RFC4417: Report of the 2004 IAB Messaging Workshop
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(Internet Architecture Board)
(internet messaging)
Network Working Group P. Resnick, Ed.
Request for Comments: 4417 IAB
Category: Informational P. Saint-Andre, Ed.
JSF
February 2006
Report of the 2004 IAB Messaging Workshop
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 (2006).
Abstract
This document reports the outcome of a workshop held by the Internet
Architecture Board (IAB) on the future of Internet messaging. The
workshop was held on 6 and 7 October 2004 in Burlingame, CA, USA.
The goal of the workshop was to examine the current state of
different messaging technologies on the Internet (including, but not
limited to, electronic mail, instant messaging, and voice messaging),
to look at their commonalities and differences, and to find
engineering, research, and architectural topics on which future work
could be done. This report summarizes the discussions and
conclusions of the workshop and of the IAB.
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Table of Contents
1. Introduction ....................................................3
2. Methodology .....................................................4
3. Issues ..........................................................5
3.1. Authorization ..............................................5
3.2. Multiple Communication Channels ............................6
3.3. Negotiation ................................................8
3.4. User Control ...............................................9
3.5. Message Transport ..........................................9
3.6. Identity Hints and Key Distribution .......................10
4. Recommendations ................................................11
4.1. Authorization .............................................11
4.2. Multiple Communication Channels ...........................12
4.3. Negotiation ...............................................13
4.4. User Control ..............................................13
4.5. Message Transport .........................................14
4.6. Identity Hints and Key Distribution .......................16
5. Security Considerations ........................................16
6. Acknowledgements ...............................................16
Appendix A. Participants .........................................17
Appendix B. Pre-Workshop Papers ..................................18
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1. Introduction
Current email infrastructure is a mixture of facilities to accomplish
its task of end-to-end communications through a relay mesh. That
mixture has come about as requirements have changed over the years.
Discussions recur over the years, often including complaints that
some desired features of email (such as internationalization,
efficient encoding of structured data, trusted communication) are
ill-served by the current infrastructure, or that some of the current
infrastructure seems to be adversely affected by current problems on
the Internet (most recently including problems such as spam, viruses,
and lack of security infrastructure). For many years, the daunting
task of revamping email infrastructure has been considered, with
justifiably little enthusiasm for taking on such a task. However,
there has been some recent informal discussion on the kinds of things
that would be desirable in a "next generation" email.
At the same time, other messaging infrastructures (including those
associated with "instant messaging" and "web logging") are currently
being deployed that appear to address many of the above desired
features and outstanding problems, while adding many features not
currently considered part of traditional email (like prior-consent-
based acceptance of messages). However, each of these technologies
(at least in their current deployment) seem to lack some of the
features commonly associated with email (such as selective and
partial message delivery, queued multi-hop relaying, offline message
management, and efficient non-textual content delivery).
The Internet Architecture Board (IAB) believed that the time was ripe
to examine the current state of messaging technologies on the
Internet and to see if there are areas of work that can be taken on
to advance these technologies. Therefore, the IAB held a workshop on
Internet messaging, taking some of the above issues as input, in
order to formulate some direction for future study of the area of
messaging.
The topic of messaging is broad, and the boundaries of what counts as
messaging are not always well-defined. Rather than limit themselves
to a philosophical discussion of the nature of messages, the workshop
participants adopted the attitude of "we know it when we see it" and
used as their primary examples such well-established types of
messaging as email and instant messaging (IM), while also discussing
more "peripheral" types of messaging such as voice messaging and
event notifications. (Message queuing systems with guaranteed
delivery and transactional integrity, such as those used in
enterprise workflow engines and some "web services" architectures,
were operationally if not intentionally out of scope.) The
participants worked to discover common themes that apply to all the
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types of messaging under consideration. Among the themes identified
were the following:
o Authorization of senders and recipients
o Negotiation of messaging parameters
o Consent models and privacy
o Identity hints, reputation, and key distribution
o Cross-protocol unification of messaging models
o Enabling greater user control over messaging
o Transport issues (unreliable links, push/pull, etc.)
o Message organization (e.g., conversations and threading)
Purposely missing from the foregoing list is the topic of unsolicited
commercial email or unsolicited bulk email (UCE or UBE, colloquially
known as "spam") and analogous communications in other messaging
environments such as instant messaging ("spim") and Internet
telephony ("spit"). While this topic was an impetus for the IAB's
holding the workshop, it was kept off the workshop agenda due to
concerns that it would crowd out discussion of other messaging-
related issues. The more general topics of authorization and
identity were thought to be broad enough to cover the architectural
issues involved with spam without devolving into more unproductive
discussions.
