| Rfc | 3157 |
|---|
| Title | Securely Available Credentials - Requirements |
|---|
| Author | A. Arsenault, S.
Farrell |
|---|
| Date | August 2001 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | INFORMATIONAL |
|---|
|
Network Working Group A. Arsenault
Request for Comments: 3157 Diversinet
Category: Informational S. Farrell
Baltimore Technologies
August 2001
Securely Available Credentials - Requirements
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 (2001). All Rights Reserved.
Abstract
This document describes requirements to be placed on Securely
Available Credentials (SACRED) protocols.
Table Of Contents
1. Introduction.................................................1
2. Framework Requirements.......................................4
3. Protocol Requirements........................................7
4. Security Considerations.....................................10
References.....................................................12
Acknowledgements...............................................12
Authors' Addresses.............................................13
Appendix A: A note on SACRED vs. hardware support..............14
Appendix B: Additional Use Cases...............................14
Full Copyright Statement.......................................20
1. Introduction
"Credentials" are information that can be used to establish the
identity of an entity, or help that entity communicate securely.
Credentials include such things as private keys, trusted roots,
tickets, or the private part of a Personal Security Environment (PSE)
[RFC2510] - that is, information used in secure communication on the
Internet. Credentials are used to support various Internet
protocols, e.g., S/MIME, IPSec and TLS.
In simple models, users and other entities (e.g., computers like
routers) are provided with credentials, and these credentials stay in
one place. However, the number, and more importantly the number of
different types, of devices that can be used to access the Internet
is increasing. It is now possible to access Internet services and
accounts using desktop computers, laptop computers, wireless phones,
pagers, personal digital assistants (PDAs) and other types of
devices. Further, many users want to access private information and
secure services from a number of different devices, and want access
to the same information from any device. Similarly credentials may
have to be moved between routers when they are upgraded.
This document identifies a set of requirements for credential
mobility. The Working Group will also produce companion documents,
which describe a framework for secure credential mobility, and a set
of protocols for accomplishing this goal.
The key words "MUST", "REQUIRED", "SHOULD", "RECOMMENDED", and "MAY"
in this document are to be interpreted as described in [RFC2119].
1.1 Background and Motivation
In simple models of Internet use, users and other entities are
provided with credentials, and these credentials stay in one place.
For example, Mimi generates a public and private key on her desktop
computer, provides the public key to a Certification Authority (CA)
to be included in a certificate, and keeps the private key on her
computer. It never has to be moved.
However, Mimi may want to able to send signed e-mail messages from
her desktop computer when she is in the office, and from her laptop
computer when she is on the road, and she does not want message
recipients to know the difference. In order to do this, she must
somehow make her private key available on both devices - that is,
that credential must be moved.
Similarly, Will may want to retrieve and read encrypted e-mail from
either his wireless phone or from his two-way pager. He wants to use
whichever device he has with him at the moment, and does not want to
be denied access to his mail or to be unable to decrypt important
messages simply because he has the wrong device. Thus, he must be
able to have the same private key available on both devices.
The following scenario relating to routers has also been offered:
"Once upon a time, a router generated a keypair. The administrators
transferred the public key of that router to a lot of other (peer)
routers and used that router to encrypt traffic to the other routers.
And this was good for many years. Then one day, the network
administrators found that this particular little router couldn't
handle an OC-192. So they trashed it and replaced it with a really
big router. While they were there, the craft workers inserted a
smart card into the router and logged into the router. They gave the
appropriate commands and entered the correct answers and so the
credentials (keypair) were transferred to the new, big router.
Alternatively, the craft people could have logged into the router,
given it a minimal configuration and transferred the credentials from
a credential server to the router. They had to perform the correct
incantations and authentications for the transfer to be successful.
In this way, the identity of the router was moved from an old router
to a new one. The administrators were glad that they didn't have to
edit the configurations of all of the peer routers as well."
It is generally accepted that the private key in these examples must
be transferred securely. In the first example, the private key
should not be exposed to anyone other than Mimi herself (and ideally,
it would not be directly exposed to her). Furthermore, it must be
transferred correctly. It must be transferred to the proper device,
and it must not be corrupted - improperly modified - during transfer.
