One document matched: draft-cui-dhc-dhcpv6-encryption-00.txt
DHC Working Group Y. Cui
Internet-Draft L. Li
Intended status: Standards Track J. Wu
Expires: December 2, 2015 Tsinghua University
May 31, 2015
Authentication and Encryption Mechanism for DHCPv6
draft-cui-dhc-dhcpv6-encryption-00
Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) enables
DHCPv6 servers to configure network parameters. However, due to the
unsecured nature, various critical identifiers used in DHCPv6 are
vulnerable to several types of attacks, particularly pervasive
monitoring. This document provides a mechanism to secure DHCPv6
messages, which achieves the client/server authentication and
encryption based on sender's certificates.
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 December 2, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Cui, et al. Expires December 2, 2015 [Page 1]
Internet-Draft DHCPv6 Encryption May 2015
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Solution A: Authentication before Encrypted DHCPv6 . . . . . 3
3.1. Solution Overview . . . . . . . . . . . . . . . . . . . . 3
3.2. Client Behavior . . . . . . . . . . . . . . . . . . . . . 5
3.3. Server Behavior . . . . . . . . . . . . . . . . . . . . . 6
3.4. Discussion: No certificate? . . . . . . . . . . . . . . . 7
3.5. Possible Problem . . . . . . . . . . . . . . . . . . . . 7
4. Solution B: Authentication with Encrypted DHCPv6 . . . . . . 7
4.1. Solution Overview . . . . . . . . . . . . . . . . . . . . 7
4.2. Client Behavior . . . . . . . . . . . . . . . . . . . . . 9
4.3. Server Behavior . . . . . . . . . . . . . . . . . . . . . 9
4.4. Possible Problem . . . . . . . . . . . . . . . . . . . . 10
5. New DHCPv6 Messages . . . . . . . . . . . . . . . . . . . . . 10
6. New DHCPv6 Options . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
The Dynamic Host Configuration Protocol for IPv6 [RFC3315] enables
DHCPv6 servers to configure network parameters dynamically.
[I-D.ietf-dhc-dhcpv6-privacy] analyses the DHCPv6 privacy issues and
discusses how various identifiers used in DHCPv6 could become a
source for gleaning additional information of an individual. Due to
the unsecured nature of DHCPv6, the various critical identifiers are
vulnerable to several types of attacks, particularly pervasive
monitoring [RFC7258].
Prior work has addressed some aspects of DHCPv6 security, but until
now there has been little work on privacy between a DHCPv6 client and
server. Secure DHCPv6 [I-D.ietf-dhc-sedhcpv6] provides the
authentication mechanism between DHCPv6 client and server along with
the DHCPv6 transaction. However, the DHCPv6 message is still
transmitted in clear text and the private information within the
DHCPv6 message is not protected from pervasive monitoring. The IETF
has expressed strong agreement that PM is an attack that needs to be
Cui, et al. Expires December 2, 2015 [Page 2]
Internet-Draft DHCPv6 Encryption May 2015
mitigated where possible.
The document discusses two possible solutions to achieve the
authentication and encryption between DHCPv6 server and client. It
should be noted that the two solutions cannot coexist at the same
time. One solution need to be selected to solve the DHCPv6 privacy
problem. Solution A specifies a security mechanism which achieves
the authentication before encrypted DHCPv6 transaction. The identity
of a DHCPv6 node is verified by the recipient before the DHCPv6
configuration process. Two new DHCPv6 messages, Encrypted-Request
and Encrypted-Reply, are defined to exchange the certificates,
timestamps, signatures of both sides. After the two-message
authentication process, the following DHCPv6 messages are encrypted
and encapsulated into two newly defined DHCPv6 messages: Encrypted-
Query and Encrypted-Response. In this way, identifiers including the
entity's DUID are protected from pervasive monitoring.
In solution B, the authentication process is done during the Solicit-
Advertise exchange. The following DHCPv6 messages are encrypted
using public key, and are also encapsulated into Encrypted-Query and
Encrypted-Response. In this way, the DHCPv6 server and client's
privacy is protected.
The proposed secure mechanism can provide the following functions to
improve security of DHCPv6 client and server:
o Identify the DHCPv6 server/client before the DHCPv6 configuration
transaction.
o Encrypt the DHCPv6 configuration messages between a DHCPv6 server
and a client once the authentication is completed.
o Anti-replay protection based on timestamps.