This document is structured so as to provide an overview of the
discussion flow as well as proposed recommendations of the workshop.
Section 3 summarizes the discussions that occurred during the
workshop on various topics or themes, while Section 4 provides an
overview of recommended research topics and protocol definition
efforts that resulted from the workshop. Section 5 provides some
perspective on the security-related aspects of the topics discussed
during the workshop. Appendix B lists the pre-workshop topic papers
submitted by workshop participants as background for the workshop
discussions.
2. Methodology
Prior to the workshop, brief topic papers were submitted to set the
context for the discussions to follow; a list of the papers and their
authors is provided in Appendix B of this document.
During the workshop itself, discussion centered on several topics or
themes, as summarized in the following sections. Naturally, it was
not possible in a two-day workshop to treat these topics in depth;
however, rough consensus was reached on the importance of these
topics, if not always on the details of potential research programs
and protocol standardization efforts that might address the issues
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raised. It is hoped that these summaries will inspire work by
additional investigators.
The in-workshop discussions quite naturally fell into three kinds of
"tracks": (1) possible engineering tasks to recommend to the IESG and
other standardization groups, (2) "blue sky" research topics to
recommend to the IRTF and other researchers, and (3) general
architectural or "framework" issues for consideration by both
engineers and researchers alike. After a full-group discussion each
morning to identify possible topics for more in-depth investigation,
participants self-selected for involvement in one of three "break-
out" sessions. Toward the end of each day, the full groups
reconvened, gathered reports from the break-out discussion leaders,
and attempted to come to consensus regarding lessons learned and
recommendations for further research. The results of the two-day
workshop therefore consist of discussion issues and research/
engineering recommendations related to the six topics described in
this report.
3. Issues
3.1. Authorization
It is one thing for a sender to send a message, and another thing for
the intended recipient to accept it. The factors that lead a
recipient to accept a message include the identity of the sender,
previous experience with the sender, the existence of an ongoing
conversation between the parties, meta-data about the message (e.g.,
its subject or size), the message medium (e.g., email vs. IM), and
temporal or psychological factors. Authorization or acceptance
applies most commonly at the level of the message or the level of the
sender, and occasionally also at other levels (conversation thread,
medium, sender domain).
Traditionally, sender authorization has been handled by recipient-
defined block and allow lists (also called "blacklists" and
"whitelists"). Block lists are of limited value, given the ease of
gaining or creating new messaging identities (e.g., an email address
or IM address). Allow lists are much more effective (since the list
of people you like or want to communicate with is smaller than the
large universe of people you don't), but they make it difficult for a
sender to initiate communication with a new or previously unknown
recipient. The workshop participants discussed several ways around
this problem, including reputation systems and better ways for one
person to introduce another person to a third party (e.g., through
signed invitations).
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Reputation systems may be especially worthy of future research, since
they emulate a pattern that is familiar from real life. (It may also
be valuable to distinguish between (1) reputation as the reactive
assessment of a sender created by one or more recipients based on
message history and (2) accreditation as a proactive assessment
provided by trusted third parties.) Reputation might be based on
summing an individual's "scores" provided by recipients on the
network. (Naturally, the more important reputation becomes, the more
bad actors might attempt to sabotage any given reputation system, so
that a distributed as opposed to centralized system might be more
desirable.) The actions taken by any given recipient based on the
sender's reputation would not necessarily be limited to a simple
allow/deny decision; more subtle actions might include placing
messages from individuals with lower reputation scores into separate
inboxes or redirecting them to other media (e.g., from IM to email).
3.2. Multiple Communication Channels
It is a fact of life that many people use multiple forms of messaging
channels: phone, email, IM, pager, and so on. Unfortunately, this
can make it difficult for a sender or initiator to know the best way
to contact a recipient at any given time. One model is for the
initiator to guess, for example, by first sending an email message
and then escalating to pager or telephone if necessary; this may
result in delivery of redundant messages to the recipient. A second
model is for the recipient to publish updated contact information on
a regular basis, perhaps as one aspect of his or her presence; this
might enable the initiator to determine beforehand which contact
medium is most appropriate. A third model is for the recipient to
use some kind of "unifier" service that enables intelligent routing
of messages or notifications to the recipient based on a set of
delivery rules (e.g., "notify me via pager if I receive a voicemail
message from my boss after 17:00").
