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rfc:rfc3930

Network Working Group D. Eastlake 3rd Request for Comments: 3930 Motorola Laboratories Category: Informational October 2004

 The Protocol versus Document Points of View in Computer Protocols

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2004).

Abstract

 This document contrasts two points of view: the "document" point of
 view, where digital objects of interest are like pieces of paper
 written and viewed by people, and the "protocol" point of view where
 objects of interest are composite dynamic network messages.  Although
 each point of view has a place, adherence to a document point of view
 can be damaging to protocol design.  By understanding both points of
 view, conflicts between them may be clarified and reduced.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
 2.  Points of View . . . . . . . . . . . . . . . . . . . . . . . .  2
     2.1.  The Basic Points of View . . . . . . . . . . . . . . . .  3
     2.2.  Questions of Meaning . . . . . . . . . . . . . . . . . .  3
           2.2.1.  Core Meaning . . . . . . . . . . . . . . . . . .  3
           2.2.2.  Adjunct Meaning. . . . . . . . . . . . . . . . .  4
     2.3.  Processing Models. . . . . . . . . . . . . . . . . . . .  5
           2.3.1.  Amount of Processing . . . . . . . . . . . . . .  5
           2.3.2.  Granularity of Processing. . . . . . . . . . . .  5
           2.3.3.  Extensibility of Processing. . . . . . . . . . .  6
     2.4.  Security and Canonicalization. . . . . . . . . . . . . .  6
           2.4.1.  Canonicalization . . . . . . . . . . . . . . . .  6
           2.4.2.  Digital Authentication . . . . . . . . . . . . .  8
           2.4.3.  Canonicalization and Digital Authentication. . .  8
           2.4.4.  Encryption . . . . . . . . . . . . . . . . . . .  9
     2.5.  Unique Internal Labels . . . . . . . . . . . . . . . . . 10
 3.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
 4.  Resolution of the Points of View . . . . . . . . . . . . . . . 11

Eastlake Informational [Page 1] RFC 3930 Protocol versus Document Viewpoints October 2004

 5.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 12
 6.  Security Considerations. . . . . . . . . . . . . . . . . . . . 12
 Informative References . . . . . . . . . . . . . . . . . . . . . . 12
 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 15

1. Introduction

 This document contrasts: the "document" point of view, where digital
 objects of interest are thought of as pieces of paper written and
 viewed by people, and the "protocol" point of view, where objects of
 interest are composite dynamic network messages.  Those accustomed to
 one point of view frequently have great difficulty appreciating the
 other:  Even after they understand it, they almost always start by
 considering things from their accustomed point of view, assume that
 most of the universe of interest is best viewed from their
 perspective, and commonly slip back into thinking about things
 entirely from that point of view.  Although each point of view has a
 place, adherence to a document point of view can be damaging to
 protocol design.  By understanding both points of view, conflicts
 between them may be clarified and reduced.
 Much of the IETF's traditional work has concerned low level binary
 protocol constructs.  These are almost always viewed from the
 protocol point of view.  But as higher level application constructs
 and syntaxes are involved in the IETF and other standards processes,
 difficulties can arise due to participants who have the document
 point of view.  These two different points of view defined and
 explored in section 2 below.
 Section 3 gives some examples.  Section 4 tries to synthesize the
 views and give general design advice in areas that can reasonably be
 viewed either way.

2. Points of View

 The following subsections contrast the document and protocol points
 of view.  Each viewpoint is EXAGGERATED for effect.
 The document point of view is indicated in paragraphs headed "DOCUM",
 and the protocol point of view is indicated in paragraphs headed
 "PROTO".

Eastlake Informational [Page 2] RFC 3930 Protocol versus Document Viewpoints October 2004

2.1. The Basic Points of View

 DOCUM: What is important are complete (digital) documents, analogous
    to pieces of paper, viewed by people.  A major concern is to be
    able to present such documents as directly as possible to a court
    or other third party.  Because what is presented to the person is
    all that is important, anything that can effect this, such as a
    "style sheet" [CSS], MUST be considered part of the document.
    Sometimes it is forgotten that the "document" originates in a
    computer, may travel over, be processed in, and be stored in
    computer systems, and is viewed on a computer, and that such
    operations may involve transcoding, enveloping, or data
    reconstruction.
 PROTO: What is important are bits on the wire generated and consumed
    by well-defined computer protocol processes.  No person ever sees
    the full messages as such; it is only viewed as a whole by geeks
    when debugging, and even then they only see some translated
    visible form.  If one actually ever has to demonstrate something
    about such a message in a court or to a third party, there isn't
    any way to avoid having computer experts interpret it.  Sometimes
    it is forgotten that pieces of such messages may end up being
    included in or influencing data displayed to a person.

