Trust Management on the World Wide Web.
5f88e3f3d6bc4cf2339a5ad58453e6dbece52ae604ac88558d513e2add732313<HTML>
<HEAD>
<title>Trust Management on the World Wide Web by Rohit Khare and Adam Rifkin</title></HEAD>
<BODY bgcolor="#ffffff" LINK="#bb7777" VLINK="#7777bb" ALINK="#ffee99" TEXT="#000000">
<BLOCKQUOTE><A HREF="../../../index.html"><IMG SRC="../../../img/logo.gif" WIDTH="256" HEIGHT="40" BORDER="0" ALT="First Monday" ALIGN="BOTTOM"></A><br>
<font size="2" face="Arial, Helvetica, sans-serif">Read related articles on
<a href="../../../subjects/subjectlist.html#privacy">Privacy</a> and <a href="../../../subjects/technical.html#security">Security</a></font>
</BLOCKQUOTE>
<HR><BLOCKQUOTE>
<BLOCKQUOTE> <a href="#author"><img src="navn.gif" border=0 alt="Trust Management on the World Wide Web by Rohit Khare and Adam Rifkin"></a>
<p> <i>As once-proprietary mission-specific information systems migrate onto
the Web, traditional security analysis cannot sufficiently protect each
subsystem atomically. The Web encourages open, decentralized systems that
span multiple administrative domains. <b>Trust Management</b> (TM) is an
emerging framework for decentralizing security decisions that helps developers
and others in asking "why" trust is granted rather than immediately focusing
on "how" cryptography can enforce it. </i>
<p><i> In this paper, we recap the basic elements of Trust Management: principles,
principals, and policies. We present pragmatic details of Web-based TM technology
for identifying principals, labeling resources, and enforcing policies.
We sketch how TM might be integrated into Web applications for document
authoring and distribution, content filtering, and mobile code security.
Finally, we measure today's Web protocols, servers, and clients against
this model, culminating in a call for stakeholders' support in bringing
automatable TM to the Web. </i>
<p> <img src="../../../buttons/quad.gif">
<p>
<h2>Contents</h2>
<a href="#d1">Introduction to Trust Management</a><br>
<a href="#d2">Tools for Trust Management</a><br>
<a href="#d3">Integrating Trust Management Into the Web</a><br>
<a href="#d4">From Web Security to Trust Management</a><br>
<a href="#d5">Weaving a Web of Trust</a><br>
<a href="#d6">Acknowledgements</a><br>
<a href="#notes">Notes</a><br>
<a href="#references">References</a>
<p><img src="../../../buttons/quad.gif"><a name="d1"></a>
<h2>1. Introduction to Trust Management </h2>
<p> To date, "Web Security" has been associated with debates over cryptographic
technology, protocols, and public policy, obscuring the wider challenges
of building <i>trusted</i> Web applications. Since the Web aims to be an
information space that reflects not just human knowledge but also human
relationships, it will soon realize the full complexity of trust relationships
among people, computers, and organizations.
<p> Within the computer security community, <i>Trust Management</i> (TM) has
emerged as a new philosophy for codifying, analyzing, and managing trust
decisions [<a href="#01">1</a>]. Asking the question <i>"Is someone trusted
to take some action on some object?"</i> entails understanding the elements
of TM [<a href="#02">2</a>]:
<dl>
<dt> <b>Principles</b>
<dd> When deciding to trust some principal to take some action on some object,
it is absolutely critical to <i>be specific</i> about the privileges granted;
to <i>trust yourself</i> when vouchsafing the claim; and to <i>be careful</i>
before and after taking that step.
<p>
<dt> <b>Principals</b>
<dd> The decision to grant trust is justified by a chain of assertions.
There are three kinds of actors making the assertional links based on
their particular identity lifetimes: <i>people</i> make assertions with
broad scope, bound to their long-lived <i>names</i>; <i>computers</i>
make narrow proofs of correct operation from their limited-scope <i>addresses</i>;
and <i>organizations</i> make assertions about people and computers because
they have the widest temporal and legal scope of all. <i>Credentials</i>
describe each kind of principal and its relationships, such as membership
and delegation.
<p>
<dt> <b>Policies</b>
<dd> These are rules about which assertions can be combined to yield permission.
Broadly speaking, policies can grant authority based on the <i>identity</i>
of the principal asking; the <i>capability</i> at issue; or an <i>object</i>
already in hand. In other words, you might be trusted based on <i>who
you are</i>, <i>what you can do</i>, or <i>what you have</i>.
<p>
<dt> <b>Pragmatics</b>
<dd> Deploying a TM infrastructure across so many administrative boundaries
on the open, distributed Web requires adapting to the <i>pragmatic</i>
limitations of the principles, principals, and policies. Since objects
can live anywhere on the Web, so can their security labels. Furthermore,
such labels should use a common, machine-readable format that recursively
uses the Web to document its language. The real benefits of TM come from
tying all of these details together within a single TM engine. This will
drive a handful of standard protocols, formats, and APIs for representing
principals and policies.
</dl>
<p> In this paper, we focus on the developments bringing TM to the Web. In
<a href="#Section2">Section 2</a>, we present some TM building-blocks that
complement cryptographic "Web Security." In <a
href="#Section3">Section 3</a>, we sketch how integrating TM affects several archetypal
applications, with special attention to the potential for automating trust
calculations. <a href="#Section4">Section 4</a>, by contrast, discusses
how current Web software technology often falls short in managing trust.
We conclude <a href="#Section5">Section 5</a> with a call for action from
the Web community.
