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Versions: 00 01 02 03 RFC 3778

Network Working Group                                            E. Taft
Internet-Draft                                                J. Pravetz
Expires: April 19, 2004                                        S. Zilles
                                                           Adobe Systems
                                                        October 20, 2003


                     The application/pdf Media Type
                        draft-zilles-pdf-00.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 except that the right to
   produce derivative works is not granted.

   Internet-Drafts are working documents of the Internet Engineering
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   The list of current Internet-Drafts can be accessed at http://
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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 19, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   PDF, the 'Portable Document Format', is a general document
   representation language that has been in use for document exchange on
   the Internet since 1993. This document provides an overview of the
   PDF format, explains the mechanisms for digital signatures and
   encryption within PDF files, and updates the media type registration
   of 'application/pdf'.







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1. Introduction

   This is a preliminary draft that is intended for disucssion and
   comment. Comments should be sent to <szilles@adobe.com>.

   Since PDF was introduced in 1993, it has grown to be the major format
   for capturing and exchanging formatted documents electronically,
   across the Web, via e-mail and virtually every other document
   exchange mechanism. For example, RFC3297 [11] on content negotiation
   for Facsimile, voice and other message services shows how PDF can be
   sent in to a recipient that identifies his ability to accept the PDF.
   And byte range retrieval is illustrated in the HTTP 1.1 specification
   RFC2616 [12]. There is even RFC2346 [13] on how to better structure
   PDF files for international exchange of documents where different
   paper sizes are used.

   Within the Prepress community, ISO 15930-1:2001 PDF/X [14] has been
   adopted as the exchange standard for electronic documents. PDF/X is a
   profile of PDF that references the PDF Reference, Third edition [2]
   as the source specification. Based on the work on PDF/X, a committee
   was formed by NPES, The Association for Suppliers of Printing,
   Publishing and Converting Technologies, and AIIM, Association for
   Information and Image Management, International in August, 2002 to
   pursue an international standard, PDF/A, that defines the use of PDF
   for archiving and preserving documents. AIIM is the secretariat for
   ISO/TC 171 SC2, Document Imaging Applications.

   This document is intended to provide updated information on the
   registration of the MIME Media Type "application/pdf" as envisaged in
   Appendix A of RFC2048 [17], with particular focus on the features
   that help mitigate security concerns. This document refers to
   features documented in the PDF References versions 1 [1], 1.3 [2],
   1.4 [3] and 1.5 [4].

   PDF is a format for representing formatted documents. These documents
   may be structured or simple. They may contain text, images, graphics
   and other multimedia content, such as video and audio. There is
   support for annotations, metadata, hypertext links, and bookmarks.

   Two of the key features of PDF are the support for encryption and
   digital signatures. These help resolve some of the security
   considerations in transmitting sensitive information and in
   identifying the signers and what can be trusted therefore. The
   encryption capability is also combined with a rights management
   capability that controls the uses that a recipient can make of a PDF
   file. This is described in more detail below.





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2. History

   PDF was originally envisioned as a universal way to communicate and
   view printed information electronically reliably across a wide
   variety of machine configurations, operating systems and
   communication networks.

   PDF relies on the same imaging model as the PostScript page
   description language to render complex text, images and graphics in a
   device and resolution-independent manner, bringing this feature to
   the screen as well as the printer. To improve performance for
   interactive viewing, PDF defines a more structured format than that
   used by most PostScript language programs. PDF also includes objects,
   such as hypertext links and annotations, that are not part of the
   page itself but are useful for building collections of related
   documents and for reviewing and commenting on documents.

   The application/pdf media type was first registered in 1993 by Paul
   Lindner for use by the gopher protocol; the registration was
   subsequently updated in 1994 by Steve Zilles.































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3. Fragment identifiers

   The handling of fragment identifiers [5] is not defined in the PDF
   Reference. The handling of these is defined by the User Agent that
   interprets a PDF file. One such agent has the following semantics for
   the fragment identifies [6]:

   A fragment identifier consists of one or more PDF-open parameters in
   a single URL, separated by the ampersand (&) or pound (#) character.
   Each parameter implies an action to be performed and the value to be
   used for that action. Actions are processed and executed from left to
   right as they appear in the character string that makes up the
   fragment identifier.

