PT-TLS: A TCP-based Posture Transport (PT) Protocol
draft-ietf-nea-pt-tls-04
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Network Working Group P. Sangster
Internet Draft Symantec Corporation
Intended status: Proposed Standard N. Cam-Winget
Expires: October 2012 J. Salowey
Cisco Systems
May 9, 2012
PT-TLS: A TCP-based Posture Transport (PT) Protocol
draft-ietf-nea-pt-tls-04.txt
Abstract
This document specifies PT-TLS, a TCP-based Posture Transport (PT)
protocol. The PT-TLS protocol carries the Network Endpoint
Assessment (NEA) message exchange under the protection of a Transport
Layer Security (TLS) secured tunnel.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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-
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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 September 9, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction...................................................3
1.1. Prerequisites.............................................4
1.2. Message Diagram Conventions...............................4
1.3. Conventions used in this document.........................4
1.4. Compatibility with other Specifications...................4
2. Design Considerations..........................................5
2.1. Benefits of TCP/IP Connectivity...........................5
2.2. Leveraging Proven TLS Security............................6
2.3. TLV-Oriented Based Message Encapsulation..................6
2.4. No Change to Base TLS Protocol............................6
3. PT-TLS Protocol................................................7
3.1. Initiating a PT-TLS Session...............................8
3.1.1. Issues with Server Initiated PT-TLS Sessions.........8
3.1.2. Establish or Re-Use Existing PT-TLS Session..........9
3.2. TCP Port Usage............................................9
3.3. Preventing MITM Attacks with Channel Bindings.............9
3.4. PT-TLS Message Flow......................................10
3.4.1. Assessment Triggers.................................10
3.4.2. PT-TLS Message Exchange Phases......................10
3.4.2.1. TLS Setup Phase................................11
3.4.2.2. PT-TLS Negotiation Phase.......................12
3.4.2.3. PT-TLS Data Transport Phase....................13
3.4.3. TLS Requirements....................................14
3.5. PT-TLS Message Format....................................14
3.6. IETF Standard PT-TLS Message Types.......................17
3.7. PT-TLS Version Negotiation...............................19
3.7.1. Version Request Message.............................20
3.7.2. Version Response Message............................21
3.8. Client Authentication using SASL.........................21
3.8.1. SASL Entity Authentication Requirements.............22
3.8.2. SASL in PT-TLS Overview.............................23
3.8.3. SASL Authentication Flow............................23
3.8.4. Aborting SASL Authentication........................24
3.8.5. Linkages to SASL Framework..........................24
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3.8.5.1. SASL Service Name..............................24
3.8.5.2. SASL Authorization Identity....................24
3.8.5.3. SASL Security Layer............................24
3.8.5.4. Multiple Authentications.......................24
3.8.6. SASL Channel Bindings...............................24
3.8.7. SASL Mechanisms.....................................25
3.8.8. SASL Mechanism Selection............................25
3.8.9. SASL Authentication Data............................26
3.8.10. SASL Result........................................27
3.9. Error Message............................................28
4. Security Considerations.......................................31
4.1. Trust Relationships......................................32
4.1.1. Posture Transport Client............................32
4.1.2. Posture Transport Server............................33
4.2. Security Threats and Countermeasures.....................34
4.2.1. Message Theft.......................................34
4.2.2. Message Fabrication.................................35
4.2.3. Message Modification................................35
4.2.4. Denial of Service...................................36
4.2.5. NEA Asokan Attacks..................................36
4.2.6. Trust Anchors.......................................37
5. Privacy Considerations........................................37
6. IANA Considerations...........................................38
6.1. Designated Expert Guidelines.............................39
6.2. Registry for PT-TLS Message Types........................39
6.3. Registry for PT-TLS Error Codes..........................40
7. Acknowledgments...............................................41
8. References....................................................41
8.1. Normative References.....................................41
8.2. Informative References...................................42
1. Introduction
This document specifies PT-TLS, a TCP-based Posture Transport (PT)
protocol protected by a TLS channel.
NEA protocols are intended to be used for pre-admission assessment of
endpoints joining the network and to assess endpoints already present
on the network. In order to support both usage models, two different
types (or bindings) of PT protocols are necessary to operate before
and after the endpoint has an assigned IP address and other network
layer information. This specification focuses on the PT protocol
used to assess endpoints already present on the network and thus is
able to use TCP/IP based transport protocols. NEA has defined
another protocol called PT-EAP [PT-EAP] to address assessment prior
to the endpoint having an assigned IP address.
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The PT protocol in the NEA architecture [RFC5209] is responsible for
transporting PB-TNC [RFC5793] batches (often containing PA-TNC
[RFC5792] attributes) over the network between the Posture Transport
Client component of the NEA Client and the Posture Transport Server
component of the NEA Server. The PT protocol also offers strong
security protections to ensure the exchanged messages are protected
from a variety of threats from hostile intermediaries.
1.1. Prerequisites
This document does not define an architecture or reference model.
Instead, it defines one binding of the PT protocol that works within
the reference model described in the NEA Overview and Requirements
specification. The reader is assumed to be thoroughly familiar with
the NEA Overview and Requirements specification. The NEA working
group compared the functionality described in this specification
against the requirements in the NEA Overview and Requirements
specification and found that each applicable requirement was
addressed.
1.2. Message Diagram Conventions
This specification defines the syntax of PT-TLS messages using
diagrams. Each diagram depicts the format and size of each field in
bits. Implementations MUST send the bits in each diagram as they are
shown, traversing the diagram from top to bottom and then from left
to right within each line (which represents a 32-bit quantity).
Multi-byte fields representing numeric values must be sent in network
(big endian) byte order.
Descriptions of bit field (e.g. flag) values are described referring
to the position of the bit within the field. These bit positions are
numbered from the most significant bit through the least significant
bit so a one octet field with only bit 0 set has the value 0x80.
1.3. Conventions used in this document
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 RFC 2119 [RFC2119].
1.4. Compatibility with other Specifications
One of the goals of the NEA effort is to deliver a single set of
endpoint assessment standards, agreed upon by all parties. For this
reason, the Trusted Computing Group (TCG) will be replacing its
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existing posture transport protocols with new versions that are
equivalent to and interoperable with the NEA specifications.
2. Design Considerations
This section discusses some of the key design considerations for the
PT protocol. This document specifies the PT binding for use when
performing an assessment or reassessment after the endpoint has been
admitted to the network and is capable of using TCP/IP to communicate
with the NEA Server. If the endpoint does not yet have TCP/IP layer
access to the NEA Server (and vice versa), the endpoint should use
the PT-EAP (Posture Transport (PT) Protocol for EAP Tunnel Methods)
protocol when performing an assessment.
Because the endpoint has TCP/IP access to the NEA Server (potentially
on a restricted portion of the network), the NEA Client and NEA
Server have the ability to establish (or re-use) a reliable TCP/IP
connection in order to perform the assessment. The TCP/IP connection
enables the assessment to occur over a relatively high performance,
reliable channel capable of supporting multiple roundtrip message
exchanges in full duplex manner. These connection properties are
very different from what is available when the endpoint is initially
joining the network (e.g. during an 802.1X based assessment),
therefore the design described in this specification follows a
different path to maximize the benefits of the underlying TCP/IP
connection.
2.1. Benefits of TCP/IP Connectivity
The PT protocol is typically able to offer to the NEA Client and NEA
Server significantly higher quality of service and flexibility of
operation than PT-EAP (Posture Transport (PT) Protocol for EAP Tunnel
Methods). However, there may be some added risks when the endpoint
is on the network prior to its initial assessment (if no admission
time assessment had been performed). Because of these risks, the
combined use of an EAP-based assessment during admission followed by
reassessment using TCP/IP may be appropriate in some environments.
Some of the benefits to having a TCP/IP based transport during an
assessment include:
o Full Duplex connectivity - used to support asynchronous initiation
of posture exchanges within a single TLS connection (e.g.
triggered by alerts of posture or policy changes)
o High Bandwidth - potentially much higher bandwidth than other
transports (e.g. EAP) allowing more in-band data (e.g.
remediation, verbose posture information)
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o Large Messages - ability to send very large PA messages without
directly fragmenting them (underlying carrier protocol may
introduce fragmentation)
o Bi-directional - NEA Client and NEA Server can initiate an
assessment or reassessment
o Multiple Roundtrips - NEA Client and NEA Server can exchange
numerous messages without fear of infrastructure timeouts.
However, the entire exchange should be kept as brief as possible
if the user has to wait for its completion.
2.2. Leveraging Proven TLS Security
All PT protocol bindings must be capable of providing strong
authentication, integrity and confidentiality protection for the PB-
TNC batches. Rather than define a new protocol over TCP/IP to
provide adequate protection, this specification requires the use of
Transport Layer Security [RFC5246] to secure the connection. TLS was
selected because it's a widely deployed protocol with parallel
protections to a number of the EAP tunnel methods, and it meets all
of the security requirements.
