Internet DRAFT - draft-ietf-pcp-authentication
draft-ietf-pcp-authentication
Network Working Group M. Wasserman
Internet-Draft S. Hartman
Updates: 6887 (if approved) Painless Security
Intended status: Standards Track D. Zhang
Expires: January 21, 2016 Huawei
T. Reddy
Cisco
July 20, 2015
Port Control Protocol (PCP) Authentication Mechanism
draft-ietf-pcp-authentication-14
Abstract
An IPv4 or IPv6 host can use the Port Control Protocol (PCP) to
flexibly manage the IP address and port mapping information on
Network Address Translators (NATs) or firewalls to facilitate
communication with remote hosts. However, the un-controlled
generation or deletion of IP address mappings on such network devices
may cause security risks and should be avoided. In some cases the
client may need to prove that it is authorized to modify, create or
delete PCP mappings. This document describes an in-band
authentication mechanism for PCP that can be used in those cases.
The Extensible Authentication Protocol (EAP) is used to perform
authentication between PCP devices.
This document updates RFC6887.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on January 21, 2016.
Wasserman, et al. Expires January 21, 2016 [Page 1]
Internet-Draft PCP Authentication July 2015
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 5
3.1.1. Authentication triggered by the client . . . . . . . 6
3.1.2. Authentication triggered by the server . . . . . . . 7
3.1.3. Authentication using EAP . . . . . . . . . . . . . . 7
3.2. Recovery from lost PA session . . . . . . . . . . . . . . 9
3.3. Session Termination . . . . . . . . . . . . . . . . . . . 10
3.4. Session Re-Authentication . . . . . . . . . . . . . . . . 11
4. PA Security Association . . . . . . . . . . . . . . . . . . . 12
5. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. Packet Format of PCP Auth Messages . . . . . . . . . . . 13
5.2. Opcode-specific information of AUTHENTICATION Opcode . . 15
5.3. NONCE Option . . . . . . . . . . . . . . . . . . . . . . 16
5.4. AUTHENTICATION_TAG Option . . . . . . . . . . . . . . . . 16
5.5. PA_AUTHENTICATION_TAG option . . . . . . . . . . . . . . 18
5.6. EAP_PAYLOAD Option . . . . . . . . . . . . . . . . . . . 19
5.7. PRF Option . . . . . . . . . . . . . . . . . . . . . . . 19
5.8. MAC_ALGORITHM Option . . . . . . . . . . . . . . . . . . 20
5.9. SESSION_LIFETIME Option . . . . . . . . . . . . . . . . . 20
5.10. RECEIVED_PAK Option . . . . . . . . . . . . . . . . . . . 21
5.11. ID_INDICATOR Option . . . . . . . . . . . . . . . . . . . 21
6. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 22
6.1. Authentication Data Generation . . . . . . . . . . . . . 22
6.2. Authentication Data Validation . . . . . . . . . . . . . 23
6.3. Retransmission Policies for PA Messages . . . . . . . . . 24
6.4. Sequence Numbers for PCP Auth Messages . . . . . . . . . 24
6.5. Sequence Numbers for Common PCP Messages . . . . . . . . 25
6.6. MTU Considerations . . . . . . . . . . . . . . . . . . . 26
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
Wasserman, et al. Expires January 21, 2016 [Page 2]
Internet-Draft PCP Authentication July 2015
7.1. NONCE . . . . . . . . . . . . . . . . . . . . . . . . . . 28
7.2. AUTHENTICATION_TAG . . . . . . . . . . . . . . . . . . . 28
7.3. PA_AUTHENTICATION_TAG . . . . . . . . . . . . . . . . . . 28
7.4. EAP_PAYLOAD . . . . . . . . . . . . . . . . . . . . . . . 29
7.5. PRF . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.6. MAC_ALGORITHM . . . . . . . . . . . . . . . . . . . . . . 29
7.7. SESSION_LIFETIME . . . . . . . . . . . . . . . . . . . . 30
7.8. RECEIVED_PAK . . . . . . . . . . . . . . . . . . . . . . 30
7.9. ID_INDICATOR . . . . . . . . . . . . . . . . . . . . . . 30
8. Security Considerations . . . . . . . . . . . . . . . . . . . 31
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31
10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.1. Changes from wasserman-pcp-authentication-02 to ietf-
pcp-authentication-00 . . . . . . . . . . . . . . . . . 32
10.2. Changes from wasserman-pcp-authentication-01 to -02 . . 32
10.3. Changes from ietf-pcp-authentication-00 to -01 . . . . . 32
10.4. Changes from ietf-pcp-authentication-01 to -02 . . . . . 32
10.5. Changes from ietf-pcp-authentication-02 to -03 . . . . . 33
10.6. Changes from ietf-pcp-authentication-03 to -04 . . . . . 33
10.7. Changes from ietf-pcp-authentication-04 to -05 . . . . . 33
10.8. Changes from ietf-pcp-authentication-05 to -06 . . . . . 33
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
11.1. Normative References . . . . . . . . . . . . . . . . . . 34
11.2. Informative References . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
Using the Port Control Protocol (PCP) [RFC6887], an application can
flexibly manage the IP address mapping information on its network
address translators (NATs) and firewalls, and control their policies
in processing incoming and outgoing IP packets. Because NATs and
firewalls both play important roles in network security
architectures, there are many situations in which authentication and
access control are required to prevent un-authorized users from
accessing such devices. This document defines a PCP security
extension that enables PCP servers to authenticate their clients with
Extensible Authentication Protocol (EAP). The EAP messages are
encapsulated within PCP messages during transportation.
The following issues are considered in the design of this extension:
o Loss of EAP messages during transportation
o Reordered delivery of EAP messages
o Generation of transport keys
Wasserman, et al. Expires January 21, 2016 [Page 3]
Internet-Draft PCP Authentication July 2015
o Integrity protection and data origin authentication for PCP
messages
o Algorithm agility
The mechanism described in this document meets the security
requirements to address the Advanced Threat Model described in the
base PCP specification [RFC6887]. This mechanism can be used to
secure PCP in the following situations:
o On security infrastructure equipment, such as corporate firewalls,
that do not create implicit mappings for specific traffic.
o On equipment (such as CGNs or service provider firewalls) that
serve multiple administrative domains and do not have a mechanism
to securely partition traffic from those domains.
o For any implementation that wants to be more permissive in
authorizing applications to create mappings for successful inbound
communications destined to machines located behind a NAT or a
firewall.
2. Terminology
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].
Most of the terms used in this document are introduced in [RFC6887].
PCP Client: A PCP software instance that is responsible for issuing
PCP requests to a PCP server. In this document, a PCP client is also
a EAP peer [RFC3748], and it is the responsibility of a PCP client to
provide the credentials when authentication is required.
PCP Server: A PCP software instance that resides on the PCP-
Controlled Device that receives PCP requests from the PCP client and
creates appropriate state in response to that request. In this
document, a PCP server is integrated with an EAP authenticator
[RFC3748]. Therefore, when necessary, a PCP server can verify the
credentials provided by a PCP client and make an access control
decision based on the authentication result.
