Port Control Protocol (PCP) Authentication Mechanism
draft-ietf-pcp-authentication-04
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| Document | Type | Active Internet-Draft (pcp WG) | |
|---|---|---|---|
| Authors | Margaret Cullen , Sam Hartman , Dacheng Zhang | ||
| Last updated | 2014-07-21 | ||
| Replaces | draft-wasserman-pcp-authentication | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-pcp-authentication-04
Network Working Group M. Wasserman
Internet-Draft S. Hartman
Intended status: Experimental Painless Security
Expires: January 22, 2015 D. Zhang
Huawei
July 21, 2014
Port Control Protocol (PCP) Authentication Mechanism
draft-ietf-pcp-authentication-04
Abstract
An IPv4 or IPv6 host can use the Port Control Protocol (PCP) to
flexibly manage the IP address and port mapping information on
Network Address Translators (NATs) or firewalls, to facilitate
communications with remote hosts. However, the un-controlled
generation or deletion of IP address mappings on such network devices
may cause security risks and should be avoided. In some cases the
client may need to prove that it is authorized to modify, create or
delete PCP mappings. This document proposes an in-band
authentication mechanism for PCP that can be used in those cases.
The Extensible Authentication Protocol (EAP) is used to perform
authentication between PCP devices.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 22, 2015.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Session Initiation . . . . . . . . . . . . . . . . . . . 5
3.2. Session Termination . . . . . . . . . . . . . . . . . . . 8
3.3. Session Re-Authentication . . . . . . . . . . . . . . . . 8
4. PA Security Association . . . . . . . . . . . . . . . . . . . 9
5. Result Code . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Packet Format of PCP Auth Messages . . . . . . . . . . . 10
6.2. Authentication OpCode . . . . . . . . . . . . . . . . . . 11
6.3. Nonce Option . . . . . . . . . . . . . . . . . . . . . . 12
6.4. Authentication Tag Option for Common PCP . . . . . . . . 12
6.5. Authentication Tag Option for PCP Auth Messages . . . . . 14
6.6. EAP Payload Option . . . . . . . . . . . . . . . . . . . 14
6.7. PRF Option . . . . . . . . . . . . . . . . . . . . . . . 15
6.8. MAC Algorithm Option . . . . . . . . . . . . . . . . . . 15
6.9. Session Lifetime Option . . . . . . . . . . . . . . . . . 16
6.10. Received Packet Option . . . . . . . . . . . . . . . . . 16
6.11. ID Indication Option . . . . . . . . . . . . . . . . . . 16
7. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 17
7.1. Authentication Data Generation . . . . . . . . . . . . . 17
7.2. Authentication Data Validation . . . . . . . . . . . . . 18
7.3. Retransmission Policies for PCP Auth Messages . . . . . . 18
7.4. Sequence Numbers for PCP Auth Messages . . . . . . . . . 19
7.5. Sequence Numbers for Common PCP Messages . . . . . . . . 20
7.6. MTU Considerations . . . . . . . . . . . . . . . . . . . 21
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 21
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.1. Changes from wasserman-pcp-authentication-02 to ietf-
pcp-authentication-00 . . . . . . . . . . . . . . . . . 22
11.2. Changes from wasserman-pcp-authentication-01 to -02 . . 22
11.3. Changes from ietf-pcp-authentication-00 to -01 . . . . . 22
11.4. Changes from ietf-pcp-authentication-01 to -02 . . . . . 22
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11.5. Changes from ietf-pcp-authentication-02 to -03 . . . . . 23
11.6. Changes from ietf-pcp-authentication-03 to -04 . . . . . 23
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
12.1. Normative References . . . . . . . . . . . . . . . . . . 23
12.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
Using the Port Control Protocol (PCP) [RFC6887], an IPv4 or IPv6 host
can flexibly manage the IP address mapping information on its network
address translators (NATs) and firewalls, and control their policies
in processing incoming and outgoing IP packets. Because NATs and
firewalls both play important roles in network security
architectures, there are many situations in which authentication and
access control are required to prevent un-authorized users from
accessing such devices. This document proposes a PCP security
extension which enables PCP servers to authenticate their clients
with Extensible Authentication Protocol (EAP). The EAP messages are
encapsulated within PCP packets during transportation.
