Network Working Group M. Wasserman
Internet-Draft S. Hartman
Intended status: Experimental Painless Security
Expires: April 05, 2014 D. Zhang
Huawei
October 02, 2013
Port Control Protocol (PCP) Authentication Mechanism
draft-ietf-pcp-authentication-02
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
communications 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 proposes 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.
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 April 05, 2014.
Copyright Notice
Copyright (c) 2013 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 5
3.2. Session Termination . . . . . . . . . . . . . . . . . . . 7
3.3. Session Re-Authentication . . . . . . . . . . . . . . . . 7
4. PA Security Association . . . . . . . . . . . . . . . . . . . 8
5. Result Code . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Packet Format of PCP Auth Messages . . . . . . . . . . . 10
6.2. Authentication OpCode Format . . . . . . . . . . . . . . 11
6.3. Nonce Option . . . . . . . . . . . . . . . . . . . . . . 12
6.4. Authentication Tag Option . . . . . . . . . . . . . . . . 12
6.5. EAP Payload Option . . . . . . . . . . . . . . . . . . . 13
6.6. PRF Option . . . . . . . . . . . . . . . . . . . . . . . 13
6.7. MAC Algorithm Option . . . . . . . . . . . . . . . . . . 14
6.8. Session Lifetime Option . . . . . . . . . . . . . . . . . 14
6.9. Received Packet Option . . . . . . . . . . . . . . . . . 14
7. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Authentication Data Generation . . . . . . . . . . . . . 15
7.2. Authentication Data Validation . . . . . . . . . . . . . 15
7.3. Retransmission Policies . . . . . . . . . . . . . . . . . 16
7.4. Sequence Number . . . . . . . . . . . . . . . . . . . . . 16
7.5. MTU Considerations . . . . . . . . . . . . . . . . . . . 17
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Changes from wasserman-pcp-authentication-02 to ietf-
pcp-authentication-00 . . . . . . . . . . . . . . . . . 18
11.2. Changes from wasserman-pcp-authentication-01 to -02 . . 18
11.3. Changes from ietf-pcp-authentication-00 to -01 . . . . . 18
11.4. Changes from ietf-pcp-authentication-01 to -02 . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 19
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
Using the Port Control Protocol (PCP) [RFC6887], an IPv4 or IPv6 host
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 proposes a PCP security
extension which enables PCP servers to authenticate their clients
with Extensible Authentication Protocol (EAP). The EAP messages are
encapsulated within PCP packets during transportation.
The following issues are considered in the design of this extension:
o Loss of EAP messages during transportation
o Disordered delivery of EAP messages
o Generation of transport keys
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 does not create implicit mappings.
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 explicit mappings than it is in authorizing implicit
mappings.
o For implementations that support the THIRD_PARTY Option (unless
they can meet the constraints outlined in Section 14.1.2.2).
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o For implementations that wish to support any deployment scenario
that does not meet the constraints described in Section 14.1.
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 device (e.g., a host) which 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 device (e.g., a NAT or a firewall) that implements
the server-side of the PCP protocol, via which PCP clients request
and manage explicit mappings. 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 (PCP Auth) Session: A series of PCP message
exchanges transferred between a PCP client and a PCP server. The PCP
message involved within a session includes the PCP Auth messages used
to perform authentication, key distribution and session management,
and the common PCP messages secured with the distributed keys. Each
PCP Auth session is assigned a distinctive Session ID.
Session Partner: A PCP device involved within a PCP Auth session.
Each PCP Auth session has two session partners (a PCP server and a
PCP client).
Session Lifetime: The life period associated with a PCP Auth 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 PCP Auth
session, using an EAP key generating method (e.g., the one defined in
[RFC5448]).
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PCP Authentication (PCP Auth) message: A PCP message containing an
Authentication OpCode. Particularly, a PCP Auth message sent from a
PCP server to a PCP client is referred to as a PCP-Auth-Request,
while PCP Auth message sent from a PCP client to a PCP server is
referred to as a PCP-Auth-Answer. Therefore, a PCP-Auth-Request is
actually a PCP response message specified [RFC6887], and a PCP-Auth-
Answer is a PCP request message.
Common PCP message: A PCP message which does not contain an
Authentication OpCode. This document specifies an authentication
option to provide integrity protection and message origin
authentication for the common PCP messages.
