Internet DRAFT - draft-pastor-i2nsf-vnsf-attestation
draft-pastor-i2nsf-vnsf-attestation
Network Working Group A. Pastor
Internet-Draft D. Lopez
Intended status: Experimental Telefonica I+D
Expires: September 21, 2016 A. Shaw
Hewlett Packard Labs
March 20, 2016
Remote Attestation Procedures for virtualized NSFs (vNSFs) through the
I2NSF Security Controller
draft-pastor-i2nsf-vnsf-attestation-02
Abstract
This document describes the procedures a user can follow to assess
the trust on a virtualized NSF and its user-defined configuration
through the I2NSF Security Controller. The procedure to assess
trustworthiness is based on a remote attestation of the
virtualization platform and the vNSFs running on it performed through
a Trusted Platform Module (TPM) invoked by the Security Controller.
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
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This Internet-Draft will expire on September 21, 2016.
Copyright Notice
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Establishing User Trust . . . . . . . . . . . . . . . . . . . 4
3.1. First Step: User-Agnostic Attestation . . . . . . . . . . 5
3.2. Second Step: User-Specific Attestation . . . . . . . . . . 5
3.3. Trusted Computing . . . . . . . . . . . . . . . . . . . . 6
4. vNSF Attestation Principles . . . . . . . . . . . . . . . . . 8
4.1. Requirements for a Trusted vNSF Platform . . . . . . . . . 9
4.1.1. Trusted Boot . . . . . . . . . . . . . . . . . . . . . 9
4.1.2. Remote Attestation Service . . . . . . . . . . . . . . 10
4.1.3. Secure Boot . . . . . . . . . . . . . . . . . . . . . 11
5. Remote Attestation Procedures . . . . . . . . . . . . . . . . 12
5.1. Trusted Channel with the Security Controller . . . . . . . 13
5.2. Security Controller Attestation . . . . . . . . . . . . . 14
5.3. Virtual Platform Attestation . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Normative References . . . . . . . . . . . . . . . . . . . 16
8.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
As described in [I-D.pastor-i2nsf-merged-use-cases], when
virtualization is applied to the NSF environment (vNSF) it implies
several additional concerns in security. The most relevant threats
associated with a security virtual platform are:
o An unknown/unauthorized user can try to impersonate another user
that can legitimately access virtualized NSF services. This
attack may lead to accessing the policies and applications of the
attacked user or to generate network traffic outside a the
security functions with a falsified identity.
o An authorized user may misuse assigned privileges to alter the
network traffic processing of other users in the virtualization
platform. This can become especially serious when such a user has
administration privileges granted by the virtualization provider,
the ISP or the local network operator.
o A user may try to install malformed elements (policy or
application), trying to directly take the control of a NSF or
virtualization platform, for example by exploiting a vulnerability
on one of the functions or may try to intercept or modify the
traffic of other users in the same platform.
o A malicious virtualization provider can modify the software
running on it (the operating system or a concrete vNSF) to alter
the behaviour of the latter. This event has a high impact on all
users accessing vNSFs as the virtualization provider has the
highest level of privilege on the software in execution.
o A user with physical access to the virtualization platform can
modify the behavior of hardware components, or the components
themselves. Furthermore, it can access a serial console (most
devices offer this interface for maintenance reasons) to access
the NSF software with the same level of privilege of the
virtualization provider.
Mutual authentication between the user and the vNSF environment and,
what is more important, the attestation of the elements in the vNSF
environment by users could address these threats to an acceptable
level of risk. In particular:
o User impersonation will be minimized by mutual authentication, and
since appropriate records of such authentications will be made
available, events will be suitable for auditing in the case of an
incident.
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o Attestation of the vNSF environment, especially when performed
periodically, will allow users to detect the alteration of the
processing elements, or the installation of malformed elements,
and mutual authentication will provide again an audit trail.
o Attestation relying on independent Trusted Third Parties will
alleviate the impact of malicious activity on the side of the
virtualization provider by issuing the appropriate alarms in the
event of vNSF environment manipulation.
o While it is true that any virtual environment is vulnerable to
malicious activity with full physical access (and this is
obviously beyond the scope of this document), the application of
attestation mechanisms raises the degree of physical control
necessary to perform an untraceable malicious modification of the
environment.