Making credentials securely available (in an interoperable fashion)
will provide substantial value to network owners, administrators, and
end users. The intent is that this value be provided largely
independent of the hardware device used to access the secure
credential and the type of storage medium to which the secure
credential is written. Different credential storage devices, (e.g.,
desktop or laptop PC computer memory, a 3.5 inch flexible diskette, a
hard disk file, a cell phone, a smart card, etc.) will have very
different security characteristics and, often very different protocol
handling capabilities. Using SACRED protocols, users will be able to
securely move their credentials between different locations,
different Internet devices, and different storage media as needed.
In the remainder of this document we present a set of requirements
for the secure transfer of software-based credentials.
1.2 Working Group Organization and Documents
The SACRED Working Group is working on the standardization of a set
of protocols for securely transferring credentials among devices. A
general framework is being developed that will give an abstract
definition of protocols which can meet the credential-transfer
requirements. This framework will allow for the development of a set
of protocols, which may vary from one another in some respects.
Specific protocols that conform to the framework can then be
developed.
Work is being done on a number of documents. This document
identifies the requirements for the general framework, as well as the
requirements for specific protocols. Another document will describe
the protocol framework. Still others will define the protocols
themselves.
1.3 Structure of This Document
Section 1 of this document provides an introduction to the problem
being solved by this working group. Section 2 describes requirements
on the framework. Section 3 identifies the overall requirements for
secure credential-transfer protocols, and separate requirements for
two different classes of solutions. Section 4 identifies Security
Considerations. Appendix A describes the relationship of the SACRED
solutions and credential-mobility solutions involving hardware
components such as smart cards. Appendix B contains some additional
scenarios which were considered when developing the requirements.
2. Framework Requirements
This section describes requirements that the SACRED framework has to
meet, as opposed to requirements that are to be met by a specific
protocol that uses the framework.
2.1 Credential Server and Direct solutions
There are at least two different ways to solve the problem of secure
credential transfer between devices. One class of solutions uses a
"credential server" as an intermediate node, and the other class
provides direct transfer between devices.
A "credential server" can be likened to a server that sits in front
of a repository where credentials can be securely stored for later
retrieval. The credential server is active in the protocol, that is,
it implements security enforcing functionality.
To transfer credentials securely from one end device to another is a
straightforward two-step process. Users can have their credentials
securely "uploaded" from one device, e.g., a wireless phone, to the
credential server. They can be stored on the credential server, and
"downloaded" when needed using another device; e.g., a two-way pager.
Some advantages of a credential server approach compared to
credential transfer are:
1. It provides a conceptually clean and straightforward approach.
For all end devices, there is one protocol, with a set of actions
defined to transfer credentials from the device to the server, and
another set of actions defined to transfer credentials from the
server to the device. Furthermore, this protocol involves clients
(the devices) and a server (the credential server), like many
other Internet protocols; thus, the design of this protocol is
likely to be familiar to most people familiar with most other
Internet protocols.
2. It provides for a place where credentials can be securely stored
for arbitrary lengths of time. Given a reasonable-quality server
operating under generally accepted practices, it is unlikely the
credentials will be permanently lost due to a hardware failure.
This contrasts with systems where credentials are only stored on
end devices, in which a failure of or the loss of the device could
mean that the credentials are lost forever.
3. The credential server may be able to enforce a uniform security
policy regarding credential handling. This is particularly the
case where credentials are issued by an organization for its own
purposes, and are not "created" by the end user, and so must be
governed by the policies of the issuer, not the user.
However, the credential server approach has some potential
disadvantages, too:
1. It might be somewhat expensive to maintain and run the credential
server, particularly if there are stringent requirements on
availability and reliability of the server. This is particularly
true for servers which are used for a large community of users.
When the credential server is intended for a small community, the
complexity and cost would be much less.
2. The credential server may have to be "trusted" in some sense and
also introduces a point of potential vulnerability. (See the
Security Considerations section for some of the issues.) Good
protocol and system design will limit the vulnerability that
exists at the credential server, but at a minimum, someone with
access to the credential server will be able to delete credentials
and thus deny the SACRED service to system users.