3. Protocol Details
3.1. Session Initiation
At be beginning of a PCP Auth Session, a set of PCP Auth messages
need to be exchanged between two PCP devices in order to carry out an
EAP authentication process. Each PCP Auth message is attached with
an Authentication OpCode and may optionally contain the Options for
various purposes (e.g., transporting authentication messages and
session managements). The Authentication OpCode consists of two
fields: Session ID, and Sequence Number. The Session ID field is
used to identify the session to which the message belongs. The
sequence number field is used to detect the disorder or the
duplication occurred during packet delivery.
When a PCP client intends to proactively initiate a PCP Auth session
with a PCP server, it sends a PCP-Auth-Initiation message (a PCP-
Auth-Answer message with the result code "INITIATION") to the PCP
server. In the message, the Session ID and Sequence Number fields of
the Authentication OpCode are set as 0. The PCP client MAY also
append a nonce option which consists of a random nonce with PCP-Auth-
Initiation message. After receiving the PCP-Auth-Initiation, if the
PCP server would like to initiate a PCP Auth session, it will reply
with a PCP-Auth-Request which contains an EAP Identity Request. The
Sequence Number field in the PCP-Auth-Request is set as 0, and the
Session ID field MUST be filled with the session identifier assigned
by the PCP server for this session. If there is a nonce option in
the received PCP-Auth-Initiation message, the PCP-Auth-Request MUST
be attached with a nonce option which contains the nonce value
learned from the PCP client. The nonce will then be used by the PCP
client to check the freshness of the PCP-Auth-Request from the PCP
server. From now on, every PCP Auth message within this session will
use this session identifier to distinguish itself from the messages
not belonging to the session. When receiving a PCP Auth message from
an unknown session, a PCP device MUST discard the message silently.
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If the PCP client intends to simplify the authentication process, it
can append an EAP Identity Response message within the PCP-Auth-
Initiation message so as to inform the PCP server that it would like
to perform EAP authentication and skip the step of waiting for the
EAP Identity Request.
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 can reply with a PCP-Auth-Request to initiate a PCP Auth
session; the result code field of the PCP-Auth-Request is set as
AUTHENTICATION-REQUIRED. In addition, the PCP server MUST assign a
session ID for the session and transfer it within the PCP-Auth-
Request. The Sequence Number field in the PCP-Auth-Request is set as
0. In the PCP Auth messages exchanged afterwards in this session,
the session ID MUST 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 PCP-Auth-Request message
from the PCP server, it can reply with a PCP-Auth-Answer message or
silently discard the request message according to its local policies.
In the PCP-Auth-Answer message, the PCP client MAY append a nonce
option which consists of a random nonce with PCP-Auth-Initiation
message. If so, in the next PCP-Auth-Request message, the PCP sever
MUST forward the nonce back within a nonce option.
In a PCP Auth session, PCP-Auth-Request messages are sent from PCP
servers to PCP clients while PCP-Auth-Answer messages are only sent
from PCP clients to PCP servers. Correspondently, an EAP request
message MUST be transported within a PCP-Auth-Request message, and an
EAP answer message MUST be transported within a PCP-Auth-Answer
message. When a PCP device receives a PCP-Auth message from its
partner and cannot generate a response within a pre-specified period
due to certain reasons (e.g., waiting for human input to construct a
EAP message), the PCP device MAY reply with a PCP-Auth-Acknowledge
message (a PCP-Auth message with the result code "PACKET-RECEIVED-
ACK") to notify the packet has been received, and thus un-necessarily
retransmission of the PCP Auth message can be avoided.
In this approach, it is mandated for a PCP client and a PCP server to
perform a key-generating EAP method in authentication. 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 traffic 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 packets. On this occasion, the PCP server needs to append the
initial PCP-Auth-Request message with a set of PRF Options and MAC
Algorithm Options. Each PRF Option contains a PRF that the PCP
server supports, and each MAC Algorithm Option contains a MAC
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(Message Authentication Code) algorithm that the PCP server supports.
After receiving the request, the PCP client selects a PRF and a MAC
algorithm which it would like to use, and sends back a PCP-Auth-
Answer with a PRF Option and a MAC Algorithm Option for the selected
algorithm.
The last PCP-Auth-Request message transported within a PCP Auth
session carries the EAP authentication and PCP authorization results.
