One document matched: draft-ietf-pcp-authentication-04.xml
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<rfc category="exp" docName="draft-ietf-pcp-authentication-04"
ipr="trust200902">
<front>
<title abbrev="PCP Authentication">Port Control Protocol (PCP)
Authentication Mechanism</title>
<author fullname="Margaret Wasserman" initials="M." surname="Wasserman">
<organization>Painless Security</organization>
<address>
<postal>
<street>356 Abbott Street</street>
<city>North Andover</city>
<region>MA</region>
<code>01845</code>
<country>USA</country>
</postal>
<phone>+1 781 405 7464</phone>
<email>mrw@painless-security.com</email>
<uri>http://www.painless-security.com</uri>
</address>
</author>
<author fullname="Sam Hartman" initials="S." surname="Hartman">
<organization>Painless Security</organization>
<address>
<postal>
<street>356 Abbott Street</street>
<city>North Andover</city>
<region>MA</region>
<code>01845</code>
<country>USA</country>
</postal>
<email>hartmans@painless-security.com</email>
<uri>http://www.painless-security.com</uri>
</address>
</author>
<author fullname="Dacheng Zhang" initials="D." surname="Zhang">
<organization>Huawei</organization>
<address>
<postal>
<street></street>
<city>Beijing</city>
<region></region>
<code></code>
<country>China</country>
</postal>
<phone></phone>
<facsimile></facsimile>
<email>zhangdacheng@huawei.com</email>
<uri></uri>
</address>
</author>
<date day="21" month="July" year="2014" />
<abstract>
<t>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.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>Using the Port Control Protocol (PCP) <xref target="RFC6887"></xref>,
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.</t>
<t>The following issues are considered in the design of this
extension:</t>
<t><list style="symbols">
<t>Loss of EAP messages during transportation</t>
<t>Disordered delivery of EAP messages</t>
<t>Generation of transport keys</t>
<t>Integrity protection and data origin authentication for PCP
messages</t>
<t>Algorithm agility</t>
</list>The mechanism described in this document meets the security
requirements to address the Advanced Threat Model described in the base
PCP specification <xref target="RFC6887"></xref>. This mechanism can be
used to secure PCP in the following situations::</t>
<t><list style="symbols">
<t>On security infrastructure equipment, such as corporate
firewalls, that does not create implicit mappings.</t>
<t>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.</t>
<t>For any implementation that wants to be more permissive in
authorizing explicit mappings than it is in authorizing implicit
mappings.</t>
<t>For implementations that support the THIRD_PARTY Option (unless
they can meet the constraints outlined in Section 14.1.2.2).</t>
<t>For implementations that wish to support any deployment scenario
that does not meet the constraints described in Section 14.1.</t>
</list></t>
</section>
<section title="Terminology ">
<t>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 <xref
target="RFC2119"></xref>.</t>
<t>Most of the terms used in this document are introduced in <xref
target="RFC6887"></xref>.</t>
<t>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 <xref target="RFC3748"></xref>, and it is the
responsibility of a PCP client to provide the credentials when
authentication is required.</t>
<t>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 <xref target="RFC3748"></xref>. 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.</t>
<t>PCP-Authentication (PA) 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 PA messages used to perform EAP
authentication, key distribution and session management, and the common
PCP messages secured with the keys distributed during authentication.
Each PA session is assigned a distinctive Session ID.</t>
<t>Session Partner: A PCP device involved within a PA session. Each PA
session has two session partners (a PCP server and a PCP client).</t>
<t>Session Lifetime: The life period associated with a PA session, which
decides the lifetime of the current authorization given to the PCP
client.</t>
<t>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.</t>
<t>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
<xref target="RFC5448"></xref>).</t>
<t>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, while PA message sent
from a PCP client to a PCP server is referred to as a PA-Client.