The following issues are considered in the design of this extension:
o Loss of EAP messages during transportation
o Disordered delivery of EAP messages
o Generation of transport keys
o Integrity protection and data origin authentication for PCP
messages
o Algorithm agility
The mechanism described in this document meets the security
requirements to address the Advanced Threat Model described in the
base PCP specification [RFC6887]. This mechanism can be used to
secure PCP in the following situations::
o On security infrastructure equipment, such as corporate firewalls,
that does not create implicit mappings.
o On equipment (such as CGNs or service provider firewalls) that
serve multiple administrative domains and do not have a mechanism
to securely partition traffic from those domains.
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o For any implementation that wants to be more permissive in
authorizing explicit mappings than it is in authorizing implicit
mappings.
o For implementations that support the THIRD_PARTY Option (unless
they can meet the constraints outlined in Section 14.1.2.2).
o For implementations that wish to support any deployment scenario
that does not meet the constraints described in Section 14.1.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Most of the terms used in this document are introduced in [RFC6887].
PCP Client: A PCP device (e.g., a host) which is responsible for
issuing PCP requests to a PCP server. In this document, a PCP client
is also a EAP peer [RFC3748], and it is the responsibility of a PCP
client to provide the credentials when authentication is required.
PCP Server: A PCP device (e.g., a NAT or a firewall) that implements
the server-side of the PCP protocol, via which PCP clients request
and manage explicit mappings. In this document, a PCP server is
integrated with an EAP authenticator [RFC3748]. Therefore, when
necessary, a PCP server can verify the credentials provided by a PCP
client and make an access control decision based on the
authentication result.
PCP-Authentication (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.
Session Partner: A PCP device involved within a PA session. Each PA
session has two session partners (a PCP server and a PCP client).
Session Lifetime: The life period associated with a PA session, which
decides the lifetime of the current authorization given to the PCP
client.
PCP Security Association (PCP SA): A PCP security association is
formed between a PCP client and a PCP server by sharing cryptographic
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keying material and associated context. The formed duplex security
association is used to protect the bidirectional PCP signaling
traffic between the PCP client and PCP server.
Master Session Key (MSK): A key derived by the partners of a PA
session, using an EAP key generating method (e.g., the one defined in
[RFC5448]).
PCP-Authentication (PA) message: A PCP message containing an
Authentication OpCode. Particularly, a PA message sent from a PCP
server to a PCP client is referred to as a PA-Server, 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 [RFC6887], 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.
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.
3. Protocol Details
3.1. Session Initiation
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.
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.
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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.
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.
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
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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.
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.
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.
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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.
3.2. Session Termination
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.
3.3. Session Re-Authentication
A session partner may select to perform EAP re-authentication if it
would like to update the PCP SA (e.g., update the MSK and rollback
the sequence numbers, or extend the session life period) without
initiating a new PA session.
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.
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.
If the EAP authentication fails, the result code of the last PA-
Server is "AUTHENTICATION-FAILED". If the EAP authentication
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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.
4. PA Security Association
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:
o IP address and UDP port number of the PCP client
o IP address and UDP port number of the PCP server
o Session Identifier
o Sequence number for the next outgoing PA message
o Sequence number for the next incoming PA message
o Sequence number for the next outgoing common PCP message (included
in the SA for PCP slient)
o Sequence number for the next incoming common PCP message (included
in the SA for PCP slient)
o Last outgoing message payload
o Retransmission interval
o MSK: The master session key generated by the EAP method.
o MAC algorithm: The algorithm that the transport key should use to
generate digests for PCP messages.
o Pseudo-random function: The pseudo random function negotiated in
the initial PA-Server and PA-Client exchange for the transport key
derivation
o Transport key: the key derived from the MSK to provide integrity
protection and data origin authentication for the messages in the
PA session. The life-time of the transport key SHOULD be
identical to the life-time of the session.
o The nonce selected by the PCP client at the initiation of the
session.
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o Key ID: the ID associated with Transport key.
Particularly, the transport key is computed in the following way:
Transport key = prf(MSK, "IETF PCP"| Session_ID| Nonce| key ID),
where:
o The prf: The pseudo-random function assigned in the Pseudo-random
function parameter.
o MSK: The master session key generated by the EAP method.
o "IETF PCP": The ASCII code representation of the non-NULL
terminated string (excluding the double quotes around it).
o Session_ID: The ID of the session which the MSK is derived from.
o Nonce: The nonce selected by the client and transported in the
Initial PA-Client packet. If the PCP client does not select one,
this value is set as 0.
o Key ID: The ID assigned for the traffic key.
5. Result Code
This message use the result code field specified in the PCP headers
to transport the information for authentication and session
management. Particularly, the values of following result codes are
specified.