<p><img src="../../../buttons/quad.gif"><a name="d2"></a>
<h2><a name="Section2">2. Tools for Trust Management</a> </h2>
<p> The topological shift from atomic trusted systems to an open network of
separately administered systems is driving the development of innovative
Web-specific TM protocols, format, and tools. In the following subsections,
we consider new technologies for <a
href="#Section2.1">identifying principals</a>, <a
href="#Section2.2">labeling Web resources</a>, and <a
href="#Section2.3">codifying and automating</a> policies.
<p>
<h3> <a name="Section2.1">2.1 Identifying Principals</a> </h3>
<p> The first step in constructing a secure system is usually to identify
the system's users, authorized or otherwise. Passwords are a common solution
for closed systems. Public-key cryptography is a far more secure way of
managing such secrets, but with the attendant overhead of a public key infrastructure
(PKI) [<a href="#03">3</a>]. The Web's radically decentralized trust model
is catalyzing new alternatives to hierarchical certification for identifying
the people, computers, and organizations holding such keys.
<p> A <i>digital certificate</i> [<a href="#04">4</a>] ensures the binding
between cryptographic keys and its owner as a signed assertion. It is the
missing link between the mathematics, which computers can verify, and the
principals. The challenge is in deciding who should sign that assertion
and why.
<p> Traditionally, a pyramid of <i>Certificate Authorities</i> (CAs) vouch
for the binding: "Joe Doaks' public key is <tt>42</tt>, (signed) UC Irvine,
(signed) UC Regents, (signed) State of California, (signed) USA." This approach
is enshrined in ISO's X.509 certificate format, X.400 addressing, and X.500
directory service. A CA's utility is directly proportional to its <i>reach</i>:
the size of the community willing to trust that CA. Climbing up the pyramid,
CAs have ever-greater reach, but with less specificity; UC Irvine can certify
the specific role "student," but the USA may be able to certify only generic
"citizens."
<p> Alternatively, every principal could just be its own CA (<i>self-signed
certificates</i>), introducing other correspondents one-on-one. The Pretty
Good Privacy (PGP) "Web of Trust" is a living example of such an anarchic
certification system [<a href="#05">5</a>]. Of course, its reach is more
limited: without a central trusted broker, it can be very difficult to scale
to large user groups such as "all UC Irvine students."
<p> The principles of TM tend to argue against hierarchical identity certificates.
First, without knowing the application at hand, a CA vouching for generic
identity cannot <i>be specific</i> about the degree of trust involved: the
capabilities verified or the privileges granted. Second, relying on hierarchical
CAs weakens the principle of <i>trusting yourself</i>, since it requires
blanket trust in very large-scale CAs, with corresponding conflicts-of-interest.
Third, the logistical challenges of centralized revocation lists make it
difficult to <i>be careful</i> using these certificates.
<p> Two new decentralized PKI proposals, Simple Distributed Security Infrastructure
(SDSI) [<a href="#06">6</a>] and Simple Public Key Infrastructure (SPKI)
[<a href="#07">7</a>] - currently being merged into a common SDSI 2.0 draft
-are better adapted to these principles and to the Web's decentralized growth.
First, their application-specific certificates identify exactly for what
each key is authorized. Second, both systems literally construct a trust
chain that must loop back to the user, instead of being diverted through
some omnipotent CA. Finally, both systems offer simple, real-time certificate
validation.
<p>
<h3><a name="Section2.2">2.2 Labeling Resources</a></h3>
<p> The second step in constructing a secure system is associating access
limits with each element of the system. <i>Security metadata</i> might encompass
principals' clearance levels, the capabilities required for an action, or
the key to access an object.
<p> Traditionally, secure computing systems wire these critical bits directly
into data structures and files. Since today's Web tools offer only a thin
wrapper around these underlying security facilities, they usually offer
the same kinds of "labels," such as filesystem permission bits and resource
limits on scripts.
<p> A more flexible solution would be to use separate security labels with
general-purpose label handling. Each of those conditions could be captured
as a separate statement bound by URL to a Web resource. Furthermore, the
conditions themselves could be categorized into a systematic scale that
is readable by machines [<a href="#08">8</a>].
<p> There are three critical differences indicating that external metadata
labels are appropriate tools for Web-based trust management systems [<a href="#09">9</a>].
First, the label can reflectively be considered a Web resource: the label
has its own name, and thus can be made available in several ways. The original
resource owner can embed a label within it, send it along with a resource,
or publish it from an external label bureau. Second, the scales, or rating
schemas, can be reflectively considered a Web resource; so, the grammar
of a machine-readable label can itself be fetched from the Web. Finally,
labels can be securely bound to Web resources by hash or by name (for dynamic
resources such as chat rooms).
<p>
<h3> <a name="Section2.3">2.3 Codifying and Automating Policies</a> </h3>
<p> The final step in implementing a secured system is specifying the authorization
decisions according to some policy. As a generic application platform, the
Web should be flexible enough to accommodate a wide range of applications
with varying trust policies centered on principals, objects, or actions.
Several policies may also need to be composed together, enforced on behalf
of several stakeholders.
<p> Consider some alternative content-selection policies, each written in
its own format: one may be a simple numerical gamut applied to Platform
for Internet Content Selection (PICS) ratings [<a
href="#10">10</a>]; another may weight the opinions of several ratings in different
systems; and yet a third may incorporate a Turing-complete content analyzer.
<p> REFEREE [<a href="#11">11</a>] does not use a single policy language,
for this reason. Instead, users load interpreters dynamically for policy
languages, while maintaining a single high-level API for trust decisions.