If the EAP authentication succeeds, the result code of the last PCP-
Auth-Request is AUTHENTICATION-SUCCEED. In this case, before sending
out the PCP-Auth-Request, the PCP server must derive a transport key
and use it to generate digests to protect the integrity and
authenticity of the PCP-Auth-Request. Such digests are transported
within Authentication Tag Options. In addition, the PCP-Auth-Request
may need to be appended with a Session Lifetime Option which includes
the life-time of the PCP Auth session (i.e., the life-time of the
MSK). If the PCP client also authenticate the PCP server, the PCP
client then generates the PCP SA and uses the derived traffic key to
secure the packet receiving acknowledgement. From then on, all the
PCP messages within the session are secured with the traffic key and
the MAC algorithm sepcified in the PCP SA, unless re-authentication
is performed. If the EAP authentication fails, the result code of
the last PCP-Auth-Request is AUTHENTICATION-FAILED. If the EAP
authentication succeeds but Authorization fails, the result code of
the last PCP-Auth-Request is AUTHORIZATION-FAILED. In the latter two
cases, the PCP Auth session MUST be terminated immediately after the
last PCP authentication message exchange.
3.2. Session Termination
A PCP Auth session can be explicitly terminated by sending a
termination-indicating PCP Auth message (a PCP Auth message with a
result code "SESSION-TERMINATION" ) from either session partner.
After receiving a termination-indicating message from the session
partner, a PCP device MUST respond with a termination-indicating PCP
Auth message and remove the PCP Auth SA immediately. When the
session partner initiating the termination process receives the
acknowledge message, it will remove the associated PCP Auth SA
immediately.
3.3. Session Re-Authentication
A session partner may select to perform EAP re-authentication if it
would like to update the PCP SA (e.g., update the MSK, or extend the
session life period) instead of initiating a new PCP Auth session.
When the PCP server initiates re-authentication, it sends a PCP-Auth-
Request message containing the EAP message for re-authentication to
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the PCP client. The result code of the PCP-Auth-Request message is
set to "RE-AUTHENTICATION", which indicates the message is for an re-
authentication process. If the PCP client would like to start the
re-authentication, it will send an PCP-Auth-Answer message containing
the EAP message for re-authentication to the PCP server, The result
code of the PCP-Auth-Answer message is set to "RE-AUTHENTICATION".
Then, the session partners exchange PCP Auth messages to transfer EAP
messages for the re-authentication. During the re-authentication
procedure, the session partners protect the integrity of PCP Auth
messages with the key and MAC algorithm specified in the current PCP
SA; the sequence numbers associated with the packet will never be
rolled back and keep increasing according to Section 6.3.
If the EAP re-authentication succeeds, the result code of the last
PCP-Auth-Request is "AUTHENTICATION-SUCCEED". In this case, before
sending out the PCP-Auth-Request, the PCP server must update the SA
and use the new key to generate digests to protect the integrity and
authenticity of the PCP-Auth-Request and any subsequent PCP message.
In addition, the PCP-Auth-Request MAY be appended with a Session
Lifetime Option which indicates the new life-time of the PCP Auth
session.
If the EAP authentication fails, the result code of the last PCP-
Auth-Request is "AUTHENTICATION-FAILED". If the EAP authentication
succeeds but Authorization fails, the result code of the last PCP-
Auth-Request is "AUTHORIZATION-FAILED". In the latter two cases, the
PCP Auth session MUST be terminated immediately after the last PCP
authentication message exchange.
4. PA Security Association
At the beginning of a PCP Auth session, a session SHOULD generate a
PCP Auth SA to maintain its state information during the session.
The parameters of a PCP Auth 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 PCP message
o Sequence number for the next incoming PCP message
o Last outgoing message payload
o Retransmission interval
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o MSK: The master session key generated by the EAP method.
o MAC algorithm: The algorithm that the transport key should use to
generate digests for PCP messages.
o Pseudo-random function: The pseudo random function negotiated in
the initial PCP-Auth-Request and PCP-Auth-Answer exchange for the
transport key derivation
o Transport key: the key derived from the MSK to provide integrity
protection and data origin authentication for the messages in the
PCP Auth session. The life-time of the transport key SHOULD be
identical to the life-time of the session.
o The nonce selected by the PCP client at the initiation of the
session.
o Key ID: the 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 The 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 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 PCP-Auth-Answer packet. If the PCP client does not select
one, this value is set as 0.
o Key ID: The ID assigned for the traffic key.
5. Result Code
This message use the result code field specified in the PCP headers
to transport the information for authentication and session
management. Particularly, the values of following result codes are
specified.