Therefore, a PA-Server is actually a PCP response message specified in
<xref target="RFC6887"></xref>, and a PA-Client is a PCP request
message. This document specifies an option, the Authentication Tag
Option for PCP Auth, to provide integrity protection and message origin
authentication for PA messages.</t>
<t>Common PCP message: A PCP message which does not contain an
Authentication OpCode. This document specifies an option, the
Authentication Tag Option for Common PCP, to provide integrity
protection and message origin authentication for the common PCP
messages.</t>
</section>
<section title="Protocol Details">
<section anchor="initiation" title="Session Initiation">
<t>At be 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 is attached with an
Authentication OpCode and may optionally contain a set of 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.</t>
<t>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. In the message,
the Session ID and Sequence Number fields of the Authentication OpCode
are set as 0. The PCP client MAY also optionally append a nonce option
which consists of a random nonce with the message.</t>
<t>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 Identity Request, and the
result code field of this PA-Server message is set as
AUTHENTICATION-REQUIRED. In addition, the server MUST assign a random
session identifier to distinctly identify this session, and fill the
identifier into the Session ID field of the Authentication OpCode in
the PA-Server message. The Sequence Number field of the Authentication
OpCode is set as 0. If there is a nonce option in the received
PA-Initiation message, the PA-Server message MUST be attached with 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. From
now on, every PCP message within this session will be attached with
this session identifier. When receiving a PA message from an unknown
session, a PCP device MUST discard the message silently. If the PCP
client intends to simplify the authentication process, it MAY append
an EAP Identity Response message within the PA-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. </t>
<t>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 PA-Server message to initiate a PA session.
The result code field of this PA-Server message is set as
AUTHENTICATION-REQUIRED. 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 is set as 0. In
the PA 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 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 sever MUST forward the nonce
back within a nonce option.</t>
<t>In a PA session, an EAP request message is transported within a
PA-Server message, and an EAP answer message is transported within a
PA-Client message. EAP relies on the underlying protocol to provide
reliable transmission; any disordered delivery or loss of packets
occurred 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 until it receives a PA-Client message
with a proper sequence number from the PCP client, and vice versa. If
a PCP device receives a PA message from its partner and cannot
generate a EAP response within a pre-specified period due to certain
reasons (e.g., waiting for human input to construct a EAP message or
waiting for the additional PA messages in order to construct a
complete EAP message), the PCP device MUST reply with a PA-Acknowledge
message (PA messages with a Received Packet Option) to notify the
packet has been received. This approach not only can avoid
un-necessarily retransmission of the PA message but also can guarantee
the reliable packet delivery in the conditions where a PCP device
needs to receive multiple PA messages before generating an EAP
response.</t>
<t>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. 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 a ID Indication Option
to direct the client to choose correct credentials.After receiving the
options, the PCP client selects the PRF and the MAC algorithm which it
would like to use, and then attach the associated PRF and MAC
Algorithm Options to the next PA-Client message.</t>
<t>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-SUCCEED. In this case, before
sending out the PA-Server message, the PCP server MUST generate a PCP
SA and use the derived transport key to generate a digest for the
message. The digest is transported within an Authentication Tag Option
for PCP Auth. A more detailed description of generating the
authentication data can be found in Section 7.1. In addition, the
PA-Server MAY also contain a Session Lifetime Option which indicates
the life-time of the PA session (i.e., the life-time 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 is
AUTHENTICATION-SUCCEED. In addition, the PCP client needs to generate
a PCP SA and uses the derived traffic key to secure the message. From
then on, all the PCP messages within the session are secured with the
traffic key and the MAC algorithm specified in the PCP SA, unless a
re-authentication is performed.</t>
<t>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.</t>
</section>
<section anchor="termination" title="Session Termination">
<t>A PA session can be explicitly terminated by sending a
termination-indicating PA message (a PA 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 PA message and remove the