PCP-Authentication (PA) Session: A series of PCP message exchanges
transferred between a PCP client and a PCP server. The PCP messages
involved within a session includes the PA messages used to perform
EAP authentication, key distribution and session management, and the
common PCP messages secured with the keys distributed during
Wasserman, et al. Expires January 21, 2016 [Page 4]
Internet-Draft PCP Authentication July 2015
authentication. Each PA session is assigned a distinctive Session
ID.
Session Partner: A PCP implementation involved within a PA session.
Each PA session has two session partners (a PCP server and a PCP
client).
PCP device: A PCP client or a PCP server.
Session Lifetime: The lifetime associated with a PA session, which
decides the lifetime of the current authorization given to the PCP
client.
PCP Security Association (PCP SA): A PCP security association is
formed between a PCP client and a PCP server by sharing cryptographic
keying material and associated context. The formed duplex security
association is used to protect the bidirectional PCP signaling
traffic between the PCP client and PCP server.
Master Session Key (MSK): A key derived by the partners of a PA
session, using an EAP key generating method (e.g., the one defined in
[RFC5448]).
PCP-Authentication (PA) message: A PCP message containing an
AUTHENTICATION Opcode. Particularly, a PA message sent from a PCP
server to a PCP client is referred to as a PA-Server message, while a
PA message sent from a PCP client to a PCP server is referred to as a
PA-Client message. Therefore, a PA-Server message is actually a PCP
response message specified in [RFC6887], and a PA-Client message is a
PCP request message. This document specifies an option, the
PA_AUTHENTICATION_TAG Option defined in Section 5.5 for PCP
authentication, to provide integrity protection and message origin
authentication for PA messages.
Common PCP message: A PCP message which does not contain an
AUTHENTICATION Opcode. This document specifies an AUTHENTICATION_TAG
Option to provide integrity protection and message origin
authentication for the common PCP messages.
3. Protocol Details
3.1. Session Initiation
At the beginning of a PA session, a PCP client and a PCP server need
to exchange a series of PA messages in order to perform an EAP
authentication process. Each PA message MUST contain an
AUTHENTICATION Opcode and may optionally contain a set of Options for
various purposes (e.g., transporting authentication messages and
Wasserman, et al. Expires January 21, 2016 [Page 5]
Internet-Draft PCP Authentication July 2015
session management). The opcode-specific information in a
AUTHENTICATION Opcode consists of two fields : Session ID and
Sequence Number. The Session ID field is used to identify the PA
session to which the message belongs. The sequence number field is
used to detect whether reordering or duplication occurred during
message delivery.
3.1.1. Authentication triggered by the client
When a PCP client intends to proactively initiate a PA session with a
PCP server, it sends a PA-Initiation message (a PA-Client message
with the result code "INITIATION") to the PCP server. Section 5.1
updates the PCP request message format with result codes for the PCP
Authentication mechanism. In the opcode-specific information of the
message, the Session ID and Sequence Number fields are set as 0. The
PA-Client message MUST also contain a NONCE option defined in
Section 5.3 which consists of a random nonce.
After receiving the PA-Initiation, if the PCP server agrees to
initiate a PA session with the PCP client, it will reply with a PA-
Server message which contains an EAP Request and the result code
field of this PA-Server message is set to AUTHENTICATION_REQUEST. In
addition, the server MUST assign a unique session identifier to
distinctly identify this session, and fill the identifier into the
Session ID field in the opcode-specific information of the PA-Server
message. The Sequence Number field of the message is set as 0. The
PA-Server message MUST contain a NONCE option so as to send the nonce
value back. The nonce will then be used by the PCP client to check
the freshness of this message. Subsequent PCP messages within this
PA session MUST contain this session identifier.
PCP PCP
client server
|-- PA-Initiation-------------------------------->|
| (Seq=0, rc=INITIATION, Session ID=0) |
| |
|<-- PA-Server -----------------------------------|
| (Seq=0, Session ID=X, EAP request, |
| rc=AUTHENTICATION_REQUEST) |
| |
|-- PA-Client ----------------------------------->|
| (Seq=1, Session ID=X, EAP response, |
| rc=AUTHENTICATION_REPLY) |
| |
|<-- PA-Server -----------------------------------|
| (Seq=1, Session ID=X, EAP request, |
| rc=AUTHENTICATION_REQUEST) |
Wasserman, et al. Expires January 21, 2016 [Page 6]
Internet-Draft PCP Authentication July 2015
3.1.2. Authentication triggered by the server
In the scenario where a PCP server receives a common PCP request
message from a PCP client which needs to be authenticated, the PCP
server rejects the request with a AUTHENTICATION_REQUIRED error code
and can reply with a unsolicited PA-Server message to initiate a PA
session. The result code field of this PA-Server message is set to
AUTHENTICATION_REQUEST. In addition, the PCP server MUST assign a
Session ID for the session and transfer it within the PA-Server
message. The Sequence Number field in the PA-Server message is set
as 0. If the PCP client retries the common request before EAP
authentication is successful then it will receive
AUTHENTICATION_REQUIRED error code from the PCP server. In the PA
messages exchanged afterwards in this session, the Session ID will be
used in order to help session partners distinguish the messages
within this session from those not within. When the PCP client
receives this initial PA-Server message from the PCP server, it can
reply with a PA-Client message or silently discard the request
message according to its local policies. In the PA-Client message, a
NONCE option which consists of a random nonce MAY be appended. If
so, in the next PA-Server message, the PCP server MUST forward the
nonce back within a NONCE option.
PCP PCP
client server
|-- Common PCP request--------------------------->|
| |
|<- Common PCP response---------------------------|
| rc=AUTHENTICATION_REQUIRED) |
| |
|<-- PA-Server -----------------------------------|
| (Seq=0, Session ID=X, EAP request) |
| rc=AUTHENTICATION_REQUEST) |
| |
|-- PA-Client ----------------------------------->|
| (Seq=0, Session ID=X, EAP response) |
| rc=AUTHENTICATION_REPLY) |
| |
|<-- PA-Server -----------------------------------|
| (Seq=1, Session ID=X, EAP request, |
| rc=AUTHENTICATION_REQUEST) |
3.1.3. Authentication using EAP
In a PA session, an EAP request message is transported within a PA-
Server message and an EAP response message is transported within a
PA-Client message. EAP relies on the underlying protocol to provide
Wasserman, et al. Expires January 21, 2016 [Page 7]
Internet-Draft PCP Authentication July 2015
reliable transmission; any reordered delivery or loss of packets
occurring during transportation must be detected and addressed.
Therefore, after sending out a PA-Server message, the PCP server will
not send a new PA-Server message in the same PA session until it
receives a PA-Client message with a proper sequence number from the
PCP client, and vice versa. If a PCP client receives a PA message
containing an EAP request and cannot generate an EAP response
immediately due to certain reasons (e.g., waiting for human input to
construct a EAP message or due to EAP message fragmentation waiting
for the additional PA messages in order to construct a complete EAP
message), the PCP device MUST reply with a PA-Acknowledgement message
(PA message with a RECEIVED_PAK Option) to indicate that the message
has been received. This approach not only can avoid unnecessary
retransmission of the PA message but also can guarantee the reliable
message delivery in conditions where a PCP device needs to receive
multiple PA messages carrying the fragmented EAP request before
generating an EAP response. The number of EAP messages exchanged
between the PCP client and PCP server depends on the EAP method used
for authentication.