The user can have a proof that their vNSFs and policies are correctly
(from the user point of view) enforced by the Security Controller.
Taking into account the threats identified above, this document first
identifies the user expectations regarding remote trust
establishment, briefly analyzes Trusted Computing techniques, and
finally describes the proposed mechanisms for remote establishment of
trust through the Security Controller.
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].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
3. Establishing User Trust
From a high-level standpoint, in a virtualized I2NSF platform, the
user connects and authenticates to the Security Controller, which
then initialises the user's vNSFs and policies. Afterwards, the user
traffic reaches the Internet via the virtualized platform which hosts
the user's vNSFs. The user's expectations of the platform behavior
are thus twofold:
o The user traffic will be treated according to the user-specified
vNSFs and policies, and no other processing will be performed by
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the Security Controller or the platform itself (e.g. traffic
eavesdropping).
o Each vNSF (and its corresponding policies) behaves as configured
by the user.
We will refer to the attestation of these two expectations as the
"user-agnostic attestation" and the "user-specific attestation".
Trusted Computing techniques play a key role in addressing this
expectations.
3.1. First Step: User-Agnostic Attestation
This is the first interaction between a user and a Security
Controller: the user wants to attest that he is connected to a
genuine Security Controller before he continues with the
authentication. In this context, two properties characterise the
genuineness of the Security Controller:
1. That the identity of the Security Controller is correct
2. That it will process the user's credentials and set up the user
vNSFs and policies properly.
Once these two properties are proven to the user, the user knows that
their credentials will only be used by the Security Controller to set
up the execution platform for their vNSFs.
3.2. Second Step: User-Specific Attestation
From the security enforcement point of view, the user agnostic
attestation focuses on the initialization of the execution platform
for the vNSFs. This second step aims to prove to the user that their
security is enforced accordingly with their choices (i.e. vNSFs and
policies). The attestation can be performed at the initialization of
the vNSFs, before the user traffic is processed by the vNSFs, or
during the execution of the vNSFs.
Support of static vNSF attestation is REQUIRED for a Security
Controller managing vNSFs, and MUST be performed before the user
traffic is redirected through any set of vNSFs. The Security
Controller MUST provide a proof to the user that the instantiated
vNSFs and policies are the ones chosen.
Additionally to the vNSFs instantiation attestation, a continuous
attestation of the vNSFs execution MAY be required by a user to
ensure their security.
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3.3. Trusted Computing
In a nutshell, Trusted Computing (TC) aims at answering the following
question: "As a user or administrator, how can I have some assurance
that a computing system is behaving as it should?". The major
enterprise level TC initiative is the Trusted Computing Group [TCG],
which has been established for more than a decade, that primarily
focuses on developing TC for commodity computers (servers, desktops,
laptops, etc.).
The overall scheme proposed by TCG for using Trusted Computing is
based on a step-by-step extension of trust, called a Chain of Trust.
It uses a transitive mechanism: if a user can trust the first
execution step and each step correctly attests the next executable
software for trustworthiness, then a user can trust the system.
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+-----------+
| | extends PCR
| Platform +------------------------+
| | |
+-----^-----+ |
| |
|measures |
+-----------+ |
| Security | extends PCR |
| +---------------------+ |
| Controller| | |
+-----^-----+ | |
| | |
|measures +-v--v----------+
+-----------+ | |
| | extends PCR | |
| Bootloader+-------------------> Root of Trust |
| | | |
+-----^-----+ | |
| +-^--^----------+
|measures | |
+-----------+ | |
| | extends PCR | |
| BIOS +---------------------+ |
| | |
+-----^-----+ |
| |
|measures |
+-----------+ |
| Bootblock | extends PCR |
| (CRTM) +------------------------+
| |
+-----------+
Figure 1: Applying Trusted Computing
Effectively, during the loading of each piece of software, the
integrity of each piece of software is measured and stored inside a
log that reflects the different boot stages, as illustrated in the
figure above. Later, at the request of a user, the platform can
present this log (signed with the unique identity of the platform),
which can be checked to prove the platform identity and attest the
state of the system. The base element for the extension of the Chain
of Trust is called the Core Root of Trust.
