Internet DRAFT - draft-wu-paws-secutity
draft-wu-paws-secutity
PAWS Y. Wu
Internet-Draft Y. Cui
Intended status: Informational Huawei
Expires: April 25, 2013 October 22, 2012
Protocol to Access White Space Database:Security Considerations
draft-wu-paws-secutity-01.txt
Abstract
This document analyses common security threats of the Protocol to
Access White Space database (PAWS), and describes their potential
impacts on message exchanges between master device and white space
database when implementing PAWS. Meanwhile, the corresponding
countermeasures are also introduced in this document. The PAWS is
used for retrieving the available white space information at a given
location and time from a white space database.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 25, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and terminology . . . . . . . . . . . . . . . . . 3
2.1. Conventions used in this Document . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. PAWS Security Threat Overview . . . . . . . . . . . . . . . . 4
4. Detailed Threat Description . . . . . . . . . . . . . . . . . 4
4.1. Impersonation of Master Device . . . . . . . . . . . . . . 4
4.2. Impersonation of Database . . . . . . . . . . . . . . . . 5
4.3. MitM Attack between Master Device and Database . . . . . . 5
4.4. Attacks on the Link of master Device and Database . . . . 5
4.5. Attacks on the Master Device Itself . . . . . . . . . . . 6
4.6. Other Potential attacks(To Be Added) . . . . . . . . . . . 6
5. Security Schemes . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Security Countermeasures . . . . . . . . . . . . . . . . . 6
5.2. Security Features . . . . . . . . . . . . . . . . . . . . 7
5.3. Analysis of Security Schemes . . . . . . . . . . . . . . . 7
5.3.1. Brief Introdution of TLS Protocol . . . . . . . . . . 7
5.3.2. Mutual Authentication . . . . . . . . . . . . . . . . 9
5.3.3. Drawbacks of TLS Protocol . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
9. Normative Reference . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Portions of the radio spectrum that are allocated to a licensed,
primary user but are unused or unoccupied at specific locations and
times are defined as "white space". To maximize utilization of these
white space spectrum, the concept of allowing secondary transmissions
(licensed or unlicensed) in these spectrum is proposed. The widely
accepted approach of sharing white space spectrum without
interference is by querying the database and the corresponding
protocol "Protocol to Access White space database" is defined.
In PAWS protocol, a master device connects to a database using White
Space (WS) interface. There are much sensitive information, such as
location information and/or identities of master devices, which MAY
be transmitted between the WS interface of the master device and the
database when the PAWS is implemented. If an attacker can have full
access to the network medium between the master device and the
database, the attacker may deploy varieties of attacks on the network
using the sensitive information if there is lack of suitable security
mechanism.Therefore, the messaging interface between the master
device and the database needs to be secured. Meanwhile, to guarantee
a legitimate and authorized master device connects to the proper
database, the mutual authentication is required before the security
association established.
In this document, the security threats, the security features and the
security mechanism for protecting the PAWS are discussed in details.
2. Conventions and terminology
2.1. Conventions used in this Document
The key words "MUST", "MUST NOT", "REQUIRED","SHALL","SHALL NOT",
"SHOULD", "SHOULD NOT","RECOMMEND", "MAY", and "OPTIONANL" that
appear in this document are to be interpreted as described in
[RFC2119].
2.2. Terminology
The Terminology Section of the latest version of [I-D.ietf-paws-
problem-stmt-usecases-rqmts] shall be included by reference.
WS interface
The interface between master device and Database specifies data model
and process of PAWS in this document.
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Database or white space database
That provides white space spectrum information to master device.
Master device
A device is able to query a database for available white space
spectrum using location information.
3. PAWS Security Threat Overview
PAWS protocol defines an approach to share the white space spectrum
for secondary transmissions, enabling a master device to acquire
available white space spectrum information from a database, and
specifies the use of HTTP/TLS as transport for the protocol.
According to PAWS protocol, a master device sends a request that
contains its location information and any parameters required by the
regulatory rules (such as device identifier, capabilities, and
characteristics) to database for the available spectrum. If the
request is valid, the database returns a response that includes an
available frequency list and related information.
An adversary has several way of harming this progress: it can
masquerade as another valid device, eavesdrop on any communications
between the master device and the database, and replay or modify the
request or response message and so on. These attacks are presented
in detail in section 4.
The different ways of attacking this querying progress may eventually
lead to unauthorized use of channels by an uncertified device, an
authorized device receives a malicious response and result in the
master device causing interference to primary user of the spectrum,
tracking of master device locations and identity.