2.2. Questions of Meaning

 The document and protocol points of view have radically different
 concepts of the "meaning" of data.  The document oriented tend to
 consider "meaning" to a human reader extremely important, but this is
 something the protocol oriented rarely think about at all.
 This difference in point of view extends beyond the core meaning to
 the meaning of addenda to data.  Both core and addenda meaning are
 discussed below.

2.2.1. Core Meaning

 DOCUM: The "meaning" of a document is a deep and interesting human
    question related to volition.  It is probably necessary for the
    document to include or reference human language policy and/or
    warranty/disclaimer information.  At an absolute minimum, some
    sort of semantic labelling is required.  The assumed situation is
    always a person interpreting the whole "document" without other
    context.  Thus it is reasonable to consult attorneys during
    message design, to require that human-readable statements be
    "within the four corners" of the document, etc.

Eastlake Informational [Page 3] RFC 3930 Protocol versus Document Viewpoints October 2004

 PROTO: The "meaning" of a protocol message should be clear and
    unambiguous from the protocol specification.  It is frequently
    defined in terms of the state machines of the sender and recipient
    processes and may have only the most remote connection with human
    volition.  Such processes have additional context, and the message
    is usually only meaningful with that additional context.  Adding
    any human-readable text that is not functionally required is
    silly.  Consulting attorneys during design is a bad idea that
    complicates the protocol and could tie a design effort in knots.

2.2.2. Adjunct Meaning

 Adjunct items can be added or are logical addenda to a message.
 DOCUM: From a document point of view, at the top level is a person
    looking at a document.  So adjunct items such as digital
    signatures, person's names, dates, etc., must be carefully labeled
    as to meaning.  Thus a digital signature needs to include, in more
    or less human-readable form, what that signature means (is the
    signer a witness, author, guarantor, authorizer, or what?).
    Similarly, a person's name needs to be accompanied by that
    person's role, such as editor, author, subject, or contributor.
    As another example, a date needs to be accompanied by the
    significance of the date, such as date of creation, modification,
    distribution, or some other event.
       Given the unrestrained scope of what can be documented, there
    is a risk of trying to enumerate and standardize all possible
    "semantic tags" for each kind of adjunct data during in the design
    process.  This can be a difficult, complex, and essentially
    infinite task (i.e., a rat hole).
 PROTO: From a protocol point of view, the semantics of the message
    and every adjunct in it are defined in the protocol specification.
    Thus, if there is a slot for a digital signature, person's name, a
    date, or whatever, the party who is to enter that data, the party
    or parties who are to read it, and its meaning are all pre-
    defined.  Even if there are several possible meanings, the
    specific meaning that applies can be specified by a separate
    enumerated type field.  There is no reason for such a field to be
    directly human readable.  Only the "meanings" directly relevant to
    the particular protocol need be considered.  Another way to look
    at this is that the "meaning" of each adjunct, instead of being
    pushed into and coupled with the adjunct itself, as the document
    point of view encourages, is commonly promoted to the level of the
    protocol specification, resulting in simpler adjuncts.

Eastlake Informational [Page 4] RFC 3930 Protocol versus Document Viewpoints October 2004

2.3. Processing Models

 The document oriented and protocol oriented have very different views
 on what is likely to happen to an object.

2.3.1. Amount of Processing

 DOCUM: The model is of a quasi-static object like a piece of paper.
    About all one does to pieces of paper is transfer them as a whole,
    from one storage area to another, or add signatures, date stamps,
    or similar adjuncts.  (Possibly one might want an extract from a
    document or to combine multiple documents into a summary, but this
    isn't the common case.)
 PROTO: The standard model of a protocol message is as an ephemeral
    composite, multi-level object created by a source process and
    consumed by a destination process.  Such a message is constructed
    from information contained in previously received messages,
    locally stored information, local calculations, etc.  Quite
    complex processing is normal.