2. Requirements Language
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 [RFC2119].
3. Solution A: Authentication before Encrypted DHCPv6
3.1. Solution Overview
This solution achieves mutual authentication before DHCPv6
transaction, and uses public keys to encrypt any following DHCPv6
messages. In the authentication process, two new DHCPv6 messages:
Encrypted-Request and Encrypted-Reply are defined for exchanging
Cui, et al. Expires December 2, 2015 [Page 3]
Internet-Draft DHCPv6 Encryption May 2015
certificate information. Encrypted-Request message is sent from
DHCPv6 client to DHCPv6 server, which contains the signature option,
the timestamp option and the certificate option defined in
[I-D.ietf-dhc-sedhcpv6]. Encrypted-Reply message is sent from DHCPv6
server to DHCPv6 client, which contains the signature option, the
certificate option, the timestamp option and server identifier
option. Once the authentication process finished, the following
DHCPv6 transaction are encrypted. One new defined DHCPv6 option:
Encrypted-Message option and two new defined DHCPv6 messages:
Encrypted-Query and Encrypted-Response are defined to fulfill the
encryption pattern. The new defined Encrypted-Message option
contains the encrypted DHCPv6 message. The Encrypted-Query message
is sent from client to server, which contains the server identifier
option and an Encrypted-Message option. The Encrypted-Response
message is sent from server to client which contains the Encrypted-
Message option.
This solution is based on the public/private key pairs of the DHCPv6
client and server. The server and client first generate a public/
private key pair and then obtain a public key certificate from CA
that signs the public key. The deployment of the PKI is out of the
scope of this document.
Before the DHCPv6 configuration process, the DHCPv6 client sends the
Encrypted-Request message to the DHCPv6 server. Note that at this
stage, the client does not send its DUID to the server for privacy
protection. The client's identity is verified and the timestamp is
checked for anti-replay protection. If the verification and
timestamp check are successful, the server records the public key in
its local key table and replies with an Encrypted-Reply message to
the client. If the verification fails or the timestamp check fails,
the server will discard the message or further blacklist the client.
Upon the receipte of the Encrypted-Reply message, the DHCPv6 client
verifies the identity of the DHCPv6 server and checks the timestamp.
If the validation and timestamp check are successful, the client gets
the server's DUID as well as the public key from the certificate.
Otherwise, the client drops the message or blacklists the server.
Cui, et al. Expires December 2, 2015 [Page 4]
Internet-Draft DHCPv6 Encryption May 2015
+-------------+ +-------------+
|DHCPv6 Client| |DHCPv6 Server|
+-------------+ +-------------+
| Encrypted-Request |
|---------------------------------------------->|
| certificate option signature option |
| |
| Encrypted-Reply |
|<----------------------------------------------|
| certificate option signature option |
| server identifier option |
| |
DHCPv6 Authentication Procedure
After successful mutual authentication, the following DHCPv6 messages
are encrypted with the recipient's public key and encapsulated into
the Encrypted-Message option. DHCPv6 client sends the Encrypted-
Query message to server, which carries the server identifier option
and an Encrypted-Message option. The Encrypted-Message option
contains the encrypted DHCPv6 message. The server identifier option
is externally visible. For the authenticated target server, it
decrypts the Encrypted-Message option by its private key. The DHCPv6
server drops message containing a server identifier option not
matching the server's DUID, thus not paying cost to decrypt the
message. The DHCPv6 server sends the Encrypted-Response message to
client which contains the Encrypted-Message option.
[RFC7283] enables relays to support the newly defined DHCPv6 messages
without any change.
3.2. Client Behavior
The client MUST have a public/private key pair. The client is
assigned a public key certificate by a CA.
If the client supports secure mode, before sending SOLICIT message,
it multicasts the Encrypted-Request to the DHCPv6 servers before
sending SOLICIT message. The Encrypted-Request message contains the
signature option, timestamp option, certificate option. The
certificate option carries the public key certificate of the client.
The timestamp option carries the current time of the client. After
creating the entire DHCPv6 header and options, the signature is
created that is signed by the client's private key. The Encrypted-
Request message MUST NOT contain the client's DUID or any other
private information.