Given a pile of facts, a target, a proposed action, and its policy, REFEREE
can determine if trust is always, sometimes, or never granted. PolicyMaker
[<a
href="#12">12</a>] also provides a single trust calculation API. On the other
hand, PICSRules 1.1 defines a language for writing policy rules to allow
or block URL access using PICS labels [<a href="#13">13</a>].
<p> Incorporating automated trust engines returns more control to the user
as a trust-granter: depending on your policy, you can seek out, collect,
and manipulate more kinds of data in pursuit of a decision. Rather than
using a closed content selection system like Antarctica Online's policy
("All our content is okay, trust us"), users have the full power of PICS
labels, from multiple sources, according to different systems, with personalized
policies. Decentralized principal identification, the integration of security
attributes with the Web metadata, and policy flexibility, all advance the
goal of automatable trust management through machine-re adable assertions.
<h2><img src="../../../buttons/quad.gif"><a name="d3"></a> </h2>
<h2><a name="Section3">3. Integrating Trust Management Into the Web</a> </h2>
<p> The shift away from closed, known user communities to open, publicly-accessible
service models complicates the security analysis for Web applications. In
the following subsections, we discuss three applications that are already
capturing the imagination of Web developers.
<p>
<h3><a name="Section3.1">3.1 Secure Document Distribution</a></h3>
<p> The publication of a Presidential speech could be as complicated as the
story of how a bill becomes a law. First, a proposal is drafted by the Press
Secretary's staffers. An ongoing editing cycle can draw, ad hoc, upon the
entire White House staff. The final press release can be made available
on <a
href="http;//www.whitehouse.gov">www.whitehouse.gov</a> only after the President
has affixed his digital signature.
<p> This is a classic secure application: a controlled set of principals with
different access levels (viewing and editing), acting on a long list of
protected documents. While the old process might have been implemented on
a single mainframe system using operating system-level security, it is neither
flexible nor scalable enough to handle today's document production cycle.
Replacing it with a secured Web server is an excellent alternative, offering
more accessible clients, better collaboration tools, and an expressive format
for linking it all together.
<p> Complications crop up when considering the Web as a drop-in replacement
as a secure authoring environment. At the very minimum, there is an open-systems
integration challenge of replacing the old monolithic username/password
database with an interoperable public key certificate infrastructure. Furthermore,
extending the trusted computing base to all those staffers' desktop PCs
adds the potential risks of leaked documents left behind in users' caches,
weak points for eavesdropping viruses, and insecure key management.
<p align="center"><img src="rif1.gif" width="269" height="115">
<p> The real benefits accrue as the web of trust surrounding these documents
expands outward from authoring to distribution, access, and reading. The
ultimate goal for each user is to judge if the President's words have been
portrayed accurately. Especially with the malleability of digital media
(such as hackable video, photographs, and even whole Web sites), digitally
signed assertions of provenance will become <i>de rigeur</i> [<a href="#14">14</a>].
<p> Each citizen has the right to establish trust in his or her own way. Some
trust their neighbors (<i>community filtering</i>), or the cameraman, or
the camera (if it had a "tamperproof" integrity check), or the news publishers.
As the Web crosses organizational boundaries - from White House to newspaper
to ISP to citizen - a common TM infrastructure can identify speakers and
make assertions about the document.
<p>
<h3><a name="Section3.2">3.2 Content Filtering</a></h3>
<p> The Web's distributed control and rapid growth continuously obsolete "black-lists"
of purveyors of objectionable content as well as "white-lists" of known
"good" sites. Furthermore, these manichean schemes cannot handle judgment
calls: if <tt>.edu</tt> is fine, and <tt>sex</tt> is verboten, what does
it imply about <tt>sex.edu</tt>?
<p> To tackle a problem <i>expanding</i> as rapidly as the Web itself, we
must harness the Web itself. PICS labels <i>can</i> scale, because labels
can be associated with objects by the author <i>or</i> by a third-party.
The key is bootstrapping the meaning of each label. Machine-readable metadata
labels themselves can leverage the Web through self-description (using PICS
schema description files).
<p> Traditional end-to-end security places such filtering exclusively at the
periphery, because there are only two players: publisher and reader. To
represent the trust relationships in this application properly, we must
account for households, schools, libraries, offices, and governments who
have a say in what constitutes acceptable content. Filters need to be relocatable
within the network under the control of any of these stakeholders.
<p> Content labels can also be used in reverse: <i>publishers</i> of intellectual
property need to select who can access their resources. Client software
could block the display of a font, for example, until it finds a signed
"receipt" label. Rights management labels of this sort can be cryptographically
bound into "pay-per-view" information goods through watermarking, steganography,
or aggregation in an encrypted package. The ongoing trust relationship between
reader and publisher to obey the label is enforceable in trusted software
[<a href="#15">15</a>] or trusted hardware [<a href="#16">16</a>].
<p> A final eCommerce-related filtering application is consumer privacy. Several
organizations, including the Internet Privacy Working Group (IPWG), TRUSTe,
and BBBonline are trying to enumerate the uses of demographic data specifically
[<a href="#17">17</a>]. W3C's Privacy Preferences Platform Project (P3P)
expects commercial sites to label their policies and to notify users as
they browse sites [<a href="#18">18</a>].
<p>
<h3><a name="Section3.3">3.3 Downloadable Code</a></h3>
<p> Installing new executables within secured systems calls for review and
explicit authorization to prevent introducing malfunctioning or malicious
code. The shift from closed to open systems does not change the threat,
but it does increase the scale of the problem - and reduces the administrative
support. Mobile code on the Web leaps across organizational trust boundaries.