   The PDF-open parameters allow the specification of a particular page
   or named destination to open. Named destinations are similar to the
   "anchors" used in HTML or the IDs used in XML. Once the target is
   specified, the view of the page in which it occurs can be specified,
   either by specifying the position of a viewing rectangle and its
   scale or size coordinates or by specifying a view relative to the
   viewing window in which the chosen page is to be presented.

   The list of PDF-open parameters and the action they imply is:

   o

   nameddest=name           action is to open to specified destination
                            (which includes a view)

                                Figure 1

   o

   page=pagenum             action is to open the specified page

                                Figure 2

   o

   zoom=scale,left,top      action is to set the "scale" and scrolling
                            factors. "left" and "top" are measured from
                            the top left corner of the page independent
                            of the size of the page. The pair "left" and
                            "top" are optional but both must appear if
                            present.

                                Figure 3




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   o

   view=keyword,position    action is to set the view to show some
                            specified portion of the page or its
                            bounding box. The keywords are defined by
                            Table 8.2 of the PDF Reference, version 1.5.
                            The "position" value is required for some of
                            the keywords and not allow for others. See
                            Table 8.2

                                Figure 4

   o

   viewrect=left,top,wd,ht  The view rectangle the is mapped into the
                            viewing window is position as for the zoom
                            parameter, but an explicit width and height
                            are given instead of a scale percentage.

                                Figure 5

   o

   highlight=lt,rt,top,btm  Highlight a rectangle on the chosen page
                            where lt,rt,top and btm are the coordinates
                            of the sides of the rectangle measured from
                            the top left corner of the page.

                                Figure 6

   Because all specified actions are executed, it is possible that later
   actions will override the effects of previous actions, so be aware of
   the order. For example, page actions should appear before zoom
   actions. Commands are not case sensitive (except for the value of a
   named destination).
















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4. Encryption

   PDF files allow access to be controlled using encryption and
   permission settings. The keys to decrypt document data, and
   permission settings for a document, are provided by encryption
   handlers. An 'Encryption Dictionary' is provided in the document
   trailer to enable encryption handlers to store document-specific
   information. Different encryption handlers can provide for different
   sets of rights.  The PDF encoding rules for password and public key
   encryption handlers is specified in the PDF Reference.

   A person that is able to 'access' a document is said to be able to
   open and view the document. Access is possible when a person can
   provide the key with which to decrypt the document. The key is
   protected and provided by the encryption handler. Encryption handlers
   will normally require some sort of authentication before a person can
   access the document decryption key. Encryption of PDF files is
   applied to all string and stream data in the document, and only to
   string and stream data. By encrypting only data portions of the PDF
   file, random access to PDF file contents is maintained. The data is
   encrypted using 40 to 128-bit RC4 [7] encryption algorithm.

   The person that has access to a document will be given certain rights
   or permissions for the document. A person that has full rights,
   including the right to save a document without encryption, is said to
   be an 'owner'. A person that has restricted rights is said to be a
   'user'. Example rights include the ability to copy text and other
   content from the PDF file, the ability to fill in form field data,
   and the ability to print the PDF file. Enforcement of rights is the
   responsibility of the viewing application.

   Password encryption allows the possibility of two different passwords
   to be used when providing access to the document. The 'author'
   password allows access to the document and full permissions,
   including the permission to save the document without encryption. The
   'user' password allows access to the document but access rights are
   restricted by a set of permissions.

   Public key encryption of PDF files uses one or more PKCS#7 [8]
   objects to store information regarding recipients that are able to
   open a document. Each PKCS#7 object contains a list of recipients, a
   document decryption key, and permission settings that apply to all
   recipients listed for that PKCS#7 object. The document decryption key
   is protected with a triple-DES key that is encrypted once with the
   public key of each listed recipient.






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5. Digital Signatures

   A digital signature can be used to authenticate the identity of a
   user and the validity of a document's contents. The nature of PDF
   ideally lends itself to digital signature applications because PDF
   provides a container within which to embed a complete record that is
   needed to reproduce a visual representation of what a person saw when
   they signed the PDF file. Additionally, PDF digital signature support
   allows for multiple signers to sign the same document and the ability
   to view the exact state of the document at the point when any
   individual signature was applied. These are positive characteristics
   when considering the legal implications of signed PDF files.

