One document matched: draft-ietf-pcp-authentication-06.xml
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<rfc category="exp" docName="draft-ietf-pcp-authentication-06"
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>
<author fullname="Tirumaleswar Reddy" initials="T." surname="Reddy">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Cessna Business Park, Varthur Hobli</street>
<street>Sarjapur Marathalli Outer Ring Road</street>
<city>Bangalore</city>
<region>Karnataka</region>
<code>560103</code>
<country>India</country>
</postal>
<email>tireddy@cisco.com</email>
</address>
</author>
<date day="" month="" year="" />
<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 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
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 do not create implicit mappings for specific
traffic.</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>
</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 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 is attached with an
Authentication Opcode and may optionally contain a set of Options for
various purposes (e.g., transporting authentication messages and
session management). The 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 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 SHOULD also 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 message with a Received Packet Option) to notify the
packet has been received. This approach not only can avoid unnecessary
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 attaches 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. This response MUST also
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 algorithm
downgrade attack. 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 without initiating a new PA session.
An re-authentication procedure could be triggered for the following
reasons:<list style="symbols">
<t>The session life period needs to be extended</t>
<t>The sequence number is going to reach the maximum value</t>
</list>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 continue to 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 message, the PCP server MUST update the SA and use
the new key to generate digest for the PA-Server and subsequent PCP
messages. In addition, the PA-Server message MAY be appended with a
Session Lifetime Option which indicates the new life-time of the PA
session. PA and PCP message sequence numbers must also be reset to
zero.</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>
<t>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.</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</t>
<t>Sequence number for the next incoming common PCP message</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="Packet Format ">
<section title="Packet Format of PCP Auth Messages">
<t>The format of PA-Server message 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 request
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>
</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
PA-Initiation 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 authentication Opcode in common PCP messages,
the authentication tag for common PCP messages needs to provide the
information 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 varies 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 varies 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 Indicator Option">
<t>The ID Indicator option is used by the PCP client to determine
which credentials to provide to the PCP server.</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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| 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 ID indicator is the identity of the authority
that issued the credentials. This value is used by the PCP client
to choose proper credentials for authentication. The method of
generating this value is out of scope of this document. This field
is encoded in UTF-8 <xref target="RFC3629"></xref> format This
field MUST end on a 32-bit boundary, padded with 0's when
necessary.</t>
</list></t>
</section>
</section>
<section title="Processing Rules">
<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 inserts 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 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 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 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 or the sequence
number is invalid (see Section 7.5), 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 or the sequence
number is invalid (see Section 7.4), 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 PA 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. If the timer is expired and no expected response is received,
the device will terminate the session and discard the current SA.</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 associated 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 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 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 applicable 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
indicates that a PA message is received. Therefore, reliable
transmission of PA-Acknowledgement message is not required. For
instance, after sending out a PA-Acknowledgement message, a device
generates a 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
PA-Acknowledgement message during transportation will cause mismatch
in sequence numbers.</t>
<t>Another exception is 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 original message and duplicate messages 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 that the
replying to duplicate PA messages must be rate 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 updates the
Sequence Number field in the Authentication tag option with the
outgoing sequence number maintained in the SA and increments outgoing
sequence number 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 device maintains.
This approach can protect the PCP device from replay attacks. After
confirming that the received packet is valid, the PCP device will
update the incoming sequence number maintained in the PCP SA with the
sequence number of the incoming packet.</t>
<t>Note that the sequence number in the incoming packet may not
exactly match the incoming sequence number maintained locally. As
discussed in the base PCP specification <xref
target="RFC6887"></xref>, If a PCP client no longer interested in the
PCP transaction and has not yet received PCP response from the server
then it will stop retransmitting the PCP request. After that, the PCP
client will 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.</t>
<t>Note that in the base PCP specification <xref
target="RFC6887"></xref>, a PCP client needs to select a nonce in each
MAP or PEER request, 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 request, this may cause potential risk of replay attacks. This
attack is addressed by using the sequence number in the PCP
response.</t>
</section>
<section title="MTU Considerations">
<t>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 <xref
target="RFC5216"></xref>, TEAP <xref target="RFC7170"></xref>, and
others that are likely to exceed reasonable MTUs provide support for
fragmentation and reassembly. Others, such as EAP-GPSK assume they
will never send packets larger than the MTU and use small EAP
packets.</t>
<t>If an EAP message is too long to be transported within a single PA
message, it will be divided into multiple sections and transports 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 replies with a PA-Acknowledgement message to notify the
sender to send the next PA message.</t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>In order to identify Authentication Opcode, a new value (TBD) needs
to be defined in the IANA registry for PCP Opcodes.</t>
<t>A set of options are defined in this specification, each of them
needs to be associated with a value defined in the IANA registry for PCP
option code:</t>
<t><list style="empty">
<t>Nonce Option TBD</t>
<t>Authentication Tag Option for Common PCP TBD</t>
<t>Authentication Tag Option for PCP Auth Messages TBD</t>
<t>EAP Payload Option TBD</t>
<t>PRF Option TBD</t>
<t>MAC Algorithm Option TBD</t>
<t>Session Lifetime Option TBD</t>
<t>Received Packet Option TBD</t>
<t>ID Indication Option TBD</t>
</list></t>
<t>A set of new result codes is specified in this specification, each
result code needs to assigned a value in the IANA registry for PCP
result codes.</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 anchor="Security" title="Security Considerations">
<t>In this work, after a successful EAP authentication process is
performed between two PCP devices, a 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 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
possible in an insecure network environment, provide user-identity
confidentiality, protection against dictionary attacks, and support
session-key establishment.</t>
<t>When a 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.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>Thanks to Dan Wing for the valuable comments.</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 authentication, and an ID
Indication Option is defined for that purpose.</t>
</list></t>
</section>
<section title="Changes from ietf-pcp-authentication-04 to -05">
<t><list style="symbols">
<t>Add contents in IANA considerations.</t>
<t>Add discussions in fragmentation.</t>
<t>Refine the PA messages retransmission policies.</t>
<t>Add IANA considerations.</t>
</list></t>
</section>
<section title="Changes from ietf-pcp-authentication-05 to -06">
<t><list style="symbols">
<t>Added mechanism to handle algorithm downgrade attack.</t>
<t>Updated Security Considerations section.</t>
<t>Updated ID Indicator Option.</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'?>
<?rfc include='reference.RFC.3629'?>
<?rfc include='reference.RFC.5216'?>
<?rfc include='reference.RFC.7170'?>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 14:21:04 |