PA SA immediately. When the session partner initiating the termination
process receives the PA message, it will remove the associated PA SA
immediately.</t>
</section>
<section title="Session Re-Authentication">
<t>A session partner may select to perform EAP re-authentication if it
would like to update the PCP SA (e.g., update the MSK and rollback the
sequence numbers, or extend the session life period) without
initiating a new PA session.</t>
<t>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 an re-authentication process. If the PCP client would like to
start the re-authentication, it will send an PA-Client message to the
PCP server, the result code of the PA-Client message is 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 packet
will never be rolled back and keep increasing according to Section
7.3.</t>
<t>If the EAP re-authentication succeeds, the result code of the last
PA-Server is "AUTHENTICATION-SUCCEED". In this case, before sending
out the PA-Server, the PCP server must update the SA and use the new
key to generate digests to protect the integrity and authenticity of
the PA-Server and any subsequent PCP message. In addition, the
PA-Server MAY be appended with a Session Lifetime Option which
indicates the new life-time of the PA session.</t>
<t>If the EAP authentication fails, the result code of the last
PA-Server is "AUTHENTICATION-FAILED". If the EAP authentication
succeeds but Authorization fails, the result code of the last
PA-Server is "AUTHORIZATION-FAILED". In the latter two cases, the PA
session MUST be terminated immediately after the last PA message
exchange.</t>
</section>
</section>
<section title="PA Security Association">
<t>At the beginning of a PA session, a session SHOULD generate a PA SA
to maintain its state information during the session. The parameters of
a PA SA are listed as follows:</t>
<t><list style="symbols">
<t>IP address and UDP port number of the PCP client</t>
<t>IP address and UDP port number of the PCP server</t>
<t>Session Identifier</t>
<t>Sequence number for the next outgoing PA message</t>
<t>Sequence number for the next incoming PA message</t>
<t>Sequence number for the next outgoing common PCP message
(included in the SA for PCP slient)</t>
<t>Sequence number for the next incoming common PCP message
(included in the SA for PCP slient)</t>
<t>Last outgoing message payload</t>
<t>Retransmission interval</t>
<t>MSK: The master session key generated by the EAP method.</t>
<t>MAC algorithm: The algorithm that the transport key should use to
generate digests for PCP messages.</t>
<t>Pseudo-random function: The pseudo random function negotiated in
the initial PA-Server and PA-Client exchange for the transport key
derivation</t>
<t>Transport key: the key derived from the MSK to provide integrity
protection and data origin authentication for the messages in the PA
session. The life-time of the transport key SHOULD be identical to
the life-time of the session.</t>
<t>The nonce selected by the PCP client at the initiation of the
session.</t>
<t>Key ID: the ID associated with Transport key.</t>
</list></t>
<t>Particularly, the transport key is computed in the following way:
Transport key = prf(MSK, "IETF PCP"| Session_ID| Nonce| key ID),
where:</t>
<t><list style="symbols">
<t>The prf: The pseudo-random function assigned in the Pseudo-random
function parameter.</t>
<t>MSK: The master session key generated by the EAP method.</t>
<t>"IETF PCP": The ASCII code representation of the non-NULL
terminated string (excluding the double quotes around it).</t>
<t>Session_ID: The ID of the session which the MSK is derived
from.</t>
<t>Nonce: The nonce selected by the client and transported in the
Initial PA-Client packet. If the PCP client does not select one,
this value is set as 0.</t>
<t>Key ID: The ID assigned for the traffic key.</t>
</list></t>
</section>
<section title="Result Code">
<t>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.</t>
<t><list style="empty">
<t>TBD INITIATION</t>
<t>TBD AUTHENTICATION-REQUIRED</t>
<t>TBD AUTHENTICATION-FAILED</t>
<t>TBD AUTHENTICATION-SUCCEED</t>
<t>TBD AUTHORIZATION-FAILED</t>
<t>TBD SESSION-TERMINATION</t>
</list></t>
</section>
<section title="Packet Format ">
<section title="Packet Format of PCP Auth Messages">
<t>The format of PA-Server messages is identical to the response
packet format specified in Section 7.2 of <xref
target="RFC6887"></xref>.</t>
<t>As illustrated in Figure 1, the PA-Client messages use the
requester header specified in Section 7.1 of<xref
target="RFC6887"></xref>. The only difference is that eight reserved
bits are used to transfer the result codes (e.g., "INITIATION",
"AUTHENTICATION-FAILED"). Other fields in Figure 1 are described in
Section 7.1 of <xref target="RFC6887"></xref>.</t>
<figure>
<artwork><![CDATA[ 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 1. PA-Client message Format]]></artwork>
</figure>
</section>
<section title="Authentication OpCode ">
<t>The following figure illustrates the format of an authentication
OpCode: <figure>
<artwork><![CDATA[ 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure></t>
<t><list style="empty">
<t>Session ID: This field contains a 32-bit PA session
identifier.</t>
