One document matched: draft-pritikin-ttimodel-00.txt
Network Working Group M. Pritikin
Internet-Draft Cisco Systems, Inc.
Expires: April 16, 2004 October 17, 2003
Trusted Transitive Introduction Model
draft-pritikin-ttimodel-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at http://
www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 16, 2004.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
We describe the 'out-of-band' exchange of data in a classical
enrollment protocol as a Trusted Transitive Introduction (TTI)
between two end entities and an introducer, thus distinguishing
introduction from enrollment. This document describes the three
system entities in the trusted transitive introduction model and the
data exchanges between them. Three introduction stages are defined
and examined in the context of a 'TTI over HTTP' introduction.
Pritikin Expires April 16, 2004 [Page 1]
Internet-Draft Trusted Transitive Introduction Model October 2003
Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
3. TTI Entities . . . . . . . . . . . . . . . . . . . . . . . . 5
4. TTI transports . . . . . . . . . . . . . . . . . . . . . . . 8
4.1 TTI over HTTP . . . . . . . . . . . . . . . . . . . . . . . 8
4.1.1 TTI over HTTP Welcome . . . . . . . . . . . . . . . . . . . 8
4.1.2 TTI over HTTP Introduction . . . . . . . . . . . . . . . . . 9
4.1.3 TTI over HTTP Completion . . . . . . . . . . . . . . . . . . 10
5. Where is the User in all this? . . . . . . . . . . . . . . . 11
6. Existing Infrastructures . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . 13
References . . . . . . . . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . 16
Pritikin Expires April 16, 2004 [Page 2]
Internet-Draft Trusted Transitive Introduction Model October 2003
1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Pritikin Expires April 16, 2004 [Page 3]
Internet-Draft Trusted Transitive Introduction Model October 2003
2. Introduction
When adding a device into a security domain the first task is to
exchange cryptographic and configuration information between the
security domain and the device. This process we term an Introduction.
Prior to a successful Introduction there are no security associations
between the device and the target security domain. After an
introduction there is enough of a security association for the device
and the security domain to communicate securely at least once. It is
our expectation that this initial secure communication will be used
to enroll and receive longer term credentials as appropriate.
Classically this enrollment process has been handled by the
'out-of-band' communication of cryptographic and configuration
information. Although this works well in the simple case, and is
common practice, complex authentication and authorization
infrastructures often require complex cryptographic keys and
configurations to be exchanged. For example PKI deployments often
involve involve manual verification of RSA public key material
hashes, complex configuration tasks, and/or specific authorization
tasks that must occur in a particular sequence. This process is a
burden on the administrator and complicates deployment scenarios
tremendously. The intuitive nature of the introduction has been lost
in the details of the complex cryptographic and configuration
material.
Here we describe the introduction process as a communication protocol
that leverages transitive trust across a third party, the introducer,
to complete the 'out-of-band' exchange of data. This maintains the
intuitive nature of an introduction while allowing complex
configuration and cryptographic material to be exchanged, thus
allowing simple enrollment procedures to be leveraged to support more
complex enrollments. This process is Trusted Transitive Introduction
(TTI).
The basic concepts follow from a real life introduction:
"Alice, meet Bob. Bob, this is Alice."
The third party in this exchange is the Introducer, known by both
Alice and Bob.
Pritikin Expires April 16, 2004 [Page 4]
Internet-Draft Trusted Transitive Introduction Model October 2003
3. TTI Entities
An introduction involves at least three logical entities. For example
the new device, the security domain, and the 'out-of-band' system
administrator(s). TTI defines these entities as,
(P) Petitioner (e.g. a new VPN client device).
(I) Introducer (e.g. a user at their browser).
(R) Registrar (e.g. the VPN network hub).
Although described here as a discrete entities an instantiation of
the TTI model may include situations where the logical entities are
themselves complex systems. For example,
(P) Petitioner (e.g. a product).
(I) Introducer (e.g. a product vendor).
(R) Registrar (e.g. a service provider).
An important and likely component of at least one of these systems is
the existing Authentication and Authorization (AA) the Petitioner is
expecting to enroll with. In some instantiations of the TTI model all
entities may include complex AA infrastructures. For clarity these
are occasionally discussed as distinct from the TTI entities
themselves.