TBD INITIATION
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TBD PACKET-RECEIVED-ACK
TBD AUTHENTICATION-REQUIRED
TBD AUTHENTICATION-FAILED
TBD AUTHENTICATION-SUCCEED
TBD AUTHORIZATION-FAILED
TBD SESSION-TERMINATION
6. Packet Format
6.1. Packet Format of PCP Auth Messages
The format of PCP-Auth-request messages is identical to the response
packet format specified in Section 7.2 of [RFC6887].
As illustrated in Figure 1, the PCP-Auth-Answer messages use the
requester header specified in Section 7.1 of [RFC6887]. The only
difference is that eight reserved bits are used to transfer the
result codes (e.g., "INITIATION"). Other fields in Figure 1 are
described in Section 7.1 of [RFC6887].
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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) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) Opcode-specific information :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) PCP Options :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. PCP-Auth-Answer message Format
6.2. Authentication OpCode Format
The following figure illustrates the format of an 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 PCP Auth session
identifier.
Sequence Number: This field contains a 32-bit sequence number. In
this solution, a sequence number needs to be incremented on every
new (non-retransmission) outgoing packet in order to provide
ordering guarantee for PCP.
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6.3. Nonce Option
Because the session identifier of PCP Auth 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 PCP-Auth-Initiation message.
In order to prevent an attacker from interrupting the authentication
process by sending off-line generated PCP-Auth-Request messages, the
PCP client needs to generate a random number as nonce in the PCP-
Auth-Initiation message. The PCP server will append the nonce within
the initial PCP-Auth-Request message. If the PCP-Auth-Request
message does not carry the correct nonce, the message will 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-Length: The length of the Nonce Option (in octet),
including the 4 octet fixed header and the variable length of the
authentication data.
Nonce: A random 32 bits number which is transported within a PCC-
Initiate message and the corresponding reply message from the PCP
server.
6.4. Authentication Tag 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 ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Data (Variable) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Option-Length: The length of the Authentication Tag Option (in
octet), including the 12 octet fixed header and the variable
length of the authentication data.
Session ID: A 32-bit field used to indicates the identifier of the
session that the message belongs to and identifies the secret key
used to create the message digest appended to the PCP message.
Key ID: The ID associated with the traffic key used to generate
authentication data. This field is filled with zero if MSK is
directly used to secure the message.
Authentication Data: A variable-length field that carries the
Message Authentication Code for the PCP packet. The generation of
the digest can be various according to the algorithms specified in
different PCP SAs. This field MUST end on a 32-bit boundary,
padded with 0's when necessary.
6.5. 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-Length: The length of the EAP Payload Option (in octet),
including the 4 octet fixed header and the variable length of the
EAP message.
EAP Message: The EAP message transferred. Note this field MUST
end on a 32-bit boundary, padded with 0's when necessary.
6.6. PRF Option
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PRF: The Pseudo-Random Function which the sender supports to generate
an MSK. This field contains an IKEv2 Transform ID of Transform Type
2 [RFC4306].
6.7. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 [RFC4306].
6.8. 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Session Lifetime: The life time of the PCP Auth Session, which is
decided by the authorization result.
6.9. Received Packet Option
This option is used in a PCP-Auth-Acknowledgement message to indicate
a packet with the contained sequence number has been received.
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Received Sequence Number: The sequence number of the last received
PCP packet.
7. Processing Rules
7.1. Authentication Data Generation
If a PCP SA is generated as the result of a successful EAP
authentication process, every subsequent PCP message within the
session MUST carry an Authentication Tag Option which contains the
digest of the PCP message for data origin authentication and
integrity protection.
Before generating a digest for a PCP message, a device needs to first
select a traffic key in the session and append the Authentication Tag
Option at the end of the PCP message being protected. The length of
the Authentication Data field is decided by the MAC algorithm adopted
in the session. The device then fills the Session ID field and the
PCP SA 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) with the MAC
algorithm and the selected traffic key, and input the generated
digest into the Authentication Data field.
7.2. Authentication Data Validation
When a device receives a PCP packet with an Authentication Tag
Option, it needs to use the session ID transported in the option to
locate the proper SA, and then find the associated transport key
(using key ID) and the MAC algorithm. If no proper SA is found, the
PCP packet MUST be discarded 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 packet (including the PCP header and
Authentication Tag Option) with the transport key and the MAC
algorithm found in the first step. If the value of the newly
generated digest is identical to the stored one, the device can
ensure that the packet has not been tampered with, and the validation
succeeds. Otherwise, the packet MUST be discarded.
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7.3. Retransmission Policies
In order to provide reliable transmission over PCP messages, the
retransmission poclies needs to be considered.