In this approach, PCP client and a PCP server MUST perform a key-
generating EAP method in authentication. Particularly, a PCP
authentication implementation MUST support EAP-TTLS [RFC5281] and
SHOULD support TEAP [RFC7170]. Therefore, after a successful
authentication procedure, a Master Session Key (MSK) will be
generated. If the PCP client and the PCP server want to generate a
transport key using the MSK, they need to agree upon a Pseudo-Random
Function (PRF) for the transport key derivation and a MAC algorithm
to provide data origin authentication for subsequent PCP messages.
In order to do this, the PCP server needs to append a set of PRF
Options and MAC_ALGORITHM Options to the initial PA-Server message.
Each PRF Option contains a PRF that the PCP server supports, and each
MAC_ALGORITHM Option contains a MAC (Message Authentication Code)
algorithm that the PCP server supports. Moreover, in the first PA-
Server message, the server MAY also attach an ID_INDICATOR Option
defined in Section 5.11 to direct the client to choose correct
credentials. After receiving the options, the PCP client MUST select
the PRF and the MAC algorithm which it would like to use, and then
adds the associated PRF and MAC Algorithm Options to the next PA-
Client message.
After the EAP authentication, the PCP server sends out a PA-Server
message to indicate the EAP authentication and PCP authorization
results. If the EAP authentication succeeds, the result code of the
PA-Server message is AUTHENTICATION_SUCCEEDED. In this case, before
sending out the PA-Server message, the PCP server MUST update the PCP
SA with the MSK and transport key, and use the derived transport key
to generate a digest for the message. The digest is transported
Wasserman, et al. Expires January 21, 2016 [Page 8]
Internet-Draft PCP Authentication July 2015
within an PA_AUTHENTICATION_TAG Option for PCP Auth. A more detailed
description of generating the authentication data can be found in
Section 6.1. In addition, the PA-Server message MUST also contain a
SESSION_LIFETIME Option defined in Section 5.9 which indicates the
lifetime of the PA session (i.e., the lifetime of the MSK). After
receiving the PA-Server message, the PCP client then needs to
generate a PA-Client message as response. If the PCP client also
authenticates the PCP server, the result code of the PA-Client
message is AUTHENTICATION_SUCCEEDED. In addition, the PCP client
needs to update the PCP SA with the MSK and transport key, and uses
the derived transport key to secure the message. From then on, all
the PCP messages within the session are secured with the transport
key and the MAC algorithm specified in the PCP SA. The first secure
PA-client message from the client MUST include the set of PRF and
MAC_ALGORITHM options received from the PCP server. The PCP server
determines if the set of algorithms conveyed by the client matches
the set it had initially sent, to detect an algorithm downgrade
attack. If the server detects a downgrade attack then it MUST send a
PA-Server message with result code DOWNGRADE_ATTACK_DETECTED and
terminate the session. If the PCP client sends common PCP request
within the PA session without AUTHENTICATION_TAG option then the PCP
server rejects the request by returning AUTHENTICATION_REQUIRED error
code.
If a PCP client/server cannot authenticate its session partner, the
device sends out a PA message with the result code,
AUTHENTICATION_FAILED. If the EAP authentication succeeds but
authorization fails, the device making the decision sends out a PA
message with the result code, AUTHORIZATION_FAILED. In these two
cases, after the PA message is sent out, the PA session MUST be
terminated immediately. It is possible for independent PCP clients
on the host to create multiple PA sessions with the PCP server.
3.2. Recovery from lost PA session
If a PCP server resets or loses the PCP SA due to reboot, power
failure, or any reason then it sends unsolicited ANNOUNCE response as
explained in section 14.1.3 of [RFC6887] to the PCP client. Upon
receiving the ANNOUNCE response with an anomalous Epoch time, PCP
client deduces that the server may have lost state. The ANNOUNCE is
either bogus (an attack), legitimate, or not seen by the client.
These three cases are described below:
o PCP client sends integrity-protected unicast ANNOUNCE request to
the PCP server to check if the PCP server has indeed lost the
state or an attacker has sent the ANNOUNCE response.
Wasserman, et al. Expires January 21, 2016 [Page 9]
Internet-Draft PCP Authentication July 2015
* If integrity-protected success response is recevied from the
PCP server then the PCP client determines that the PCP server
has not lost the PA session, and the unsolicited ANNOUNCE
response was sent by an attacker.
* If the PCP server responds to the ANNOUNCE request with
UNKNOWN_SESSION_ID error code then the PCP client MUST initiate
full EAP authentication with the PCP server as explained in
Section 3.1.1. After EAP authentication is successful PCP
client updates the PCP SA and issues new common PCP requests to
recreate any lost mapping state.
o In a scenario where the PCP server has lost the PCP SA but did not
inform the PCP client, if the PCP client sends PCP request
integrity-protected then the PCP server rejects the request with
UNKNOWN_SESSION_ID error code. The PCP client then initiates full
EAP authentication with the PCP server as explained in
Section 3.1.1 and updates the PCP SA after successful
authentication.
If the PCP client resets or loses the PCP SA due to reboot, power
failure, or any reason and sends common PCP request then the PCP
server rejects the request with AUTHENTICATION_REQUIRED error code.
The PCP client MUST authenticate with the PCP server and after EAP
authentication is successful retry the common PCP request with
AUTHENTICATION_TAG option. The PCP server MUST update the PCP SA
after successful EAP authentication.
3.3. Session Termination
A PA session can be explicitly terminated by either session partner.
A PCP Server may explicitly request termination of the session by
sending an unsolicited termination-indicating PA response (a PA
response with a result code "SESSION-TERMINATED"). Upon receiving a
termination-indicating message, the PCP client MUST respond with a
termination-indicating PA message, and MUST then remove the
associated PCP SA. To accommodate packet loss, the PCP server MAY
transmit the termination-indicating PA response up to ten times (with
an appropriate Epoch Time value in each to reflect the passage of
time between transmissions) provided that the interval between the
first two notifications is at least 250 ms, and the interval between
subsequent notification at least doubles.
A PCP client may explicitly request termination of the session by
sending a termination-indicating PA request (a PA request with a
result code "SESSION-TERMINATED"). After receiving a termination-
indicating message from the PCP client, a PCP server MUST respond
with a termination-indicating PA response and remove the PCP SA
Wasserman, et al. Expires January 21, 2016 [Page 10]
Internet-Draft PCP Authentication July 2015
immediately. When the PCP client receives the termination-indicating
PA response, it MUST remove the associated PCP SA immediately.
3.4. Session Re-Authentication
A session partner may select to perform EAP re-authentication if it
would like to update the PCP SA without initiating a new PA session.
For example a re-authentication procedure could be triggered for the
following reasons:
o The session lifetime needs to be extended.
o The sequence number is going to reach the maximum value.
Specifically, when the sequence number reaches 2**32 - 2**16, the
session partner MUST trigger re-authentication.