2.3. TLV-Oriented Based Message Encapsulation
The design of the PT-TLS protocol is based upon the use of type-
length-value (TLV) oriented protocol message that identifies the type
of message, the message's length and a potentially variable length
payload value. The use of a TLV orientated encoding was chosen to
match the Internet standard PA-TNC and PB-TNC protocols. Because the
PA-TNC, PB-TNC and PT-TLS protocols are typically implemented inside
the same process space, this allows a common set of message parsing
code to be used. Similarly creation of debugging tools is simplified
by the common encoding methodologies. TLV-based encoding was used in
each of the NEA protocols in part because it enables a very space
efficient representation on the network and is simpler to parse than
some other encodings to benefit lower powered (or battery
constrained) devices.
2.4. No Change to Base TLS Protocol
During the design of the PT-TLS protocol, several approaches were
considered with different costs and benefits. Several considered
approaches involved integrating the PT protocol into the TLS
handshake protocol. Because the PT protocol requires the underlying
TLS carrier to provide security protections, the PT protocol couldn't
operate before the cipher suites were negotiated and in use. One
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option was to integrate into the TLS handshake protocol after the
ChangeCipherSpec phase allowing the PT message to be protected. The
benefit of this approach is that the assessment protocol could
operate below the application protocols allowing for easier
integration into applications. However, making this change would
require some extensions to the TLS handshake protocol standards and
existing widely deployed TLS implementations, so it wasn't clear that
the cost was warranted, particularly because the application
independence can also be offered by a shim library between the
application and TLS library that provides the PT protocol
encapsulation/decapsulation.
The other general approach considered was to have PT-TLS layer on top
of TLS as an application protocol (using the standard
application_data ContentType). This has the advantage that existing
TLS software could be used. However, the PB-TNC traffic would need
to be encapsulated/decapsulated by a new PT-TLS protocol layer before
being passed to the TLS library. This didn't seem like a significant
issue as PB-TNC is architected to layer on PT anyway.
After considering the different options, it was determined that
layering the PT protocol on top of the TLS protocol without requiring
current TLS protocol implementations to change met all the
requirements and offered the best path toward rapid adoption and
deployment. Therefore the following sections describe a PT protocol
that is carried on top of TLS.
3. PT-TLS Protocol
This section specifies the PT-TLS protocol, a Posture Transport (PT)
protocol carried by the Transport Layer Security (TLS) protocol over
a TCP/IP network. As shown in Figure 1, this protocol runs directly
on top of TLS as an application. This means PT-TLS is encapsulated
within the TLS Record Layer protocol using the standard ContentType
for applications (application_data).
+---------------------------------------------------------------+
| TLV Encapsulation of PB-PA message |
+---------------------------------------------------------------+
| TLS |
+---------------------------------------------------------------+
| TCP |
+---------------------------------------------------------------+
Figure 1: PT-TLS Layering Model
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3.1. Initiating a PT-TLS Session
The PT-TLS protocol may be initiated by a Posture Transport Client or
a Posture Transport Server. This flexibility supports different use
cases. For example, a Posture Transport Client that wishes to
trigger a NEA assessment to determine whether its security posture is
good can start up a PT-TLS session and request a posture assessment.
On the other hand, when an endpoint requests access to a protected
network or resource, a Posture Transport Server can start up a PT-TLS
session and perform a posture assessment before deciding whether to
grant access.
The party that initiates a PT-TLS session is known as the "PT-TLS
Initiator". The other party in the session (which receives the
request to open a PT-TLS session) is known as the "PT-TLS session
responder".
3.1.1. Issues with Server Initiated PT-TLS Sessions
In order for a NEA Server to establish a PT-TLS session, the NEA
Client needs to be listening for a connection request on a TCP port
known by the NEA Server. In many deployments, the security policies
(e.g. firewall software) of an endpoint are designed to minimize the
number of open inbound TCP/UDP ports that are available to the
network to reduce the potential attack footprint. This is one issue
that makes it difficult for a NEA Server to initiate a PT-TLS
session.
Another issue with this scenario involves X.509 certificates. When
the NEA Server creates a TLS session to the NEA Client, the NEA
Client is effectively acting as the TLS server during the TLS
protocol exchange. This means the NEA Client would typically need to
possess an X.509 certificate to protect the initial portion of the
TLS handshake. In situations where the NEA Server initiates the
creation of the TLS session, both the NEA Client and NEA Server MUST
possess X.509 certificates to fully authenticate the session. For
many deployments, provisioning X.509 certificates to all NEA Clients
has scalability and cost issues; therefore, it is recommended that
the NEA Client not listen for connection requests from the NEA Server
but instead establish and maintain a TLS session to the NEA Server
proactively, so either party can initiate an assessment using the
preexisting TLS session as required.
In most cases the traditional methods of server certificate ID
validation will not apply when the NEA Server initiates the
connection. In this case, the NEA Client and Server need to follow
the certificate path validation rules in RFC 5280 [RFC5280]. In
addition, each side needs to be able to authorize its peer based upon
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matching Subject and SubjectAltName fields for certificates issued by
a particular trust root.
Therefore, NEA Clients SHOULD be capable of establishing and holding
open a TLS session with the NEA Server immediately after obtaining
network access. A NEA Client MAY listen for connection requests from
the NEA Server and establish a new PT-TLS session when one does not
already exist. Having an existing PT-TLS session allows either party
to initiate an assessment without requiring the NEA Client to be
listening for new connection requests. In order to keep the TLS
session alive, the NEA Client and NEA Server SHOULD be capable of
supporting the TLS heartbeat protocol [RFC6520].
3.1.2. Establish or Re-Use Existing PT-TLS Session
A single PT-TLS session can support multiple NEA assessments, which
can be started by either party (the PT-TLS Initiator or the PT-TLS
Responder). The party that starts a NEA assessment is known as the
"assessment initiator" and the other party is known as the
"assessment responder".
If the assessment initiator already has a PT-TLS session to the
assessment responder, the initiator can re-use this session;
otherwise, a new PT-TLS session must be established.
3.2. TCP Port Usage
In order for a PT-TLS Initiator to establish a TCP connection to a
PT-TLS Responder, the initiator needs to know the TCP port number on
which the responder is listening for assessment requests. Therefore,
this specification requests the IANA reserve a TCP port number for
use with the PT-TLS protocol upon publication of this specification
as an Internet standard RFC.
3.3. Preventing MITM Attacks with Channel Bindings
As described in the NEA Asokan Attack Analysis [ASOKAN], a
sophisticated MITM attack can be mounted against NEA systems. The
attacker forwards PA-TNC messages from a healthy machine through an
unhealthy one so that the unhealthy machine can gain network access.
Because there are easier attacks on NEA systems, like having the
unhealthy machine lie about its configuration, this attack is
generally only mounted against machines with an External Measurement
Agent (EMA). The EMA is a separate entity, difficult to compromise,
which measures and attests to the configuration of the endpoint.
To protect against NEA Asokan attacks, the Posture Broker Client on
an EMA-equipped endpoint should pass the tls-unique channel binding
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[RFC5929] for PT-TLS's underlying TLS session to the EMA. This value
can then be included in the EMA's attestation and the Posture
Validator responsible for communicating with the EMA may then confirm
that the value matches the tls-unique channel binding for its end of
the connection. If the values match, the posture sent by the EMA and
NEA Client is from the same endpoint as the client side of the TLS
connection (since the endpoint knows the tls-unique value), so no
man-in-the-middle is forwarding posture. If they differ, an attack
has been detected. The Posture Validator MUST fail its verification
of the endpoint if an attack has been detected.
3.4. PT-TLS Message Flow
This section discusses the general flow of messages between the NEA
Client's Posture Transport Client and the NEA Server's Posture
Transport Server in order to perform NEA assessments using the PT-TLS
protocol.
3.4.1. Assessment Triggers
Initially, the NEA Client or NEA Server will decide that an
assessment is needed. What stimulates the decision to perform an
assessment is outside the scope of this specification, but some
examples include:
o NEA Server becoming aware of suspicious behavior on an endpoint
o NEA Server receiving new policies requiring immediate action
o NEA Client noticing a change in local security posture
o NEA Client wishing to access a protected network or resource
Because either the NEA Client or NEA Server can trigger the
establishment of the TLS session and initiate the assessment, this
document will use the terms "assessment initiator" and the
"assessment responder". This nomenclature allows either NEA
component to fill either of the PT-TLS roles.
3.4.2. PT-TLS Message Exchange Phases
The PT-TLS message exchange occurs in three distinct phases:
o TLS Setup (including TLS Handshake protocol)
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o PT-TLS Negotiation
o PT-TLS Data Transport
The TLS Setup phase is responsible for the establishment of the TCP
connection and the TLS protections for the PT-TLS messages. The TLS
Setup phase normally starts with the establishment of a TCP
connection between the Posture Transport Client and Posture Transport
Server. The new connection triggers the TLS Handshake protocol to
establish the cryptographic protections for the TLS session. Once
the TLS setup phase has completed, the TLS session MUST NOT be
renegotiated. TLS session renegotiation MAY be used before the TLS
Setup phase ends and the PT-TLS Negotiation phase begins. This phase
also enables the establishment of the tls-unique shared secret. The
tls-unique shared secret can later be used by PA to protect against
some forms of man-in-the-middle attack.