Thus, some users may prefer a different class of solution, in which
credentials are transferred directly from one device to another
(i.e., having no intermediary element that processes or has any
understanding of the credentials).
For example, consider the case where Mimi sends a message from her
wireless phone containing the credentials in question, and retrieves
it using her two-way pager. In getting from one place to another,
the bits of the message cross the wireless phone network to a base
station. These bits are likely transferred over the wired phone
network to a message server run by the wireless phone operator, and
are transferred from there over the Internet to a message server run
by the paging operator. From the paging operator they are
transferred to a base station and then finally to Mimi's pager.
Certainly, there are devices other than the original wireless phone
and ultimate pager that are involved in the credential transfer, in
the sense that they transmit bits from one place to another.
However, to all devices except the pager and the wireless phone, what
is being transferred is an un-interpreted and unprocessed set of
bits. No security-related decisions are made, and no actions are
taken based on the fact that this message contains credentials, at
any of the intermediate nodes. They exist simply to forward bits.
Thus, we consider this to be a "direct" transfer of credentials.
Solutions involving the direct transfer of credentials from one
device to another are potentially somewhat more complex than the
credential-server approach, owing to the large number of different
devices and formats that may have to be supported. Complexity is
also added due to the fact that each device may in turn have to
exhibit the behavior of both a client and a server.
We believe that both classes of solutions are useful in certain
environments, and thus that the SACRED framework will have to define
solutions for both. The extent to which elements of the above
solutions overlap remains to be determined.
This all leads to our first set of requirements:
F1. The framework MUST support both "credential server" and
"direct" solutions.
F2. The "credential server" and "direct" solutions SHOULD use the
same technology as far as possible.
2.2 User authentication
There is a wide range of deployment options for credential mobility
solutions. In many of these cases, it is useful to be able to re-use
an existing user authentication scheme, for example where passwords
have previously been established, it may be more secure to re-use
these than try to manage a whole new set of passwords. Different
devices may also limit the types of user authentication scheme that
are possible, e.g., not all mobile devices are practically capable of
carrying out asymmetric cryptography.
F3. The framework MUST allow for protocols which support different
user authentication schemes
2.3 Credential Formats
Today there is no single standard format for credentials and
this is not likely to change in the near future. There are a
number of fairly widely deployed formats, e.g., [PGP],
[PKCS#12] that have to be supported. This means that the
framework has to allow for protocols supporting any credential
format.
F4. The details of the actual credential type or format MUST be
opaque to the protocol, though not to processing within the
protocol's peers. The protocol MUST NOT depend on the internal
structure of any credential type or format.
2.4 Transport Issues
Different devices allow for different transport layer possibilities,
e.g., current WAP 1.x devices do not support TCP. For this reason
the framework has to be transport "agnostic".
F5. The framework MUST allow use of different transports.
3. Protocol Requirements
In this section, we identify the requirements for secure credential-
transfer solutions. We will begin by listing a set of relevant
vulnerabilities and the requirements that must be met by all
solutions. Then we identify additional requirements that must be met
by solutions involving a credential server, followed by additional
requirements that must be met by solutions involving direct transfer
of credentials.
3.1 Vulnerabilities
This section lists the vulnerabilities against which a SACRED
protocol SHOULD offer protection. Any protocol claiming to meet the
requirements listed in this document MUST explicitly indicate how (or
whether) it offers protection for each of these vulnerabilities.
V1. A passive attacker can watch all packets on the network and
later carry out a dictionary attack.
V2. An attacker can attempt to masquerade as a credential server
in an attempt to get a client to reveal information on line
that allows for a later dictionary attack.
V3. An attacker can attempt to get a client to decrypt a chosen
"ciphertext" and get the client to make use of the resulting
plaintext - the attacker may then be able to carry out a
dictionary attack (e.g., if the plaintext resulting from
"decryption" of a random string is used as a DSA private
key).
V4. An attacker could overwrite a repository entry so that when
a user subsequently uses what they think is a good
credential, they expose information about their password
(and hence the "real" credential).
V5. An attacker can copy a credential server's repository and
carry out a dictionary attack.
V6. An attacker can attempt to masquerade as a client in an
attempt to get a server to reveal information that allows
for a later dictionary attack.