While idly surfing the Web, a browser might take the opportunity to download,
install, and execute objects and scripts automatically from unknown sources.
<p> Once invoked, applets have wide-open access, because there are few specific
limits on their trust. Worse, initial implementations did not carefully
log and audit downloaded code activities, nor defend against "simple" system
bugs such as self-modifying virtual machines, unprotected namespaces, and
loopholes in filesystem access.
<p> Microsoft's ActiveX architecture emphasized install-time reviews of trust
relationships. To that end, Authenticode provides identity-centric policy
based on VeriSign "software publisher" identity certificates. Java, on the
other hand, is a bytecode-interpreted language with wider scope for "sandboxing"
the interfaces an applet can execute. JavaSoft and Netscape both promote
security policies which specifically grant or deny such capabilities [<a href="#19">19</a>].
<p> In practice, no single security policy will suffice for safely using downloaded
code, any more than a single policy can capture every household's morals
for content filtering. Even the earliest secure operating systems, such
as Multics, combined identity and capability limits on programs. Today,
users might further expect their trust manager to fetch software reviews
and place quality limits as well ("At least four stars from <tt>PCPundit.com</tt>").
<p align="center"><img src="rif2.gif" width="311" height="177">
<p> Managing the trust placed in downloadable components will draw on the
same list of TM tools suggested throughout this paper: identity certification
of authors and endorsers; machine-readable metadata about the trustworthiness
of principals, objects, and actions; and flexible TM engines that can compose
the policies of end-users, administrators, and publishers.
<p><img src="../../../buttons/quad.gif"><a name="d4"></a> </p>
<h2><a name="Section4">4. From Web Security to Trust Management</a></h2>
<p> Amid the rush of new protocols, ciphers, patches, and press releases which
is the Web Security industry, it is easy to lose sight of the fact that
conventional security technology, even if implemented perfectly, does not
add up to Trust Management. In part, this stems from incorrect or incomplete
specifications of security rules. More fundamentally, it comes from the
closed-system worldview that securing the Web translates to securing Web
servers and Web clients alone. In fact, trust needs to be managed in several
layers of the network connection, as well as in several software components.
<p> The Web as an information system does not publish political press releases,
corrupt youth, or reprogram computers. It is merely a request-response protocol
for importing and exporting bags of bits across the network. If you draw
a circle around Web clients and Web servers, you actually capture very little
of the value gatewayed onto the Web using fill-in-form scripts, databases,
and filesystems. "Securing a Web Transaction" proves only that a pile of
bits has moved from one machine to another without anyone peeking or poking.
<p align="center"><img src="rif3.gif" width="363" height="201">
<p>
<p>
<h3><a name="Section4.1">4.1 Securing Web Transactions</a></h3>
<p> There are three levels at which we can protect Web transactions: in the
transport layer underlying HTTP, within the HTTP messages themselves, or
in the content exchanged atop HTTP [<a href="#20">20</a>]. The transport
layer can only provide a secure bitstream; it cannot be used to reason about
the protection of individual "documents" or HTTP "actions" within that opaque
stream. Those measures are properly part of the application layer, driving
the development of security within HTTP messages. Finally, application developers
can circumvent Web security entirely, and build their own end-to-end solutions,
by using HTTP as a black-box for exchanging files.
<p> Transport Layer Security (TLS, née SSL) can establish a private
channel between two processes. A temporary session key is set up for each
cryptographic handshake between any client and server. The emphasis, however,
is on <i>any</i>: the only way to be sure that the device on the other end
speaks for some person or organization is through patches that exchange
X.509 identity certificates. TLS alone cannot further establish trust in
those principals, an "out-of-band" certification problem. Without those
checks, TLS can be spoofed in practice by man-in-the-middle attacks [<a href="#21">21</a>].
<p> At the application layer, where such decisions ought to reside, security
features are even weaker. With the lukewarm market acceptance of Secure
HTTP (S-HTTP), today's developers have few options for securing Web semantics.
Recent revisions address intermediaries in the trust topology, authenticating
to proxies as well as to origin servers and to clients.
<p> Above the application layer, security can be flexible, but its gains are
minimal without its underlying layers being secure. Similar problems occur
with other "generic" tools; for example, firewalls and tunnels that form
Virtual Private Networks cannot overcome security loopholes in the underlying
infrastructure, such as a stray machine behind the firewall with an exposed
dial-in port.
<p>
<h3> <a name="Section4.2">4.2 Web Servers</a> </h3>
<p> A typical HTTP server might offer to "protect" some URLs by requesting
a username/password challenge before granting access. This kind of access
privilege is still overbroad. It requires the server administrator to be
vigilant about what content is in the "protected" and open areas; it does
not typically restrict the range of methods available (<tt>GET</tt>, <tt>PUT</tt>,
<tt>DELETE</tt>, and so on) in the protected area; and it does not establish
the identity or credentials of each individual user. Essentially, the security
policy here can talk only about the "form" of a request (that is, its method
and URL), but not the "substance," or contents, of that request. When every
resource is just an opaque stream of bits, it is difficult to protect "all
files containing next year's budget projections."
<p> When measured against the taxonomy of issues outlined in <a
href="#Section1">Section 1</a>, it is understandably difficult from a pragmatics
standpoint to build trusted information systems atop common Web servers:
<p> <i>Principles.</i> HTTP servers often cannot <i>be specific</i>, because
they cannot accurately identify the particular privileges of each principal.