   To avoid redundancy in the specification of the digital signature
   features of PDF, the reader is referred to the full specification in
   the PDF Reference. The PDF Reference [4] section 8.7 and Appendix I
   specifies a syntax for representing digital signatures of PDF files
   using public key cryptography. An overview is provided here to
   indicate the nature of the information that is collected and how it
   is used.

   A signature digest is always of all bytes of the PDF file being
   signed, beginning at the first byte of the file and ending at the
   last byte of the file following the %EOF, but excluding the signature
   value because the signature value must be added after the signing
   process is complete. The offset values of the byte ranges that are
   signed are stored in the signature and are covered by the signature
   value. When verifying signatures these byte range values are used to
   determine which bytes to digest. Verification software must also
   ensure that the signature value is the only data that is not covered
   by the signature digest.

   Multiple signatures are supported using the incremental save
   capabilities of PDF. When changes to a file are made and a new
   signature is applied to the document, the changes are appended after
   the last byte of the previously existing document and then the new
   signature digest is of all bytes of the new file. In this manner
   changes can be made to a document and new signatures added to a
   document without invalidating earlier signatures that have been
   applied to the PDF file. Any change to a document is detected because
   all bytes of the PDF file are digested.

   The state of a signed document, when an earlier signature of a
   multiple signature document was applied, can be viewed by extracting
   the earlier set of bytes of the file and opening them in a PDF
   viewing application. This process is called 'rollback' and allows
   viewing of the exact state of the document when it was signed.




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   PDF syntax allows for 'author' and 'user' signatures. Under normal
   circumstances the first signature of a document is considered an
   author signature and all other signatures are considered user
   signatures. Authors can specify what changes are to be allowed to the
   PDF file before the author's signature is presented as invalid.
   Example changes include the ability to fill in form field data, the
   ability to add comments to a document, the ability to make no
   changes, and the ability to make any changes. Changes are detected by
   opening the existing document and the author's version of the
   document and performing a complete object compare of the two
   documents. Change detection is not a substitute for the legal value
   of document rollback.

   PDF public key digital signature syntax is specified for PKCS#1 [10]
   and PKCS#7 signatures. In both cases, all bytes of the PDF file are
   signed, with the exclusion of the PKCS#1 or PKCS#7, signature value,
   objects. PKCS#7, when used in this manner, acts in its detached
   signature mode. When using PKCS#7, the certificate chain of the
   signer is included in the PKCS#7 object. When using PKCS#1, the
   certificate chain of the signer is included with other signature
   information in the signed document.






























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6. Intellectual Property

   The following is copied verbatim from the PDF Reference [4]:

   The general idea of using an interchange format for electronic
   documents is in the public domain. Anyone is free to devise a set of
   unique data structures and operators that define an interchange
   format for electronic documents. However, Adobe Systems Incorporated
   owns the copyright for the particular data structures and operators
   and the written specification constituting the interchange format
   called the Portable Document Format. Thus, these elements of the
   Portable Document Format may not be copied without Adobe's
   permission.

   Adobe will enforce its copyright. Adobe's intention is to maintain
   the integrity of the Portable Document Format standard. This enables
   the public to distinguish between the Portable Document Format and
   other interchange formats for electronic documents. However, Adobe
   desires to promote the use of the Portable Document Format for
   information interchange among diverse products and applications.
   Accordingly, Adobe gives anyone copyright permission, subject to the
   conditions stated below, to:

   o  Prepare files whose content conforms to the Portable Document
      Format

   o  Write drivers and applications that produce output represented in
      the Portable Document Format

   o  Write software that accepts input in the form of the Portable
      Document Format and displays, prints, or otherwise interprets the
      contents

   o  Copy Adobe's copyrighted list of data structures and operators, as
      well as the example code and PostScript language function
      definitions in the written specification, to the extent necessary
      to use the Portable Document Format for the purposes above

   The conditions of such copyright permission are:

   o  Authors of software that accepts input in the form of the Portable
      Document Format must make reasonable efforts to ensure that the
      software they create respects the access permissions and
      permissions controls listed in Table 3.20 of this specification,
      to the extent that they are used in any particular document.

   o  Anyone who uses the copyrighted list of data structures and
      operators, as stated above, must include an appropriate copyright



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      notice.

   o  Accessing the document in ways not permitted by the document's
      access permissions is a violation of the document author's
      copyright.