The PT-TLS Negotiation phase is only performed at the start of the
first assessment on a TLS session. During this phase, the NEA Client
and NEA Server discover each other's PT-TLS capabilities and
establish a context that will apply to all future PT-TLS messages
sent over the TLS session. The PT-TLS Negotiation phase MUST NOT be
repeated after the session has entered the Data Transport phase. NEA
assessment messages (PB-TNC batches) MUST NOT be sent by the NEA
Client or NEA Server prior to the completion of the PT-TLS
Negotiation phase to ensure that the security protections for the
session are properly established and applied to the NEA assessment
messages.
Finally the Data Transport phase allows the NEA Client and NEA Server
to exchange PT messages under the protection of the TLS session
consistent with the capabilities established in earlier phases. The
exchanged messages can be a PT-TLS protected NEA assessment as
described in this specification or other vendor-defined PT-TLS
exchanged messages.
3.4.2.1. TLS Setup Phase
After a new TCP connection is established between the Posture
Transport Client and Posture Transport Server, a standard TLS
exchange is performed to negotiate a common security context for
protecting subsequent communications. As discussed in section 3.4.1,
the TCP connection establishment and/or the TLS handshake protocol
could be initiated by either the NEA Client or NEA Server. The most
common situation would be for the assessment initiator to trigger the
creation of the TCP connection and TLS handshake, so an assessment
could begin when no session already exists. When the NEA Server has
initiated the TLS Setup, the NEA Server is acting as a TLS client and
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the NEA Client is the TLS server (accepting the inbound TLS session
request). The expected normal case is that the NEA Client initiates
this phase, so that the NEA Server is acting as the TLS server and
therefore the bootstrapping of the security of the TLS session is
using the NEA Server's certificate. Having the NEA Client initiate
the TLS session avoids the need for the NEA Client to also possess a
certificate.
During the TLS Setup phase of PT-TLS, the PT-TLS Initiator contacts
the listening port of the PT-TLS Responder and performs a TLS
handshake. The PT-TLS Responder MUST possess a trustworthy X.509
certificate used to authenticate to the TLS initiator and used to
bootstrap the security protections of the TLS session. The PT-TLS
Initiator MAY also use an X.509 certificate to authenticate to the
PT-TLS Responder providing for a bi-directional authentication of the
PT-TLS session. The NEA client MUST provide certificate validation
according to the rules in RFC 5280 when evaluating the server
certificate. In addition the NEA client MUST follow the
recommendations in RFC 6125 [RFC6125] when validating the NEA server
domain name against the contents of the server certificate. Details
for the reverse direction are given in section 3.1.
Due to deployment issues with issuing and distributing certificates
to a potentially large number of NEA Clients, this specification
allows the NEA Client to be authenticated during the PT-TLS
Negotiation phase using other more cost effective methods. At the
conclusion of a successful initial TLS Setup phase, the NEA Client
and NEA Server have a protected session to exchange messages. This
allows the protocol to transition to the PT-TLS Negotiation phase.
3.4.2.2. PT-TLS Negotiation Phase
Once a TLS session has been established between Posture Transport
Client and Posture Transport Server, the PT-TLS Initiator sends a
Version Request Message indicating its supported PT-TLS protocol
version range. Next, the PT-TLS Responder sends a Version Response
Message which selects a protocol version from within the range
offered. The PT-TLS Responder SHOULD select the preferred version
offered if supported; otherwise, the highest version that the
responder is able to support from the received Version Request
Message. If the PT-TLS Responder is unable or unwilling to support
any of the versions included in the Version Request Message, the
responder SHOULD send a Version Not Supported error message.
If no client side authentication occurred during the TLS Setup phase,
the Posture Transport Server can authenticate the client using PT-TLS
client authentication messages as described in section 3.8. The
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NEA Server initiates the client authentication and indicates when the
authentication is complete.
When the NEA Client receives the SASL [RFC4422] Mechanisms list, the
NEA Client responds with a SASL Mechanism Selection TLV indicating
the method of authentication to be used. Upon selecting an
appropriate SASL mechanism, the NEA Client and Server exchange SASL
mechanism specific messages in order to authenticate the NEA Client.
When the client authentication successfully completes and no
additional authentications are required (as indicated by the NEA
Server sending an empty SASL Mechanisms list), the PT-TLS session
transitions into the Data Transport phase, where it will remain for
the duration of the session. Note that the NEA Server could choose
to not authenticate the client (indicated by only sending an empty
SASL Mechanisms list) or to continue performing a posture assessment
even if the authentication did not complete successfully.
3.4.2.3. PT-TLS Data Transport Phase
Once a PT-TLS session is available to carry NEA assessments, PT-TLS
allows either side of the connection to send the first PB-TNC batch.
The PB-TNC standard prescribes whether the Posture Broker Client or
Posture Broker Server starts the assessment. The assessment
initiator first envelopes the PB-TNC batch in a PT-TLS message, then
assigns a message identifier to the message and finally transmits it
over the session. The assessment responder validates the PT-TLS
message and delivers the encapsulated PB-TNC batch to its upstream
component (Posture Broker Client or Server).
Most PT-TLS messages contain PB-TNC batches that house PA-TNC
requests for posture information or a response containing the
requested posture information. The Posture Transport Client and
Posture Transport Server may also exchange messages between them,
such as a PT-TLS Error Message indicating that a problem occurred
processing a message. During an assessment, the Posture Transport
Client and Server merely encapsulate and exchange the PB-TNC batches
and are unaware of the state of the assessment.
The PT-TLS protocol allows either party to send a PT-TLS message at
any time, reflecting the full duplex nature of the underlying TLS
session. For example, an assessment initiator may send several PT-
TLS messages prior to receiving any responses from the assessment
responder. All implementations of PT-TLS MUST support full duplex
PT-TLS message exchange. However, some NEA protocols may not be able
to make use of the full-duplex message exchange.
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3.4.3. TLS Requirements
In order to ensure that strong security is always available for
deployers and to improve interoperability, this section discusses
some requirements on the underlying TLS transport used by PT-TLS.
Implementations of PT-TLS MUST support use of TLS 1.1 [RFC4346] and
SHOULD also include support for TLS 1.2 [RFC5246]. For each TLS
version supported, implementations of the PT-TLS MUST at least
support the TLS_RSA_WITH_AES_128_CBC_SHA cipher suite. This cipher
suite requires the server to provide a certificate that can be used
during the key exchange. Implementations SHOULD NOT include support
for cipher suites that do not minimally offer PT-TLS Responder
(typically Posture Transport Server) authentication, such as the
anonymous Diffie-Hellman cipher suites (e.g.
TLS_DH_anon_WITH_AES_128_CBC_SHA). Implementations MUST support RFC
5746 [RFC5746]. Implementations MAY allow renegotiation to provide
confidentiality for the client certificate. If renegotiation is
allowed implementations need to select the appropriate handshake
messages as described in RFC 5929 for the tls-unique value.
3.5. PT-TLS Message Format
This section describes the format and semantics of the PT-TLS
message. Every message sent over a PT-TLS session MUST start with
the PT-TLS header described in this section.
The following is the PT-TLS header:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Message Type Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Value (e.g. PB-TNC Batch) . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
Reserved for future use. This field MUST be set to 0 on
transmission and ignored upon reception.
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Message Type Vendor ID
This field indicates the owner of the name space associated with
the Message Type. This is accomplished by specifying the 24 bit
SMI Private Enterprise Number (Vendor ID) of the party who owns
the Message Type name space. IETF Standard PT-TLS Message Types
MUST use zero (0) in this field.
The PT-TLS Message Type Vendor ID 0xffffff is reserved. Posture
Transport Clients and Servers MUST NOT send PT-TLS messages in
which the PT-TLS Message Type Vendor ID has this reserved value
(0xffffff). If a Posture Transport Client or Posture Transport
Server receives a message containing this reserved value
(0xffffff) in the PT-TLS Message Type Vendor ID, the recipient
SHOULD respond with an Invalid Parameter error code in a PT-TLS
Error message.
Message Type
This field defines the type of the PT-TLS message within the
scope of the specified Message Type Vendor ID that is included in
the Message Value field. The specific IETF standard values
allowable in this field when the Message Type Vendor ID is the
IETF SMI Private Enterprise Number value (0) are defined in
section 3.6. Recipients of a message containing a Message Type
Vendor ID and Message Type that is unrecognized SHOULD respond
with a Type Not Supported error code in a PT-TLS Error message.
Posture Transport Clients and Posture Transport Servers MUST NOT
require support for particular vendor-defined PT-TLS Message
Types and MUST interoperate with other parties despite any
differences in the set of vendor-defined PT-TLS Message Types
supported (although they MAY permit administrators to configure
them to require support for specific vendor-defined PT-TLS
message types).