Since Web servers often outsource work to their (buggy) operating systems,
you cannot <i>trust yourself</i>. Furthermore, such outsourcing makes Web
servers overly reliant on other subsystems' security at multiple points
of entry: the corruptible file system can be clobbered on the FTP, Telnet,
and E-mail channels; viruses can make subvert the operating system; and
extensibility features such as servlets might exploit security flaws. Adding
insult to injury, Web servers have trouble <i>being careful</i>, too. Their
logging features are rudimentary (that is, they flood the client with information,
without any intelligent anomaly detection). Rollback is virtually nonexistent,
due to the loose coordination with the underlying information sources.
<p> <i>Principals.</i> Few Web servers can reliably identify any of the three
types of principals. Worse, administrators often rely on very weak security
when Web servers need to make assertions today: passwords are crackable
(when not sent in the clear using BASIC authentication!), IP addresses are
spoofable, and DNS entries are corruptible. Sometimes, there is an appropriate
tool for determining principals, but the implementation is in the wrong
layer entirely: TLS client-authentication does not propagate up, so passwords
must be re-implemented with HTTP Authentication above it.
<p> <i>Policies.</i> Web servers offer very little flexibility when it comes
to policy. Protection techniques are usually hardcoded; identities are abstracted
no further than to user and group lists; and objects are grouped by URL
path in lieu of any more meaningful policy binding.
<p>
<h3><a name="Section4.3">4.3 Web Clients</a></h3>
<p> Browsers are such general-purpose interfaces to the Web that they cannot
afford to customize their behaviors to the context or content of a particular
transaction. Usability and security suffer as users eagerly swat aside the
"Show alert each time unsecured data is sent?" dialog box - because it is
raised for any private transaction, whether submitting a credit card number
or a sweater color. Inattentiveness while Web surfing is rarely cured by
blanket warnings such as, "Think very carefully before accepting a digitally
signed program; how competent and trustworthy is the signer?" [<a href="#22">22</a>].
<p> <i>Principles.</i> Web browsers have difficulty in <i>being specific</i>;
they work in exactly the same way throughout Web space, although Microsoft
Internet Explorer 4 can adapt security preferences for built-in "zones"
[<a
href="#23">23</a>].Clients offer no means by which to <i>trust yourself</i>. Users
cannot actively establish - or passively monitor - trust in organizations
and individuals who publish Web resources. Finally, who can <i>be careful</i>
implementing on top of typical client operating systems? Disk caches can
leak information to other users; flaws in mobile code interpreters; overabundant
or nonexistent activity logging; and so on.
<p> <i>Principals.</i> End-user OSes often cannot identify principals. Regarding
<i>humans</i>, for example, Windows 95 has a weak concept of a "uniquely-identifiable
user," and user IDs were easily cracked in early Windows NT. Identifying
<i>computers</i> or <i>organizations</i> is difficult too, since the user
interface often hides the what little location cues there are, leading to
spoofer sites [<a href="#24">24</a>]; or over Domain Name System trademark
disputes.
<p> <i>Policies.</i> Web clients can barely even claim to having security
policies: often what little protection there is, is compiled in and not
user-configurable. Only a few clients have incorporated rudimentary PICS
filters, much less the sophisticated P3P privacy control panels or PICSRules
interpreters.
<h2><img src="../../../buttons/quad.gif"><a name="d5"></a> </h2>
<h2><a name="Section5">5. Weaving a Web of Trust</a></h2>
<p> We believe that as Web-based applications replace closed information systems,
transactions will cross more and more organizational boundaries, often magnifying
latent flaws in existing trust relationships. For example, consider the
U.S. <a href="http://www.ssa.gov/">Social Security Administration's</a>
ill-fated attempt to put its records on the Web. Each American worker has
a trust relationship with the SSA regarding his or her pensions, sealed
by the "secrecy" of his or her Social Security Number, mother's maiden name,
and birth state. For decades, those were the keys to obtaining one's <a
href="http://s3abaca.ssa.gov/pro/batch-pebes/bp-7004home.shtml">Personal Earnings
and Benefit Estimate Statement</a> (PEBES). When the exact same interface
was reflected on the Web, however, nationwide outrage erupted over the perceived
loss of privacy, resulting in a hurried shutdown and "reevaluation" [<a href="#25">25</a>].
<p> In this case, fast and easy HTTP access has raised the potential for large-scale
abuse not present in the existing postal system. The SSA is ensconced in
a trust relationship that is not represented by a corresponding secret,
so cryptography cannot solve their problem. Computers can alter the equation
only by substituting the explicit power of cryptography for the implicit
power of psychology. The irony is that they do share one secret record with
each worker: that worker's earnings history - which is why workers request
a PEBES in the first place!
<p align="center"><img src="rif4.gif" width="253" height="173">
<p> In the end, there will have to be a more secure way of accessing such
records - perhaps with a digital identity certificate corresponding to today's
Social Security Card. Such precautions may even strengthen how the "traditional"
paper system works. Cryptography can offer much stronger proofs than traditional
means, so trust relationships will tend to be cemented with shared secrets
that enable those protocols, such as PIN numbers, shared keys, and credentials.
<p> Web publishers, administrators, and readers will all need infrastructure
"to help users decide what to trust on the Web" [<a href="#26">26</a>].
This paper represents a call to arms to the parties who have a role in bringing
this vision to fruition:
<p>
<dl>
<dt> <b>Web Developers</b>
<dd> The people and organizations ultimately responsible for reducing Web
standard formats, protocols, and APIs to practice in software and hardware
should be committed to developing Trust Management technologies. They
should become engaged in the current standardization debates surrounding
public key infrastructure (the SPKI/SDSI working group at the IETF); digital
signatures (in the legislatures and courts, as well as IETF and W3C);
and formats for adding security and trust metadata to the Web (at W3C).