When the PCP server would like to initiate a re-authentication, it
sends the PCP client a PA-Server message. The result code of the
message is set to "RE-AUTHENTICATION", which indicates the message is
for a re-authentication process. If the PCP client would like to
start the re-authentication, it will send a PA-Client message to the
PCP server, with the result code of the PA-Client message set to "RE-
AUTHENTICATION". Then, the session partners exchange PA messages to
transfer EAP messages for the re-authentication. During the re-
authentication procedure, the session partners protect the integrity
of PA messages with the key and MAC algorithm specified in the
current PCP SA; the sequence numbers associated with the message will
continue to keep increasing according to Section 6.3. The result
code for PA-Sever message carrying EAP request will be set to
AUTHENTICATION_REQUIRED and PA-Client message carrying EAP response
will be set to AUTHENTICATION_REPLY.
If the EAP re-authentication succeeds, the result code of the last
PA-Server message is "AUTHENTICATION_SUCCEEDED". In this case,
before sending out the PA-Server message, the PCP server MUST update
the SA and use the new key to generate a digest for the PA-Server
message and subsequent PCP messages. In addition, the PA-Server
message MUST be appended with a SESSION_LIFETIME Option which
indicates the new lifetime of the PA session. PA and PCP message
sequence numbers must also be reset to zero.
If the EAP authentication fails, the result code of the last PA-
Server message is "AUTHENTICATION_FAILED". If the EAP authentication
succeeds but authorization fails, the result code of the last PA-
Server message is "AUTHORIZATION_FAILED". In the latter two cases,
the PA session MUST be terminated immediately after the last PA
message exchange. If for some unknown reason re-authentication is
Wasserman, et al. Expires January 21, 2016 [Page 11]
Internet-Draft PCP Authentication July 2015
not performed and session lifetime has expired then PA session MUST
be terminated immediately.
During re-authentication, the session partners can also exchange
common PCP messages in parallel. The common PCP messages MUST be
protected with the current SA until the new SA has been generated.
The sequence of EAP messages exchanged for re-authentication will not
change, regardless of the PCP device triggering re-authentication.
If the PCP server receives re-authentication request from the PCP
client after it had signaled re-authentication request then it should
discard its request and respond to the re-authentication request from
the PCP client.
4. PA Security Association
At the beginning of a new PA session, each PCP device must create and
initialize state information for a new PA Security Association (PCP
SA) to maintain its state information for the duration of the PA
session. The parameters of a PCP SA are listed as follows:
o IP address and UDP port number of the PCP client
o IP address and UDP port number of the PCP server
o Session Identifier
o Sequence number for the next outgoing PA message
o Sequence number for the next incoming PA message
o Sequence number for the next outgoing common PCP message
o Sequence number for the next incoming common PCP message
o Last outgoing message payload
o Retransmission interval
o The master session key (MSK) generated by the EAP method.
o The MAC algorithm that the transport key should use to generate
digests for PCP messages.
o The pseudo random function negotiated in the initial PA-Server and
PA-Client message exchange for the transport key derivation
o The transport key derived from the MSK to provide integrity
protection and data origin authentication for the messages in the
Wasserman, et al. Expires January 21, 2016 [Page 12]
Internet-Draft PCP Authentication July 2015
PA session. The lifetime of the transport key SHOULD be identical
to the lifetime of the session.
o The nonce selected by the PCP client at the initiation of the
session.
o The Key ID associated with Transport key.
Particularly, the transport key is computed in the following way:
Transport key = prf(MSK, "IETF PCP" || Session ID || Nonce || key
ID), where:
o prf: The pseudo-random function assigned in the Pseudo-random
function parameter.
o MSK: The master session key generated by the EAP method.
o "IETF PCP": The ASCII code representation of the non-NULL
terminated string (excluding the double quotes around it).
o '||' : is the concatenation operator.
o Session ID: The ID of the session which the MSK is derived from.
o Nonce: The nonce selected by the client and transported in the
Initial PA-Client message.
o Key ID: The ID assigned for the transport key.
5. Packet Format
5.1. Packet Format of PCP Auth Messages
The format of the PA-Server message is identical to the response
message format specified in Section 7.2 of [RFC6887]. The result
code for PA-Sever message carrying EAP request MUST be set to
AUTHENTICATION_REQUEST.
As illustrated in Figure 1, this document updates the reserved field
in the request header specified in Section 7.1 of [RFC6887] to carry
Opcode-specific data.
Wasserman, et al. Expires January 21, 2016 [Page 13]
Internet-Draft PCP Authentication July 2015
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version = 2 |R| Opcode | Reserved |Opcode-specific|
| | | | | data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requested Lifetime (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| PCP Client's IP Address (128 bits) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Opcode-specific information :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) PCP Options :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. Request Packet Format
As illustrated in Figure 2, the PA-Client messages use the request
header specified in Figure 1. The Opcode-specific data is used to
transfer the result codes (e.g., "INITIATION",
"AUTHENTICATION_FAILED"). Other fields in Figure 2 are described in
Section 7.1 of [RFC6887]. The result code for PA-Client message
carrying EAP response MUST be set to AUTHENTICATION_REPLY.
Wasserman, et al. Expires January 21, 2016 [Page 14]
Internet-Draft PCP Authentication July 2015
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version = 2 |R| Opcode | Reserved | Result Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requested Lifetime (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| PCP Client's IP Address (128 bits) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Opcode-specific information :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) PCP Options :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. PA-Client message Format
The Requested Lifetime field of PA-Client message and Lifetime field
of PA-Server message are both set to 0 on transmission and ignored on
reception.
5.2. Opcode-specific information of AUTHENTICATION Opcode
The following diagram shows the format of the Opcode-specific
information for the AUTHENTICATION Opcode.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Session ID: This field contains a 32-bit PA session identifier.
Sequence Number: This field contains a 32-bit sequence number. A
sequence number needs to be incremented on every new (non-
retransmission) outgoing PA message in order to provide an
ordering guarantee for PA messages.
Wasserman, et al. Expires January 21, 2016 [Page 15]
Internet-Draft PCP Authentication July 2015
5.3. NONCE Option
Because the session identifier of a PA session is determined by the
PCP server, a PCP client does not know the session identifier which
will be used when it sends out a PA-Initiation message. In order to
prevent an attacker from interrupting the authentication process by
sending off-line generated PA-Server messages, the PCP client needs
to generate a random number as a nonce in the PA-Initiation message.
The PCP server will append the nonce within the initial PA-Server
message. If the PA-Server message does not carry the correct nonce,
the message MUST be discarded silently.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Code: TBA-130.
Reserved: 8 bits. MUST be set to 0 on transmission and MUST be
ignored on reception.
Option-Length: 4 octets.
Nonce: A random 32 bit number which is transported within a PA-
Initiation message and the corresponding reply message from the
PCP server.
5.4. AUTHENTICATION_TAG Option
Wasserman, et al. Expires January 21, 2016 [Page 16]
Internet-Draft PCP Authentication July 2015
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Data (Variable) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Because there is no authentication Opcode in common PCP messages, the
authentication tag for common PCP messages needs to carry the Session
ID and Sequence Number.
Option Code: TBA-131.
Reserved: 8 bits. MUST be set to 0 on transmission and MUST be
ignored on reception.
Option-Length: The length of the AUTHENTICATION_TAG Option for
Common PCP message (in octets), including the 12 octet fixed
header and the variable length of the authentication data.
Session ID: A 32-bit field used to identify the session to which
the message belongs and identify the secret key used to create the
message digest appended to the PCP message.