The workshop participants did not think it necessary to choose
between these models, but did identify several issues that are
relevant in unifying or at least coordinating communication across
multiple messaging channels:
o While suppression of duplicate messages could be enabled by
setting something like a "seen" flag on copies received via
different messaging media, in general the correlation of multi-
channel, multi-message exchanges is not well supported by existing
standards.
o A recipient could communicate his or her best contact mechanism to
the initiator by explicitly granting permission to the initiator,
perhaps by means of a kind of "authorization token".
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o It may be worthwhile to define frameworks or protocols for
recipient-defined delivery rules. Currently, routing decisions
tend to be made mostly by the sender through the choice of a
messaging channel, but in the future the recipient may play a
larger role in such decisions.
o The logic behind contact publication needs to be explored, for
example, whether it is an aspect of or extension to presence and
whether contact addresses for one medium are best obtained by
communicating in a different medium ("email me to get my mobile
number").
A multiplicity of delivery channels also makes it more complex for a
senders to establish a "reliable" relationship with a recipient.
From the sender's point of view, it is not obvious that a recipient
on one channel is the same recipient on another channel. How these
recipient "identities" are tied together is an open question.
Another area for investigation is that of recipient capabilities.
When the sender does not have capability information, the most common
result is downgrading to a lowest common denominator of
communication, which seriously underutilizes the capabilities of the
entire system. Previous standards efforts (e.g., LDAP, Rescap,
vCard, Conneg) have attempted to address parts of the capability
puzzle, but without great success.
The existing deployment model uses several out-of-band mechanisms for
establishing communications in the absence of programmatic
capabilities information. Many of these mechanisms are based on
direct human interaction and social policies, which in many cases are
quite efficient and more appropriate than any protocol-based means.
However, a programmatic means for establishing communications between
"arms length" parties (e.g., business-to-business and business-to-
customer relationships) might be very beneficial.
Any discussion of relationships inevitably leads to a discussion of
trust (e.g., "from what kinds of entities do I want to receive
messages?"). While this is a large topic, the group did discuss
several ideas that might make it easier to broker communications
within different relationships, including:
o Whitelisting is the explicit definition of a relationship from the
recipient's point of view, consisting of a list of senders with
whom a recipient is willing to engage in conversation. While
allow lists can be a workable solution, they are a relatively
static authorization scheme.
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o Token-based authorization enables the recipient to define a one-
time or limited-time relationship with a sender. The issuer
possesses a token that grants a limited-time right to communicate
with the recipient. This is a more dynamic authorization scheme.
o Rule-based authorization involves an algorithmic assessment of the
viability of a relationship based on a wide set of criteria. This
is a more general authorization scheme that can incorporate both
allow lists and tokens, plus additional evaluation criteria such
as message characterization and issuer characterization.
3.3. Negotiation
In the area of negotiation, the workshop participants focused mainly
on the process by which a set of participants agree on the media and
parameters by which they will communicate. (One example of the end
result of such a "rendezvous" negotiation is a group of colleagues
who agree to hold a voice conference, with a textual "groupchat" as a
secondary communications channel.) In order to enable cross-media
negotiation, it may be necessary to establish a bridge between
various identities. For example, the negotiation may occur via
email, but the communication may occur via phone, and in order to
authorize participants the conference software needs to know their
phone numbers, not their email addresses. Furthermore, the
parameters to be negotiated may include a wide variety of aspects,
including:
o Prerequisites for the communication (e.g., distribution of a
"backgrounder" document).
o Who will initiate the communication.
o Who will participate in the communication.
o The primary "venue" (e.g., a telephone number that all
participants will call).
o One or more secondary venues (e.g., a chatroom address).
o Backup plans if the primary or secondary venue is not available.
o The topic or topics for the discussion.
o The identities of administrators or moderators.
o Whether or not the discussion will be logged or recorded.
o Scheduling of the event, including recurrence (e.g., different
instances may have different venues or other details).
Indeed, in some contexts it might even be desirable to negotiate or
re-negotiate parameters after communication has already begun (e.g.,
to invite new participants or change key parameters such as logging).