The TCG has created a standard for the the design and usage of a
secure cryptoprocessor to address the storage of keys, general
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secrets, identities and platform integrity measurements: the Trusted
Platform Module (TPM). When using a TPM as a root of trust,
measurements of the software stack are stored in special on-board
Platform Configuration Registers (PCRs) on a discrete TPM. There are
normally a small number of PCRs that can be used for storing
measurements, however it is not possible to directly write to a PCR;
instead measurements must be stored using a process called Extending
PCRs.
The extend operation can update a PCR by producing a global hash of
the concatenated values of the previous PCR value with the new
measurement value. The Extend operation allows for an unlimited
number of measurements to be captured in a single PCR, since the size
of the value is always the same and it retains a verifiable ordered
chain of all the previous measurements.
Attestation of the virtualization platform will thus rely on a
process of measuring the booted software and storing a chained log of
measurements, typically referred to as Trusted Boot. The user will
either validate the signed set of measurements with a trusted third
party verifier who will assess whether the software configuration is
trusted, or the user can check for themselves against their own set
of reference digest values (measurements) that they have obtained a
priori, and having already known the public endorsement key of the
remote Root of Trust.
Trusted Boot should not be confused with a different mechanism known
as "Secure Boot", as they both are designed to solve different
problems. Secure Boot is a mechanism for a platform owner to lock a
platform to only execute particular software. Software components
that do not match the configuration digests will not be loaded or
executed. This mechanism is particularly useful in preventing
bootkits from successfully infecting a platform on reboot. A common
standard for implementing Secure Boot is described in [UEFI]. Secure
Boot only enforces a particular configuration of software, it does
not allow a user to attest or quote for a series of measurements.
4. vNSF Attestation Principles
As a general principle, in the I2NSF environment users directly
interact with the Security Controller, which will become the
essential element to implement the measurements described above,
relaying on a TPM for the Root of Trust.
Given the role of the Security Controller, a mutual authentication of
users and the Security Controller MUST be performed, establishing the
desired level of assurance. This level of assurance will determine
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how stringent are the requirements for authentication (in both
directions), and how detailed the collected measurements and their
verification will be. Furthermore, the virtualization platform MUST
run a TPM, able to collect measurements of the platform itself, the
Security Controller, and the vNSFs being executed. The Security
Controller MUST make the attestation measurements available to the
user, directly or by means of a Trusted Third Party.
NOTE: The reference to results from WGs such as NEA and SACM is
currently under consideration and will be included here.
Upon successful authentication, a trusted connection with the
Security Controller (or an endpoint designated by it) SHALL be
established. All traffic to and from the virtualized NSF environment
will flow through this connection. The connection is intended not
only to be secure, but trusted in the sense that it SHOULD be bound
to the mutual authentication between user and Security Controller,
with the only exception of the application of the lowest levels of
assurance, in which case the user MUST be made aware of this
circumstance.
4.1. Requirements for a Trusted vNSF Platform
Although a discrete hardware TPM is RECOMMENDED, relaxed alternatives
(such as embedded CPU TPMs, or memory and execution isolation
mechanisms) MAY also be applied when the required level of assurance
is lower. This reduced level of assurance MUST be communicated to
the user by the Security Controller during the initial mutual
authentication phase.
4.1.1. Trusted Boot
All users who interact with a Security Controller MUST be able to:
a. Identify the Security Controller based on the public key of a
Root of Trust.
b. Retrieve a set of measurements of all the base software the
Security Controller has booted (i.e. the vNSF platform).
This requires that firmware and software MUST be measured before
loading, with the resulting value being used to extend the
appropriate PCR register. The general usage of PCRs by each software
component SHOULD conform to open standards, in order to make
verifying attestation reports interoperable, as it is the case of TCG
Generic Server Specification [TCGGSS].