Sequence Number: A 32-bit sequence number. In this solution, a
sequence number needs to be incremented on every new (non-
retransmission) outgoing common PCP message in order to provide
ordering guarantee for common PCP messages.
Key ID: The ID associated with the transport key used to generate
authentication data. This field is filled with zero if the MSK is
directly used to secure the message.
Authentication Data: A variable-length field that carries the
Message Authentication Code for the Common PCP message. The
generation of the digest varies according to the algorithms
Wasserman, et al. Expires January 21, 2016 [Page 17]
Internet-Draft PCP Authentication July 2015
specified in different PCP SAs. This field MUST end on a 32-bit
boundary, padded with 0's when necessary.
5.5. PA_AUTHENTICATION_TAG option
This option is used to provide message authentication for PA
messages. Compared with the AUTHENTICATION_TAG Option for Common PCP
Messages, the Session ID field and the Sequence Number field are
removed because such information is provided in the Opcode-specific
information of AUTHENTICATION Opcode.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Data (Variable) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Code: TBA-132.
Reserved: 8 bits. MUST be set to 0 on transmission and MUST be
ignored on reception.
Option-Length: The length of the PA_AUTHENTICATION Option for PCP
Auth message (in octet), including the 4 octet fixed header and
the variable length of the authentication data.
Key ID: The ID associated with the transport key used to generate
authentication data. This field is filled with zero if the MSK is
directly used to secure the message.
Authentication Data: A variable-length field that carries the
Message Authentication Code for the PCP Auth message. The
generation of the digest varies according to the algorithms
specified in different PCP SAs. This field MUST end on a 32-bit
boundary, padded with null characters when necessary.
Wasserman, et al. Expires January 21, 2016 [Page 18]
Internet-Draft PCP Authentication July 2015
5.6. EAP_PAYLOAD Option
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| EAP Message |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Code: TBA-133.
Reserved: 8 bits. MUST be set to 0 on transmission and MUST be
ignored on reception.
Option-Length: Variable
EAP Message: The EAP message transferred. Note this field MUST
end on a 32-bit boundary, padded with 0's when necessary.
5.7. PRF Option
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PRF |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Code: TBA-134.
Reserved: 8 bits. MUST be set to 0 on transmission and MUST be
ignored on reception.
Option-Length: 4 octets.
PRF: The Pseudo-Random Function which the sender supports to generate
an MSK. This field contains an IKEv2 Transform ID of Transform Type
2 [RFC7296][RFC4868]. A PCP implementation MUST support
PRF_HMAC_SHA2_256 (5).
Wasserman, et al. Expires January 21, 2016 [Page 19]
Internet-Draft PCP Authentication July 2015
5.8. MAC_ALGORITHM Option
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Algorithm ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Code: TBA-135.
Reserved: 8 bits. MUST be set to 0 on transmission and MUST be
ignored on reception.
Option-Length: 4 octets.
MAC Algorithm ID: Indicate the MAC algorithm which the sender
supports to generate authentication data. The MAC Algorithm ID field
contains an IKEv2 Transform ID of Transform Type 3
[RFC7296][RFC4868]. A PCP implementation MUST support
AUTH_HMAC_SHA2_256_128 (12).
5.9. SESSION_LIFETIME Option
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Code: TBA-136.
Reserved: 8 bits. MUST be set to 0 on transmission and MUST be
ignored on reception.
Option-Length: 4 octets.
Session Lifetime: An unsigned 32-bit integer, in seconds, ranging
from 0 to 2^32-1 seconds. The lifetime of the PA Session, which is
decided by the authorization result.
Wasserman, et al. Expires January 21, 2016 [Page 20]
Internet-Draft PCP Authentication July 2015
5.10. RECEIVED_PAK Option
This option is used in a PA-Acknowledgement message to indicate that
a PA message with the contained sequence number has been received.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Received Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Code: TBA-137.
Reserved: 8 bits. MUST be set to 0 on transmission and MUST be
ignored on reception.
Option-Length: 4 octets.
Received Sequence Number: The sequence number of the last received PA
message.
5.11. ID_INDICATOR Option
The ID_INDICATOR option is used by the PCP client to determine which
credentials to provide to the PCP server.
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| ID Indicator |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Code: TBA-138.
Reserved: 8 bits. MUST be set to 0 on transmission and MUST be
ignored on reception.
Option-Length: Variable.
ID Indicator: The identity of the authority that issued the EAP
credentials to be used to authenticate the client. The field MUST
Wasserman, et al. Expires January 21, 2016 [Page 21]
Internet-Draft PCP Authentication July 2015
NOT be null terminated and its length is indicated by the Option-
Length field. In particular when a client receives a ID_INDICATOR
option, it MUST NOT rely on the presence of a NUL character in the
wire format data to identify the end of the ID Indicator field.
The field MUST end on a 32-bit boundary, padded with 0's when
necessary. The ID indicator field is UTF-8 encoded [RFC3629]
Unicode string conforming to the "UsernameCaseMapped" profile of
the PRECIS IdentifierClass [I-D.ietf-precis-saslprepbis]. The PCP
client validates that the ID indicator field conforms to the
"UsernameCaseMapped" profile of the PRECIS IdentifierClass. The
PCP client enforces the rules specified in section 3.2.2 of
[I-D.ietf-precis-saslprepbis] to map the ID indicator field. The
PCP client compares the resulting string with the ID indicators
stored locally on the PCP client to pick the credentials for
authentication. The two indicator strings are to be considered
equivalent by the client if and only if they are an exact octet-
for-octet match.
6. Processing Rules
6.1. Authentication Data Generation
After successful EAP authentication process, every subsequent PCP
message within the PA session MUST carry an authentication tag which
contains the digest of the PCP message for data origin authentication
and integrity protection.
o Before generating a digest for a PA message, a device needs to
first locate the PCP SA according to the session identifier and
then get the transport key. Then the device appends an
PA_AUTHENTICATION_TAG Option for PCP Auth at the end of the PCP
Auth message. The length of the Authentication Data field is
decided by the MAC algorithm adopted in the session. The device
then fills the Key ID field with the key ID of the transport key,
and sets the Authentication Data field to 0. After this, the
device generates a digest for the entire PCP message (including
the PCP header and PA_AUTHENTICATION_TAG Option) using the
transport key and the associated MAC algorithm, and inserts the
generated digest into the Authentication Data field.
o Similar to generating a digest for a PA message, before generating
a digest for a common PCP message, a device needs to first locate
the PCP SA according to the session identifier and then get the
transport key. Then the device appends the AUTHENTICATION_TAG
Option at the end of common PCP message. The length of the
Authentication Data field is decided by the MAC algorithm adopted
in the session. The device then uses the corresponding values
Wasserman, et al. Expires January 21, 2016 [Page 22]
Internet-Draft PCP Authentication July 2015
derived from the SA to fill the Session ID field, the Sequence
Number field and the Key ID field, and sets the Authentication
Data field to 0. After this, the device generates a digest for
the entire PCP message (including the PCP header and
AUTHENTICATION_TAG Option) using the transport key and the
associated MAC algorithm, and inputs the generated digest into the
Authentication Data field.