V7. An attacker can persuade a server that a successful login
has occurred, even if it hasn't.
V8. (Upload) An attacker can overwrite someone else's
credentials on the server.
V9. (When using password-based authentication) An attacker can
force a password change to a known (or "weak") password.
V10. An attacker can attempt a man-in-the-middle attack for lots
V11. User enters password instead of name.
V12. An attacker could attempt various denial-of-service attacks.
3.2 General Protocol Requirements
Looking again at the examples described in Section 1.1, we can
readily see that there are a number of requirements that must apply
to the transfer of credentials if the ultimate goal of supporting the
Internet security protocols (e.g., TLS, IPSec, S/MIME) is to be met.
For example, the credentials must remain confidential at all times;
it is unacceptable for nodes other than the end-user's device(s) to
see the credentials in any readable, cleartext form.
These, then, are the requirements that apply to all secure
credential-transfer solutions:
G1. Credential transfer both to and from a device MUST be
supported.
G2. Credentials MUST NOT be forced by the protocol to be present
in cleartext at any device other than the end user's.
G3. The protocol SHOULD ensure that all transferred credentials
be authenticated in some way (e.g., digitally signed or
MAC-ed).
G4. The protocol MUST support a range of cryptographic
algorithms, including symmetric and asymmetric algorithms,
hash algorithms, and MAC algorithms.
G5. The protocol MUST allow the use of various credential types
and formats (e.g., X.509, PGP, PKCS12, ...).
G6. One mandatory to support credential format MUST be defined.
G7. One mandatory to support user authentication scheme MUST be
defined.
G8. The protocol MAY allow credentials to be labeled with a text
handle, (outside the credential), to allow the end user to
select amongst a set of credentials or to name a particular
credential.
G9. Full I18N support is REQUIRED (via UTF8 support) [RFC2277].
G10. It is desirable that the protocol be able to support
privacy, that is, anonymity for the client.
G11. Transferred credentials MAY incorporate timing information,
for example a "time to live" value determining the maximum
time for which the credential is to be usable following
transfer/download.
3.3 Requirements for Credential Server-based solutions
The following requirements assume that there is a credential server
from which credentials are downloaded to the end user device, and to
which credentials are uploaded from an end user device.
S1. Credential downloads (to an end user) and upload (to the
credential server) MUST be supported.
S2. Credentials MUST only be downloadable following user
authentication or else only downloaded in a format that
requires completion of user authentication for deciphering.
S3. It MUST be possible to ensure the authenticity of a
credential during upload.
S4. Different end user devices MAY be used to
download/upload/manage the same set of credentials.
S5. Credential servers SHOULD be authenticated to the user for
all operations except download. Note: This requirement can
be ignored if the credential format itself is strongly
protected, as there is no risk (other than user confusion)
from an unauthenticated credential server.
S6. It SHOULD be possible to authenticate the credential server
to the user as part of a download operation.
S7. The user SHOULD only have to enter a single secret value in
order to download and use a credential.
S8. Sharing of secrets across multiple servers MAY be possible,
so that penetration of some servers does not expose the
private parts of a credential ("m-from-n" operation).
S9. The protocol MAY support "away-from-home" operation, where
the user enters both a name and a domain (e.g.
RoamingStephen@baltimore.ie) and the domain can be used in
order to locate the user's credential server.
S10. The protocol MUST provide operations allowing users to
manage their credentials stored on the credential server,
e.g., to retrieve a list of their credentials stored on a
server; add credentials to the server; delete credentials
from the server.
S11. Client-initiated authentication information (e.g., password)
change MUST be supported.
S12. The user SHOULD be able to retrieve a list of
accesses/changes to their credentials.
S13. The protocol MUST support user self-enrollment. One
scenario calling for this is where a previously unknown user
uploads his credential without requiring manual operator
intervention.
S14. The protocol MUST NOT prevent bulk initializing of a
credential server's repository.
S15. The protocol SHOULD require minimal client configuration.
3.4 Requirements for Direct-Transfer Solutions
The full set of requirements for this case has not been elucidated,
and this list is therefore provisional. An additional requirements
document (or a modification of this one) will be required prior to
progression of a direct-transfer protocol.