The following list describes which PCR registers SHOULD be used
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during a Trusted Boot process:
o PCRs 00-03: for use by the CRTM (Initial EEPROM or PC BIOS)
o PCRs 04-07: for use by the bootloader stages
o PCRs 08-15: for use by the booted base system
As well as for providing a signed audit log of boot measurements, the
PCR values can also be used as an identity for dynamically decrypting
encrypted blobs on the platform (such as encryption keys or
configurations that belong to operating system components). Software
can choose to submit pieces of data to be encrypted by the Root of
Trust (which has its own private asymmetric key and PCR registers)
and only have it decrypted based on a criteria. This criteria can be
that the platform booted into a particular state (e.g. a set of PCR
values). Once the desired criteria is described and the sensitive
data is encrypted by the root of trust, the data has been sealed to
that platform state. The sealed data will only be decrypted when the
platform measurements held in the root of trust match the particular
state.
Trusted Boot requires the use of a root of trust for safely storing
measurements and secrets. Since the Root of Trust is self-contained
and isolated from all the software that is measured, it is able to
produce a signed set of platform measurements to a local or remote
user. Trusted Boot however does not provide enforcement of a
configuration, since the root of trust is a passive component not in
the execution path, and is solely used for safe independent storage
of secrets and platform measurements. It will respond to attestation
requests with the exact measurements that were made during the
software boot process. Sealing and unsealing of sensitive data is
also a strong advantage of Trusted Boot, since it prevents leakage of
secrets in the event of an untrusted software configuration.
4.1.2. Remote Attestation Service
A service MUST be present for providing signed attestation report
(e.g. the measurements) from the Root of Trust (RoT) to the end user.
In case of failure to communicate with the service, the end user MUST
assume the service cannot be trusted and seek an alternative Security
Controller.
Since some forms of RoT require serialised access (i.e. due to slow
access to hardware), latency of getting an attestation report could
increase with simultaneous requests. Simultaneous requests could
occur if multiple Trusted Third Parties (TTP) request for attestation
reports at the same time. This MAY be improved through batching of
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requests, in a special manner. In a typical remote attestation
protocol, the user sends a random number ("nonce") to the RoT in
order to detect any replay attacks. Therefore, cacheing of an
attestation report does not work, since there is the possibility that
it may not be a fresh report. The solution is to batch the nonce for
each requestor until the RoT is ready for creating the attestation
report. The report will be signed by the embedded identity of the
RoT to provide data integrity and authenticity, and the report will
include all the nonces of the requestors. Regardless of the number
of the number of nonces included, the requestor verifying the
attestation report MUST check to see if the requestor's nonce was
included in order to detect replay attacks. In addition to the
attestation report containing PCRs, an additional report known as an
SML (Secure Measurement Log) can be returned to the requestor to
provide more information on how to verify the report (e.g. how to
reproduce the PCR values). The integrity of the SML is protected by
a PCR measurement in the RoT. An example of an open standard for
responses is [TCGIRSS]. Further details are discussed in
Section 5.2.
As part of initial contact, the Security Controller MAY present a
list of external TTPs that the requestor can use to verify it.
However, the user MUST assess whether these external verifiers can be
trusted. The user can also choose to ignore or discard the presented
verifiers.
Finally, to prevent malicious relaying of attestation reports from a
different host, the authentication material of the secure channel
(e.g. TLS, IPSec, etc.) SHOULD be bound to the RoT and verified by
the connected user, unless the lowest levels of assurance have been
chosen and an explicit warning made to the user. This is also
addressed in Section 5.1.
4.1.3. Secure Boot
Using a mechanism such as Secure Boot helps provide strong prevention
of software attacks. Furthermore, in combination with a hardware-
based TPM, Secure Boot can provide some resilience to physical
attacks (e.g. preventing a class of offline attacks and unauthorised
system replacement). For vNSF platform providers, it is RECOMMENDED
that Secure Boot is employed wherever possible with an appropriate
firmware update mechanism, due to the possible threat of software/
firmware modifications in either public places or privately with
inside attackers.
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5. Remote Attestation Procedures
The establishment of trust with the Security Controller and the vNSF
platform consists of three main phases, which need to be coordinated
by the user through a trusted application executed by a trusted
network-attached device:
1. Trusted channel with the Security Controller. During this phase,
the user securely connects to the Security Controller to avoid
that user data can be tampered with or modified by an attacker if
the network cannot be considered trusted. The establishment of
the trusted channel is completed after the next step.