If the PT-TLS Message Type Vendor ID field has the value zero
(0), then the PT-TLS Message Type field contains an IETF Standard
PT-TLS Message Type, as listed in the IANA registry. IANA
maintains a registry of PT-TLS Message Types. Entries in this
registry are added by Expert Review with Specification Required,
following the guidelines in section 6.1. Section 3.6. of this
specification defines the initial set of IETF Standard PT-TLS
Message Types.
The PT-TLS Message Type 0xffffffff is reserved. Posture
Transport Clients and Posture Transport Servers MUST NOT send PT-
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TLS messages in which the PT-TLS Message Type has this reserved
value (0xffffffff). If a Posture Transport Client or Posture
Transport Server receives a message in which the PT-TLS Message
Type has this reserved value (0xffffffff), it SHOULD respond with
an Invalid Parameter error code in a PT-TLS Error message.
Message Length
This field contains the length in octets of the entire PT-TLS
message (including the entire header). Therefore, this value
MUST always be at least 16. Any Posture Transport Client or
Posture Transport Server that receives a message with a PT-TLS
Message Length field whose value is less than 16 SHOULD respond
with an Invalid Parameter PT-TLS error code. Similarly, if a
Posture Transport Client or Posture Transport Server receives a
PT-TLS message for a Message Type that has a known Message Length
and the Message Length indicates a different value (greater or
less than the expected value), the recipient SHOULD respond with
an Invalid Parameter PT-TLS error code.
Message Identifier
This field contains a value that uniquely identifies the PT-TLS
message on a per message sender (Posture Transport Client or
Server) basis. This value is copied into the body of the PT-TLS
Error Message so the recipient can determine which message caused
the error.
The Message Identifier MUST be a monotonically increasing counter
starting at zero indicating the number of the messages the sender
has transmitted over the TLS session. It is possible that a busy
or long lived session might exceed 2^32-1 messages sent, so the
message sender MUST roll over to zero upon reaching the 2^32nd
message, thus restarting the increasing counter. During a
rollover, it is feasible that the message recipient could be
confused if it keeps track of every previously received Message
Identifier, so recipients MUST be able to handle roll over
situations without generating errors.
Message Value
The contents of this field vary depending on the particular
Message Type Vendor ID and Message Type given in the PT-TLS
header for this PT-TLS message. This field most frequently
contains a PB-TNC batch. The contents of this field for each of
the IETF Standard PT-TLS Message Types are defined in this
specification.
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3.6. IETF Standard PT-TLS Message Types
This section defines the NEA standard PT-TLS Message Types used to
carry PT-TLS messages and PB-TNC batches between the Posture
Transport Client and Posture Transport Server.
The following table summarizes the initial set of IETF standard
message type values, which are used with the PT-TLS Message Type
Vendor ID field set to the IETF SMI PEN (0).
Value (Name) Definition
------------ ----------
0 (Experimental) Reserved for experimental use. This
type will not offer interoperability
but allows for experimentation. This
message type MUST only be sent when
the NEA Client and NEA Server are in
the Data Transport phase and only on a
restricted, experimental network.
Production code MUST send an Invalid
Message error code in a PT-TLS Error
message if an Experimental message is
received.
1 (Version Request) Version negotiation request including
the range of versions supported by the
sender. This message type MUST only
be sent by the TLS session initiator
as the first PT-TLS message in the PT-
TLS Negotiation phase. Recipients
MUST send an Invalid Message error
code in a PT-TLS Error message if a
Version Request is received at another
time.
2 (Version Response) PT-TLS protocol version selected by
the responder. This message type MUST
only be sent by the TLS session
responder as the second message in the
PT-TLS Negotiation phase. Recipients
MUST send an Invalid Message error
code in a PT-TLS Error message if a
Version Response is received at
another time.
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3 (SASL Mechanisms) Sent by the NEA Server to indicate
what SASL mechanisms it is willing to
use for authentication on this
session. This message type MUST only
be sent by the NEA Server in the PT-
TLS Negotiation phase. The NEA Client
MUST send an Invalid Message error
code in a PT-TLS Error message if a
SASL Mechanisms message is received at
another time.
4 (SASL Mechanism Selection) Sent by the NEA Client to select a
SASL mechanism from the list offered
by the NEA Server. This message type
MUST only be sent by the NEA Client in
the PT-TLS Negotiation phase. The NEA
Server MUST send an Invalid Message
error code in a PT-TLS Error message
if a SASL Mechanism Selection is
received after the PT-TLS Negotiation
phase. Once a SASL mechanism has been
selected, it may not change until the
mechanism completes either
successfully or as a failure.
5 (SASL Authentication Data) Opaque octets exchanged between the
NEA Client and NEA Server's SASL
mechanisms to perform the client
authentication. This message type
MUST only be sent during the PT-TLS
Negotiation phase. Recipients MUST
send an Invalid Message error code in
a PT-TLS Error message if a SASL
Authentication Data message is
received after the PT-TLS Negotiation
phase.
6 (SASL Result) Indicates the result code of the SASL
mechanism authentication. A success
result indicates that the NEA Client
and NEA Server will transition to the
Data Transport phase, thus allowing
the assessment to start. Note that
the NEA Server may choose to allow the
transition to Data Transport phase
even if authentication is unsuccessful
before making its access control
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decision. This message type MUST only
be sent by the NEA Server when the NEA
Client and NEA Server are in the PT-
TLS Negotiation phase. The NEA Client
MUST send an Invalid Message error
code in a PT-TLS Error message if a
SASL Result is received after the PT-
TLS Negotiation phase.
7 (PB-TNC Batch) Contains a PB-TNC batch. For more
information on PB-TNC batches see
section 4 of the PB-TNC specification.
This message type MUST only be sent
when the NEA Client and NEA Server are
in the PT-TLS Data Transport phase.
Recipients SHOULD send an Invalid
Message error code in a PT-TLS Error
message if a PB-TNC Batch is received
outside of the Data Transport phase.
8 (PT-TLS Error) PT-TLS Error message as described in
section 3.9. This message type may be
used during any PT-TLS phase.
9+ (Reserved) These values are reserved for future
allocation following guidelines
defined in the IANA Considerations
section 6.1. Recipients of messages
of type 9 or higher that do not
support the PT-TLS Message Type Vendor
ID and PT-TLS Message Type of a
received PT-TLS message MUST respond
with a Type Not Supported PT-TLS error
code in a PT-TLS Error message.
3.7. PT-TLS Version Negotiation
This section describes the message format and semantics for the PT-
TLS protocol version negotiation. This exchange is used by the PT-
TLS Initiator to trigger a version negotiation at the start of an
assessment. The PT-TLS Initiator MUST send a Version Request message
as its first PT-TLS message and MUST NOT send any other PT-TLS
messages on this connection until it receives a Version Response
message or an Error message. The PT-TLS Responder MUST complete the
version negotiation (or cause an error) prior to sending or accepting
reception of any additional messages. After the successful
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completion of the version negotiation, both the Posture Transport
Client and Posture Transport Server MUST only send messages compliant
with the negotiated protocol version. Subsequent assessments on the
same session MUST use the negotiated version number and therefore
MUST NOT send additional version negotiation messages.
3.7.1. Version Request Message
This message is sent by a PT-TLS Initiator as the first PT-TLS
message in a PT-TLS session. This message discloses the sender's
supported versions of the PT-TLS protocol. To ensure compatibility,
this message MUST always be sent using version 1 of the PT-TLS
protocol. Recipients of this message MUST respond with a Version
Response, or a PT-TLS Error message (Version Not Supported or Invalid
Message). The following diagram shows the format of the Version
Request Message:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Min Vers | Max Vers | Pref Vers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
Reserved for future use. This field MUST be set to 0 on
transmission and ignored upon reception.
Min Vers
This field contains the minimum version of the PT-TLS
protocol supported by the sender. This field MUST be set to
1 indicating support for the first version of PT-TLS.
However, future versions of this specification will probably
remove this requirement so PT-TLS Responders MUST be
prepared to receive other values.
Max Vers
This field contains the maximum version of the PT-TLS
protocol supported by the sender. This field MUST be set to
1 indicating support for the first version of PT-TLS.
However, future versions of this specification will probably
remove this requirement so PT-TLS Responders MUST be
prepared to receive other values.
Pref Vers
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This field contains the sender's preferred version of the
PT-TLS protocol. This is a hint to the recipient that the
sender would like this version selected if supported. The
value of this field MUST fall within the range of Min Vers
to Max Vers. This field MUST be set to 1 indicating support
for the first version of PT-TLS. However, future versions
of this specification will probably remove this requirement
so PT-TLS Responders MUST be prepared to receive other
values.
3.7.2. Version Response Message
This message is sent in response to receiving a Version Request
Message at the start of a new assessment session. If a recipient
receives a Version Request after a successful version negotiation has
occurred on the session, the recipient SHOULD send an Invalid Message
error code in a PT-TLS Error message and have TLS close the session.