While the workshop participants recognized that in-depth negotiation
of a full set of parameters is likely to be unnecessary in many
classes of communication, parts of a generalized framework or
protocol for the negotiation of multiparty communication might prove
useful in a wide range of applications and contexts.
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3.4. User Control
A common perception among "power users" (and, increasingly, average
users) on the Internet is that messaging is not sufficiently under
their control. This is not merely a matter of unsolicited
communications, but also of managing multiple messaging media and
handling the sheer volume of messages received from familiar and
unfamiliar senders alike. Currently, individuals attempt to cope
using various personal techniques and ad hoc software tools, but
there may be an opportunity to provide more programmatic support
within Internet protocols and technologies.
One area of investigation is message filtering. Based on certain
information -- the identity of the sender and/or recipient(s), the
sender's reputation, the message thread or conversational context,
message headers, message content (e.g., the presence of attachments),
and environmental factors such as time of day or personal mood -- a
user or agent may decide to take one of a wide variety actions with
regard to a message (bounce, ignore, forward, file, replicate,
archive, accept, notify, etc.). While it is an open question how
much formalization would be necessary or even helpful in this
process, the workgroup participants identified several areas of
possible investigation:
o Cross-media threads and conversations -- it may be helpful to
determine ways to tag messages as belonging to a particular thread
or conversation across media (e.g., a forum discussion that
migrates to email or IM), either during or after a message
exchange.
o Communication hierarchies -- while much of the focus is on
messages, often a message does not stand alone but exists in the
context of higher-level constructs such as a thread (i.e., a
coherent or ordered set of messages within a medium), a
conversation (i.e., a set of threads that may cross media), or an
activity (a set of conversations and related resources, such as
documents).
o Control protocols -- the workgroup participants left as an open
question whether there may be a need for a cross-service control
protocol for use in managing communications across messaging
media.
3.5. Message Transport
Different messaging media use different underlying transports. For
instance, some messaging systems are more tolerant of slow links or
lossy links, while others may depend on less loss-tolerant transport
mechanisms. Integrating media that have different transport profiles
can be difficult. For one, assuming that the same addressing
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endpoint represents the same entity over time may not be warranted
(it is possible that further work in identifying, addressing, and
discovering endpoints may be appropriate, even at the URI level). It
is also possible that the same endpoint or entity could be available
via different transport mechanisms at different times, or even
available via multiple transports at the same time. The process of
choosing an appropriate transport mechanism when there are multiple
paths introduces addressing issues that have not yet been dealt with
in Internet protocol development (possible heuristics might include
predictive routing, opportunistic routing, and scheduled routing).
For links that can be unreliable, there may be value in being able to
gracefully restart the link after any given failure, possibly by
switching to a different transport mechanism.
Another issue that arises in cross-media and cross-transport
integration is synchronization of references. This applies to
particular messages but might also apply to message fragments. It
may be desirable for some message fragments, such as large ancillary
data, to be transported separately from others, for example small
essential text data. Message fragments might also be forwarded,
replicated, archived, etc., separately from other parts of a message.
One factor relevant to synchronization across transports is that some
messaging media are push-oriented (e.g., IM) whereas others are
generally pull-oriented (e.g., email); when content is pushed to a
recipient in one medium before it has been pulled by the recipient in
another medium, it is possible for content references to get out of
sync.
If message fragments can be transported over different media,
possibly arriving at separate times or through separate paths, the
issue of package security becomes a serious one. Traditionally,
messages are secured by encrypting the entire package at the head end
and then decrypting it on the receiving end. However, if we want to
allow transports to fragment messages based upon the media types of
the parts, that approach will not be feasible.
3.6. Identity Hints and Key Distribution
While it is widely recognized that both message encryption and
authentication of conversation partners are highly desirable, the
consensus of the workshop participants was that current business and
implementation models in part discourage deployment of existing
solutions. For example, it is often hard to get new root
certificates installed in clients, certificates are (or are perceived
to be) difficult or expensive to obtain, one-click or zero-click
service enrollment is a worthy but seemingly unreachable goal, and
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once one has created a public/private key pair and certified the
public key, it is less than obvious how to distribute that
certificate or discover other people's certificates.