TBD INITIATION
TBD AUTHENTICATION-REQUIRED
TBD AUTHENTICATION-FAILED
TBD AUTHENTICATION-SUCCEED
TBD AUTHORIZATION-FAILED
TBD SESSION-TERMINATION
6. Packet Format
6.1. Packet Format of PCP Auth Messages
The format of PA-Server messages is identical to the response packet
format specified in Section 7.2 of [RFC6887].
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As illustrated in Figure 1, the PA-Client messages use the requester
header specified in Section 7.1 of[RFC6887]. The only difference is
that eight reserved bits are used to transfer the result codes (e.g.,
"INITIATION", "AUTHENTICATION-FAILED"). Other fields in Figure 1 are
described in Section 7.1 of [RFC6887].
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
6.2. Authentication OpCode
The following figure illustrates the format of an authentication
OpCode:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Session ID: This field contains a 32-bit PA session identifier.
Sequence Number: This field contains a 32-bit sequence number. In
this solution, a sequence number needs to be incremented on every
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new (non-retransmission) outgoing packet in order to provide
ordering guarantee for PCP.
6.3. Nonce Option
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.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option-Length: The length of the Nonce Option (in octet),
including the 4 octet fixed header and the variable length of the
authentication data.
Nonce: A random 32 bits number which is transported within a PCC-
Initiate message and the corresponding reply message from the PCP
server.
6.4. Authentication Tag Option for Common PCP
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Data (Variable) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
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.
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.
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.
Key ID: The ID associated with the traffic key used to generate
authentication data. This field is filled with zero if MSK is
directly used to secure the message.
Authentication Data: A variable-length field that carries the
Message Authentication Code for the PCP packet. The generation of
the digest can be various according to the algorithms specified in
different PCP SAs. This field MUST end on a 32-bit boundary,
padded with 0's when necessary.
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6.5. Authentication Tag Option for PCP Auth Messages
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.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Authentication Data (Variable) |
~ ~
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option-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.
Key ID: The ID associated with the traffic key used to generate
authentication data. This field is filled with zero if MSK is
directly used to secure the message.
Authentication Data: A variable-length field that carries the
Message Authentication Code for the PCP packet. The generation of
the digest can be various according to the algorithms specified in
different PCP SAs. This field MUST end on a 32-bit boundary,
padded with 0's when necessary.
6.6. EAP Payload Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| EAP Message |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Option-Length: The length of the EAP Payload Option (in octet),
including the 4 octet fixed header and the variable length of the
EAP message.
EAP Message: The EAP message transferred. Note this field MUST
end on a 32-bit boundary, padded with 0's when necessary.
6.7. PRF Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PRF |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option-Length: The length of the PRF Option (in octet), including the
4 octet fixed header and the variable length of the EAP message.
PRF: The Pseudo-Random Function which the sender supports to generate
an MSK. This field contains an IKEv2 Transform ID of Transform Type
2 [RFC4306][RFC4868]. A PCP implementation MUST support
PRF_HMAC_SHA2_256 (5).
6.8. MAC Algorithm Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC Algorithm ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option-Length: The length of the MAC Algorithm Option (in octet),
including the 4 octet fixed header and the variable length of the EAP
message.
MAC Algorithm ID: Indicate the MAC algorithm which the sender
supports to generate authentication data. The MAC Algorithm ID field
contains an IKEv2 Transform ID of Transform Type 3
[RFC4306][RFC4868].A PCP implementation MUST support
AUTH_HMAC_SHA2_256_128 (12).
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6.9. Session Lifetime Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option-Length: The length of the Session Lifetime Option (in octet),
including the 4 octet fixed header and the variable length of the EAP
message.
Session Lifetime: The life time of the PA Session, which is decided
by the authorization result.
6.10. Received Packet Option
This option is used in a PA-Acknowledgement message to indicate a
packet with the contained sequence number has been received.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Received Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option-Length: The length of the Received Packet Option (in octet),
including the 4 octet fixed header and the variable length of the EAP
message.
Received Sequence Number: The sequence number of the last received
PCP packet.
6.11. ID Indication Option
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.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| ID Indicator |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
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.
7. Processing Rules
7.1. Authentication Data Generation
If a PCP SA is generated as the result of a successful EAP
authentication process, every subsequent PCP message within the
session MUST carry an Authentication Tag Option which contains the
digest of the PCP message for data origin authentication and
integrity protection.
Before generating a digest for a 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.
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
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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.
7.2. Authentication Data Validation
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.
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.