<t>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.</t>
</list></t>
<t></t>
</section>
<section title="Nonce Option">
<t>Because the session identifier of 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 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
will be discarded silently.<figure>
<artwork><![CDATA[ 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork>
</figure><list style="empty">
<t>Option-Length: The length of the Nonce Option (in octet),
including the 4 octet fixed header and the variable length of the
authentication data.</t>
<t>Nonce: A random 32 bits number which is transported within a
PCC-Initiate message and the corresponding reply message from the
PCP server.</t>
</list></t>
</section>
<section title="Authentication Tag Option for Common PCP">
<t><figure>
<artwork><![CDATA[ 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) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork>
</figure></t>
<t>Because there is no authenticaiton OpCode in common PCP messages,
the authentication tag for common PCP messages needs to provide the
inforamtion of session ID and sequence numbers.<list style="empty">
<t>Option-Length: The length of the Authentication Tag Option for
Common PCP (in octet), including the 12 octet fixed header and the
variable length of the authentication data.</t>
<t>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.</t>
<t>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 common PCP messages.</t>
<t>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.</t>
<t>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.</t>
</list></t>
</section>
<section title="Authentication Tag Option for PCP Auth Messages">
<t>This option is used to provide message authentication for PA
messages. Compared with the Authentication Tag Option for Common PCP,
the session ID field and the sequence number field are removed because
such information is provided in the Authentication OpCode.</t>
<t><figure>
<artwork><![CDATA[ 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) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork>
</figure><list style="empty">
<t>Option-Length: The length of the Authentication Tag Option for
PCP Auth (in octet), including the 12 octet fixed header and the
variable length of the authentication data.</t>
<t>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.</t>
<t>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.</t>
</list></t>
</section>
<section title="EAP Payload Option">
<t><figure>
<artwork><![CDATA[ 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 |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork>
</figure></t>
<t><list style="empty">
<t>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.</t>
<t>EAP Message: The EAP message transferred. Note this field MUST
end on a 32-bit boundary, padded with 0's when necessary.</t>
</list></t>
</section>
<section title="PRF Option">
<t><figure>
<artwork><![CDATA[ 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork>
</figure></t>
<t>Option-Length: The length of the PRF Option (in octet), including
the 4 octet fixed header and the variable length of the EAP
message.</t>
<t>PRF: The Pseudo-Random Function which the sender supports to
generate an MSK. This field contains an IKEv2 Transform ID of
Transform Type 2 <xref target="RFC4306"></xref><xref
target="RFC4868"></xref>. A PCP implementation MUST support
PRF_HMAC_SHA2_256 (5).</t>
</section>
<section title="MAC Algorithm Option">
<t><figure>
<artwork><![CDATA[ 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure></t>
<t>Option-Length: The length of the MAC Algorithm Option (in octet),
including the 4 octet fixed header and the variable length of the EAP
message.</t>
<t>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 <xref
target="RFC4306"></xref><xref target="RFC4868"></xref>.A PCP
implementation MUST support AUTH_HMAC_SHA2_256_128 (12).</t>
</section>
<section title="Session Lifetime Option">
<t><figure>
<artwork><![CDATA[ 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure></t>
<t>Option-Length: The length of the Session Lifetime Option (in
octet), including the 4 octet fixed header and the variable length of
the EAP message.</t>
<t>Session Lifetime: The life time of the PA Session, which is decided
by the authorization result.</t>
</section>
<section title="Received Packet Option">
<t>This option is used in a PA-Acknowledgement message to indicate a
packet with the contained sequence number has been received.<figure>
<artwork><![CDATA[ 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure></t>
<t>Option-Length: The length of the Received Packet Option (in octet),
including the 4 octet fixed header and the variable length of the EAP
message.</t>
<t>Received Sequence Number: The sequence number of the last received
PCP packet.</t>
</section>
<section title="ID Indication Option">
<t> This option provide the an identifier to the PCP client that the
client can use to choose which credentials to provide to the PCP
server.<figure>
<artwork><![CDATA[ 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 |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ]]></artwork>
</figure><list style="empty">
<t>Option-Length: The length of the ID Indication Option (in