(A) Authority (e.g. a radius server, CA, or other)
Graphically this looks like:
+------------+ +-------------------+
+------------+ | Petitioner | | P's Authority (A) |
| |<------>| (P) |--| (AAA, CA or other)|
| | | | +-------------------+
| | +------------+
| |
| Introducer | (there is no initial trust relationship
| (I) | between P and R)
| | +------------+
| | | Registrar | +-------------------+
| |<------>| (R) |--| R's Authority (A) |
+------------+ | | | (AAA, CA or other)|
+------------+ +-------------------+
Figure 1
Pritikin Expires April 16, 2004 [Page 5]
Internet-Draft Trusted Transitive Introduction Model October 2003
The Petitioner is the entity obtaining new credentials after the TTI
exchange. The Registrar is the entity issuing the new credentials.
One possibility is that an entity may be both a Registrar and a
Petitioner. The TTI protocols must consider such situations.
The specifics of the relationship between each entity and its own
Authority are out of the scope of the TTI model. The existence of
either a Petition's or a Registrar's Authority does not effect the
sequence of communication events, although it may effect the
enrollment and configuration protocols that depend on TTI for their
'out-of-band' data exchange and it may effect the configuration
information exchanged by TTI.
The Introducer must authenticate to the Petitioner and Registrar
using the authentication and authorization mechanisms currently in
place. This recursive use of prior associations is the strength of
TTI. It allows complex authentication and authorization mechanisms to
be built from relatively simple default mechanisms. It is important
to note that current enrollment scenarios also depend on existing
authentication mechanisms. For example when a certificate request
hash for PKI enrollment is transfered 'out-of-band' it is obtained,
sent, and checked using the existing authentication/authorization
mechanisms.
After introduction is complete the Petitioner and Registrar have
exchanged key and configuration material and can complete an
authenticated exchange with each other. Due to the transitive and
possibly manual nature of the introduction process TTI is not
envisioned as as a full featured policy, configuration distribution,
or enrollment mechanism. Instead peers are expected to conclude the
introduction with an appropriate 'in band' enrollment mechanism. The
specifics of this exchange are out of scope of this document.
The peer entities now communicate directly to enroll:
+------------+ +-------------------+
+------------+ | Petitioner | | P's Authority (A) |
| | | (P) |--| (AAA, CA or other)|
| | | | +-------------------+
| | +------------+
| | |
| Introducer | | (Now can run enrollment protocol)
| (I) | |
| | +------------+
| (No longer | | Registrar | +-------------------+
| involved) | | (R) |--| R's Authority (A) |
+------------+ | | | (AAA, CA or other)|
+------------+ +-------------------+
Pritikin Expires April 16, 2004 [Page 6]
Internet-Draft Trusted Transitive Introduction Model October 2003
Figure 2
Pritikin Expires April 16, 2004 [Page 7]
Internet-Draft Trusted Transitive Introduction Model October 2003
4. TTI transports
TTI should be transport independent. It is envisioned that the
different TTI protocol instantiations of the TTI model may run on a
variety of systems and protocols and should not be locked into a
particular transport mechanism.
Some areas that should be considered include:
IP Layer 2 (e.g. over an 802.1x EAP or EAP/TLS exchange)
IP Layer 3 (e.g. over an HTTP web/user based exchange)
Storage medium (e.g. an introduction should be 'distributable'
over a cd, smartcard, or other physical transport device)
4.1 TTI over HTTP
The use of HTTP mechanisms for the TTI transport allows a common HTML
web browser to be used as the Introducer in a TTI exchange. This
provides support for an extremely important and useful example; where
a user with their web browser initiates and completes the intuitive
introduction of two network entities without having to know or
understand the details of an introduction or enrollment.
This document provides a brief overview of what this would look like
to help explain the TTI model. The specific details of the TTI over
HTTP redirections, encoding of cryptographic information,
configuration information and resulting enrollment are out of scope
of this document. For a simple implementation of TTI over HTTP the
TTI entities are,
1. Petitioner - the device or product running a simple HTTP[S]
server used by the TTI exchange.
2. Introducer - a user at their web browser. This may be on the same
system as the Petitioner or it may be on a different system.
3. Registrar - the service or provider running a simple HTTP[S]
server used by the TTI exchange.
There are three phases to TTI over HTTP, each of these include an
HTTP GET or an HTTP POST of data as described in the following
sections.
4.1.1 TTI over HTTP Welcome
Pritikin Expires April 16, 2004 [Page 8]
Internet-Draft Trusted Transitive Introduction Model October 2003
Welcome. The user initiates their web browser (Introducer) to do an
HTTP[S] GET from the Petitioner. This requires that the user, or the
users web browser, log into the Petitioner according to the
authentication and authorization infrastructure currently in place.