<dt> <b>Web Users</b>
<dd> Users have the power to persuade developers to follow this agenda.
Web users should be aware of the laundry list of trust decisions confronting
them every day: whether they are talking to the right organization, whether
they should run an applet, or whether they should allow their children
to access a site.
<dt> <b>Application Designers</b>
<dd> The business people, programmers, and regulators responsible for creating
and controlling new, secure Web applications should use the concepts identified
in this paper to identify and control security risks. It is not merely
a cryptographer's problem to uphold the principles of Trust Management,
identify principals, construct policies, and integrate them with the Web.
Each participant in application development should think carefully about
whom s/he is trusting, in what roles, to permit some action.
<dt> <b>Citizens</b>
<dd> The emergence of the Web as a social phenomenon will even affect people
who do not use the Web. As informed citizens, we must consider the impact
of automating trust decisions and moving our human bonds into WebSpace.
Trust Management tools allow communities of people to define their own
world views - at what risk of balkanization?
</dl>
<p> If we all work together, automatable Trust Management could indeed weave
a World Wide Web of Trust, spun from the filaments of our faith in one another.
<p> </p>
<h2><img src="../../../buttons/quad.gif"><a name="d6"></a> </h2>
<h2>Acknowledgements</h2>
<p> Mr. Khare's work was sponsored by the Defense Advanced Research Projects
Agency and Air Force Research Laboratory, Air Force Materiel Command, USAF,
under agreement number F30602-97-2-0021. He would also like to thank MCI
Internet Architecture for its support in this research.
<p> Mr. Rifkin's work was supported under the Caltech Infospheres Project,
sponsored by the CISE directorate of the National Science Foundation under
Problem Solving Environments grant CCR-9527130 and by the NSF Center for
Research on Parallel Computation under Cooperative Agreement Number CCR-9120008.
<p><img src="../../../buttons/quad.gif"><a name="author"></a>
<h2>About the Authors</h2>
<p><a href="http://www.ics.uci.edu/~rohit/"><b>Rohit Khare</b></a> joined
the Ph.D. program in computer science at the University of California, Irvine
in Fall 1997, after serving as a member of the MCI Internet Architecture
staff. He was previously on the technical staff of the World Wide Web Consortium
at MIT, where he focused on security and electronic commerce issues. He
has been involved in the development of cryptographic software tools and
Web-related standards development. Rohit received a B.S. in Engineering
and Applied Science and in Economics from California Institute of Technology
in 1995. <br>
e-mail: <a href="mailto:rohit@uci.edu">rohit@uci.edu</a>
<p> <a href="http://www.cs.caltech.edu/~adam/"><b>Adam Rifkin</b></a> received
his B.S. and M.S. in Computer Science from the College of William and Mary.
He is presently pursuing a Ph.D. in computer science at the California Institute
of Technology, where he works with the <a
href="http://www.infospheres.caltech.edu/">Caltech Infospheres Project</a> on
the composition of active distributed objects. He has done Internet consulting
and performed research with several organizations, including Canon, Hewlett-Packard,
Griffiss Air Force Base, and the NASA-Langley Research Center. <br>
e-mail: <a href="mailto:adam@cs.caltech.edu">adam@cs.caltech.edu</a>
<p> <br>
<p><img src="../../../buttons/quad.gif"><a name="notes"></a>
<h2>Notes</h2>
<p><a name="01">1</a>. <a href="#Blaze96">Blaze et al., 1996</a>; <a
href="#Brickell96">Brickell et al., 1996</a>.
<p> <a name="02">2</a>. <a href="#Khare97">Khare and Rifkin, 1997</a>.
<p> <a name="03">3</a>. <a href="#Schneier96">Schneier, 1996</a>.
<p> <a name="04">4</a>. <a href="#Kohnfelder78">Kohnfelder, 1978</a>.
<p> <a name="05">5</a>. <a href="#Garfinkel94">Garfinkel, 1994</a>.
<p> <a name="06">6</a>. <a href="#Lampson96">Lampson and Rivest, 1996</a>.
<p> <a name="07">7</a>. <a href="#Ellison97">Ellison et al., 1997</a>.
<p> <a name="08">8</a>. <a href="#Khare97b">Khare, 1997</a>.
<p> <a name="09">9</a>. <a href="#Khare96">Khare, 1996</a>.
<p> <a name="10">10</a>. <a href="#Resnick96">Resnick and Miller, 1996</a>.
<p> <a name="11">11</a>. <a href="#Chu97">Chu et al., 1997</a>.
<p> <a name="12">12</a>. <a href="#Blaze97">Blaze et al., 1997</a>.
<p> <a name="13">13</a>. <a href="#Presler-Marshall97">Presler-Marshall et
al., 1997</a>.
<p> <a name="14">14</a>. <a href="#DesAutels97">DesAutels et al., 1997</a>.
<p> <a name="15">15</a>. <a href="#Cox96">Cox, 1996</a>.
<p> <a name="16">16</a>. <a href="#Yee95">Yee and Tygar, 1995</a>.
<p> <a name="17">17</a>. <a href="#Hoffman97">Hoffman et al., 1997</a>.
<p> <a name="18">18</a>. <a href="#Ackerman97">Ackerman, 1997</a>.
<p> <a name="19">19</a>. <a href="#McGraw96">McGraw and Felten, 1996</a>.
<p> <a name="20">20</a>. <a href="#Khare96b">Khare, 1996b</a>.