octet), including the 4 octet fixed header and the variable length
of the EAP message.</t>
<t>ID Indicator: The value for a PCP client to choose proper
credentials for authentication. The method of generating this
value is out of scope of this document. Note this field MUST end
on a 32-bit boundary, padded with 0's when necessary.</t>
</list></t>
</section>
</section>
<section title="Processing Rules">
<t></t>
<section title="Authentication Data Generation">
<t>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.</t>
<t>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 traffic key. Then the device appends an 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 traffic 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 Authentication Tag Option) using the
traffic key and the associated MAC algorithm, and insert the generated
digest into the Authentication Data field.</t>
<t>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 traffic
key. Then the device appends the Authentication Tag Option for common
PCP at the end of the message. The length of the Authentication Data
field is decided by the MAC algorithm adopted in the session. The
device then use the corresponding values derived from the SA to fills
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 traffic key and the
associated MAC algorithm, and inputs the generated digest into the
Authentication Data field.</t>
</section>
<section title="Authentication Data Validation">
<t>When a device receives a common PCP packet with an Authentication
Tag Option for Common PCP, 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 key ID in the option) and the MAC
algorithm. If no proper SA or traffic key 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.</t>
<t>Similarly, when a device receives a PA message with an
Authentication Tag Option for PCP Auth, 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 key ID in the option) and the
MAC algorithm. If no proper SA or traffic key 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.</t>
</section>
<section title="Retransmission Policies for PCP Auth Messages">
<t>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 an expect PA message
(the PA message with a proper sequence number) from the peer. If no
such a message is received in a certain period, the PCP device will
re-send the last message according to certain 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.</t>
<t>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.</t>
<t>When a device receives such a duplicate PA message from its session
partner, it MUST try to answer it by sending the last outgoing PA
message again. In order to achieve this function, the device needs to
maintain the last incoming and the assoicated outgoing packet. In this
case, if no outgoing PA message has been generated for the received
duplicate PA message yet, the device needs to generate a
PA-Acknowledgement message and sends it out. The rate of replying the
duplicate PA messages MUST be limited.</t>
</section>
<section title="Sequence Numbers for PCP Auth Messages">
<t>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 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 packet, the device attaches the associated outgoing sequence number
to the packet and increments the sequence number maintained in the SA
by 1. When receiving a PA 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.</t>
<t>The above rules are not applied to PA-Acknowledgement messages
(i.e., PA messages containing a Received Packet Option). A
PA-Acknowledgement message does not transport any EAP message and only
indicate at a PA message is received. Therefore, the reliable
transmission of PA-Acknowledgement message does not have to be
guaranteed. For instance, after sending out a PA-Acknowledgement
message, a device generates a EAP response. In this case, the device
should send it to its session partner directly and need not 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, the lost of
a PA-Acknowledgement message during transportation will cause the
mismatching issues with the sequence numbers.</t>
<t>Another exception is in the message retransmission scenarios. When
a device does not receive any response from its session partner in a
certain period, it needs to retransmit the last outgoing PA message
with a limited rate. The duplicate messages and the original message
MUST use the identical sequence number. When the device receives such
a duplicate PA message from its session partner, it MUST try to answer
it by sending the last outgoing PA message again. Note the rate of
replying the duplicate PA messages must be limited. In such cases, the
maintained incoming and outgoing sequence numbers will not be affected
by the message retransmission.</t>
</section>
<section title="Sequence Numbers for Common PCP Messages">
<t>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 messages, the PCP device attaches the
outgoing sequence number for common PCP messages to the messages and
increments the sequence number maintained in the SA by 1.</t>
<t>When receiving a PCP packet from its session partner, the PCP
device will not accept it if the sequence number carried in the packet
is smaller than the incoming sequence number the server maintains.