In the base PCP protocol, only PCP clients are responsible for
reliable delivery of PCP request messages according to policies
specified in Section 8.1.1 of [RFC6887], However, in this document,
both PCP clients and PCP servers need to provide reliable delivery of
PCP Auth messages. Therefore, such retransmission policy can be also
applied by the PCP servers.
7.4. Sequence Number
PCP adopts 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
ensure the EAP messages are exchanged in a reliable way, every PCP
packet exchanged during EAP authentication must carry an
monotonically increasing sequence number. During a PCP Auth session,
a PCP device needs to maintain two sequence numbers, one for incoming
packets and one for outgoing packets. When generating an outgoing
PCP packet, the device attaches the outgoing sequence number to the
packet and increments the sequence number maintained in the SA by 1.
When receiving a PCP packet from its session partner, the device will
not accept it if the sequence number carried in the packet does not
match the incoming sequence number the device maintains. After
confirming that the received packet is valid, the device increments
the incoming sequence number maintained in the SA by 1.
The above rules are not applied to PCP-Auth-Acknowledgement messages
whose result code fields are set as PACKET-RECEIVED-ACK. This type
of message is optionally used to avoid un-necessary packet
retransmission and the reliable transmission does not have to be
guaranteed. Therefore, when receiving or sending out a PCP-Auth-
Acknowledgement message, the device MUST not increase the
corresponding sequence number stored in the SA. Otherwise, the lost
of a PCP-Auth-Acknowledgement message during transportation will
cause the mismatching issues with the sequence numbers.
Another exception is message retransmission. When a device does not
receive any response from its session partner in a certain period, it
needs to retransmit the last outgoing PCP Auth message with a limited
rate. The duplicate messages and the original message MUST use the
identical sequence number. When the device receives such duplicate
PCP Auth messages from its session partner, it MUST try to answer
them by sending the last outgoing PCP Auth message with a limited
rate unless it has received another valid message with a larger
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sequence number from its session. In such cases, the maintained
incoming and outgoing sequence numbers will not be affected by the
message retransmission.
7.5. MTU Considerations
EAP methods are responsible for MTU handling, so no special
facilities are required in this protocol to deal with MTU issues.
8. IANA Considerations
TBD
9. Security Considerations
This section applies only to the in-band key management mechanism.
It will need to be updated if the WG choose to pursue the out-of-band
key management mechanism discussed above.
In this work, after a successful EAP authentication process performed
between two PCP devices, a MSK will be exported. The MSK can be used
to derive the transport keys to generate MAC digests for subsequent
PCP message exchanges. This work does not exclude the possibility of
using the MSK to generate keys for different security protocols to
enable per-packet cryptographic protection. The methods of deriving
the transport key for the security protocols is out of scope of this
document.
However, before a transport key has been generated, the PCP Auth
messages exchanged within a PCP Auth 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 PCP-Auth-Request and PCP-Auth-Answer 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 PCP-Auth-Request message and force the client choose the
weakest algorithms. Therefore, the server needs to guarantee that
all the PRF and MAC algorithms it provids support are strong enough.
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In order to prevent very basic DOS attacks, a PCP device SHOULD
generate state information as little as possible in the initial PCP-
Auth-Request and PCP-Auth-Answer exchanges. The choice of EAP method
is also very important. The selected EAP method must be resilient to
the attacks possibly in an insecure network environment, and the
user-identity confidentiality, protection against dictionary attacks,
and session-key establishment must be supported.
10. Acknowledgements
11. Change Log
11.1. 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.
11.2. 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 traffic keys.
o Specify that when a PCP device receives a PCP-Auth-Request or a
PCP-Auth-Answer 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.
11.3. Changes from ietf-pcp-authentication-00 to -01
o Editorial changes, added use cases to introduction.
11.4. Changes from ietf-pcp-authentication-01 to -02
o Add the support of re-authentication initiated by PCP server.
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o Specify that when a PCP device receives a PCP-Auth-Request or a
PCP-Auth-Answer 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
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
12.2. Informative References
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
3748, June 2004.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC
4306, December 2005.
[RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", RFC 5191, May 2008.
[RFC5448] Arkko, J., Lehtovirta, V., and P. Eronen, "Improved
Extensible Authentication Protocol Method for 3rd
Generation Authentication and Key Agreement (EAP-AKA')",
RFC 5448, May 2009.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013.
Authors' Addresses
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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
Dacheng Zhang
Huawei
Beijing
China
Email: zhangdacheng@huawei.com
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