2.3.2. Granularity of Processing

 DOCUM: The document view is generally of uniform processing or
    evaluation of the object being specified.  There may be an
    allowance for attachments or addenda, but, if so, they would
    probably be simple, one level, self documenting attachments or
    addenda.  (Separate processing of an attachment or addenda is
    possible but not usual.)
 PROTO: Processing is complex and almost always affects different
    pieces of the message differently.  Some pieces may be intended
    for use only by the destination process and may be extensively
    processed there.  Others may be present so that the destination
    process can, at some point, do minimal processing and forward them
    in other messages to yet more processes.  The object's structure
    can be quite rich and have multilevel or recursive aspects.
    Because messages are processed in a local context, elements of the
    message may include items like a signature that covers multiple
    data elements, some of which are in the message, some received in
    previous messages, and some locally calculated.

Eastlake Informational [Page 5] RFC 3930 Protocol versus Document Viewpoints October 2004

2.3.3. Extensibility of Processing

 DOCUM: The document oriented don't usually think of extensibility as
    a major problem.  They assume that their design, perhaps with some
    simple version scheme, will meet all requirements.  Or, coming
    from an SGML/DTD world of closed systems, they may assume that
    knowledge of new versions or extensions can be easily and
    synchronously distributed to all participating sites.
 PROTO: Those who are protocol oriented assume that protocols will
    always need to be extended and that it will not be possible to
    update all implementations as such extensions are deployed and/or
    retired.  This is a difficult problem but those from the protocol
    point of view try to provide the tools needed.  For example, they
    specify carefully defined versioning and extension/feature
    labelling, including the ability to negotiate versions and
    features where possible and at least a specification of how
    parties running different levels should interact, providing
    length/delimiting information for all data so that it can be
    skipped if not understood, and providing destination labelling so
    that a process can tell that it should ignore data except for
    passing it through to a later player.

2.4. Security and Canonicalization

 Security is a subtle area.  Sometime problems can be solved in a way
 that is effective across many applications. Those solutions are
 typically incorporated into standard security syntaxes such as those
 for ASN.1 [RFC3852] and XML [RFC3275, XMLENC].  But there are almost
 always application specific questions, particularly the question of
 exactly what information needs to be authenticated or encrypted.
 Questions of exactly what needs to be secured and how to do so
 robustly are deeply entwined with canonicalization.  They are also
 somewhat different for authentication and encryption, as discussed
 below.

2.4.1. Canonicalization

 Canonicalization is the transformation of the "significant"
 information in a message into a "standard" form, discarding
 "insignificant" information, for example, encoding into a standard
 character set or changing line endings into a standard encoding and
 discarding the information about the original character set or line
 ending encodings.  Obviously, what is "significant" and what is
 "insignificant" varies with the application or protocol and can be
 tricky to determine.  However, it is common that for each particular
 syntax, such as ASCII [ASCII], ASN.1 [ASN.1], or XML [XML], a

Eastlake Informational [Page 6] RFC 3930 Protocol versus Document Viewpoints October 2004

 standard canonicalization (or canonicalizations) is specified or
 developed through practice.  This leads to the design of applications
 that assume one of such standard canonicalizations, thus reducing the
 need for per-application canonicalization.  (See also [RFC3076,
 RFC3741].)
 DOCUM: From the document point of view, canonicalization is suspect
    if not outright evil.  After all, if you have a piece of paper
    with writing on it, any modification to "standardize" its format
    can be an unauthorized change in the original message as created
    by the "author", who is always visualized as a person.  Digital
    signatures are like authenticating signatures or seals or time
    stamps on the bottom of the "piece of paper".  They do not justify
    and should not depend on changes in the message appearing above
    them.  Similarly, encryption is just putting the "piece of paper"
    in a vault that only certain people can open and does not justify
    any standardization or canonicalization of the message.
 PROTO: From the protocol point of view, canonicalization is simply a
    necessity.  It is just a question of exactly what canonicalization
    or canonicalizations to apply to a pattern of bits that are
    calculated, processed, stored, communicated, and finally parsed
    and acted on.  Most of these bits have never been seen and never
    will be seen by a person.  In fact, many of the parts of the
    message will be artifacts of encoding, protocol structure, and
    computer representation rather than anything intended for a person
    to see.
       Perhaps in theory, the "original", idiosyncratic form of any
    digitally signed part could be conveyed unchanged through the
    computer process, storage, and communications channels that
    implement the protocol and could be usefully signed in that form.
    But in practical systems of any complexity, this is unreasonably
    difficult, at least for most parts of messages.  And if it were
    possible, it would be virtually useless, because to authenticate
    messages you would still have to determine their equivalence with
    the preserved original form.
       Thus, signed data must be canonicalized as part of signing and
    verification to compensate for insignificant changes made in
    processing, storage, and communication.  Even if, miraculously, an
    initial system design avoids all cases of signed message
    reconstruction based on processed data or re-encoding based on
    character set or line ending or capitalization or numeric
    representation or time zones or whatever, later protocol revisions
    and extensions are certain to require such reconstruction and/or
    re-encoding eventually.  If such "insignificant" changes are not
    ameliorated by canonicalization, signatures won't work, as
    discussed in more detail in 2.4.3 below.