The following requirements apply to solutions supporting the "direct"
transfer of credentials from one device to another. (See Section 2
for the note on the meaning of "direct" in this case.)
D1. It SHOULD be possible for the receiving device to authenticate
that the credential package indeed came from the purported
sending device.
D2. In order for a sender to know that a credential has been
received by a recipient, it SHOULD be possible for the
receiving device to send an acknowledgment of credential
receipt back to the sending device, and for the sending device
to authenticate this acknowledgment.
4. Security Considerations
4.1 Hardware vs. Software
Mobile credentials will never be as secure as a "pure" hardware-based
solution, because of potential attacks through the operating system
of the end-user device. However, an acceptable level of security may
be accomplished through some simple means. In fact the level of
security may be improved (compared to password encrypted files)
through the use of SACRED protocols.
The platforms to which credentials are downloaded usually cannot be
regarded as tamper-resistant, and it therefore is not too hard to
analyze contents of their memories. Further, storage of private
keys, even if they are encrypted, on a credential server, will be
unacceptable in some environments. Lastly, replacement of installed
or downloaded SACRED client software with a Trojan horse program will
always be possible, such a program could email the username and
password to the program's author.
4.2 Auditing
Although out of scope of the SACRED protocol development work,
implementations should carefully audit events that may be security
relevant. In particular credential server implementations should
audit all operations and should include information about the time
and source (e.g., IP address) of the operation, the claimed identity
of the client (possibly masked - see below), the type and result of
the operation and possibly other operation specific information.
Implementations should also take care not to include security
sensitive information in the audit trail, especially not sensitive
authentication information.
It may be sensible to mask the claimed identity in some way in order
to ensure that even if a user enters her password in a "username"
field, that that information is not in clear in the audit trail,
regardless of whether or not it was received in clear.
Similar mechanisms which should be supported, but which are out of
scope of protocol development include alerts and account locking, in
particular following repeated authentication failures.
4.3 Defense against attacks
Credential servers are major targets. Someone who can successfully
attack a credential server might be able to gain access to the
credentials of a number of users, unless those credentials are
sufficiently protected (e.g., encrypted sufficiently that they cannot
be read or used by someone who gains access to them). Attackers
might also be able to substitute credentials of users, to carry out
other system attacks (e.g., an attacker could provide a user with a
"trusted root" credential that the attacker controls, which would
later allow the attacker to have some other certificate accepted by
the user counter to policy).
In addition, a credential server is a major target for denial of
service attacks. Ensuring that a credential server is unavailable to
legitimate users can be of great assistance to attackers. Users who
were not able to retrieve needed credentials might be forced to
operate insecurely, or not operate at all. Credential servers are
especially vulnerable to denial of service attacks if they do lots of
expensive cryptographic operations - it might not take very many
operations for the attacker to bring service to an unacceptable
level.
Thus, great care should be taken in designing systems that use
credential servers to protect against these attacks.
References
[PGP] Callas, J., Donnerhacke, L., Finney, H. and R. Thayer,
"OpenPGP Message Format", RFC 2440, November 1998.
[PKCS12] "PKCS #12 v1.0: Personal Information Exchange Syntax
Standard", RSA Laboratories, June 24, 1999.
[CMS] Housley, R., "Cryptographic Message Syntax", RFC 2630,
June 1999.
[PKCS15] "PKCS #15 v1.1: Cryptographic Token Information Syntax
Standard," RSA Laboratories, June 2000.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2277] Alvestrand, H., " IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, January 1998.
[RFC2510] Adams, C. and S. Farrell, "Internet X.509 Public Key
Infrastructure Certificate Management Protocols", RFC
2510, March 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frysyk, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol - HTTP/1.1", RFC 2616, June 1999.
Acknowledgements
The authors gratefully acknowledge the text containing additional use
cases in Appendix B that was supplied by Neal Mc Burnett
(nealmcb@avaya.com).
Authors' Addresses
Alfred Arsenault
Diversinet Corp.