   This limited right to use the copyrighted list of data structures and
   operators does not include the right to copy this book, other
   copyrighted material from Adobe, or the software in any of Adobe's
   products that use the Portable Document Format, in whole or in part,
   nor does it include the right to use any Adobe patents, except as may
   be permitted by an official Adobe Patent Clarification Notice (see
   the Bibliography).

   Acrobat, Acrobat Capture, Adobe Reader, ePaper, the "Get Adobe
   Reader" Web logo, the "Adobe PDF" Web logo, and all other trademarks,
   service marks, and logos used by Adobe (the "Marks") are the
   registered trademarks or trademarks of Adobe Systems Incorporated in
   the United States and other countries. Nothing in this book is
   intended to grant you any right or license to use the Marks for any
   purpose.






























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7. PDF implementations

   There are multiple, independent, interoperable implementations of
   PDF. In addition, there are more than 1800 tools that work on
   application/pdf files. For example, see Planet PDF [15] or
   PDFzone.com [16] for lists of applicable tools. Note that it is not
   the case that all implementations implement all features. Therefore
   care in choosing tools is advised; check if the features you require
   are provided. There is good interoperability among implementations
   that do implement the same features.









































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8. Security considerations

   An "application/pdf" resource contains information to be parsed and
   processed by the recipient's PDF system. Because PDF is both a
   representation of formatted documents and a container system for the
   resources need to reproduce or view said documents, it is possible
   that a PDF file has embedded resources not described in the PDF
   Reference.

   Although it is not a defined feature of PDF, a PDF processor could
   extract these resources and store them on the recipients system.
   Furthermore, PDF processor may accept and execute "plug-in" modules
   accessible to the recipient. These may also access material in the
   PDF file or on the recipients system. Therefore, care in establishing
   the source, security and reliability of such plug-ins is recommended.
   Message-sending software should not make use of arbitrary plug-ins
   without prior agreement on their presence at the intended recipients.
   Message-receiving and -displaying software should make sure that any
   non-standard plug-ins are secure and do not present a security
   threat.

   PDF  may contain "scripts" to customize the displaying and processing
   of PDF files. These scripts are expressed in a version of  JavaScript
   [9] based on JavaScript version 1.5 of ISO-16262 (formerly known as
   ECMAScript). These scripts have access to an API that is similar to
   the "plug-in" API. They are intended for execution by the PDF
   processor. Some such script might compromise the security of the
   system when executed.

   In general, any information stored outside of the direct control of
   the user -- including referenced application software or plug-ins and
   embedded files, scripts or other material not covered in the PDF
   reference  -- can be a source of insecurity, by either obvious or
   subtle means.  For example, a script can modify the content of a
   document prior to its being displayed.  Thus, the security of any PDF
   document may be dependent on the resources referenced by that
   document.

   As noted above, PDF provides mechanism for helping insure the
   integrity of a PDF file, Encryption (Section 4), and to be able to
   digitally sign (Section 5) a PDF file. The latter capability allows a
   recipient to decide if he is willing to trust the file.

   Where there is concern that tampering with the PDF file might be a
   problem it is recommended that the encryption and digital signature
   features be used to protect and authoritate the PDF.

   In addition, PDF processors may have mechanisms that track the source



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   of scripts or plug-ins and will execute only those scripts or
   plug-ins that meet the processors requirements for trustworthiness of
   the sources.
















































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9. IANA considerations

   IANA update the registration of 'application/pdf'. This is a media
   type registration as defined in Multipurpose Internet Mail Extensions
   (MIME) Part Four: Registration Procedures [17]

     MIME media type name: application
     MIME subtype name: pdf
     Required parameters: none
     Optional parameter: none
     Encoding considerations:
        PDF files frequently contain binary data, and thus
        must be encoded in non-binary contexts.
      Security considerations:
        See Security Considerations section of this document
      Interoperability considerations:
        See PDF Implementations section of this document
      Published specification:
         Adobe Systems Incorporated, "PDF Reference, Fourth Edition",
         Version 1.5, August 2003
         http://partners.adobe.com/asn/tech/pdf/specifications.jsp,
      Applications which use this media type:
        See PDF Implementations section of this document
     Additional information:
     Magic number(s):
        All PDF files start with the characters '%PDF-'
        using the PDF version number, e.g., '%PDF-1.4'.
        These characters are in US-ASCII encoding.
    File extension(s): .pdf
    Macintosh File Type Code(s): "PDF"
    For further information:
            Adobe Developer Support %lt;dev-support@adobe.com%gt;
            345 Park Ave
            San Jose, CA 95110
            (408) 536-xxxx
            http://www.adobe.com/xxxxx

     Intended usage: COMMON
     Author/Change controller:
            Adobe Systems Incorporated
            Attn: Adobe Developer Support
            ....