One factor that may make widespread message encryption more feasible
is that email, instant messaging, and Internet telephony have quite
similar trust models. Yet the definition of communication differs
quite a bit between these technologies: in email "the message is the
thing", and it is a discrete object in its own right; in telephony
the focus is on the real-time flow of a conversation or session
rather than discrete messages; and IM seems to hold a mediate
position since it is centered on the rapid, back-and-forth exchange
of text messages (which can be seen as messaging sessions).
Another complicating factor is the wide range of contexts in which
messaging technologies are used: everything from casual conversations
in public chatrooms and social networking applications, through
communications between businesses and customers, to mission-critical
business-to-business applications such as supply chain management.
Different audiences may have different needs with regard to messaging
security and identity verification, resulting in varying demand for
services such as trusted third parties and webs of trust.
In the context of communication technologies, identity hints --
shared knowledge, conversational styles, voice tone, messaging
patterns, vocabulary, and the like -- can often provide more useful
information than key fingerprints, digital signatures, and other
electronic artifacts, which are distant from the experience of most
end users. To date, the checking of such identity hints is intuitive
rather than programmatic.
4. Recommendations
4.1. Authorization
The one clearly desired engineering project that came out of the
authorization discussion was a distributed reputation service. It
was agreed that whatever else needed to be done in regard to
authorization of messages, at some point the recipient of the message
would want to be able to check the reputation of the sender of the
message. This is especially useful in the case of senders with whom
the recipient has no prior experience; i.e., using a reputation
service as a way to get an "introduction to a stranger". There was
clearly a need for this reputation service to be decentralized;
though a single centralized reputation service can be useful in some
contexts, it does not scale to an Internet-wide service.
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Two potential research topics in authorization were discussed.
First, a good deal of discussion centered around the use of
whitelists and blacklists in authorization decision, but it was
thought that research was necessary to examine the relative
usefulness of each of the approaches fully. It was clear to the
participants that blacklists can weed out known non-authorized
senders, but do not stop "aggressive" unwanted senders because of the
ease of simply obtaining a new identity. Whitelists can be useful
for limiting messages to only those known to the recipient, but would
require the use of some sort of introduction service in order to
allow for messages from unknown parties. Participants also thought
that there might be useful architectural work done in this area.
The other potential research area was in recipient responses to
authorization decisions. Upon making an authorization decision,
recipients have to do two things: First, obviously the recipient must
dispatch the message in some way either to deliver it or to deny it.
But that decision will also have side effects back into the next set
of authorization decisions the recipient may make. The decision may
feed back into the reputation system, either "lauding" or "censuring"
the sender of the message.
4.2. Multiple Communication Channels
Several interesting and potentially useful ideas were discussed
during the session, which the participants worked to transform into
research or engineering tasks, as appropriate.
In the area of contact information management, the workshop
participants identified a possible engineering task to define a
service that publishes contact information such as availability,
capabilities, channel addresses (routing information), preferences,
and policies. While aspects of this work have been attempted
previously within the IETF (with varying degrees of success), there
remain many potential benefits with regard to managing business-to-
business and business-to-customer relationships.
The problem of suppressing redundant messages is becoming more
important as the use of multiple messaging channels becomes the rule
for most Internet users, and as users become accustomed to receiving
notifications in one channel of communications received in another
channel. Unfortunately, there are essentially no standards for
cross-referencing and linking of messages across channels; standards
work in this area may be appropriate.
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Another possible engineering task is defining a standardized
representation for the definition and application of recipient
message processing rules. Such an effort would extend existing work
on the Sieve language within the IETF to incorporate some of the
concepts discussed above.
Discussion of token-based authorization focused on the concept of
defining a means for establishing time-limited or usage-limited
relationships for exchanging messages. The work would attempt to
define the identity, generation, and use of tokens for authorization
purposes. Most likely this is more of a research topic than an
engineering topic.
Work on recipient rules processing and token-based authentication may
be related at a higher level of abstraction (we can call it
"recipient authorization processing"). When combined with insights
into authorization (see Sections 3.1 and 4.1), this may be an
appropriate topic for further research.
4.3. Negotiation
Discussion in the area of negotiation resulted mostly in research-
oriented output. The session felt that participants in a
conversation would require some sort of rendezvous mechanism during
which the parameters of the conversation would be negotiated. To
facilitate this, a "conversation identifier" would be needed so that
participants could identify the conversation that they wished to
participate in. In addition, there are at least five dimensions
along which a conversation negotiation may occur:
o The participants in the conversation
o The topic for the conversation
o The scheduling and priority parameters
o The mechanism used for the conversation
o The capabilities of the participants
o The logistical details of the conversation
Research into how to communicate these different parameters may prove
useful, as may research into the relationship between the concepts of
negotiation, rendezvous, and conversation.