2. Security Controller attestation. During this phase, the user
verifies that the Security Controller components responsible for
handling the user's credentials and for the isolation with
respect to other potential users are behaving correctly.
Furthermore, it is verified that the identity of the platform
attested is the same of the one presented by the Security
Controller during the establishment of the secure connection.
3. Virtual platform attestation. During this step, that can be
repeated periodically until the user connection is terminated,
the Security Controller verifies the integrity of the elements
composing the user vNSF platform. The components responsible for
this task have been already attested during the previous phase.
+----------+
3. Attestation | Trusted | 3. Attestation
+--------------------> Third <----------+
| | Party | |
| +----------+ +--------+-------+
+----------v-------+ | +-----v-----+ |
| User Application | | | Security | |
| | 1. Trusted channel | | Controller| |
| 2. Get Cert +------+ handshake +---------> | |
| 3. Attestation | | +-----------+ |
| 4. Cont.handshake| | |
| | | |
| | | +---------+ |
| | | | vNSF | |
| | | +---------+ |
+------------------+ +----------------+
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Figure 2: Steps for remote attestation
In the following each step, as depicted in the above figure, is
discussed in more detail.
5.1. Trusted Channel with the Security Controller
A trusted channel is an enhanced version of the secured channel that,
differently from the latter, requires the integrity verification of
the contacted endpoint by the other peer during the initial
handshake. However, simply transmitting the integrity measurements
over the channel does not guarantee that the platform verified is the
channel endpoint. The public key or the certificate for the secure
communication MUST be included as part of the measurements presented
by the contacted endpoint during the remote attestation. This way, a
malicious platform cannot relay the attestation to another platform
as its certificate will not be present in the measurements list of
the genuine platform.
In addition, the problem of a potential loss of control of the
private key must be addressed (a malicious endpoint could prove the
identity of the genuine endpoint). This is done by defining a long-
lived Platform Property Certificate. Since this certificate connects
the platform identity to the AIK public key, an attacker cannot use a
stolen private key without revealing his identity, as it may use the
certificate of the genuine endpoint but cannot create a quote with
the AIK of the other platform.
Finally, since the platform identity can be verified from the
Platform Property Certificate, the information in the certificate to
be presented during the establishment of a secure communication are
redundant. This allows for the use of self-signed certificates, what
would simplify operational procedures in virtualized environments,
especially when they are multi-tenant. Thus, in place of
certificates signed by trusted CAs, the use of self-signed
certificates (which still need to be included in the measurements
list) is RECOMMENDED.
The steps required for the establishment of a trusted channel with
the Security Controller are as follows:
1. The user application begins the trusted channel handshake with
the selected Security Controller.
2. The certificate of the Security Controller is collected and used
for verifying the binding of the attestation result to the
contacted endpoint.
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3. The user application performs the remote attestation protocol
with the Security Controller, either directly or with the help of
a Trusted Third Party. The Trusted Third Party MAY perform the
verification of attestation quotes on behalf of multiple user
applications.
4. If the result of the attestation is positive, the application
continues the handshake and establishes the trusted channel.
Otherwise, it closes the connection.
5.2. Security Controller Attestation
During the establishment of the trusted channel, the user attests the
Security Controller by verifying the identity of the contacted
endpoint and its integrity. Initially the Security Controller
measures all the hardware and software components involved in the
boot process of the vNSF platform, in order to build the chain of
trust.
Since a user terminal may not have enough capabilities to perform the
integrity verification of a Security Controller the user application
MAY request the status of a Security Controller to a Trusted Third
Party (TTP), which is in charge of communicating with it. This
choice has the additional advantage of preventing an attacker from
easily determining the software running at the Security Controller.
If the user application directly performs the remote attestation it
performs the following steps:
1. Ask the Security Controller to generate an integrity report with
the format defined in [TCGIRSS].
2. The Security Controller retrieves the measurements and asks the
TPM to sign the PCRs with an Attestation Identity Key (AIK).
This signature provides the user with the evidence that the
measurements received belong to the Security Controller being
attested.