When the DHCPv6 client receives the Encrypted-Reply message, it
Cui, et al. Expires December 2, 2015 [Page 5]
Internet-Draft DHCPv6 Encryption May 2015
validates the server's identity according to the rule defined in
[RFC5280] and checks the timestamp according to the rule defined in
[I-D.ietf-dhc-sedhcpv6]. The client creates a local trusted
certificate record for the verified certificate and the corresponding
server identifier. The client obtains the server's public key from
the certificate.
Once the authentication is completed, the client selects one
authenticated DHCPv6 server for the following DHCPv6 transaction.
The DHCPv6 messages sent from client to server are encrypted using
the public key retrieved from the server's certificate. The
encrypted DHCPv6 message is encapsulated into the Encrypted-Message
option. The Encrypted-Query message is constructed with the
Encrypted-Message option and server identifier option. The server
identifier option is externally visible to avoid extra cost by those
unselected servers. If the client fails to get the proper parameters
from the chosen server, it will send the Encrypted-Query message to
other authenticated servers for IPv6 configuration.
For the received Encrypted-Response message, the client extracts the
Encrypted-Message option and decrypts it using its private key to
obtain the original DHCPv6 message. Then it handles the message as
per [RFC3315].
3.3. Server Behavior
When the DHCPv6 server receives the Encrypted-Request message, it
validates the certificate according to the rule defined in [RFC5280]
and checks timestamp according to the rule defined in
[I-D.ietf-dhc-sedhcpv6]. If the verification and check are
successful, the server creates a local trusted certificate record for
verified certificates. And then it sends the Encrypted-Reply message
to the client, which includes the server's digital signature,
certificate, timestamp and server identifier. If the verification
fails or the timestamp check fails, the server will discard the
message or further blacklist the client.
On the receipt of Encrypted-Query message, the server checks the
visible server identifier option. It decrypts the Encrypted-Message
option using its private key if it is the target server. The DHCPv6
server drops the messages that are not for it, thus not paying cost
to decrypt the message.
The DHCPv6 messages, which is sent from server to client, is
encrypted using the public key from the client's certificate. The
encrypted DHCPv6 message is encapsulated into the Encrypted-Message
option. The Encrypted-Response message contains the Encrypted-
Message option.
Cui, et al. Expires December 2, 2015 [Page 6]
Internet-Draft DHCPv6 Encryption May 2015
3.4. Discussion: No certificate?
A trust relationship for a public key can be the result of
Opportunistic Security [RFC7435] or explicit security policy. The
explicit security policies preempt Opportunistic security.
Opportunistic security maximizes the deployment of usable security
without impeding communication. Cleartext is used as the baseline
communication security policy if the authentication and encryption
both are not supported. For more widely, authentication is optional
for the encryption process. If the client does not have certificate
but has public/private key pair to support encryption, any
authentication check is disabled in order to avoid unnecessary
communication failure. The use of encryption without authentication
defends against pervasive monitoring and other passive attacks.
3.5. Possible Problem
Once the authentication is completed, one DHCPv6 server is selected
for addr ess allocation from the authenticated DHCPv6 servers. And
the following DHCPv6 message is encrypted using the selected server's
public key. If the client fails to get the proper parameters from
the chosen server, it will send the Encrypted-Query message to other
authenticated server for parameters configuration until the client
obtains the proper parameters. It should be noted that if the client
does not have connectivity to an authority, there might be problem
for the client to get the certificate and validate it, which
potentially breaks the mechanism.
4. Solution B: Authentication with Encrypted DHCPv6
4.1. Solution Overview
Another solution is also provided, which does not introduce new
messages exchange procedure. The two solutions cannot coexist. One
solution could be selected to solve the DHCPv6 privacy problem. This
proposed solution is also based on the public/private key pairs of
the DHCPv6 client and server. The deployment of the PKI is out of
the scope of this document.
The mutual authentication and public key exchange process are
completed along with the DHCPv6 transaction. We recommend that the
Solicit message is modified to carry no privacy information about the
client, such as the client's DUID. In Solicit message, the client
includes its certificate for authentication, while in Advertise
message, the server would include its own certificate.