Eastlake Informational [Page 7] RFC 3930 Protocol versus Document Viewpoints October 2004

2.4.2. Digital Authentication

 DOCUM: The document-oriented view on authentication tends to be a
    "digital signature" and "forms" point of view.  (The "forms" point
    of view is a subset of the document point of view that believes
    that a principal activity is presenting forms to human beings so
    that they can fill out and sign portions of those forms [XForms]).
    Since the worry is always about human third parties and viewing
    the document in isolation, those who are document oriented always
    want "digital signature" (asymmetric key) authentication, with its
    characteristics of "non-repudiability", etc.  As a result, they
    reject secret key based message authentication codes, which
    provide the verifier with the capability of forging an
    authentication code, as useless.  (See any standard reference on
    the subject for the usual meaning of these terms.)
       From their point of view, you have a piece of paper or form
    which a person signs.  Sometimes a signature covers only part of a
    form, but that's usually because a signature can only cover data
    that is already there.  And normally at least one signature covers
    the "whole" document/form.  Thus the document oriented want to be
    able to insert digital signatures into documents without changing
    the document type and even "inside" the data being signed, which
    requires a mechanism to skip the signature so that it does not try
    to sign itself.
 PROTO: From a protocol point of view, the right kind of
    authentication to use, whether "digital signature" or symmetric
    keyed authentication code (or biometric or whatever), is just
    another engineering decision affected by questions of efficiency,
    desired security model, etc.  Furthermore, the concept of signing
    a "whole" message seems very peculiar (unless it is a copy being
    saved for archival purposes, in which case you might be signing a
    whole archive at once anyway).  Typical messages are made up of
    various pieces with various destinations, sources, and security
    requirements.  Furthermore, there are common fields that it is
    rarely useful to sign because they change as the message is
    communicated and processed.  Examples include hop counts, routing
    history, and local forwarding tags.

2.4.3. Canonicalization and Digital Authentication

 For authenticating protocol system messages of practical complexity,
 you are faced with the choice of doing
 (1) "too little canonicalization" and having brittle authentication,
     useless due to verification failures caused by surface
     representation changes without significance,

Eastlake Informational [Page 8] RFC 3930 Protocol versus Document Viewpoints October 2004

 (2) the sometimes difficult and tricky work of selecting or designing
     an appropriate canonicalization or canonicalizations to be used
     as part of authentication generation and verification, producing
     robust and useful authentication, or
 (3) "too much canonicalization" and having insecure authentication,
     useless because it still verifies even when significant changes
     are made in the signed data.
 The only useful option above is number 2.

2.4.4. Encryption

 In terms of processing, transmission, and storage, encryption turns
 out to be much easier to get working than signatures.  Why?  Because
 the output of encryption is essentially random bits.  It is clear
 from the beginning that those bits need to be transferred to the
 destination in some absolutely clean way that does not change even
 one bit.  Because the encrypted bits are meaningless to a human
 being, there is no temptation among the document oriented to try to
 make them more "readable".  So appropriate techniques of encoding at
 the source, such as Base64 [RFC2045], and decoding at the
 destination, are always incorporated to protect or "armor" the
 encrypted data.
 Although the application of canonicalization is more obvious with
 digital signatures, it may also apply to encryption, particularly
 encryption of parts of a message.  Sometimes elements of the
 environment where the plain text data is found may affect its
 interpretation.  For example, interpretation can be affected by the
 character encoding or bindings of dummy symbols.  When the data is
 decrypted, it may be into an environment with a different character
 encoding or dummy symbol bindings.  With a plain text message part,
 it is usually clear which of these environmental elements need to be
 incorporated in or conveyed with the message.  But an encrypted
 message part is opaque.  Thus some canonical representation that
 incorporates such environmental factors may be needed.
 DOCUM: Encryption of the entire document is usually what is
    considered.  Because signatures are always thought of as human
    assent, people with a document point of view tend to vehemently
    assert that encrypted data should never be signed unless the plain
    text of it is known.
 PROTO: Messages are complex composite multi-level structures, some
    pieces of which are forwarded multiple hops.  Thus the design
    question is what fields should be encrypted by what techniques to
    what destination or destinations and with what canonicalization.