6.2. Authentication Data Validation
When a device receives a common PCP message with an
AUTHENTICATION_TAG Option for Common PCP Messages, the device needs
to use the Session ID transported in the option to locate the proper
SA, and then find the associated transport key (using the key ID in
the option) and the MAC algorithm. If no proper SA or transport key
is found or the sequence number is invalid (see Section 6.5), the PCP
device stops processing the PCP message and discards the message
silently. After storing the value of the Authentication field of the
AUTHENTICATION_TAG Option, the device fills the Authentication field
with zeros. Then, the device generates a digest for the message
(including the PCP header and Authentication Tag Option) with the
transport key and the MAC algorithm. If the value of the newly
generated digest is identical to the stored one, the device can
ensure that the message has not been tampered with, and the
validation succeeds. Otherwise, the PCP device stops processing the
PCP message and silently discards the message.
Similarly, when a device receives a PA message with an
PA_AUTHENTICATION_TAG Option for PCP Authentication, the device needs
to use the Session ID transported in the Opcode to locate the proper
SA, and then find the associated transport key (using the key ID in
the option) and the MAC algorithm. If no proper SA or transport key
is found or the sequence number is invalid (see Section 6.4), the PCP
device stops processing the PCP message and discards the message.
After storing the value of the Authentication field of the
PA_AUTHENTICATION_TAG Option, the device fills the Authentication
field with zeros. Then, the device generates a digest for the
message (including the PCP header and PA_AUTHENTICATION_TAG Option)
with the transport key and the MAC algorithm. If the value of the
newly generated digest is identical to the stored one, the device can
ensure that the message has not been tampered with, and the
validation succeeds. Otherwise, the PCP device stops processing the
PCP message and silently discards the message.
Wasserman, et al. Expires January 21, 2016 [Page 23]
Internet-Draft PCP Authentication July 2015
6.3. Retransmission Policies for PA Messages
Because EAP relies on the underlying protocols to provide reliable
transmission, after sending a PA message, a PCP client/server MUST
NOT send out any subsequent messages until receiving a PA message
with a proper sequence number from the peer. If no such a message is
received the PCP device will re-send the last message according to
retransmission policies. This work reuses the retransmission
policies specified in the base PCP protocol (Section 8.1.1 of
[RFC6887]). In the base PCP protocol, such retransmission policies
are only applied by PCP clients. However, in this work, such
retransmission policies are also applied by the PCP servers. If
Maximum retransmission duration seconds have elapsed and no expected
response is received, the device will terminate the session and
discard the current SA.
As illustrated in Section 3.1.3, in order to avoid unnecessary re-
transmission, the device receiving a PA message MUST send a PA-
Acknowledgement message to the sender of the PA message when it
cannot send a PA response immediately. The PA-Acknowledgement
message is used to indicate the receipt of the PA message. When the
sender receives the PA-Acknowledgement message, it will stop the
retransmission.
Note that the last PA messages transported within the phases of
session initiation, session re-authentication, and session
termination do not have to follow the above policies since the
devices sending out those messages do not expect any further PA
messages.
When a device receives a re-transmitted last incoming PA message from
its session partner, it MUST try to answer it by sending the last
outgoing PA message again. However, if the duplicate message has the
same sequence number but is not bit-wise identical to the original
message then the device MUST discard it. In order to achieve this
function, the device may need to maintain the last incoming and the
associated outgoing messages. In this case, if no outgoing PA
message has been generated for the received duplicate PA message yet,
the device needs to send a PA-Acknowledgement message. The rate of
replying to duplicate PA messages MUST be limited to provide
robustness against denial of service (DoS) attacks. The details of
rate limiting are outside the scope of this specification.
6.4. Sequence Numbers for PCP Auth Messages
PCP uses UDP to transport signaling messages. As an un-reliable
transport protocol, UDP does not guarantee ordered packet delivery
and does not provide any protection from packet loss. In order to
Wasserman, et al. Expires January 21, 2016 [Page 24]
Internet-Draft PCP Authentication July 2015
ensure the EAP messages are exchanged in a reliable way, every PCP
message exchanged during EAP authentication must carry a
monotonically increasing sequence number. During a PA session, a PCP
device needs to maintain two sequence numbers for PA messages, one
for incoming PA messages and one for outgoing PA messages. When
generating an outgoing PA message, the device adds the associated
outgoing sequence number to the message and increments the sequence
number maintained in the SA by 1. When receiving a PA message from
its session partner, the device will not accept it if the sequence
number carried in the message does not match the incoming sequence
number the device maintains. After confirming that the received
message is valid, the device increments the incoming sequence number
maintained in the SA by 1.
The above rules are not applicable to PA-Acknowledgement messages
(i.e., PA messages containing a RECEIVED_PAK Option). A PA-
Acknowledgement message does not transport any EAP message and only
indicates that a PA message is received. Therefore, reliable
transmission of PA-Acknowledgement messages is not required. For
instance, after sending out a PA-Acknowledgement message, a device
generates an EAP response. In this case, the device need not have to
confirm whether the PA-Acknowledgement message has been received by
its session partner or not. Therefore, when receiving or sending out
a PA-Acknowledgement message, the device MUST NOT increase the
corresponding sequence number stored in the SA. Otherwise, loss of a
PA-Acknowledgement message will cause a mismatch in sequence numbers.
Another exception is the message retransmission scenario. As
discussed in Section 6.3, when a PCP device does not receive any
response from its session partner it needs to retransmit the last
outgoing PA message following the retransmission procedure specified
in section 8.1.1 of [RFC6887]. The original message and duplicate
messages MUST be bit-wise identical. When the device receives such a
duplicate PA message from its session partner, it MUST send the last
outgoing PA message again. In such cases, the maintained incoming
and outgoing sequence numbers will not be affected by the message
retransmission.
6.5. Sequence Numbers for Common PCP Messages
When transporting common PCP messages within a PA session, a PCP
device needs to maintain a sequence number for outgoing common PCP
messages and a sequence number for incoming common PCP messages.
When generating a new outgoing PCP message, the PCP device updates
the Sequence Number field in the AUTHENTICATION_TAG option with the
outgoing sequence number maintained in the SA and increments the
outgoing sequence number by 1.
Wasserman, et al. Expires January 21, 2016 [Page 25]
Internet-Draft PCP Authentication July 2015
When receiving a PCP message from its session partner, the PCP device
will not accept it if the sequence number carried in the message is
smaller than the incoming sequence number the device maintains. This
approach can protect the PCP device from replay attacks. After
confirming that the received message is valid, the PCP device will
update the incoming sequence number maintained in the PCP SA with the
sequence number of the incoming message.
Note that the sequence number in the incoming message may not exactly
match the incoming sequence number maintained locally. As discussed
in the base PCP specification [RFC6887], if a PCP client is no longer
interested in the PCP transaction and has not yet received a PCP
response from the server then it will stop retransmitting the PCP
request. After that, the PCP client might generate new PCP requests
for other purposes using the current SA. In this case, the sequence
number in the new request will be larger than the sequence number in
the old request and so will be larger than the incoming sequence
number maintained in the PCP server.
Note that in the base PCP specification [RFC6887], a PCP client needs
to select a nonce in each MAP or PEER request, and the nonce is sent
back in the response. However, it is possible for a client to use
the same nonce in multiple MAP or PEER requests, and this may cause a
potential risk of replay attacks. This attack is addressed by using
the sequence number in the PCP response.