This approach can protect the PCP server from replay attacks. After
confirming that the received packet is valid, the PCP server will use
the sequence number in the incoming packet to take place the incoming
sequence number for common PCP messages maintained in the SA.</t>
<t>Note that the sequence number in the incoming packet may not
exactly match the incoming sequence number maintained locally. In the
base PCP specification <xref target="RFC6887"></xref>, a PCP client
may stop retransmitting a PCP request without receiving any expected
PCP answer when the client is no longer interested in the PCP
transaction. After that, the PCP client will try to generate new PCP
requests for other purposes. In this case, the sequence number in the
new request will be larger than the incoming sequence number
maintained in the PCP server.</t>
</section>
<section title="MTU Considerations">
<t>EAP methods are responsible for MTU handling, so no special
facilities are required in this protocol to deal with MTU issues. If
an EAP message is too long for a single PA message to transport, it
will be divided into multiple sections and transport them within
different PA messages. Note that the receiver may not be able to know
what to do in the next step until receiving all the sections and
constructing the complete EAP message. In this case, in order to
guarantee reliable message transmission, after receiving a PA message,
the receiver MUST reply with a PA-Acknowledgement message until all
the sections have been received.</t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>TBD</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>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.</t>
<t>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. 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 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 are
strong enough.</t>
<t>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 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.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t></t>
</section>
<section title="Change Log">
<section title="Changes from wasserman-pcp-authentication-02 to ietf-pcp-authentication-00">
<t><list style="symbols">
<t>Added discussion of in-band and out-of-band key management
options, leaving choice open for later WG decision.</t>
<t>Removed support for fragmenting EAP messages, as that is
handled by EAP methods.</t>
</list></t>
</section>
<section title="Changes from wasserman-pcp-authentication-01 to -02">
<t><list style="symbols">
<t>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.</t>
<t>Add the key ID field into the authentication tag option so that
a MSK can generate multiple traffic keys.</t>
<t>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.</t>
<t>Add the support of fragmenting EAP messages.</t>
</list></t>
</section>
<section title="Changes from ietf-pcp-authentication-00 to -01">
<t><list style="symbols">
<t>Editorial changes, added use cases to introduction.</t>
</list></t>
</section>
<section title="Changes from ietf-pcp-authentication-01 to -02">
<t><list style="symbols">
<t>Add the support of re-authentication initiated by PCP
server.</t>
<t>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.</t>
<t>Discuss the format of the PCP-Auth-Acknowledge message.</t>
<t>Remove the redundant information from the Auth OpCode, and
specify new result codes transported in PCP packet headers</t>
<t></t>
</list></t>
</section>
<section title="Changes from ietf-pcp-authentication-02 to -03">
<t><list style="symbols">
<t>Change the name "PCP-Auth-Request" to "PCP-Auth-Server"</t>
<t>Change the name "PCP-Auth-Response" to "PCP-Auth-Client"</t>
<t>Specify two new sequence numbers for common PCP messages in the
PCP SA, and describe how to use them</t>
<t>Specify a Authentication Tag Option for PCP Common Messages</t>
<t>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.</t>
</list></t>
</section>
<section title="Changes from ietf-pcp-authentication-03 to -04">
<t><list style="symbols">
<t>Change the name "PCP-Auth" to "PA".</t>
<t>Refine the retransmission policies.</t>
<t>Add more discussion about the sequence number management .</t>
<t>Provide the discussion about how to instruct a PCP client to
choose proper credential during authenticaiton, and an ID
Indication Option is defined for that purpose.</t>
</list></t>
</section>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.3748'?>
<?rfc include='reference.RFC.4306'?>
<?rfc include='reference.RFC.5191'?>
<?rfc include='reference.RFC.5448'?>
<?rfc include='reference.RFC.6887'?>
<?rfc include='reference.RFC.4868'?>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 14:22:38 |