, March
         2001.

   [6]   Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
         September 1981.

   [7]   Crocker, D. and P. Overell, "Augmented BNF for Syntax
         Specifications: ABNF", RFC 2234, November 1997.

   [8]   Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
         August 1996.

   [9]   Alvestrand, H., "Tags for the Identification of Languages", RFC
         BCP 47, RFC 3066, January 2001.

   [10]  Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
         Resource Identifiers (URI): Generic Syntax", RFC 2396, August
         1998.

   [11]  Newman, C., "The One-Time-Password SASL Mechanism", RFC 2444,
         October 1998.

   [12]  Kent, S. and R. Atkinson, "Security Architecture for the
         Internet Protocol", RFC 2401, November 1998.

   [13]  Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
         2279, January 1998.

   [14]  Linn, J., "Generic Security Service Application Program
         Interface, Version 2", RFC 2078, January 1997.




Rose                        Standards Track                    [Page 54]

RFC 3080                     The BEEP Core                    March 2001


   [15]  <http://www.isi.edu/in-notes/iana/assignments/sasl-mechanisms>

Author's Address

   Marshall T. Rose
   Invisible Worlds, Inc.
   1179 North McDowell Boulevard
   Petaluma, CA  94954-6559
   US

   Phone: +1 707 789 3700
   EMail: mrose@invisible.net
   URI:   http://invisible.net/






































Rose                        Standards Track                    [Page 55]

RFC 3080                     The BEEP Core                    March 2001


Appendix A. Acknowledgements

   The author gratefully acknowledges the contributions of: David Clark,
   Dave Crocker, Steve Deering, Wesley Michael Eddy, Huston Franklin,
   Marco Gazzetta, Danny Goodman, Steve Harris, Robert Herriot, Ken
   Hirsch, Greg Hudson, Ben Laurie, Carl Malamud, Michael Mealling,
   Keith McCloghrie, Paul Mockapetris, RL 'Bob' Morgan, Frank Morton,
   Darren New, Chris Newman, Joe Touch, Paul Vixie, Gabe Wachob, Daniel
   Woods, and, James Woodyatt.  In particular, Dave Crocker provided
   helpful suggestions on the nature of segmentation in the framing
   mechanism.








































Rose                        Standards Track                    [Page 56]

RFC 3080                     The BEEP Core                    March 2001


Appendix B. IANA Considerations

   The IANA registers "beep" as a GSSAPI [14] service name, as specified
   in Section 4.1.

   The IANA maintains a list of:

   o  standards-track BEEP profiles, c.f., Section 5.1; and,

   o  standards-track features for the channel management profile, c.f.,
      Section 5.2.

   For each list, the IESG is responsible for assigning a designated
   expert to review the specification prior to the IANA making the
   assignment.  As a courtesy to developers of non-standards track BEEP
   profiles and channel management features, the mailing list
   bxxpwg@invisible.net may be used to solicit commentary.

   The IANA makes the registrations specified in Section 6.2 and Section
   6.3.  It is recommended that the IANA register these profiles using
   the IANA as a URI-prefix, and populate those URIs with the respective
   profile registrations.





























Rose                        Standards Track                    [Page 57]

RFC 3080                     The BEEP Core                    March 2001


Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
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   kind, provided that the above copyright notice and this paragraph are
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
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   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















Rose                        Standards Track                    [Page 58]