3. Once the integrity report has been generated it is sent back to
the user application.
4. The user application first checks if the integrity report is
valid by verifying the quote and the certificate associated to
the AIK, and then determines if the Security Controller is
behaving as expected, i.e. its software has not been compromised
and isolation among the users connected to it is enforced. As
part of the verification, the application also checks that the
digest of the certificate, received during the trusted channel
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handshake, is present among measurements.
If the user application is running on a terminal with low computation
resources, it may contact a TTP which, in turn, attests the Security
Controller and returns the result of the integrity evaluation to the
user, following the same steps depicted above.
5.3. Virtual Platform Attestation
The main outcome of the Security Controller attestation is to detect
whether or not it is correctly configuring the virtualization
container for the vNSFs belonging to the connecting user (the
virtualization platform, or vNSF platform) in a way that the user's
traffic is processed only by the NSFs within the container. The
virtual platform attestation, instead, evaluates the integrity of the
NSFs running within the platform.
The virtual platform attestation does not imply a validation of the
mechanisms the Security Controller can apply to select the
appropriate NSFs (virtual or physical) to enforce the Service
Policies applicable to a user. The selection of these NSFs is
supposed to happen independently of the attestation procedures, and
trust on the selection process and the translation of policies into
function capabilities has to be based on the trust the user has on
the Security Controller being attested as the one it was intended to
be used. An attestation of the selection and policy mapping
procedures constitute an interesting research matter, but it is out
of the scope of this document.
The procedures are essentially similar to the ones described in the
previous section. This step MAY be applied periodically if the level
of assurance selected by the user requires it.
Attesting vNSFs typically running as virtual machines can become a
rather costly operation, especially if periodic monitoring is
required by the requested level of assurance, and there are several
proposals to make them feasible, from the proposal of virtual TPMs in
[VTPM] to the application of Virtual Machine Introspection through an
integrity monitor described by [VMIA].
6. Security Considerations
This document is specifically oriented to security and it is
considered along the whole text.
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7. IANA Considerations
This document requires no IANA actions.
8. References
8.1. Normative References
[I-D.pastor-i2nsf-merged-use-cases]
Pastor, A., Lopez, D., Wang, K., Zhuang, X., Qi, M.,
Zarny, M., Majee, S., Leymann, N., Dunbar, L., and M.
Georgiades, "Use Cases and Requirements for an Interface
to Network Security Functions",
draft-pastor-i2nsf-merged-use-cases-00 (work in progress),
June 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[TCG] "Trusted Computing Group (TCG)",
<https://www.trustedcomputinggroup.org/>.
[TCGGSS] "TCG Generic Server Specification, Version 1.0",
<http://www.trustedcomputinggroup.org/>.
[TCGIRSS] "Infrastructure Work Group Integrity Report Schema
Specification, Version 1.0",
<https://www.trustedcomputinggroup.org/>.
8.2. Informative References
[UEFI] "UEFI Specification Version 2.2 (Errata D), Tech. Rep.".
[VMIA] Schiffman, J., Vijayakumar, H., and T. Jaeger, "Verifying
System Integrity by Proxy",
<http://dl.acm.org/citation.cfm?id=2368379>.
[VTPM] "vTPM:Virtualizing the Trusted Platform Module", <https://
www.usenix.org/legacy/events/sec06/tech/berger.html>.
Pastor, et al. Expires September 21, 2016 [Page 16]
Internet-Draft Remote Attestation for vNFs March 2016
Authors' Addresses
Antonio Pastor
Telefonica I+D
Zurbaran, 12
Madrid, 28010
Spain
Phone: +34 913 128 778
Email: antonio.pastorperales@telefonica.com
Diego R. Lopez
Telefonica I+D
Zurbaran, 12
Madrid, 28010
Spain
Phone: +34 913 129 041
Email: diego.r.lopez@telefonica.com
Adrian L. Shaw
Hewlett Packard Labs
Long Down Avenue
Bristol, BS34 8QZ
UK
Phone: +44 117 316 2877
Email: als@hpe.com
Pastor, et al. Expires September 21, 2016 [Page 17]