6.6. MTU Considerations
EAP methods are responsible for MTU handling, so no special
facilities are required in PCP to deal with MTU issues.
Particularly, EAP lower layers indicate to EAP methods and AAA
servers the MTU of the lower layer. EAP methods such as EAP-TLS
[RFC5216], TEAP [RFC7170], and others that are likely to exceed
reasonable MTUs provide support for fragmentation and reassembly.
Others, such as EAP-GPSK [RFC5433] assume they will never send
packets larger than the MTU and use small EAP packets.
If an EAP message is too long to be transported within a single PA
message, it will be divided into multiple sections and sent within
different PA messages. Note that the receiver may not be able to
know what to do in the next step until it has received all the
sections and reconstructed the complete EAP message. In this case,
in order to guarantee reliable message transmission, after receiving
a PA message, the receiver replies with a PA-Acknowledgement message
to notify the sender to send the next PA message.
Wasserman, et al. Expires January 21, 2016 [Page 26]
Internet-Draft PCP Authentication July 2015
7. IANA Considerations
The following PCP Opcode is to be allocated in the mandatory-to-
process range from the standards action range (the registry for PCP
Opcodes is maintained in http://www.iana.org/assignments/pcp-
parameters):
TBA AUTHENTICATION Opcode.
The following PCP result codes are to be allocated in the mandatory-
to-process range from the standards action range (the registry for
PCP result codes is maintained in http://www.iana.org/assignments/
pcp-parameters):
TBA INITIATION: The client indication to the server for
authentication.
TBA AUTHENTICATION_REQUIRED: The error response is signaled to the
client that EAP authentication is required.
TBA AUTHENTICATION_FAILED: This error response is signaled to the
client if EAP authentication had failed.
TBA AUTHENTICATION_SUCCEEDED:This success response is signaled to
the client if EAP authentication had succeeded.
TBA AUTHORIZATION_FAILED: This error response is signaled to the
client if the EAP authentication had succeeded but authorization
failed.
TBA SESSION_TERMINATED: This PCP result code indicates to the
partner that the PA session must be terminated.
TBA UNKNOWN_SESSION_ID: The error response is signaled from the
PCP server that there is no known PA session associated with the
Session ID signaled in the PA request or common PCP request from
the PCP client.
TBA DOWNGRADE_ATTACK_DETECTED: This error response is signaled to
the client if the server detects downgrade attack.
TBA AUTHENTICATION_REQUEST: The server indication to the client
that EAP request is signaled in the PA message.
TBA AUTHENTICATION_REPLY: The client indication to the server that
EAP response is signaled in the PA message.
Wasserman, et al. Expires January 21, 2016 [Page 27]
Internet-Draft PCP Authentication July 2015
The following PCP Option Codes are to be allocated in the mandatory-
to-process range from the standards action range (the registry for
PCP Options is maintained in http://www.iana.org/assignments/pcp-
parameters):
7.1. NONCE
Option Name: NONCE
option-code: TBA-130 in the mandatory-to-process range (IANA).
Purpose: See Section 5.3.
Valid for Opcodes: Authentication Opcode.
option-len: Option Length is 4 octets.
May appear in: request and response.
Maximum occurrences: 1.
7.2. AUTHENTICATION_TAG
Option Name: AUTHENTICATION_TAG
option-code: TBA-131 in the mandatory-to-process range (IANA).
Purpose: See Section 5.4.
Valid for Opcodes: MAP, PEER and ANNOUNCE Opcodes.
option-len: Variable length.
May appear in: request and response.
Maximum occurrences: 1.
7.3. PA_AUTHENTICATION_TAG
Option Name: PA_AUTHENTICATION_TAG
option-code: TBA-132 in the mandatory-to-process range (IANA).
Purpose: See Section 5.5.
Valid for Opcodes: Authentication Opcode.
option-len: Variable length.
Wasserman, et al. Expires January 21, 2016 [Page 28]
Internet-Draft PCP Authentication July 2015
May appear in: request and response.
Maximum occurrences: 1.
7.4. EAP_PAYLOAD
Option Name: EAP_PAYLOAD.
option-code: TBA-133 in the mandatory-to-process range (IANA).
Purpose: See Section 5.6.
Valid for Opcodes: Authentication Opcode.
option-len: Variable length.
May appear in: request and response.
Maximum occurrences: 1.
7.5. PRF
Option Name: PRF.
option-code: TBA-134 in the mandatory-to-process range (IANA).
Purpose: See Section 5.7.
Valid for Opcodes: Authentication Opcode.
option-len: Option Length is 4 octets.
May appear in: request and response.
Maximum occurrences: as many as fit within maximum PCP message size.
7.6. MAC_ALGORITHM
Option Name: MAC_ALGORITHM.
option-code: TBA-135 in the mandatory-to-process range (IANA).
Purpose: See Section 5.8.
Valid for Opcodes: Authentication Opcode.
option-len: Option Length is 4 octets.
Wasserman, et al. Expires January 21, 2016 [Page 29]
Internet-Draft PCP Authentication July 2015
May appear in: request and response.
Maximum occurrences: as many as fit within maximum PCP message size.
7.7. SESSION_LIFETIME
Option Name: SESSION_LIFETIME.
option-code: TBA-136 in the mandatory-to-process range (IANA).
Purpose: See Section 5.9.
Valid for Opcodes: Authentication Opcode.
option-len: Option Length is 4 octets.
May appear in: response.
Maximum occurrences: 1.
7.8. RECEIVED_PAK
Option Name: RECEIVED_PAK.
option-code: TBA-137 in the mandatory-to-process range (IANA).
Purpose: See Section 5.10.
Valid for Opcodes: Authentication Opcode.
option-len: Option Length is 4 octets.
May appear in: request and response.
Maximum occurrences: 1.
7.9. ID_INDICATOR
Option Name: ID_INDICATOR.
option-code: TBA-138 in the mandatory-to-process range (IANA).
Purpose: See Section 5.11.
Valid for Opcodes: Authentication Opcode.
option-len: Variable length.
Wasserman, et al. Expires January 21, 2016 [Page 30]
Internet-Draft PCP Authentication July 2015
May appear in: response.
Maximum occurrences: 1.
8. Security Considerations
In this work, after a successful EAP authentication process is
performed between two PCP devices, an MSK will be exported. The MSK
will be used to derive the transport keys to generate MAC digests for
subsequent PCP message exchanges. However, before a transport key
has been generated, the PA messages exchanged within a PA session
have little cryptographic protection, and if there is no already
established security channel between two session partners, these
messages are subject to man-in-the-middle attacks and DOS attacks.
For instance, the initial PA-Server and PA-Client message exchange is
vulnerable to spoofing attacks as these messages are not
authenticated and integrity protected. In addition, because the PRF
and MAC algorithms are transported at this stage, an attacker may try
to remove the PRF and MAC options containing strong algorithms from
the initial PA-Server message and force the client choose the weakest
algorithms. Therefore, the server needs to guarantee that all the
PRF and MAC algorithms it provides support for are strong enough.