4.4. User Control
A clear architectural topic to come out of the user control
discussion was work on activities, conversations, and threads. In
the course of the discussion, the user's ability to organize messages
into threads became a focus. The participants got some start on
defining threads as a semi-ordered set of messages, a conversation as
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a set of threads, and an activity as a collection of conversations
and related resources. The discussion expanded the traditional
notion of a thread as an ordered tree of messages. Conversations can
collect together threads and have them be cross-media. Messages can
potentially belong to more than one thread. Threads themselves might
have subthreads. All of these topics require an architectural
overview to be brought into focus.
There is also engineering work that is already at a sufficient level
of maturity to be undertaken on threads. Though there is certainly
some simple threading work being done now with messaging, it is
pretty much useful only for a unidirectional tree of messages in a
single context. Engineering work needs to be done on identifiers
that could used in threads that cross media. Additionally, there is
likely work to be done for messages that may not be strictly ordered
in a thread.
The topics of "control panels" and automated introductions were
deemed appropriate for further research.
4.5. Message Transport
A central research topic that came out of the transport session was
that of multiple transports. It was felt that much research could be
done on the idea of transporting pieces of messages over separate
transport media in order to get the message to its final destination.
Especially in some high-latency, low-bandwidth environments, the
ability to run parallel transports with different parts of messages
could be extremely advantageous. The hard work in this area is
re-associating all of the pieces in a timely manner, and identifying
the single destination of the message when addressing will involve
multiple media.
A common theme that arose in several of the discussions (including
user control and message unification), but that figured prominently
in the transport discussion, was a need for some sort of identifier.
In the transport case, identifiers are necessary on two levels.
Identifiers are needed to mark the endpoints in message transport.
As described in the discussion, there are many cases where a message
could reasonably be delivered to different entities that might all
correspond to a single person. Some sort of identifier to indicate
the target person of the message, as well as identifiers for the
different endpoints, are all required in order to get any traction in
this area. In addition, identifiers are also required for the
messages being transported, as well as their component parts.
Certainly, the idea of transporting different parts of a message over
different mechanisms requires the identification of the containing
message so that re-assembly can occur at the receiving end. However,
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identifying the entire package is also necessary for those cases
where duplicate copies of a message might be sent using two different
mechanisms: The receiving end needs to find out that it has already
received a copy of the message through one mechanism and identify
that another copy of the message is simply a duplicate.
Workshop participants felt that, at the very least, a standard
identifier syntax was a reasonable engineering work item that could
be tackled. Though there exist some identifier mechanisms in current
messaging protocols, none were designed to be used reliably across
different transport environments or in multiple contexts. There is
already a reasonable amount of engineering work done in the area of
uniform resource identifiers (URI) that participants felt could be
leveraged. Syntax would be required for identifiers of messages and
their components as well as for identifiers of endpoint entities.
Work on the general problem of identifier use might have some
tractable engineering aspects, especially in the area of message part
identifiers, but workshop participants felt that more of the work was
ripe for research. The ability to identify endpoints as belonging to
a single recipient, and to be able to distribute identifiers of those
endpoints with information about delivery preferences, is certainly
an area where research could be fruitful. Additionally, it would be
worthwhile to explore the collection of identified message components
transported through different media, while delivering to the correct
end-recipient with duplicate removal and re-assembly.
Package security was seen as an area for research. As described in
Section 3.5, the possibility that different components of messages
might travel over different media and need to be re-assembled at the
recipient end breaks certain end-to-end security assumptions that are
currently made. Participants felt that a worthwhile research goal
would be to examine security mechanisms that could be used for such
multi-component messages without sacrificing desirable security
features.
Finally, a more architectural topic was that of restartability. Most
current message transports, in the face of links with reliability
problems, will cancel and restart the transport of a message from the
beginning. Though some mechanisms do exist for restart mid-session,
they are not widely implemented, and they certainly can rarely be
used across protocol boundaries. Some architectural guidance on
restart mechanisms would be a useful addition.