This message MUST be sent using the syntax, semantics, and
requirements of the protocol version specified in this message.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
Reserved for future use. This field MUST be set to 0 on
transmission and ignored upon reception.
Version
This field contains the version selected by the sender of
this message. The version selected MUST be within the Min
Vers to Max Vers inclusive range sent in the Version Request
Message. If a PT-TLS Initiator receives a message with an
invalid Version selected, the PT-TLS Initiator MUST respond
with a Version Not Supported PT-TLS error message.
3.8. Client Authentication using SASL
This section includes a description of the message format and
semantics necessary to perform client authentication
(authentication of the NEA Client) over PT-TLS. Client
authentication could be necessary if the NEA Server requires
such an authentication and it was not performed during the TLS
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handshake. The general model used for performing an
authentication of the client using PT-TLS messages is to
integrate the Simple Authentication and Security Layer (SASL)
[RFC4422] framework. SASL provides a number of standards-
based authentication mechanisms capable of authenticating the
NEA Client using a variety of base technologies.
Client authentication may occur during the TLS handshake using
TLS defined authentication techniques. Because this client
authentication is optional, the NEA Server's policy may require
the client to be authenticated by PT-TLS before performing the
assessment. Similarly, the NEA Server may require a PT-TLS
authentication even if the NEA Client was authenticated during
the TLS handshake (e.g. to allow a user authentication after a
system level authentication occurred during the TLS handshake).
The decision of whether a SASL client authentication is to
occur is left to the NEA Server's policy.
As discussed in section 3.1.1, it is possible that the NEA
Server may initiate the TLS session to the NEA Client, thus
causing it to fill the role of TLS Client during the TLS
handshake. Because the NEA Server is required to possess an
X.509 certificate for when it is acting as the TLS Server role
(normal case), PT-TLS requires that the NEA Server MUST use its
X.509 certificate for TLS client authentication during the TLS
handshake to authenticate itself even when it is acting as the
TLS Client. In this case, the NEA Client and NEA Server will
authenticate using certificates during the TLS handshake, so
the PT-TLS SASL client authentication might not be required
unless NEA Server policy required an additional authentication
of the NEA Client. Therefore, the normal usage for the SASL
messages is when the NEA Client acted as the TLS client and did
not authenticate during the TLS handshake.
3.8.1. SASL Entity Authentication Requirements
Implementations compliant with the PT-TLS specification MUST
implement the SASL authentication messages described in this
section. In order to ensure interoperability, all PT-TLS
implementations compliant with this specification MUST at least
support the PLAIN SASL mechanism [RFC4616]. Similarly,
implementations MUST provide the EXTERNAL SASL mechanism if
both parties are authenticated during the TLS establishment.
In order to be able to take advantage of other strong, widely
deployed authentication technologies such as Kerberos and
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support for channel bindings, implementations MAY include
support for GS2 (second GSS-API bridge for SASL) [RFC5801].
GS2 includes negotiable support for channel binding for use
with SASL (see section 5 of RFC 5801).
3.8.2. SASL in PT-TLS Overview
Mechanism negotiation is initiated by the NEA Server sending the SASL
Mechanisms TLV to the NEA Client to indicate the zero or more SASL
mechanisms the NEA Server's policy is willing to use with the NEA
Client. The NEA Client selects one SASL mechanism from the list and
sends a SASL Mechanism Selection TLV completing the negotiation.
Subsequent challenges and responses are carried within the SASL
Authentication Data TLV carrying the authentication data for the
selected mechanism. The authentication outcome is communicated in a
SASL Result TLV containing a status code. If additional
authentications are required, the NEA Server could trigger the next
authentication by sending another SASL Mechanisms TLV after sending
the SASL Result TLV for the current authentication mechanism.
3.8.3. SASL Authentication Flow
The SASL client authentication starts when the NEA Server
enters the PT-TLS Negotiation phase and its policy indicates
that an authentication of the NEA Client is necessary but was
not performed during the TLS handshake protocol. The NEA
Server is responsible for triggering the client authentication
by sending the SASL Mechanisms TLV to the NEA Client listing
the set of SASL mechanisms the server is willing to use based
upon its policy.
The NEA Client selects a SASL mechanism from the list proposed
by the NEA Server or sends a PT-TLS Invalid Message error code
indicating it is unable or unwilling to perform any of the
mechanisms that were offered. If the NEA Server receives a
SASL Mechanism Selection TLV that contains an unacceptable SASL
mechanism, the NEA Server would respond with a SASL Mechanism
Error in a PT-TLS Error TLV.
In situations where the NEA Server does not require a client
authentication (either authentication isn't necessary or was
performed during the TLS Setup phase), the NEA Server MUST send
a SASL Mechanisms TLV with no mechanisms included (only the PT-
TLS header) indicating the connection should transition to the
PT-TLS Data Transport phase. The same mechanism is employed to
indicate that a SASL authentication already performed in this
session is adequate to permit transition to the PT-TLS Data
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Transport phase. So the NEA Server MUST always send a SASL
Mechanisms TLV with no mechanisms as the last message in the
PT-TLS Negotiation phase and the NEA Client MUST NOT transition
to the PT-TLS Data Transport phase until it receives such a
message.
If the NEA Server receives a NEA assessment message before the
completion of the client authentication, the NEA Server MUST
send an Authentication Required PT-TLS Error indicating to the
NEA Client that an authentication exchange is required prior to
entering the PT-TLS Data Transport phase.
3.8.4. Aborting SASL Authentication
The NEA Server may abort the authentication exchange by sending the
SASL Result TLV with a status code of ABORT. The NEA Client may
abort the authentication exchange by sending a PT-TLS Error message
with an Error Code of SASL Mechanism Error.
3.8.5. Linkages to SASL Framework
3.8.5.1. SASL Service Name
The service name for PT-TLS is "nea-pt-tls".
3.8.5.2. SASL Authorization Identity
The PT-TLS protocol does not make use of a SASL authorization
identity string as described in RFC4422.
3.8.5.3. SASL Security Layer
The NEA PT-TLS protocol always runs under the protection of TLS.
SASL security layers are not used and thus MUST be negotiated off
during SASL authentication.
3.8.5.4. Multiple Authentications
Only one SASL mechanism authentication may be in progress at any one
time. Once a SASL mechanism completes (successfully or
unsuccessfully) the NEA Server may trigger an additional
authentication by sending a SASL Mechanisms TLV.
3.8.6. SASL Channel Bindings
SASL channel bindings are used to bind the SASL authentication to the
outer TLS tunnel to ensure that the authenticating endpoints are the
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same as the TLS endpoints. For SASL mechanisms that support channel
bindings the TLS-unique value defined in RFC 5929 is carried by the
SASL Mechanism. For most mechanisms this means including the tls-
unique value with the appropriate prefix defined in RFC 5929 in the
application data portion of the SASL Mechanism channel binding data.
If the validation of the channel-binding fails then the connection
MUST be aborted.
3.8.7. SASL Mechanisms
This TLV is sent by the NEA Server to indicate the list of SASL
mechanisms that it is willing and able to use to authenticate the NEA
Client. Each mechanism name consists of a length followed by a
name. The total length of the list is determined by the TLV Length
field.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rsvd| Mech Len| Mechanism Name (1-20 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rsvd| Mech Len| Mechanism Name (1-20 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . . . . . . . . . |
Rsvd (Reserved)
Reserved for future use. This field MUST be set to 0 on
transmission and ignored upon reception.
Mech Len (Mechanism Name Length)
The length of the Mechanism-Name field in octets.
Mechanism Name
SASL mechanism name adhering to the rules defined in
RFC4422.
3.8.8. SASL Mechanism Selection
This TLV is sent by the NEA Client in order to select a SASL
mechanism for use on this session.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Rsvd| Mech Len| Mechanism Name (1-20 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional Initial Mechanism Response |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Rsvd (Reserved)
Reserved for future use. This field MUST be set to 0 on
transmission and ignored upon reception.
Mech Len (Mechanism Name Length)
The length of the Mechanism-Name field in octets.
Mechanism Name
SASL mechanism name adhering to the rules defined in
RFC4422.
Optional Initial Mechanism Response
Initial set of authentication information required from the
NEA Client to kick start the authentication. This data is
optional and if not provided would be solicited by the NEA
Server in the first SASL Authentication Data TLV request.
3.8.9. SASL Authentication Data
This TLV carries an opaque (to PT-TLS) blob of octets being exchanged
between the NEA Client and the NEA Server. This TLV facilitates
their communications without interpreting any of the bytes. The SASL
Authentication Data TLV MUST NOT be sent until a SASL mechanism has
been established for a session. The SASL Authentication Data TLV
associated with the current authentication mechanism MUST NOT be sent
after a SASL Result is sent with a Successful status. Additional
SASL Authentication Data TLVs would be sent if the PT-TLS Initiator
and Responder desire a subsequent SASL authentication to occur but
only after another SASL mechanism selection exchange occurs.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SASL Mechanism Data (Variable Length) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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SASL Mechanism Data
Opaque, variable length set of bytes exchanged between the
PT-TLS Initiator's SASL mechanism and its peer PT-TLS
Responder's SASL mechanism. These bytes MUST NOT be
interpreted by the PT-TLS layer.