<p> <a name="21">21</a>. <a href="#Felten97">Felten et al., 1997</a>.
<p> <a name="22">22</a>. <a href="#Felten97b">Felten, 1997</a>.
<p> <a name="23">23</a>. <a href="#Microsoft97">Microsoft, 1997</a>.
<p> <a name="24">24</a>. <a href="#Felten97">Felten et al., 1997</a>.
<p> <a name="25">25</a>. <a href="#Garfinkel97">Garfinkel, 1997</a>.
<p> <a name="26">26</a>. <a href="#Khare97b">Khare, 1997</a>.
<p> <a name="27">27</a>. <a href="#Khare97b">Khare, 1997</a>.
<p> <a name="28">28</a>. <a href="#Khare97b">Khare, 1997</a>.
<h2><img src="../../../buttons/quad.gif"><a name="references"></a> </h2
>
<h2>References</h2
>
<p><a name="Ackerman97">Mark Ackerman</a>. <cite>General Overview of the P3P
Architecture</cite>, W3C Working Draft (Work in Progress), October 1997;
available at <a
href="http://www.w3.org/TR/WD-P3P-arch.html"> http://www.w3.org/TR/WD-P3P-arch.html</a>
</p
>
<p> <a name="Blaze96">Matt Blaze</a>, Joan Feigenbaum, and Jack Lacy. <cite>Decentralized
Trust Management</cite>, Proceedings of the 1996 IEEE Symposium on Security
and Privacy, Los Alamitos, Calif.: IEEE Computer Society Press, 1966, pp.
164-173; available as a DIMACS Technical Report from <a
href="ftp://dimacs.rutgers.edu/pub/dimacs/TechnicalReports/TechReports/1996/96-1
7.ps.gz"> ftp://dimacs.rutgers.edu/pub/dimacs/TechnicalReports/TechReports/1996/96-17.ps.g
z</a>
<p> <a name="Blaze97">Matt Blaze</a>, Joan Feigenbaum, Paul Resnick, and Martin
Strauss. <cite>Managing Trust in an Information-Labeling System</cite>,
European Transactions on Telecommunications, 1997; available as AT &
T Technical Report 96.15.1, <a
href="http://www.si.umich.edu/~presnick/papers/bfrs/"> http://www.si.umich.edu/~presnick/papers/bfrs/</a>
<p> <a name="Brickell96">Ernie Brickell</a>, Joan Feigenbaum, and David Maher.
<cite>DIMACS Workshop on Trust Management in Networks</cite>, South Plainfield,
N.J., September 1996; available at <a
href="http://dimacs.rutgers.edu/Workshops/Management/"> http://dimacs.rutgers.edu/Workshops/Management/</a>
<p> <a name="Chu97">Yang-Hua Chu</a>, Joan Feigenbaum, Brian LaMacchia, Paul
Resnick, and Martin Strauss. <cite>REFEREE: Trust Management for Web Applications</cite>,
Proceedings of the Sixth International World Wide Web Conference, Santa
Clara, Calif., April 1997; available at <a
href="http://www6.nttlabs.com/HyperNews/get/PAPER116.html"> http://www6.nttlabs.com/HyperNews/get/PAPER116.html</a>
<p> <a name="Cox96">Brad Cox</a>. <cite>Superdistribution: Objects as Property
on the Electronic Frontier</cite>, Reading, Mass: Addison-Wesley, 1996.
<p> <a name="DesAutels97">Philip DesAutels</a>, Yang-hua Chu, Brian LaMacchia,
and Peter Lipp. <cite>DSig 1.0 Signature Labels: Using PICS 1.1 Labels for
Making Signed Assertions</cite>, W3C Working Draft (Work in Progress), November
1997; available at <a
href="http://www.w3.org/TR/WD-DSIG-label-971111.html"> http://www.w3.org/TR/WD-DSIG-label-971111.html</a>
<p> <a name="Ellison97">Carl Ellison</a>, Bill Frantz, Ron Rivest, and Brian
M. Thomas. <cite>Simple Public Key Certificate</cite>, Internet Draft (Work
in Progress), April 1997; available at <a
href="http://www.clark.net/pub/cme/spki.txt"> http://www.clark.net/pub/cme/spki.txt</a>
<p> <a name="Felten97b">Edward W. Felten</a>. <cite>Security Tradeoffs: Java
vs. ActiveX</cite>, April 1997; available at <a
href="http://www.cs.princeton.edu/sip/java-vs-activex.html"> http://www.cs.princeton.edu/sip/java-vs-activex.html</a>
<p> <a name="Felten97">Edward W. Felten</a>, Dirk Balfanz, Drew Dean, and
Dan S. Wallach. <cite>Web Spoofing: An Internet Con Game</cite>, Princeton
University Technical Report 540-96 (revised), revised February 1997; available
at <a href="http://www.cs.princeton.edu/sip/pub/spoofing.html"> http://www.cs.princeton.edu/sip/pub/spoofing.html</a>
<p> <a name="Garfinkel94">Simson Garfinkel</a>. <cite>PGP: Pretty Good Privacy</cite>,
Sebastopol, Calif.: O'Reilly and Associates, 1994.
<p> <a name="Garfinkel97">Simson Garfinkel</a> <cite>Few Key Bits of Info
Open Social Security Records</cite>, <i>USA Today</i>, p. A1, May 12, 1997.
<p> <a name="Hoffman97">Donna Hoffman</a>, Thomas Novak, and Marcos Peralta.