Eastlake Informational [Page 9] RFC 3930 Protocol versus Document Viewpoints October 2004

    It sometimes makes perfect sense to sign encrypted data you don't
    understand; for example, the signature could just be for integrity
    protection or for use as a time stamp, as specified in the
    protocol.

2.5. Unique Internal Labels

 It is desirable to be able to reference parts of structured messages
 or objects by some sort of "label" or "id" or "tag".  The idea is
 that this forms a fixed "anchor" that can be used "globally", at
 least within an application domain, to reference the tagged part.
 DOCUM: From the document point of view, it seems logical just to
    provide for a text tag.  Users or applications could easily come
    up with short readable tags.  These would probably be meaningful
    to a person if humanly generated (e.g., "Susan") and at least
    fairly short and systematic if automatically generated (e.g.,
    "A123").  The ID attribute type in XML [XML] appears to have been
    thought of this way, although it can be used in other ways.
 PROTO: From a protocol point of view, unique internal labels look
    very different than they do from a document point of view.  Since
    this point of view assumes that pieces of different protocol
    messages will later be combined in a variety of ways, previously
    unique labels can conflict.  There are really only three
    possibilities if such tags are needed, as follows:
    (1) Have a system for dynamically rewriting such tags to maintain
        uniqueness.  This is usually a disaster, as it (a) invalidates
        any stored copies of the tags that are not rewritten, and it
        is usually impossible to be sure there aren't more copies
        lurking somewhere you failed to update, and (b) invalidates
        digital signatures that cover a changed tag.
    (2) Use some form of hierarchical qualified tags.  Thus the total
        tag can remain unique even if a part is moved, because its
        qualification changes.  This avoids the digital signature
        problems described above.  But it destroys the concept of a
        globally-unique anchor embedded in and moving with the data.
        And stored tags may still be invalidated by data moves.
        Nevertheless, within the scope of a particular carefully
        designed protocol, such as IOTP [RFC2801], this can work.
    (3) Construct a lengthy globally-unique tag string.  This can be
        done successfully by using a good enough random number
        generator and big enough random tags (perhaps about 24
        characters) sequentially, as in the way email messages IDs are
        created [RFC2822].

Eastlake Informational [Page 10] RFC 3930 Protocol versus Document Viewpoints October 2004

    Thus, from a protocol point of view, such tags are difficult but
    if they are needed, choice 3 works best.

3. Examples

 IETF protocols are replete with examples of the protocol viewpoint
 such as TCP [RFC793], IPSEC [RFC2411], SMTP [RFC2821], and IOTP
 [RFC2801, RFC2802].
 The eXtensible Markup Language [XML] is an example of something that
 can easily be viewed both ways and where the best results frequently
 require attention to both the document and the protocol points of
 view.
 Computerized court documents, human-to-human email, and the X.509v3
 Certificate [X509v3], particularly the X509v3 policy portion, are
 examples primarily designed from the document point of view.

4. Resolution of the Points of View

 There is some merit to each point of view.  Certainly the document
 point of view has some intuitive simplicity and appeal and is OK for
 applications where it meets needs.
 The protocol point of view can come close to encompassing the
 document point of view as a limiting case.  In particular, it does so
 under the following circumstances:
 1. As the complexity of messages declines to a single payload
    (perhaps with a few attachments).
 2. As the mutability of the payload declines to some standard format
    that needs little or no canonicalization.
 3. As the number of parties and amount of processing declines as
    messages are transferred.
 4. As the portion of the message intended for more or less direct
    human consumption increases.
 Under the above circumstances, the protocol point of view would be
 narrowed to something quite close to the document point of view.
 Even when the document point of view is questionable, the addition of
 a few options to a protocol will usually mollify the perceived needs
 of those looking at things from that point of view.  For example,
 adding optional non-canonicalization or an optional policy statement,
 or inclusion of semantic labels, or the like.

Eastlake Informational [Page 11] RFC 3930 Protocol versus Document Viewpoints October 2004

 On the other hand, the document point of view is hard to stretch to
 encompass the protocol case.  From a strict piece of paper
 perspective, canonicalization is wrong; inclusion of human language
 policy text within every significant object and a semantic tag with
 every adjunct should be mandatory; and so on.  Objects designed in
 this way are rarely suitable for protocol use, as they tend to be
 improperly structured to accommodate hierarchy and complexity,
 inefficient (due to unnecessary text and self-documenting
 inclusions), and insecure (due to brittle signatures).
 Thus, to produce usable protocols, it is best to start with the
 protocol point of view and add document point of view items as
 necessary to achieve consensus.