3.8.10. SASL Result
This TLV is sent by the NEA Server at the conclusion of the SASL
exchange to indicate the authentication result. Upon reception of a
SASL Result TLV indicating an Abort, the NEA Client MUST terminate
the current authentication conversation. The recipient may retry the
authentication in the event of an authentication failure. Similarly,
the NEA Server may request additional SASL authentication(s) be
performed after the completion of a SASL mechanism by sending another
SASL Mechanisms TLV including any mechanisms dictated by its policy.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Result Code | Optional Result Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . . . . . . . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Result Code
This field contains the result of the SASL authentication
exchange.
Value (Name) Definition
------------ ----------
0 (Success) SASL authentication was successful and
identity was confirmed.
1 (Failure) SASL authentication failed. This
might be caused by the client
providing an invalid user identity
and/or credential pair. Note that
this is not a mechanism failure to
process the authentication as reported
by the Mechanism Failure code.
2 (Abort) SASL authentication exchange was
aborted by the sender
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3 (Mechanism Failure) SASL "mechanism failure" during the
processing of the client's
authentication (e.g. not related to
the user's input).
Optional Result Data
This field contains a variable length set of additional data
for a successful result. This field MUST be zero length
unless the NEA Server is returning a Result Code of Success
and has more data to return. For more information on the
additional data with success in SASL, see RFC 4422.
3.9. Error Message
This section describes the format and contents of the PT-TLS Error
Message sent by the NEA Client or NEA Server when it detects a PT-TLS
level protocol error. Each error message contains an error code
indicating the error that occurred, followed by a copy of the message
that caused the error.
When a PT-TLS error is received, the recipient MUST NOT respond with
a PT-TLS error because this could result in an infinite loop of error
messages being sent. Instead, the recipient MAY log the error,
modify its behavior to avoid future errors, ignore the error,
terminate the assessment, or take other action as appropriate (as
long as it is consistent with the requirements of this
specification).
The Message Value portion of a PT-TLS Error Message contains the
following information:
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Error Code Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Copy of Original Message (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . . . . . |
Reserved
Reserved for future use. This field MUST be set to 0 on
transmission and ignored upon reception.
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Error Code Vendor ID
This field contains the IANA assigned SMI Private Enterprise
Number for the vendor whose Error Code name space is being
used in the message. For IETF standard Error Code values
this field MUST be set to zero (0). For other vendor-
defined Error Code name spaces this field MUST be set to the
SMI Private Enterprise Number of the vendor.
Error Code
This field contains the error code. This error code exists
within the scope of Error Code Vendor ID in this message.
Posture Transport Clients and Posture Transport Servers MUST
NOT require support for particular vendor-specific PT-TLS
Error Codes and MUST interoperate with other parties despite
any differences in the set of vendor-specific PT-TLS Error
Codes supported (although they MAY permit administrators to
configure them to require support for specific PT-TLS error
codes).
When the Error Code Vendor ID is set to the IETF Private
Enterprise Number, the following table lists the supported
IETF standard numeric error codes:
Value (Name) Definition
------------ ----------
0 (Reserved) Reserved value indicates that the PT-
TLS Error Message SHOULD be ignored by
all recipients. This MAY be used for
debugging purposes to allow a sender
to see a copy of the message that was
received while a receiver is operating
on its contents.
1 (Malformed Message) PT-TLS message unrecognized or
unsupported. This error code SHOULD
be sent when the basic message content
sanity test fails. The sender of this
error code MUST consider it a fatal
error and abort the assessment.
2 (Version Not Supported) This error SHOULD be sent when a PT-
TLS Responder receives a PT-TLS
Version Request message containing a
range of version numbers that doesn't
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include any version numbers that the
recipient is willing and able to
support on the session. All PT-TLS
messages carrying the Version Not
Supported error code MUST use a
Version number of 1. All parties that
receive or send PT-TLS messages MUST
be able to properly process an error
message that meets this description,
even if they cannot process any other
aspect of PT-TLS version 1. The
sender and receiver of this error code
MUST consider this a fatal error and
close the TLS session after sending or
receiving this PT-TLS message.
3 (Type Not Supported) PT-TLS message type unknown or not
supported. When a recipient receives
a PT-TLS message type that it does not
support, it MUST send back this error,
ignore the message and proceed. For
example, this could occur if the
sender used a Vendor ID for the
Message Type that is not supported by
the recipient. This error message
does not indicate a fatal error has
occurred, so the assessment is allowed
to continue.
4 (Failed Authentication) The authentication of the identity of
the client failed. This could occur
if the SASL mechanism was unable to
authenticate the claimed identity of
the PT-TLS Initiator. This error
message does not indicate a fatal
error has occurred, so the
authentication is allowed to be re-
started.
5 (Invalid Message) PT-TLS message received was invalid
based on the protocol state. For
example, this error would be sent if a
recipient receives a message
associated with the PT-TLS Negotiation
Phase (such as Version messages) after
the protocol has reached the PT-TLS
Data Transport Phase. The sender and
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receiver of this error code MUST
consider it a fatal error and close
the TLS session after sending or
receiving this PT-TLS message.
6 (SASL Mechanism Error) A fatal error occurred while trying to
perform the client authentication.
For example, the NEA Client is unable
to support any of the offered SASL
mechanisms. The sender and receiver
of this error code MUST consider it a
fatal error and close the TLS session
after sending or receiving this PT-TLS
message.
7 (Invalid Parameter) The PT-TLS error message sender has
received a message with an invalid or
unsupported value in the PT-TLS
header. This could occur if the NEA
Client receives a PT-TLS message from
the NEA Server with a Message Length
of zero (see section 3.5) for
details. The sender and receiver of
this error code MUST consider it a
fatal error and close the TLS session
after sending or receiving this PT-TLS
message.
Copy of Original Message
This variable length value MUST contain a copy (up to 1024
bytes) of the original PT-TLS message that caused the error.
If the original message is longer than 1024 bytes, only the
initial 1024 bytes will be included in this field. This
field is included so the error recipient can determine which
message sent caused the error. In particular, the recipient
can use the Message Identifier field from the Copy of
Original Message to determine which message caused the
error.
4. Security Considerations
This section discusses the major threats potentially faced by each
binding of the PT protocol and countermeasures provided by the PT-TLS
protocol.
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4.1. Trust Relationships
In order to understand where security countermeasures are necessary,
this section starts with a discussion of where the NEA architecture
envisions some trust relationships between the processing elements of
the PT-TLS protocol. The following sub-sections discuss the trust
properties associated with each portion of the NEA reference model
directly involved with the processing of the PT-TLS protocol.
4.1.1. Posture Transport Client
The Posture Transport Client is trusted by the Posture Broker Client
to:
o Not observe, fabricate or alter the contents of the PB-TNC batches
received from the network
o Not observe, fabricate or alter the PB-TNC batches passed down
from the Posture Broker Client for transmission on the network
o Transmit on the network any PB-TNC batches passed down from the
Posture Broker Client
o Deliver properly security protected messages received from the
network that are destined for the Posture Broker Client
o Provide configured security protections (e.g. authentication,
integrity and confidentiality) for the Posture Broker Client's PB-
TNC batches sent on the network
o Expose the authenticated identity of the Posture Transport Server
only to the PB-TNC layer within the NEA Client
o Verify the security protections placed upon messages received from
the network to ensure the messages are authentic and protected
from attacks on the network
o Provide a secure, reliable, in order delivery, full duplex
transport for the Posture Broker Client's messages
The Posture Transport Client is trusted by the Posture Transport
Server to:
o Not send malicious traffic intending to harm (e.g. denial of
service) the Posture Transport Server
o Not send malformed messages (e.g. messages lacking PT-TLS header)
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o Not send invalid or incorrect responses to messages (e.g. errors
when no error is warranted)
o Not ignore or drop messages causing issues for the protocol
processing (e.g. dropping PT-TLS SASL Authentication Data
messages)
o Verify the security protections placed upon messages received from
the network to ensure the messages are authentic and protected
from attacks on the network
4.1.2. Posture Transport Server
The Posture Transport Server is trusted by the Posture Broker Server
to:
o Not observe, fabricate or alter the contents of the PB-TNC batches
received from the network
o Not observe, fabricate or alter the PB-TNC batches passed down
from the Posture Broker Server for transmission on the network
o Transmit on the network any PB-TNC batches passed down from the
Posture Broker Server
o Deliver properly security protected messages received from the
network that are destined for the Posture Broker Server
o Provide configured security protections (e.g. authentication,
integrity and confidentiality) for the Posture Broker Server's
messages sent on the network
o Expose the authenticated identity of the Posture Transport Client
only to the PB-TNC layer within the NEA Server
o Verify the security protections placed upon messages received from
the network to ensure the messages are authentic and protected
from attacks on the network
o Provide a secure, reliable, in order delivery, full duplex
transport for the Posture Broker Server's messages
The Posture Transport Server is trusted by the Posture Transport
Client to:
o Not send malicious traffic intending to harm (e.g. denial of
service) the Posture Transport Server
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o Not send malformed messages (e.g. messages lacking PT-TLS header)
o Not send invalid or incorrect responses to messages (e.g. errors
when no error is warranted)
o Not ignore or drop messages causing issues for the protocol
processing (e.g. dropping PT-TLS SASL Result messages)
o Verify the security protections placed upon messages received from
the network to ensure the messages are authentic and protected
from attacks on the network
4.2. Security Threats and Countermeasures
Beyond the trusted relationships assumed in section 4.1 the PT-TLS
protocol faces a number of potential security attacks that could
require security countermeasures.