4. Detailed Threat Description
For each threat, described in the below, a description of the
corresponding attack is given as follows.
4.1. Impersonation of Master Device
If there is no authentication of the master device, the white space
database cannot detect the rogue master device, and the available
white space channel list will be passed to the Rogue master device.
This enables a rogue master device to use the available channels.
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Besides, the rogue master device can connect to the white space
database by using the registration exchanges, the DoS type attacks
may be initiated. This shows that it is essential to perform some
type of authentication of master device.
4.2. Impersonation of Database
If there is no authentication of the database, an attacker may
attempt to spoof a white space database and provide responses to a
master device which are malicious and result in the master device
causing interference to the primary user of the spectrum. At the
same time, the attacker also can retrieve an available white space
channel list from a legal database using the registration exchanges,
which received from the authorized master device.
4.3. MitM Attack between Master Device and Database
A man in the middle (MitM) node is inserted between the master device
and database, which can be considered to be a variant of the above
attacks. The real master device will connect to the MitM node and
the MitM node can connect to the real database. The MitM node can
transparently transmit, receive, view, and modify the traffic between
the real master device and the database without either of those nodes
being aware of it. The important security point illustrated by this
attack is that not only is it essential to perform mutual
authentication of the master device and the white space database, it
is important to ensure that all security tunnels from the master
device terminate in the trusted white space database instead of in a
MitM node.
4.4. Attacks on the Link of master Device and Database
The link between the master device and the white space database can
be wired or wireless. An attacker may wiretap the communication
between a valid master device and database. The threats are as
follows:
1) Steal the confidential data transmitted in the packet payload,
such as utilize the information about available channels by utilizing
those channels. The result of such an attack is unauthorized use of
channels by an unauthorized device.
2) The location/identity information can be gleaned by an
eavesdropper and be used for tracking purposes.
3) An attacker could falsify the communication between the master
device and the database. The channel information and some other type
parameters could be modified by an attacker which may result in
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interference to the primary user of that channel. Alternatively the
attacker may indicate no channel availability at a location resulting
in a denial of service to the master device.
4.5. Attacks on the Master Device Itself
The master device may be deployed in vulnerable locations, and the
less trusted types of transmission links will be used to interconnect
that equipment to the database. Breaking the master device to get
sensitive data is theoretically possible. The attacker may dig out
the master device-database shared secret or a long term certificate
from the master device and tries to add another master device.
4.6. Other Potential attacks(To Be Added)
5. Security Schemes
5.1. Security Countermeasures
To mitigate the above threats, the security countermeasures below
should be used. Namely:
1) The master device shall be authenticated based on a globally
unique and permanent master device identity before it can obtain the
service from a suitable database.
2) The master device shall authenticate the identity of database to
guarantee the connected database is proper.
3) The master device and the white space database shall also check
that both of them are authorized by the regulator body of white
space.
4) Sensitive data including authentication credentials, user
information, cryptographic keys shall not be transmitted between the
master device and the white space database in plaintext in
unauthorized access. It means that the transport of data over the
interface between the master device and the database shall be
integrity, confidentiality, and replay protected from unauthorized
access.
5) The master device should have a secure module to store long term
keys or certificates. The identity of master device could be stored
in a trusted physical module and/or a possible non-removable
smartcard.
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5.2. Security Features
To satisfy the security countermeasures, the security mechanism shall
be able to provide the following features:
1) Mutual authentication
Mutual authentication between the master device and the database
shall be performed before the service can be transmitted using
certificates or pre-shared keys or some other methods. Besides, the
database shall further check whether the master device is authorized
by Regulatory Body of White Space (RBWS) due to the fact that some
device may be not allowed to use the white space spectrum. The
credentials and critical security functions for authentication shall
be protected inside physically secure environment, such as Trusted
Environment (TrE).
2) The protection mechanisms of the data
The data over the interface between the master device and the
database shall be protected for integrity, confidentiality and anti-
replay from unauthorized parties.
3) Trusted environment
The TrE shall be a logical entity which provides a trustworthy
environment for the execution of sensitive functions and the storage
of sensitive data. All data produced through execution of functions
within the TrE shall be unknowable to unauthorized external entities.
5.3. Analysis of Security Schemes
There are several possible alternative schemes can be considered to
provide the security features detailed in section 5.2, such as TLS
and IPsec. In this document only TLS is introduced due to the fact
that the HTTP protocol is used for PAWS and the cost of IPsec is
higher.
5.3.1. Brief Introdution of TLS Protocol
TLS protocol provides the communications privacy over the internet
which is composed of two layers: the TLS Record Protocol and the TLS
Handshake Protocol.