5. Conclusion

 I hope that this document will help explain to those of either point
 of view where those with the other view are coming from.  It is my
 hope that this will decrease conflict, shed some light -- in
 particular on the difficulties of security design -- and lead to
 better protocol designs.

6. Security Considerations

 This document considers the security implications of the Document and
 Protocol points of view, as defined in Sections 2.1 and 2.2, and
 warns of the security defects in the Document view.  Most of these
 security considerations appear in Section 2.4 but they are also
 touched on elsewhere in Section 2 which should be read in its
 entirety.

Informative References

 [ASCII]      "USA Standard Code for Information Interchange", X3.4,
              American National Standards Institute: New York, 1968.
 [ASN.1]      ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998,
              "Information Technology - Abstract Syntax Notation One
              (ASN.1):  Specification of Basic Notation".
              ITU-T Recommendation X.690 (1997) | ISO/IEC 8825-1:1998,
              "Information Technology - ASN.1 Encoding Rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER)".  <http://www.itu.int/ITU-
              T/studygroups/com17/languages/index.html>.

Eastlake Informational [Page 12] RFC 3930 Protocol versus Document Viewpoints October 2004

 [CSS]        "Cascading Style Sheets, level 2 revision 1 CSS 2.1
              Specification", B. Bos, T. Gelik, I. Hickson, H. Lie,
              W3C Candidate Recommendation, 25 February 2004.
              <http://www.w3.org/TR/CSS21>
 [RFC793]     Postel, J., "Transmission Control Protocol", STD 7, RFC
              793, September 1981.
 [RFC2045]    Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.
 [RFC2411]    Thayer, R., Doraswamy, N., and R. Glenn, "IP Security
              Document Roadmap", RFC 2411, November 1998.
 [RFC3852]    Housley, R., "Cryptographic Message Syntax (CMS)", RFC
              3852, July 2004.
 [RFC2801]    Burdett, D., "Internet Open Trading Protocol - IOTP
              Version 1.0", RFC 2801, April 2000.
 [RFC2802]    Davidson, K. and Y. Kawatsura, "Digital Signatures for
              the v1.0 Internet Open Trading Protocol (IOTP)", RFC
              2802, April 2000.
 [RFC2821]    Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
              April 2001.
 [RFC2822]    Resnick, P., "Internet Message Format", RFC 2822, April
              2001.
 [RFC3076]    Boyer, J., "Canonical XML Version 1.0", RFC 3076, March
              2001.
 [RFC3275]    Eastlake 3rd, D., Reagle, J., and D. Solo, "(Extensible
              Markup Language) XML-Signature Syntax and Processing",
              RFC 3275, March 2002.
 [RFC3741]    Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Functional Description", RFC 3471,
              January 2003.
 [X509v3]     "ITU-T Recommendation X.509 version 3 (1997),
              Information Technology - Open Systems Interconnection -
              The Directory Authentication Framework", ISO/IEC 9594-
              8:1997.

Eastlake Informational [Page 13] RFC 3930 Protocol versus Document Viewpoints October 2004

 [XForms]     "XForms 1.0", M. Dubinko, L. Klotz, R. Merrick, T.
              Raman, W3C Recommendation 14 October 2003.
              <http://www.w3.org/TR/xforms/>
 [XML]        "Extensible Markup Language (XML) 1.0 Recommendation
              (2nd Edition)".  T.  Bray, J. Paoli, C. M. Sperberg-
              McQueen, E. Maler, October 2000.
              <http://www.w3.org/TR/2000/REC-xml-20001006>
 [XMLENC]     "XML Encryption Syntax and Processing", J. Reagle, D.
              Eastlake, December 2002.
              <http://www.w3.org/TR/2001/RED-xmlenc-core-20021210/>

Author's Address

 Donald E. Eastlake 3rd
 Motorola Laboratories
 155 Beaver Street
 Milford, MA 01757 USA
 Phone:  +1 508-786-7554 (w)
         +1 508-634-2066 (h)
 Fax:    +1 508-786-7501 (w)
 EMail:  Donald.Eastlake@motorola.com

Eastlake Informational [Page 14] RFC 3930 Protocol versus Document Viewpoints October 2004

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Eastlake Informational [Page 15]

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