7.3. Retransmission Policies for PCP Auth Messages
Because EAP relies on the underlying protocols to provide reliable
transmission, after sending a PA message, a PCP client/server MUST
NOT send out any subsequent messages until receiving 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
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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.
Note that the last PA messages transported within the phases of
session initiation, session re-authentication, and session
termination do not have to follow the above policies since the
devices sending out those messages do not expect any further PA
messages.
When a device receives 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.
7.4. Sequence Numbers for PCP Auth Messages
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.
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
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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.
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.
7.5. Sequence Numbers for Common PCP Messages
When transporting common PCP messages within a PA session, a PCP
device needs to maintain a sequence number for outgoing common PCP
messages and a sequence number for incoming common PCP messages.
When generating a new outgoing PCP 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.
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.
Note that the sequence number in the incoming packet may not exactly
match the incoming sequence number maintained locally. In the base
PCP specification [RFC6887], 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.
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7.6. MTU Considerations
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.
8. IANA Considerations
TBD
9. Security Considerations
This section applies only to the in-band key management mechanism.
It will need to be updated if the WG choose to pursue the out-of-band
key management mechanism discussed above.
In this work, after a successful EAP authentication process performed
between two PCP devices, a MSK will be exported. The MSK can be used
to derive the transport keys to generate MAC digests for subsequent
PCP message exchanges. 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.
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.
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10. Acknowledgements
11. Change Log
11.1. Changes from wasserman-pcp-authentication-02 to ietf-pcp-
authentication-00
o Added discussion of in-band and out-of-band key management
options, leaving choice open for later WG decision.
o Removed support for fragmenting EAP messages, as that is handled
by EAP methods.
11.2. Changes from wasserman-pcp-authentication-01 to -02
o Add a nonce into the first two exchanged PCP-Auth message between
the PCP client and PCP server. When a PCP client initiate the
session, it can use the nonce to detect offline attacks.
o Add the key ID field into the authentication tag option so that a
MSK can generate multiple traffic keys.
o Specify that when a PCP device receives a PCP-Auth-Server or a
PCP-Auth-Client message from its partner the PCP device needs to
reply with a PCP-Auth-Acknowledge message to indicate that the
message has been received.
o Add the support of fragmenting EAP messages.
11.3. Changes from ietf-pcp-authentication-00 to -01
o Editorial changes, added use cases to introduction.
11.4. Changes from ietf-pcp-authentication-01 to -02
o Add the support of re-authentication initiated by PCP server.
o Specify that when a PCP device receives a PCP-Auth-Server or a
PCP-Auth-Client message from its partner the PCP device MAY reply
with a PCP-Auth-Acknowledge message to indicate that the message
has been received.
o Discuss the format of the PCP-Auth-Acknowledge message.
o Remove the redundant information from the Auth OpCode, and specify
new result codes transported in PCP packet headers
o
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11.5. Changes from ietf-pcp-authentication-02 to -03
o Change the name "PCP-Auth-Request" to "PCP-Auth-Server"
o Change the name "PCP-Auth-Response" to "PCP-Auth-Client"
o Specify two new sequence numbers for common PCP messages in the
PCP SA, and describe how to use them
o Specify a Authentication Tag Option for PCP Common Messages
o Introduce the scenario where a EAP message has to be divided into
multiple sections and transported in different PCP-Auth messages
(for the reasons of MTU), and introduce how to use PCP-Auth-
Acknowledge messages to ensure reliable packet delivery in this
case.
11.6. Changes from ietf-pcp-authentication-03 to -04
o Change the name "PCP-Auth" to "PA".
o Refine the retransmission policies.
o 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.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
12.2. Informative References
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
3748, June 2004.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC
4306, December 2005.
[RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
384, and HMAC-SHA-512 with IPsec", RFC 4868, May 2007.
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[RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", RFC 5191, May 2008.
[RFC5448] Arkko, J., Lehtovirta, V., and P. Eronen, "Improved
Extensible Authentication Protocol Method for 3rd
Generation Authentication and Key Agreement (EAP-AKA')",
RFC 5448, May 2009.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013.
Authors' Addresses
Margaret Wasserman
Painless Security
356 Abbott Street
North Andover, MA 01845
USA
Phone: +1 781 405 7464
Email: mrw@painless-security.com
URI: http://www.painless-security.com
Sam Hartman
Painless Security
356 Abbott Street
North Andover, MA 01845
USA
Email: hartmans@painless-security.com
URI: http://www.painless-security.com
Dacheng Zhang
Huawei
Beijing
China
Email: zhangdacheng@huawei.com
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