For the encrypted message transaction, it follow the same encryption
pattern as specified in solution A. There are one newly DHCPv6
Cui, et al. Expires December 2, 2015 [Page 7]
Internet-Draft DHCPv6 Encryption May 2015
option: Encrypted-Message option and two newly defined DHCPv6
message: Encrypted-Query and Encrypted-Response. The Encrypted-
Message carries the encrypted DHCPv6 message. The Encrypted-Query
message is sent from client to server, which contains the server
identifier option and an Encrypted-Message option. The Encrypted-
Response message is sent from server to client which contains the
Encrypted-Message option.
The Solicit message is recommended to carry no privacy information of
the client. Simultaneously, the client's certificate, timestamp,
signature are included in the Solicit message. The DHCPv6 server
validates the identity of the client and checks timestamp. If the
verification and timestamp check is successful, the server
encapsulates the Advertise message encrypted with the client's public
key into the Encrypted-Message option. The server then sends the
Encrypted-Response message to the client with Encrypted-Message
option, the certificate option, the signature option, the timestamp
option. The DHCPv6 client validates the server's identity and checks
the timestamp. If the validation and timestamp check are successful,
the client decrypts the Encrypted-Message option and get the
Advertise message. For the following DHCPv6 transaction, the client
sends the Encrypted-Query message to the server, which contains the
server identifier option and Encrypted-Message option. The server
sends the Encrypted-Response message to the client, which contains
the Encrypted-Message option.
+-------------+ +-------------+
|DHCPv6 Client| |DHCPv6 Server|
+-------------+ +-------------+
| Solicit message |
|---------------------------------------------->|
| certificate option signature option |
| |
| Encrypted-Response message |
|<----------------------------------------------|
| certificate option signature option |
| Encrypted-Message option |
| |
| Encrypted-Query message |
|---------------------------------------------->|
| Server ID option Encrypted-Message option |
| |
| Encrypted-Response message |
|<----------------------------------------------|
| Encrypted-Message option |
| |
DHCPv6 Authentication Procedure
Cui, et al. Expires December 2, 2015 [Page 8]
Internet-Draft DHCPv6 Encryption May 2015
4.2. Client Behavior
The client MUST have a public/private key pair. The client is
assigned a public key certificate by a CA.
If the client supports secure mode, it generates the Solicit message
that carries no privacy information about the client, such as
client's DUID. The client multicasts the Solicit message to the
DHCPv6 servers, which contains the client's certificate, timestamp
and signature. After creating the entire DHCPv6 header and options,
the signature is created that is signed by the client's private key.
When the DHCPv6 client receives the Encrypted-Response message with
the certificate option, signature option, and timestamp option, it
verifies the certificate according to the rule defined in [RFC5280]
and checks the timestamps according to the rule defined in
[I-D.ietf-dhc-sedhcpv6]. The client creates a local trust
certificate record for the verified certificate and the corresponding
server identifier. Simultaneously, the client decrypts the content
of Encrypted-Message option to obtain the Advertise message.
Once the authentication is completed, the client sends the Encrypted-
Query message to the server, which contains the server identifier
option and Encrypted-Message option. The Encrypted-Message option
contains the DHCPv6 message encrypted with the server's public key.
The server identifier option is externally visible to avoid extra
decryption cost by those unchosen servers.
When the client receives the Encrypted-Response message, the client
decrypts the Encrypted-Message option to obtain the DHCPv6 message.
The client follows the rules in [RFC3315] when handling the original
DHCPv6 messages.
4.3. Server Behavior
When the DHCPv6 server receives a Solicit message, it verifies the
certificate according to the rule defined in [RFC5280] and checks the
timestamp. If the authentication is successful, the server creates a
local trusted certificate record for verified certificates. And then
it sends the Encrypted-Response message to the client, which includes
the server's certificate, timestamp, signature and Encrypted-Message
option containing the encrypted Advertise message.
After the Authentication, the server sends the Encrypted-Response
message to client, which contains the Encrypted-Message option. For
the received Encrypted-Query message, the server checks the server
identifier option. It decrypts the Encrypted-Message option using
its private key if it is the target server. The DHCPv6 server drops
Cui, et al. Expires December 2, 2015 [Page 9]
Internet-Draft DHCPv6 Encryption May 2015
messages that are not targeted for it, thus not paying cost to
decrypt the message.