P.O. Box 6530
Ellicott City, MD 21042
USA
Phone: +1 410-480-2052
EMail: aarsenault@dvnet.com
Stephen Farrell,
Baltimore Technologies,
39 Parkgate Street,
Dublin 8,
IRELAND
Phone: +353-1-881-6000
EMail: stephen.farrell@baltimore.ie
Appendix A: A note on SACRED vs. hardware support.
One way of accomplishing many of the goals of the SACRED WG is to put
the credentials on hardware tokens - e.g., smart cards, PCMCIA cards,
or other devices. There are a number of types of hardware tokens
today that provide secure storage for sensitive information, some
degree of authentication, and interfaces to a number of types of
wireless and other devices. Thus, in the second example from section
1.1, Will could simply put his private key on a smart card, always
take the smart card with him, and be assured that whichever device he
uses to retrieve his e-mail, he will have all of the information
necessary to decrypt and read messages.
However, hardware tokens are not appropriate for every environment.
They cost more than software-only solutions, and the additional
security they provide may or may not be worth the incremental cost.
Not all devices have interfaces for the same hardware tokens. And
hardware tokens are subject to different failure modes than typical
computers - it is not at all unusual for a smart card to be lost or
stolen; or for a PCMCIA card to physically break.
Thus, it is appropriate to develop complementary software-based
solution that allows credentials to be moved from one device to
another, and provides a level of security sufficient for its
environments. While we recognize that the level of security provided
by a software solution may not be as high as that provided by the
hardware solutions discussed above, and some organizations may not
consider it sufficient at all, we believe that a worthwhile solution
can be developed.
Finally, SACRED protocols can also complement hardware credential
solutions by providing standard mechanisms for the update of
credentials which are stored on the hardware device. Today, this
often requires returning (with) the device to an administrative
centre, which is often inconvenient and may be costly. SACRED
protocols provide a way to update and manage credentials stored on
hardware devices without requiring such physical presence.
Appendix B: Additional Use Cases
This appendix describes some additional use cases for SACRED
protocols. SACRED protocols are NOT REQUIRED to support all these
use cases, that is, this text is purely informative.
B.1 Home/Work Desktop Computer
Scenario Overview
A university utilizing a PKI for various applications and services
on-campus is likely to find that many of its users would like to make
use of the same PKI-enabled services and applications on computers
located in their residence. These home computers may be owned either
by the university or by the individual but are permanently located at
the residence as opposed to laptop systems that may be taken home.
The usage depicted in this scenario may be motivated by formal
telecommuting arrangements or simply by the need to catch up on work
from home in the evenings. The basic scenario should apply equally
well to the commercial, health care, and higher education
environments.
Assumptions
This scenario assumes that the institution has not implemented a
hardware token-based PKI mobility solution
The home computer has a dial-up as opposed to a permanent network
connection.
The PKI applications, whenever practical, should be functional in
both on-line and off-line modes. For example, the home user signing
an email message to be queued for later bulk sending and the reading
of a received encrypted message may be supported off-line while
composing and queuing of an encrypted message might not be supported
in off-line mode.
Applications using digital signatures may require "non-repudiation".
The institution prefers that the user be identified via a single
certificate / key-pair from all computers used by the individual.
The home computer system can not be directly supported by the
institution's IT staff. Hardware, operating system versions, and
operating system configurations will vary widely. Significant
software installation or specialized configurations will be difficult
to implement.
Uniqueness of Scenario
vThe PKI mobility support needed for this scenario is, in general,
similar to the other mobility scenarios. However, it does have
several unique aspects:
1. The home-user scenario differs from the general public workstation
case in that it provides the opportunity to permanently store the
user's certificate and key-pair on the workstation.
2. Likewise the appropriate CA certificates and even certificates for
other users can be permanently stored or cached on the home
workstation.
3. Another key difference is the need to support off-line use of the
PKI credentials given the assumed dial-up network connection.
4. The level of hardware and software platform consistency (operating
system versions and configurations) will vary widely.
5. Finally, the level of available technical support is significantly
less for home systems than for equivalent systems managed by the
IT staff at the office location.