The web page received includes 'hidden' input elements with
cryptographic information that identifies the Petitioner device and
and input field for the Registrar's HTTP address. The HTML input type
'hidden' avoids displaying complex cryptographic information and
confusing the naive user, it is not a security mechanism. The user
inputs the Registrar's HTTP[S] URL and clicks the 'next' button.
The Introducer does an HTTP GET from Petitioner:
+------------+ +-------------------+
+------------+ | Petitioner | | P's Authority (A) |
| |<-------| (P) |--| (AAA, CA or other)|
| | | | +-------------------+
| | +------------+
| |
| Introducer |
| (I) |
| Web | +------------+
| Browser | | Registrar | +-------------------+
| | | (R) |--| R's Authority (A) |
+------------+ | | | (AAA, CA or other)|
+------------+ +-------------------+
Figure 3
4.1.2 TTI over HTTP Introduction
Introduction. The Petitioner's cryptographic information is HTTP[S]
POSTed to the Registrar's server. This requires that the user, or the
user's web browser, log into the Registrar's server. As a result of
the HTTP[S] POST, and authorization of the Introducer, the resulting
web page includes, as hidden attributes, the cryptographic and
configuration information for the Petitioner device. The user clicks
the 'next' button.
Introducer does an HTTP POST to the Registrar:
+------------+ +-------------------+
+------------+ | Petitioner | | P's Authority (A) |
| | | (P) |--| (AAA, CA or other)|
| | | | +-------------------+
| | +------------+
| |
Pritikin Expires April 16, 2004 [Page 9]
Internet-Draft Trusted Transitive Introduction Model October 2003
| Introducer |
| (I) |
| Web | +------------+
| Browser |------->| Registrar | +-------------------+
| |<-------| (R) |--| R's Authority (A) |
+------------+ | | | (AAA, CA or other)|
+------------+ +-------------------+
(Note that an HTML page is recieved after doing an HTTP POST)
Figure 4
4.1.3 TTI over HTTP Completion
Completion. The cryptographic and configuration information from the
registrar is HTTP[S] POSTed to the Petitioner.
Introducer does an HTTP POST back to the Petitioner:
+------------+ +-------------------+
+------------+ | Petitioner | | P's Authority (A) |
| |------->| (P) |--| (AAA, CA or other)|
| | | | +-------------------+
| | +------------+
| |
| Introducer |
| (I) |
| Web | +------------+
| Browser | | Registrar | +-------------------+
| | | (R) |--| R's Authority (A) |
+------------+ | | | (AAA, CA or other)|
+------------+ +-------------------+
Figure 5
At this point the Petitioner and the Registrar have exchanged the
appropriate information to engage in a secure enrollment protocol as
in Figure 2.
Pritikin Expires April 16, 2004 [Page 10]
Internet-Draft Trusted Transitive Introduction Model October 2003
5. Where is the User in all this?
The user drives an introduction by initiating events in an intuitive
order. What they do not do is manually exchange or process data. The
software tools they are using perform the actual work of the data
exchange.
In the above TTI over HTTP scenario the user drives the introduction
process using a generic web browser. The user, at their web browser,
is involved in every aspect of the TTI exchange. They are playing the
role of the Introducer with only the very thin layer of their web
browser to 'protect' them from being exposed to the raw cryptographic
and configuration material. In the example presented they could
examine this material by viewing the source of the HTML pages. Other
uses of the TTI model can provide a thicker layer on top of the user
experience. For example, custom introduction software, or tools,
might be used.
The user driving the introduction might not be at the Introducer at
all. There is nothing in the TTI model to preclude a Petitioner from
requesting an introduction from an Introducer. For example consider a
user on their corporate laptop as the Petitioner. The user might
initiate an introduction to one corporate resource by contacting the
corporate Introducer resource. The Introducer, after authenticating
and authorizing the user and/or laptop, proceeds to introduce the
user's laptop to the resource. The laptop enrolls with the ultimate
resource. Note that this is a transitive operation, the Introducer no
longer needs to be involved during subsequent communications between
the laptop and the resource.
A common scenario may involve the user working from the Registrar to
establish a security association with a new entity. From the user's
perspective this should be the same as initiating an introduction
from the Petitioner, with the only distinction being that data
traffic (which AA infrastructure will be used).