In order to prevent very basic DOS attacks, a PCP device SHOULD
generate state information as little as possible in the initial PA-
Server and PA-Client message exchanges. The choice of EAP method is
also very important. The selected EAP method must be resilient to
the attacks possible in an insecure network environment, provide
user-identity confidentiality, protection against dictionary attacks,
and support session-key establishment.
When a PCP proxy [I-D.ietf-pcp-proxy] is located between a PCP server
and PCP clients, the proxy may perform authentication with the PCP
server before it processes requests from the clients. In addition,
re-authentication between the PCP proxy and PCP server will not
interrupt the service that the proxy provides to the clients since
the proxy is still allowed to send common PCP messages to the PCP
server during that period.
9. Acknowledgements
Thanks to Dan Wing, Prashanth Patil, Dave Thaler, Peter Saint-Andre,
Carlos Pignataro, Brian Haberman, Paul Kyzivat, Jouni Korhonen,
Stephen Farrell and Terry Manderson for the valuable comments.
Wasserman, et al. Expires January 21, 2016 [Page 31]
Internet-Draft PCP Authentication July 2015
10. Change Log
[Note: This section should be removed by the RFC Editor upon
publication]
10.1. Changes from wasserman-pcp-authentication-02 to ietf-pcp-
authentication-00
o Added discussion of in-band and out-of-band key management
options, leaving choice open for later WG decision.
o Removed support for fragmenting EAP messages, as that is handled
by EAP methods.
10.2. Changes from wasserman-pcp-authentication-01 to -02
o Add a nonce into the first two exchanged PCP-Auth message between
the PCP client and PCP server. When a PCP client initiate the
session, it can use the nonce to detect offline attacks.
o Add the key ID field into the authentication tag option so that a
MSK can generate multiple transport keys.
o Specify that when a PCP device receives a PCP-Auth-Server or a
PCP-Auth-Client message from its partner the PCP device needs to
reply with a PCP-Auth-Acknowledge message to indicate that the
message has been received.
o Add the support of fragmenting EAP messages.
10.3. Changes from ietf-pcp-authentication-00 to -01
o Editorial changes, added use cases to introduction.
10.4. Changes from ietf-pcp-authentication-01 to -02
o Add the support of re-authentication initiated by PCP server.
o Specify that when a PCP device receives a PCP-Auth-Server or a
PCP-Auth-Client message from its partner the PCP device MAY reply
with a PCP-Auth-Acknowledge message to indicate that the message
has been received.
o Discuss the format of the PCP-Auth-Acknowledge message.
o Remove the redundant information from the Auth Opcode, and specify
new result codes transported in PCP packet headers
Wasserman, et al. Expires January 21, 2016 [Page 32]
Internet-Draft PCP Authentication July 2015
o
10.5. Changes from ietf-pcp-authentication-02 to -03
o Change the name "PCP-Auth-Request" to "PCP-Auth-Server"
o Change the name "PCP-Auth-Response" to "PCP-Auth-Client"
o Specify two new sequence numbers for common PCP messages in the
PCP SA, and describe how to use them
o Specify a Authentication Tag Option for PCP Common Messages
o Introduce the scenario where a EAP message has to be divided into
multiple sections and transported in different PCP-Auth messages
(for the reasons of MTU), and introduce how to use PCP-Auth-
Acknowledge messages to ensure reliable packet delivery in this
case.
10.6. Changes from ietf-pcp-authentication-03 to -04
o Change the name "PCP-Auth" to "PA".
o Refine the retransmission policies.
o Add more discussion about the sequence number management .
o Provide the discussion about how to instruct a PCP client to
choose proper credential during authentication, and an ID
Indicator Option is defined for that purpose.
10.7. Changes from ietf-pcp-authentication-04 to -05
o Add contents in IANA considerations.
o Add discussions in fragmentation.
o Refine the PA messages retransmission policies.
o Add IANA considerations.
10.8. Changes from ietf-pcp-authentication-05 to -06
o Added mechanism to handle algorithm downgrade attack.
o Updated Security Considerations section.
o Updated ID Indicator Option.
Wasserman, et al. Expires January 21, 2016 [Page 33]
Internet-Draft PCP Authentication July 2015
11. References
11.1. Normative References
[I-D.ietf-pcp-proxy]
Perreault, S., Boucadair, M., Penno, R., Wing, D., and S.
Cheshire, "Port Control Protocol (PCP) Proxy Function",
draft-ietf-pcp-proxy-09 (work in progress), July 2015.
[I-D.ietf-precis-saslprepbis]
Saint-Andre, P. and A. Melnikov, "Preparation,
Enforcement, and Comparison of Internationalized Strings
Representing Usernames and Passwords", draft-ietf-precis-
saslprepbis-18 (work in progress), May 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <http://www.rfc-editor.org/info/rfc3629>.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
<http://www.rfc-editor.org/info/rfc3748>.
[RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
384, and HMAC-SHA-512 with IPsec", RFC 4868,
DOI 10.17487/RFC4868, May 2007,
<http://www.rfc-editor.org/info/rfc4868>.
[RFC5281] Funk, P. and S. Blake-Wilson, "Extensible Authentication
Protocol Tunneled Transport Layer Security Authenticated
Protocol Version 0 (EAP-TTLSv0)", RFC 5281,
DOI 10.17487/RFC5281, August 2008,
<http://www.rfc-editor.org/info/rfc5281>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<http://www.rfc-editor.org/info/rfc6887>.
Wasserman, et al. Expires January 21, 2016 [Page 34]
Internet-Draft PCP Authentication July 2015
[RFC7170] Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna,
"Tunnel Extensible Authentication Protocol (TEAP) Version
1", RFC 7170, DOI 10.17487/RFC7170, May 2014,
<http://www.rfc-editor.org/info/rfc7170>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <http://www.rfc-editor.org/info/rfc7296>.
11.2. Informative References
[RFC5216] Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216,
March 2008, <http://www.rfc-editor.org/info/rfc5216>.
[RFC5433] Clancy, T. and H. Tschofenig, "Extensible Authentication
Protocol - Generalized Pre-Shared Key (EAP-GPSK) Method",
RFC 5433, DOI 10.17487/RFC5433, February 2009,
<http://www.rfc-editor.org/info/rfc5433>.
[RFC5448] Arkko, J., Lehtovirta, V., and P. Eronen, "Improved
Extensible Authentication Protocol Method for 3rd
Generation Authentication and Key Agreement (EAP-AKA')",
RFC 5448, DOI 10.17487/RFC5448, May 2009,
<http://www.rfc-editor.org/info/rfc5448>.
Authors' Addresses
Margaret Wasserman
Painless Security
356 Abbott Street
North Andover, MA 01845
USA
Phone: +1 781 405 7464
Email: mrw@painless-security.com
URI: http://www.painless-security.com
Sam Hartman
Painless Security
356 Abbott Street
North Andover, MA 01845
USA
Email: hartmans@painless-security.com
URI: http://www.painless-security.com
Wasserman, et al. Expires January 21, 2016 [Page 35]
Internet-Draft PCP Authentication July 2015
Dacheng Zhang
Huawei
Beijing
China
Email: zhang_dacheng@hotmail.com
Tirumaleswar Reddy
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: tireddy@cisco.com
Wasserman, et al. Expires January 21, 2016 [Page 36]