<cite>Information Privacy in the Marketspace: Implications for the Commercial
Uses of Anonymity on the Web</cite>, Workshop on Anonymous Communications
on the Internet: Uses and Abuses, University of California at Irvine, November
21-23, 1997. To appear In: <cite>The Information Society</cite>; available
at <a
href="http://www2000.ogsm.vanderbilt.edu/papers/anonymity/anonymity2_nov10.htm">
http://www2000.ogsm.vanderbilt.edu/papers/anonymity/anonymity2_nov10.htm</a>
<p> <a name="Khare96">Rohit Khare</a>. <cite>Using PICS Labels for Trust Management</cite>,
DIMACS Workshop on Trust Management in Networks, South Plainfield, N.J.,
September 1996; available at <a
href="http://dimacs.rutgers.edu/Workshops/Management/Khare.html"> http://dimacs.rutgers.edu/Workshops/Management/Khare.html</a>
<p> <a name="Khare96b">Rohit Khare</a>. <cite>Security Extensions for the
Web</cite>, RSA Data Security Conference, 1996; available at <a
href="http://www.w3.org/pub/WWW/Talks/960119-RSA/"> http://www.w3.org/pub/WWW/Talks/960119-RSA/</a>
<p> <a name="Khare97b">Rohit Khare</a>. <cite>Digital Signature Label Architecture</cite>,
<i>World Wide Web Journal</i>, special issue on security, Volume 2, Number
3, pp. 49-64, Summer 1997.
<p> <a name="Khare97">Rohit Khare</a> and Adam Rifkin. <cite>Weaving a Web
of Trust</cite>, <i>World Wide Web Journal</i>, special issue on security,
Volume 2, Number 3, pp. 77-112, Summer 1997; available at <a
href="http://www.cs.caltech.edu/~adam/papers/trust.html"> http://www.cs.caltech.edu/~adam/papers/trust.html</a>
<p> <a name="Kohnfelder78">Loren M. Kohnfelder</a>. <cite>Towards a Practical
Public-Key Cryptosystem</cite>, B.S. thesis supervised by Len Adleman, May
1978.
<p> <a name="Lampson96">Butler Lampson</a> and Ron Rivest. <cite>SDSI - A
Simple Distributed Security Infrastructure</cite>, DIMACS Workshop on Trust
Management in Networks, South Plainfield, N.J., September 1996; available
at <a href="http://dimacs.rutgers.edu/Workshops/Management/Lampson.html">
http://dimacs.rutgers.edu/Workshops/Management/Lampson.html</a> ; see also
the SDSI page at <a href="http://theory.lcs.mit.edu/~cis/sdsi.html"> http://theory.lcs.mit.edu/~cis/sdsi.html</a>
<p> <a name="McGraw96">Gary McGraw</a> and Edward W. Felten. <cite>Java Security:
Hostile Applets, Holes and Antidotes</cite>. N.Y.: John Wiley and Sons,
1996; available at <a
href="http://www.rstcorp.com/java-security.html"> http://www.rstcorp.com/java-security.html</a>
<p> <a name="Microsoft97">Microsoft Corporation</a>. <cite>Microsoft Security
Management Architecture White Paper</cite>, May 1997; available at <a
href="http://www.microsoft.com/ie/security/">http://www.microsoft.com/ie/securit
y/</a>
<p> <a name="Presler-Marshall97">Martin Presler-Marshall</a>, Christopher
Evans, Clive Feather, Alex Hopmann, Martin Presler-Marshall, and Paul Resnick.
<cite>PICSRules 1.1</cite>, W3C Working Draft (Work in Progress), November
1997; available at <a href="http://www.w3.org/TR/PR-PICSRules-971104"> http://www.w3.org/TR/PR-PICSRules-971104</a>
<p> <a name="Resnick96">Paul Resnick</a> and Jim Miller. <cite>PICS: Internet
Access Controls without Censorship</cite>, <i>Communications of the ACM</i>,
Volume 39 (1996), pp 87-93; available as <a
href="http://www.w3.org/pub/WWW/PICS/iacwcv2.htm"> http://www.w3.org/pub/WWW/PICS/iacwcv2.htm</a>
<p> <a name="Schneier96">Bruce Schneier</a>. <cite>Applied Cryptography: Protocols,
Algorithms, and Source Code in C</cite>, Second Edition, N.Y.: John Wiley
and Sons, 1996; available at <a
href="http://www.openmarket.com/techinfo/applied.htm"> http://website-1.openmarket.com/techinfo/applied.htm</a>
<p> <a name="Yee95">Bennet Yee</a> and Doug Tygar. <cite>Secure Coprocessors
in Electronic Commerce Applications</cite>, Proceedings of The First USENIX
Workshop on Electronic Commerce, New York, N.Y., July 1995; available at
<a
href="http://www-cse.ucsd.edu/users/bsy/papers.html"> http://www-cse.ucsd.edu/users/bsy/papers.html</a>
</BLOCKQUOTE>
</BLOCKQUOTE>
<HR>
<BLOCKQUOTE>
<A HREF="../index.html"><img src="../../../buttons/contents.gif" BORDER="0" ALT="Contents" ALIGN="BOTTOM"></A>
<A HREF="../../index.html"><img border=0 src="../../../buttons/index.gif" alt="Index"></A>
<p>Copyright <A HREF="../../../copy.html">©</A> 1998, ƒ ¡ ® s † - m ¤ ñ d @ ¥ </BLOCKQUOTE>
</BODY></HTML>
© 2024 Packet Storm. All rights reserved.
%7Cutmcsr%3D(direct)%7Cutmcmd%3D(none)){kind=small}
Follow us on Twitter
Follow us on Facebook
Subscribe to an RSS Feed