1) The TLS Handshake Protocol is responsible for negotiating a
session, which is used to allow peers to agree upon security
parameters for the record layer, authenticate themselves, instantiate
negotiated security parameters, and report error conditions to each
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other.
a)The peer's identity can be authenticated using asymmetric, or
public key, cryptography (e.g., RSA, DSA, etc). X509 certificate is
recommended. When the certificate is used to authenticate the
identity of the entity, each party shall verify the other's
certificate whether it is valid and has not expired or revoked.
b)According the [RFC5246], RSA or Diffie-Hellman can be used for
authentication and key exchange.
c)A pre_master_secret is created by key exchange process in TLS
handshake protocol, which will be used to generate the master_secret.
The master secret is required to generate the encryption keys and
integrity keys.
2) The TLS Record Protocol takes messages to be transmitted,
fragments the data into manageable blocks, optionally compresses the
data, applies a MAC, encrypts, and transmits the result. Received
data is decrypted, verified, decompressed, and reassembled, then
delivered to higher level clients. Two basic security properties are
as follows:
a)Confidentiality: symmetric cryptography is used for data encryption
(e.g., AES, etc). The derivation of encryption keys are based on a
secret negotiated by the TLS handshake protocol.
b)Integrity: A keyed MAC is used to message integrity check. Secure
hash functions (e.g., SHA-1, etc) are used for MAC generated.
When the TLS protocol is choose to protect the communication, all
HTTP data between master device and the white space database must be
sent as TLS "application data". Normal HTTP behavior should be
followed. It means that security association shall be set up by
using TLS protocol before establishment of the HTTP connection. The
master device acting as the HTTP client should also act as the TLS
client. It should initiate a connection to the white space database
on the appropriate port and then sent the TLS ClientHello to begin
the TLS handshake.
The following TLS handshake procedures shall be implemented first
before the master device contacts to the database using a well-
defined access method when it has determined a relevant white space
database.
a)The first stage: security capabilities including protocol version,
session ID, cipher suite, compression method, and initial random
numbers are established;
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b)The second stage: certificate of the database, key exchange, and
request certificate shall be sent by database;
c)The third phase: master device sends certificate if requested. Key
exchange and certificate verification may be sent by master device;
d)The last phase: change cipher suite and finish handshake protocol.
In above procedure, the database server shall be authenticated,
whether the master device is authenticated or not in TLS handshake
protocol should be considered separately in the below.
5.3.2. Mutual Authentication
For business reasons or ease of management, databases may be deployed
by a different third-party that is authorized by RBWS. And the
master devices are deployed by the third-party and authorized by the
RBWS to use the white space spectrum. For this reason, there may be
two cases needed to consider how the master device authentication
should be implemented because the RBWS may not allow the database to
do this. One case is that the credential of the master device is
authenticated by the database, and the other case is that the RBWS
insures whether the master device is a valid device. The nuts and
bolts of these two architectures are described as follows:
1. Master device is authenticated by database
At this situation, the mutual authentication will be implemented
between the master device and database. How the identity of master
device is authenticated can be divided into following two situations.
1)if only a legal master device is able to connect to the database,
the database can determine whether a device is a master device or
not, then the mutual authentication should be finished in procedure
of TLS secure channel establishment for ease of operating. When the
certificates are used to authenticate each other, the certificate
message shall provide a valid certificate chain leading to an
acceptable certificate authority. They are responsible for verifying
that the other's certificate is valid and has not expired or been
revoked. When the pre-shared keys (PSK) are chosen to authenticate
each other, there are three sets of ciphersuits specified in
[RFC4279] for supporting authentication based on pre-shared keys.
The first set of ciphersuites uses only symmetric key operations for
authentication, the second set uses a Diffie-Hellman exchange
authenticated with PSK, and the last set combines public key (RSA)
authentication of database with PSK authentication of the master
device.
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2)The other situation is that only unilateral authentication is
needed in TLS handshake protocol when the master device
authentication is running within TLS secure tunnel. The
authentication procedure using mixed mode is given in figure 1. In
this scene, the database is authenticated using a valid certificate
signed by a trusted certificate authority. When the TLS tunnel is
established, the protocol used to authenticate the master device is
tunneled within the existing TLS tunnel. The credential of the
master device can also be the pre-shared key or certificate or some
other schemes. Legacy protocols provide a preferred means for master
device authentication due to their existing key management
infrastructure and widespread deployment. However, when run in the
open environment they may be vulnerable to identity spoofing and
other attacks against protocol exchange messages. In practical
situations, this mixed mode usage is not recommended because of its
possibility to lead in a man-in-the-middle attack, as noted in
[RFC4169].