Instantiations of the TTI model should be careful to consider the
possibilities that the initiating user may be initiating the process
through any one of the TTI entities.
Pritikin Expires April 16, 2004 [Page 11]
Internet-Draft Trusted Transitive Introduction Model October 2003
6. Existing Infrastructures
The TTI model depends on an existing security association between the
Introducer and the Petitioner (and between the Introducer and the
Registrar). These security associations may have been established
with the help of a prior TTI exchange but some will have come about
using one of the common mechanisms of,
Imprinting (e.g. a new device with no password or authentication
mechanism accepts the first entity to contact it as being an
administrator).
Assigned password (e.g. the most intuitive and simple of the
'out-of-band' mechanisms where an administrator selects an initial
password and provides this to the new user. This includes one time
password scenarios).
Pre-provisioning (e.g. a more complex version of the 'assigned
password' mechanism where an administrator pre-configures a device
while it is in a 'safe' location. This is an expensive solution
and it is usually used only when complex configurations and/or
complex keys are being used)
Self-introduction. (e.g. when a user generates a new account with
minimal authorization steps involved. We see this at free email
providers. "Hi Alice, my name is Bob".)
These mechanisms are in common use because, by reducing the
dependency on an out-of-band data exchange, they provide for
simplified deployment scenarios (security is of course compromised by
this approach). The TTI model allows us to limit their use to one
time enrollment. After enrollment more secure authentication and
authorization infrastructures can be used.
Pritikin Expires April 16, 2004 [Page 12]
Internet-Draft Trusted Transitive Introduction Model October 2003
7. Security Considerations
This document discusses models for deploying security
infrastructures. Any resulting TTI protocols will need to carefully
consider how the protocol elements will be protected.
The TTI model assumes that cryptographic material can be produced on
the Petitioner and Registrar, passed over third parties (the
Introducer) and later be be used to secure an enrollment between the
Petitioner and Registrar. It is expected that asymmetric key material
should be used for this portion of the exchange.
This document develops the concept of the Introducer, a new construct
in the normally bi-entity discussions of secure enrollment. This
serves as an alternative to the historically loosely defined
'out-of-band' security measures. The security implications of a
transitive relationship still apply. A compromised introducer could
act to enable enrollment of unexpected elements into a secure domain
in much the same way that a compromised 'out-of-band' mechanism can
be used to subvert a classic enrollment scenario. Care must be taken
not to overlook this when designing the TTI protocols.
The transitive nature of TTI (and any 'out-of-band' data exchange)
means that the Registrar does not know how secure the communication
channel between the Petitioner and the Introducer is.
An example of this is a Petitioner device, a wireless camera, that is
being deployed over a wireless connection. Assuming the camera was
purchased as a consumer product it might supports something like the
Imprinting model above, the first consumer to activate and connect to
it can establish an initial security association with the device.
Possibly by configuring the administrator password on the device (A
more complex scenario may involve an initial introduction to their
home network).
When the consumer then Introduces the device to a service, such as a
video conferencing provider, the provider may be concerned that such
a wireless imprinting provides too great of an attack risk. In such a
situation the Registrar may require that the camera assert an
identity (e.g. a manufacturer ID certificate) which can be verified
by having the Introducer confirm some characteristic of the device
(e.g. inputing a serial number off the device).
In such scenarios the TTI protocol should provide a clear mechanism
by which the Registrar can coach the Introducer through the
appropriate sequence of events without undue confusion. The above
examples of TTI over HTTP provides for this by leveraging a
manufacturer PKI (the manufacturer ID certificate). Similar care
Pritikin Expires April 16, 2004 [Page 13]
Internet-Draft Trusted Transitive Introduction Model October 2003
should be taken to consider when the process is being initiated by
automated deployment systems, or when the user is at the Petitioner
device itself.
Pritikin Expires April 16, 2004 [Page 14]
Internet-Draft Trusted Transitive Introduction Model October 2003
References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Author's Address
Max Pritikin
Cisco Systems, Inc.
EMail: pritikin@cisco.com
Pritikin Expires April 16, 2004 [Page 15]
Internet-Draft Trusted Transitive Introduction Model October 2003
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this
document. For more information consult the online list of claimed
rights.
Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assignees.
Pritikin Expires April 16, 2004 [Page 16]
Internet-Draft Trusted Transitive Introduction Model October 2003
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Pritikin Expires April 16, 2004 [Page 17]
| PAFTECH AB 2003-2026 | 2026-04-21 19:41:39 |