B.2 Public Lab / On-campus Shared Workstation
Scenario Overview
Many colleges and universities operate labs full of computer systems
that are available for use by the general student population. These
computers are typically configured with identical hardware and an
operating system build that is replicated to all of the systems in
the lab. Many typical configurations provide no permanent storage of
any type while others may offer individual disk space for personal
files on a central server. Some scheme is generally used to ensure
that the configuration of the operating system is preserved across
users and that temporary files created by one user are removed before
the next user logs in. Students generally sit down at the next
available workstation without any clear pattern of usage.
The same basic technical solutions used to operate public labs are
often also used in general environments where several people share a
single workstation. This is often found in locations with shift work
such as medical facilities and service bureaus that provide services
to multiple time zones.
Assumptions
1. This scenario assumes that the institution has not implemented a
hardware token-based PKI mobility solution.
2. The computer systems are permanently networked with LAN
connections.
3. The configuration of the computer system is centrally maintained
and customizations are relatively easy to implement. For example
it would be easy to load enterprise root certificates, LDAP server
configurations, specialized software, and any other needed
components of the PKI on to the workstations.
4. Applications using digital signatures may require "non-
repudiation" in some of the anticipated environments. Examples of
this might include homework submission in a public lab environment
or medical records in a health care environment.
5. The institution prefers that the user be identified via a single
certificate / key-pair from all computers used by the individual.
6. Many anticipated implementations of this scenario will not
implement any user authentication at the desktop operating system
level. Instead, user authentication will occur at during the
startup of networked applications such as email, web-based
services, etc. Login at the desktop level may be with generic
user names that are more targeted at matching printouts to
machines than identifying users.
7. Users, with almost ridiculous frequency, will walk away from a
system forgetting to first logout from running authenticated
applications.
Uniqueness of Scenario
The PKI mobility support needed for this scenario is, in general,
similar to the other mobility scenarios. However, it does have
several unique aspects:
1. Unlike situations with personal workstations, there is no
permanent storage available to hold user key pairs and
certificates.
2. Appropriate CA certificates and custom software are easily added
and maintained for these types of shared systems.
3. The workstations are installed in public locations and users will
frequently forget to close applications before permanently walking
away from the workstation.
B.3 Public Kiosk Mobility
Overview
This scenario describes the needs of the traveler or the shopper.
This person is traveling light (no computer) or is burdened with
everything but a computer. It recognizes the increasing availability
of Internet access points in public spaces, such as libraries,
airports, shopping malls, and "cyber cafes".
The Need
In our increasingly mobile society, the chances of needing
information when away from the normal computing place are great. One
may need to look up a telephone number. Have you tried to find a
phone book at a public phone lately? It may become necessary to use
a data device to find the next place to rush to. With the
proliferation of wireless devices (electronic leashes), others have
the ability to create a need for quick access to electronic
information. A pager can generate a need to check the email inbox or
address book. A cell phone can drive you to your database to answer
a pressing question.
The ability to quickly access sensitive or protected information or
services from publicly available devices will only become more
necessary as we become more and more "connected".
The Device
The access device is more a function of the best discount or
marketing effort than of design. Any number of hardware platforms
will be encountered.
Since these devices are open to the public I/O ports are not likely
to be. In order to protect the device and its immediate network
environment, most devices will be in some sort of protective
container. Access to serial, parallel, USB, firewire, SCSI, or
PCMCIA connections will not be possible. Likewise floppy, zip, or CD
drives. Therefore, any software "token" must be obtained from the
network itself.
The Concerns
1. Getting the "token". Since it will be necessary to obtain the
token (key, certificate, credential) from across the network. How
can it be protected during transit?
2. Where did you get it? One of the primary controls in PKI is
protection of the private key. Placing the key on a host that is
accessible from a public network means that there is an inherent
exposure from that network. The access controls and other
security measures on the host machine are an area of concern.
3. How did you get it? When you obtained the token from the server,
how did it know that you are you? Authentication becomes
critical.
4. What happens to the token when you leave? You've checked your
mail, downloaded a recipe from that super-secure recipe server,
found out how to get to the adult beverage store for the... uh...
accessories... for the meal, and you're off! Is your token? Or
is it still sitting there on the public kiosk waiting for those
youngsters coming out of the music store to notice and cruise the
information highway on your ticket?
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