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10. Registration form for application/pdf media type


















































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References

   [1]   Adobe Systems Incorporated, "Portable Document Format Reference
         Manual", Version 1.0, ISBN: 0-201-62628-4,  Addison-Wesley, New
         York NY, 1993.

   [2]   Adobe Systems Incorporated, "PDF Reference, Second Edition",
         Version 1.3, ISBN: 0-201-61588-6,  Addison-Wesley, New York NY,
         2000.

   [3]   Adobe Systems Incorporated, "PDF Reference, Third Edition",
         Version 1.4, ISBN: 0-201-75839-3,  Addison-Wesley, New York NY,
         November 2001.

   [4]   Adobe Systems Incorporated, "PDF Reference, Fourth Edition",
         Version 1.5,  http://partners.adobe.com/asn/tech/pdf/
         specifications.jsp, August 2003.

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

   [6]   Adobe Systems Incorporated, "PDF Open Parameters", Technical
         Note 5428,  http://partners.adobe.com/asn/acrobat/sdk/public/
         docs/PDFOpenParams.pdf, May 2003.

   [7]   Rivest, R., "RC4 - an unpublished, trade secret encryption
         algorithm",  http://theory.lcs.mit.edu/~rivest/faq.html,
         http://www.rsasecurity.com/rsalabs/faq/3-6-3.html, November
         1993.

   [8]   RSA Laboratories, "PKCS #7 - Cryptographic Message Syntax
         Standard", Version 1.5,  http://www.rsasecurity.com/rsalabs/
         pkcs/pkcs-7/index.html, November 1993.

   [9]   Adobe Systems Incorporated, "Acrobat JavaScript Scripting
         Reference", Technical Note 5431,  http://partners.adobe.com/
         asn/acrobat/sdk/public/docs/AcroJS.pdf, September 2003.

   [10]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards
         (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC
         3447, February 2003.









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Informative References

   [11]  Klyne, G., Iwazaki, R. and D. Crocker, "Content Negotiation for
         Messaging Services based on Email", RFC 3297, July 2002.

   [12]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
         Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
         HTTP/1.1", RFC 2616, June 1999.

   [13]  Palme, J., "Making Postscript and PDF International", RFC 2346,
         May 1998.

   [14]  International Standards Organization, "Graphic technology --
         Prepress digital data exchange -- Use of PDF -- Part 1:
         Complete exchange using CMYK data (PDF/X-1 and PDF/X-1a)", ISO
         15930-1:2001, November 2002.

   [15]  Planet PDF, "Planet PDF Tools List",  http://www.planetpdf.com/
         mainpage.asp?MenuID=193&WebPageID=612.

   [16]  InternetBiz.net, LLC, "PDF Toolbox",  http://www.pdfzone.com/
         toolbox/.

   [17]  Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet
         Mail Extensions (MIME) Part Four: Registration Procedures", RFC
         2048, November 1996.


Authors' Addresses

   Edward A. Taft
   Adobe Systems
   345 Park Ave
   San Jose, CA  95110
   US

   EMail: taft@adobe.com


   James D. Pravetz
   Adobe Systems
   345 Park Ave
   San Jose, CA  95110
   US

   EMail: jpravetz@adobe.com





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   Stephen Zilles
   Adobe Systems
   345 Park Ave
   San Jose, CA  95110
   US

   Phone: +1 408 356 7692
   EMail: szilles@adobe.com
   URI:   http://










































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Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights. Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11. Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive
   Director.


Full Copyright Statement

   Copyright (C) The Internet Society (2003). All Rights Reserved.

   This document and translations of it may be copied and furnished to
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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
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION



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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgment

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











































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