Generally, the PT-TLS protocol is responsible for offering strong
security protections for all of the NEA protocols so any threats to
its ability to protect NEA protocol messages could be very damaging
to deployments. Once the message is delivered to the Posture Broker
Client or Posture Broker Server, the posture brokers are trusted to
properly and safely process the messages.
4.2.1. Message Theft
When PT-TLS messages are sent over unprotected network links or
spanning local software stacks that are not trusted, the contents of
the messages may be subject to information theft by an intermediary
party. This theft could result in information being recorded for
future use or analysis by the adversary. Messages observed by
eavesdroppers could contain information that exposes potential
weaknesses in the security of the endpoint, or system fingerprinting
information easing the ability of the attacker to employ attacks more
likely to be successful against the endpoint. The eavesdropper might
also learn information about the endpoint or network policies that
either singularly or collectively is considered sensitive
information. For example, if PT-TLS does not provide confidentiality
protection, an adversary could observe the PA-TNC attributes included
in the PT-TLS message and determine that the endpoint is lacking
patches, or particular sub-networks have more lenient policies.
In order to protect against NEA assessment message theft, the PT-TLS
protocol provides strong cryptographic authentication, integrity and
confidentiality protection. Deployers are strongly encouraged to
employ best practice of the day TLS ciphers to ensure the information
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remains safe despite advances in technology and discovered cipher
weaknesses. The use of bi-directional authentication of the
assessment transport session ensures that only properly authenticated
and authorized parties may be involved in an assessment dialog. The
PT-TLS protocol also provides strong cryptography for all of the PB-
TNC and PA-TNC protocol messages traveling over the network allowing
the message contents to be hidden from potential theft by the
adversary even if the attacker is able to observe the encrypted PT-
TLS session.
4.2.2. Message Fabrication
Attackers on the network or present within the NEA system could
introduce fabricated PT-TLS messages intending to trick or create a
denial of service against aspects of an assessment. For example, an
adversary could attempt to insert into the message exchange fake PT-
TLS error codes in order to disrupt communications.
The PT-TLS protocol provides strong security protections for the
complete message exchange over the network. These security
protections prevent an intermediary from being able to insert fake
messages into the assessment. In particular, the TLS's protocol use
of hashing algorithms provides strong integrity protections that
allow for detection of any changes in the content of the message
stream. Additionally, adversaries are unable to observe the PT-TLS
protocol exchanges because they are encrypted by the TLS ciphers, so
would have difficulty in determining where to insert the falsified
message, since the attacker is unable to determine where the message
boundaries exist. Even a successful message insertion did occur; the
recipient would be able to detect it due to the TLS cipher suite's
integrity checking failing.
4.2.3. Message Modification
This attack could allow an active attacker capable of intercepting a
message to modify a PT-TLS message or transported PA-TNC attribute to
a desired value to ease the compromise of an endpoint. Without the
ability for message recipients to detect whether a received message
contains the same content as what was originally sent, active
attackers can stealthily modify the attribute exchange.
The PT-TLS protocol leverages the TLS protocol to provide strong
authentication and integrity protections as a countermeasure to this
theat. The bi-directional authentication prevents the attacker from
acting as an active man-in-the-middle to the protocol that could be
used to modify the message exchange. The strong integrity
protections (e.g. hashing) offered by TLS allows PT-TLS message
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recipients to detect message alterations by other types of network
based adversaries.
4.2.4. Denial of Service
A variety of types of denial of service attacks are possible against
the PT-TLS protocol if the message exchanges are left unprotected
while traveling over the network. The Posture Transport Client and
Posture Transport Server are trusted not to participate in the denial
of service of the assessment session, leaving the threats to come
from the network.
The PT-TLS protocol provides bi-directional authentication
capabilities in order to prevent a man-in-the-middle on the network
from becoming an undetected active proxy of PT-TLS messages. Because
the PT-TLS protocol runs after the TLS handshake and thus cipher
establishment/use, all of the PT-TLC messages are protected from
undetected modification that could create a denial of service
situation. However it is possible for an adversary to alter the
message flows causing each message to be rejected by the recipient
because it fails the integrity checking.
The PT-TLS protocol operates as an application protocol on top of TLS
and thus TCP/IP protocols, so is subject to denial of service attacks
against the TLS, TCP and IP protocols.
4.2.5. NEA Asokan Attacks
As described in section 3.3 and in the NEA Asokan Attack Analysis
[ASOKAN], a sophisticated MITM attack can be mounted against NEA
systems. The attacker forwards PA-TNC messages from a healthy
machine through an unhealthy one so that the unhealthy machine can
gain network access. Section 3.3. and the NEA Asokan Attack Analysis
provide a detailed description of this attack and of the
countermeasures that can be employed against it.
Because lying endpoint attacks are much easier than Asokan attacks
and the only known effective countermeasure against lying endpoint
attacks is the use of an External Measurement Agent (EMA),
countermeasures against an Asokan attack are not necessary unless an
EMA is in use. However, PT-TLS implementers may not know whether an
EMA will be used with their implementation. Therefore, PT-TLS
implementers SHOULD support the Asokan attack countermeasures
described in section 3.3 by providing the value of the tls-unique
channel binding to higher layers in the NEA reference model: Posture
Broker Clients, Posture Broker Servers, Posture Collectors, and
Posture Validators.
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The Asokan attack can also apply to authentication mechanisms carried
within TLS. SASL mechanisms providing channel bindings use the tls-
unique channel binding data as defined in section 3.3 to protect
against the attack.
4.2.6. Trust Anchors
The TLS protocol bases its trust decision about the signer of the
certificates received during the TLS authentication using a set of
trust anchor certificate. It is essential that these trust anchor
certificates are integrity protected from unauthorized modification.
Many common software components (e.g. browsers, operating systems,
security protocols) include a set of trust anchor certificates that
are relevant to their operation. The PT-TLS SHOULD use a PT-TLS
specific set of trust anchor certificates in order to limit what
Certificate Authorities are authorized to issue certificates for use
with NEA.
5. Privacy Considerations
The role of PT-TLS is to act as a secure transport for PB-TNC and
other higher layer protocols. As such, PT-TLS does not directly
utilize personally identifiable information (PII) except when client
authentication is enabled. When client authentication is being used,
the NEA Client will be asked to use SASL which may disclose a local
identifier (e.g. username) associated with the endpoint and an
authenticator (e.g. password) to authenticate that identity. Because
the identity and authenticator are potentially privacy sensitive
information, the NEA Client MUST offer a mechanism to restrict which
NEA Servers will be sent this information. Similarly, the NEA Client
should provide an indication to the person being identified that a
request for their identity has been made in case they choose to opt
out of the authentication to remain anonymous.
PT-TLS provides cryptographic peer authentication, message integrity
and data confidentiality protections to higher layer NEA protocols
that may exchange data potentially including PII. These security
services can be used to protect any PII involved in an assessment
from passive and active attackers on the network. Endpoints sending
potentially privacy sensitive information should ensure that the PT-
TLS security protections (TLS cipher suites) negotiated for an
assessment of the endpoint are adequate to avoid interception and
off-line attacks of any long term privacy sensitive information.
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6. IANA Considerations
This specification requests the creation of two new IANA
registries and the assignment of a TCP port number. First, this
specification requests the IANA reserve a registered TCP port
number for use with the PT-TLS protocol upon publication of
this specification as an Internet standard RFC.
This section also defines the contents of two new IANA
registries: PT-TLS Message Types, and PT-TLS Error Codes. This
section explains how these registries work.
All of the registries defined in this document support IETF
standard values and vendor-defined values. To explain this
phenomenon, we will use the PT-TLS Message Type as an example
but the other registries work the same way.