4.4. Possible Problem
According to [RFC3315], the client DUID is used for selecting
addresses to assign to an IA. Other options which carries the
privacy information, such as IA_NA or IA_TA, may also affect the
address selection. In addtion, the Solicit message without client
DUID violates Solicit message validation described in [RFC3315].
5. New DHCPv6 Messages
For solution A, there are four DHCPv6 message defined: Encrypted-
Request, Encrypted-Reply, Encrypted-Query and Encrypted-Response.
For sulution B, there are only two DHCPv6 message defined: Encrypted-
Query and Encrypted-Response. Both DHCPv6 messages defined in this
document share the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. options .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The format of New DHCPv6 Messages
msg-type For solution A: Encrypted-Query (TBA1), Encrypted-
Response (TBA2) Encrypted-Request (TBA3), Encrypted-
Reply (TBA4). For solution B: Encrypted-Query
(TBA1), Encrypted-Response (TBA2).
transaction-id The transaction ID for this message exchange.
options Options carried in this message.
6. New DHCPv6 Options
For the two solution, the Encrypted-Message option are all defined,
which carries the DHCPv6 message that is encrypted with the
recipient's public key.
The format of the DHCPv4 Message option is:
Cui, et al. Expires December 2, 2015 [Page 10]
Internet-Draft DHCPv6 Encryption May 2015
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encrypted DHCPv6 message .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Encrypted-Message Option Format
option-code OPTION_Encrypted_MSG (TBA5 for solution A; TBA3 for
solution B).
option-len Length of the encrypted DHCPv6 message.
encrypted DHCPv6 message The encrypted DHCPv6 message sent by the
client or the server. In a Encrypted-Query message, it contains
encrypted DHCPv6 message sent by a client. An Encrypted-response
message contains encrypted DHCPv6 message sent by a server in
response to a client.
7. Security Considerations
TBD
8. IANA Considerations
For solution A, there are four new DHCPv6 messages defined and one
new DHCPv6 option defined. If the solution A is selected, the IANA
is requested to assign values for these four new messages and one new
option.
The four messages are:
o Encrypted-Query message (TBA1).
o Encrypted-Response message (TBA2).
o Encrypted-Request message (TBA3).
o Encrypted-Reply message (TBA4).
The one option is:
o Encrypted-Message option (TBA5).
Cui, et al. Expires December 2, 2015 [Page 11]
Internet-Draft DHCPv6 Encryption May 2015
For solution B, there are two new DHCPv6 messages defined and one new
DHCPv6 option defined. If the solution B is selected, the IANA is
requested to assign values for these two new messages and one new
option.
The four messages are:
o Encrypted-Query message (TBA1).
o Encrypted-Response message (TBA2).
The one option is:
o Encrypted-Message option (TBA3).
9. Contributors
The authors would like to thank Bernie Volz, Ralph Droms, Yiu Lee,
Tomek Mrugalski, Fred Baker, Qi Sun, Zilong Liu, Cong Liu.
10. References
10.1. Normative References
[I-D.ietf-dhc-sedhcpv6]
Jiang, S., Shen, S., Zhang, D., and T. Jinmei, "Secure
DHCPv6", draft-ietf-dhc-sedhcpv6-07 (work in progress),
March 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC7283] Cui, Y., Sun, Q., and T. Lemon, "Handling Unknown DHCPv6
Messages", RFC 7283, July 2014.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, December 2014.
Cui, et al. Expires December 2, 2015 [Page 12]
Internet-Draft DHCPv6 Encryption May 2015
10.2. Informative References
[I-D.ietf-dhc-dhcpv6-privacy]
Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy
considerations for DHCPv6", draft-ietf-dhc-
dhcpv6-privacy-00 (work in progress), February 2015.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, May 2014.
Authors' Addresses
Yong Cui
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6260-3059
Email: yong@csnet1.cs.tsinghua.edu.cn
Lishan Li
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-15201441862
Email: lilishan9248@126.com
Jianping Wu
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5983
Email: jianping@cernet.edu.cn
Cui, et al. Expires December 2, 2015 [Page 13]
| PAFTECH AB 2003-2026 | 2026-04-24 08:10:25 |