+-------------+ +--------+
|master device| |database|
+-----+-------+ +----+---+
| |
|-----|--------------------------------------|------|
| Establishing a TLS tunnel(database authenticated) |
| |------------------------------------->| |
| | | |
| |<---TLS-protocol based on database--->| |
| | | |
| |<------Request/Identity message-------| |
|-----|--------------------------------------|------|
|-----|--------------------------------------|------|
| |Secured by TLS tunnel | |
| |<----legacy protocol for master------>| |
| | device authentication | |
|-----|--------------------------------------|------|
| |
| |
Figure 1: Mater device is authenticated by database using a mixed
mode
2. Master device is authenticated by RBWS
In this case, the credential of master device shall be authenticated
by RBWS through the TLS secure tunnel or in procedure of the TLS
handshake protocol. The notable difference between the two cases is
that the credential of master device shall be transported to RBWS by
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database which is connected to the RBWS in latter case. The data
transport between the database and RBWS shall be protected which is
out of the scope of this document. It also contains two possible
authentication architectures: one is that mutual authentication
implementing in TLS establishment procedure, the other is using a
mixed mode which procedure can be depicted in figure 2.
+-------------+ +--------+ +----+
|master device| |database| |RBWS|
+-----+-------+ +----+---+ +--+-+
| | |
|------|-------------------------------------|-------| |
| establishing a TLS tunnel(database authenticated) | |
| |------------------------------------>| | |
| | | | |
| |<---TLS-protocol based on database-->| | |
| | certificate | | |
| | | | |
| |<-----Request/Identity message-------| | |
|------|-------------------------------------|-------| |
| | |
|------|-------------------------------------|-----------|--|
| |Secured by TLS tunnel | | |
| | | | |
| |<------ Lagency protocol formaster device------->| |
| | authentication | | |
|------|-------------------------------------|-----------|--|
| | |
Figure 1: Mater device is authenticated by RBWS using a mixed mode
3. Analysis of methods for master device authentication
In section 5.3.2, the master device can be authenticated by using
symmetric pre-shared keys (PSKs) or by certificates. In the PSK
case, the shared key needs to be configured in advance among the
master device and the database or RBWS. When the PSK authentication
is selected, the certificate and the certificate request payloads are
omitted from the response; In the certificate case, the master device
can obtain a certificate through the enrolment procedure or pre-
configured. The master device may enroll a device certificate
according the certificate enrolment procedure prior to communicate
with a proper database, the certificate may then be used for
establishing a secure channel between the master device and database.
The use of certificates has advantage that there is a standardized
procedure for enrolling the private key corresponding to the
certificate while the use of the PSK requires manual operation in
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general for establishing the PSK. The manually provisioned symmetric
keys will severely limit the ability for master device to flexibly
move from one database provider to another. However, on the other
hand, the use of a PSK has the advantage that no PKI is required and
the procedure after pre-establishment of PSK is simple.
5.3.3. Drawbacks of TLS Protocol
Because the TLS runs over TCP, it is susceptible to a number of
denial-of-service (DoS) attacks. An attacker who initiates a large
number of TCP connections can consume lots of computation resources
of a server by doing RSA decryption. Besides, attackers can forge
TCP packets such as RSTs etc. or forge partial TLS records to
terminate connections. In this case, implementers or users who are
concerned with this class of attack should use IPsec.
6. Security Considerations
All contents of this document are dealing with security.
7. IANA Considerations
There have been no IANA considerations so far in this document.
8. Acknowledgments
Thanks to Lei Zhu, Peter McCann and Xinpeng Wei for their sincerely
help and comments when drafting this document.
9. Normative Reference
[I-D.ietf-paws-problem-stmt-usecases-rqmts]
Probasco, S. and B. Patil, "Protocol to Access White Space
database: PS, use cases and rqmts",
draft-ietf-paws-problem-stmt-usecases-rqmts-03 (work in
progress), February 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4169] Torvinen, V., Arkko, J., and M. Naslund, "Hypertext
Transfer Protocol (HTTP) Digest Authentication Using
Authentication and Key Agreement (AKA) Version-2",
RFC 4169, November 2005.
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[RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
for Transport Layer Security (TLS)", RFC 4279,
December 2005.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
Authors' Addresses
Yizhuang Wu
Huawei Technologies
Email: wuyizhuang@huawei.com
Yang Cui
Huawei Technologies
Email: cuiyang@huawei.com
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