Whenever a PT-TLS Message Type appears on a network, it is
always accompanied by an SMI Private Enterprise Number (PEN),
also known as a vendor ID. If this vendor ID is zero, the
accompanying PT-TLS Message Type is an IETF standard value
listed in the IANA registry for PT-TLS Message Types and its
meaning is defined in the specification listed for that PT-TLS
Message Type in that registry. If the vendor ID is not zero,
the meaning of the PT-TLS Message Type is defined by the vendor
identified by the vendor ID (as listed in the IANA registry for
SMI PENs). The identified vendor is encouraged but not required
to register with IANA some or all of the PT-TLS Message Types
used with their vendor ID and publish a specification for each
of these values.
This delegation of namespace is analogous to the technique used
for OIDs. It can result in interoperability problems if
vendors require support for particular vendor-specific values.
However, such behavior is explicitly prohibited by this
specification, which dictates that "Posture Transport Clients
and Posture Transport Servers MUST NOT require support for
particular vendor-specific PT-TLS Error Codes and MUST
interoperate with other parties despite any differences in the
set of vendor-specific PT-TLS Error Codes supported (although
they MAY permit administrators to configure them to require
support for specific PT-TLS error codes)." Similar
requirements are included for PT-TLS Message Types.
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6.1. Designated Expert Guidelines
For all of the IANA registries defined by this specification,
new values are added to the registry by Expert Review with
Specification Required, using the Designated Expert process
defined in RFC 5226 [RFC5226].
This section provides guidance to designated experts so that
they may make decisions using a philosophy appropriate for
these registries.
The registries defined in this document have plenty of values.
In most cases, the IETF has approximately 2^32 values available
for it to define and each vendor has the same number of values
for its use. Because there are so many values available,
designated experts should not be terribly concerned about
exhausting the set of values.
Instead, designated experts should focus on the following
requirements. All values in these IANA registries MUST be
documented in a specification that is permanently and publicly
available. IETF standard values MUST also be useful, not
harmful to the Internet, and defined in a manner that is clear
and likely to ensure interoperability.
Designated experts should encourage vendors to avoid defining
similar but incompatible values and instead agree on a single
IETF standard value. However, it is beneficial to document
existing practice.
There are several ways to ensure that a specification is
permanently and publicly available. It may be published as an
RFC. Alternatively, it may be published in another manner that
makes it freely available to anyone. However, in this latter
case, the vendor MUST supply a copy to the IANA and authorize
the IANA to archive this copy and make it freely available to
all if at some point the document becomes no longer freely
available to all through other channels.
The following two sections provide guidance to the IANA in
creating and managing the new IANA registries defined by this
specification.
6.2. Registry for PT-TLS Message Types
The name for this registry is "PT-TLS Message Types". Each
entry in this registry should include a human-readable name, an
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SMI Private Enterprise Number, a decimal integer value between
0 and 2^32-1, and a reference to the specification where the
contents of this message type are defined. This specification
must define the meaning of the PT-TLS message type and the
format and semantics of the PT-TLS Message Value field that
include the designated Private Enterprise Number in the PT-TLS
Message Type Vendor ID field and the designated numeric value
in the PT-TLS Message Type field.
The following entries for this registry are defined in this
document. Once this document becomes an RFC, they should
become the initial entries in the registry for PT-TLS Message
Types. Additional entries to this registry are added by Expert
Review with Specification Required, following the guidelines in
section 6.1.
PEN Value Name Defining Specification
--- ----- ---- ----------------------
0 0 Experimental RFC # Assigned to this I-D
0 1 Version Request RFC # Assigned to this I-D
0 2 Version Response RFC # Assigned to this I-D
0 3 SASL Mechanisms RFC # Assigned to this I-D
0 4 SASL Mechanism Selection RFC # Assigned to this I-D
0 5 SASL Authentication Data RFC # Assigned to this I-D
0 6 SASL Result RFC # Assigned to this I-D
0 7 PB-TNC Batch RFC # Assigned to this I-D
0 8 PT-TLS Error RFC # Assigned to this I-D
0 9+ Reserved RFC # Assigned to this I-D
6.3. Registry for PT-TLS Error Codes
The name for this registry is "PT-TLS Error Codes". Each entry
in this registry should include a human-readable name, an SMI
Private Enterprise Number, a decimal integer value between 0
and 2^32-1, and a reference to the specification where this
error code is defined. This specification must define the
meaning of this error code, a PT-TLS Message Type of PT-TLS
Error, the designated Private Enterprise Number in the PT-TLS
Error Code Vendor ID field, and the designated numeric value in
the PT-TLS Error Code field.
The following entries for this registry are defined in this
document. Once this document becomes an RFC, they should
become the initial entries in the registry for PT-TLS Error
Codes. Additional entries to this registry are added by Expert
Review with Specification Required, following the guidelines in
section 6.1.
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PEN Value Name Defining Specification
--- ----- ---- ----------------------
0 0 Reserved RFC # Assigned to this I-D
0 1 Malformed Message RFC # Assigned to this I-D
0 2 Version Not Supported RFC # Assigned to this I-D
0 3 Type Not Supported RFC # Assigned to this I-D
0 4 Failed Authentication RFC # Assigned to this I-D
0 5 Invalid Message RFC # Assigned to this I-D
0 6 SASL Mechanism Error RFC # Assigned to this I-D
0 7 Invalid Parameter RFC # Assigned to this I-D
7. Acknowledgments
Thanks to the Trusted Computing Group for contributing the initial
text upon which this document was based [IFT-TLS].
The authors of this draft would also like to acknowledge the
following people who have contributed to or provided substantial
input on the preparation of this document or predecessors to it: Syam
Appala, Stuart Bailey, Lauren Giroux, Steve Hanna, Josh Howlett,
Carolin Latze, Scott Kelly, Sung Lee, Lisa Lorenzin, Ravi Sahita,
Subbu Srinivasan, Susan Thomson and Mark Townsend.
This document was prepared using 2-Word-v2.0.template.dot.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4346] Dierks T., Rescorla E., "The Transport Layer Security (TLS)
Protocol Version 1.1", RFC 4346, April 2006.
[RFC4422] Melnikov A., Zeilenga K., "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC4616] Zeilenga K., "The PLAIN Simple Authentication and Security
Layer (SASL) Mechanism", RFC 4616, August 2006.
[RFC5226] Narten T., Alvestrand H., "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 5226, May 2008.
[RFC5246] Dierks T., Rescorla E., "The Transport Layer Security (TLS)
Protocol Version 1.2", RFC 5246, August 2008.
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[RFC5280] Cooper, D., Santesson, S., Farrel, S., Boeyen, S., Housley,
R., Polk, W., "Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile",
RFC 5280, May 2008.
[RFC5746] Rescorla E., Ray M., Oskov N., "Transport Layer Security
(TLS) Renegotiation Indication Extension", RFC 5746,
February 2010.
[RFC5792] Sangster P., Narayan K., "PA-TNC: A Posture Attribute
Protocol (PA) Compatible with TNC", RFC 5792, March 2010.
[RFC5793] Sahita, R., Hanna, S., and R. Hurst, "PB-TNC: A Posture
Broker Protocol (PB) Compatible with TNC", RFC 5793, March
2010.
[RFC5929] Altman, J., Williams, N., Zhu L., "Channel Bindings for
TLS", RFC 5929, July 2010.
[RFC6125] Saint-Andre, P., Hodges, J., "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
[RFC6520] Segglemann, R., Tuexen, M., Williams M., "Transport Layer
Security (TLS) and Datagram Transport Layer Security (DTLS)
Heartbeat Extension", RFC 6520, February 2012.
8.2. Informative References
[ASOKAN] Salowey, J., Hanna, S., "NEA Asokan Attack Analysis",
draft-ietf-nea-asokan-00.txt (work in progress), April
2012.
[IFT-TLS] Trusted Computing Group, "TNC IF-T: Binding to TLS",
http://www.trustedcomputinggroup.org/files/resource_files/5
1F0757E-1D09-3519-
AD63B6FD099658A6/TNC_IFT_TLS_v1_0_r16.pdf, May 2009.
[PT-EAP] Cam-Winget, N., S., Sangster, P., "PT-EAP: Posture
Transport (PT) Protocol For EAP Tunnel Methods", draft-
ietf-nea-pt-eap-01.txt (work in progress), March 2012.
[RFC5209] Sangster, P., Khosravi, H., Mani, M., Narayan, K., and J.
Tardo, "Network Endpoint Assessment (NEA): Overview and
Requirements", RFC 5209, June 2008.
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[RFC5801] Josefsson, S., Williams, N., "Using Generic Security
Service Application Program Interface (GSS-API) Mechanisms
in Simple Authentication and Security Layer (SASL): The GS2
Mechanism Family", RFC 5801, July 2010.
Authors' Addresses
Paul Sangster
Symantec Corporation
6825 Citrine Dr
Carlsbad, CA 92009
Email: paul_sangster@symantec.com
Nancy Cam-Winget
Cisco Systems
80 West Tasman Drive
San Jose, CA 95134
US
Email: ncamwing@cisco.com
Joseph Salowey
Cisco Systems
2901 Third Avenue
Seattle, WA 98121
US
Email: jsalowey@cisco.com
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