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4.6. Identity Hints and Key Distribution
It would be helpful to develop Internet-wide services to publish and
retrieve keying material. One possible solution is to build such a
service into Secure DNS, perhaps as an engineering item in an
existing working group. However, care is needed since that would
significantly increase the size and scope of DNS. A more research-
oriented approach would be to investigate the feasibility of building
Internet-wide key distribution services outside of DNS. In doing so,
it is important to keep in mind that the problem of distribution is
separate from the problem of enrollment, and that name subordination
(control over what entities are allowed to create sub-domains)
remains necessary.
Research may be needed to define the different audiences for message
security. For example, users of consumer-oriented messaging services
on the open Internet may not generally be willing or able to install
new trusted roots in messaging client software, which may hamper the
use of security technologies between businesses and customers. By
contrast, within a single organization it may be possible to deploy
new trusted roots more widely, since (theoretically) all of the
organization's computing infrastructure is under the centralized
control.
In defining security frameworks for messaging, it would be helpful to
specify more clearly the similarities and differences among various
messaging technologies with regard to trust models and messaging
metaphors (e.g., stand-alone messages in email, discrete
conversations in telephony, messaging sessions in instant messaging).
The implications of these trust models and messaging metaphors for
communications security have not been widely explored.
5. Security Considerations
Security is discussed in several sections of this document,
especially Sections 3.5, 3.6, 4.5, and 4.6.
6. Acknowledgements
The IAB would like to thank QUALCOMM Incorporated for their
sponsorship of the meeting rooms and refreshments.
The editors would like to thank all of the workshop participants.
Eric Allman, Ted Hardie, and Cullen Jennings took helpful notes,
which eased the task of writing this document.
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Appendix A. Participants
Eric Allman
Nathaniel Borenstein
Ben Campbell
Dave Crocker
Leslie Daigle
Mark Day
Mark Crispin
Steve Dorner
Lisa Dusseault
Kevin Fall
Ned Freed
Randy Gellens
Larry Greenfield
Ted Hardie
Joe Hildebrand
Paul Hoffman
Steve Hole
Scott Hollenbeck
Russ Housley
Cullen Jennings
Hisham Khartabil
John Klensin
John Levine
Rohan Mahy
Alexey Melnikov
Jon Peterson
Blake Ramsdell
Pete Resnick
Jonathan Rosenberg
Peter Saint-Andre
Greg Vaudreuil
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Appendix B. Pre-Workshop Papers
The topic papers circulated before the workshop were as follows:
Calendaring Integration (Nathaniel Borenstein)
Channel Security (Russ Housley)
Collaborative Authoring (Lisa Dusseault)
Consent-Based Messaging (John Klensin)
Content Security (Blake Ramsdell)
Event Notifications (Joe Hildebrand)
Extended Messaging Services (Dave Crocker)
Group Messaging (Peter Saint-Andre)
Identity and Reputation (John Levine)
Instant Messaging and Presence Issues in Messaging (Ben Campbell)
Large Email Environments (Eric Allman)
Mail/News/Blog Convergence (Larry Greenfield)
Messaging and Spam (Cullen Jennings)
Messaging Metaphors (Ted Hardie)
MUA/MDA, MUA/MSA, and MUA/Message-Store Interaction (Mark Crispin)
Presence for Consent-Based Messaging (Jon Peterson)
Rich Payloads (Steve Hole)
Session-Oriented Messaging (Rohan Mahy)
Spam Expectations for Mobile Devices (Greg Vaudreuil)
Communication in Difficult-to-Reach Networks (Kevin Fall)
Store-and-Forward Needs for IM (Hisham Khartabil)
Syndication (Paul Hoffman)
Transport Security (Alexey Melnikov)
VoIP Peering and Messaging (Jonathan Rosenberg)
Webmail, MMS, and Mobile Email (Randy Gellens)
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Authors' Addresses
Peter W. Resnick (Editor)
Internet Architecture Board
QUALCOMM Incorporated
5775 Morehouse Drive
San Diego, CA 92121-1714
US
Phone: +1 858 651 4478
EMail: presnick@qualcomm.com
URI: http://www.qualcomm.com/~presnick/
Peter Saint-Andre (Editor)
Jabber Software Foundation
P.O. Box 1641
Denver, CO 80201-1641
US
Phone: +1 303 308 3282
EMail: stpeter@jabber.org
URI: http://www.jabber.org/people/stpeter.shtml
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