1. Role of Trusted Third Party in Preserving the
Electric Vehicle Identity
Manikanta Ragi, Pujitha Galla, Stephen W. Turner, and Suleyman Uludag
Department of Computer Science, University of Michigan - Flint, MI, USA
Abstract—Vehicle-to-Grid (V2G) concept describes that Elec-
tric Vehicles (EV’s) interact with Smart Grid to sell demand
response facilities by providing electricity to the Grid and vice-
versa. In this process to provide reliability and efficiency, the
operator of V2G should monitor EVs continuously to know
the Initial state of charge, Required charge, Departure time
and Charging rate of EV. This may lead to loss of identity
privacy, so we need to protect the IDs of EVs. In this paper, we
propose ”Role of Trusted Third Party in Preserving the Electric
Vehicle Identity”. In this case, the IDs of Electric Vehicle will
not be disclosed to any of the other entities excluding Trusted
Third Party. The proposed scheme can achieve Identity Privacy,
Communication and Confidentiality.
I. INTRODUCTION
The traditional power grid is currently evolving into the
smart grid. Smart grid integrates the traditional power grid
with information and communication which empowers the
electrical utilities by constantly monitoring, controlling and
managing customers demands. Vehicle to Grid (V2G) is one
of the features provided by Smart Grid which has a vital
role where it’s components provide better ancillary services
to the customers. The communication between the Electric
Vehicles(EVs) with smart grid enables the demand response
by delivering the power to the grid. The benefits of the smart
grid to the EV owners makes profit through demand-response
by charging Electric Vehicles during off-peak hours and dis-
charges during peak- hours.The scenario of V2G is shown in
Fig. 1.Smart Grid Control Center manages and distributes its
power to all the aggregators without any interuptions to the
customers according to the requirement.SGCC maintains and
manages the control center and its operations.This integration
from traditional grid to smart grid increases reliability, effi-
ciency and high standanrds of operability in the system.There
are numerous research and projects being conducted on the
V2G networks till date. Additionally, the standards for V2G
technology have been conducted by International Organiza-
tion for Standardization (ISO), European Telecommunications
Standards Institute (ETSI), and Society of Automotive Engi-
neers (SAE) in Europe and the USA.
In Section III we have proposed a new entity named ’ TTP ’
which enhances the system architecture by meeting the supply
demand challenges and privacy in the system. The Trusted
Third Party enhances the system by providing safe and secure
communication between the EV owners and other entities in
the system. TTP acts as a middleman between the EVs and
Aggregator(AG), Smart Grid Control Center(SGCC). TTP is
introduced in this system to enhance the Privacy issues in this
technology, where EVs using smart grid service in their daily
lives. TTP has all the information about the EV owners, due to
the security reasons it hides all the information in its system
and create a new identity to the EVs named ” Pseudo-Identity”
through which the EVs communicate with the other entities
in the system. TTP guarantees the security and computational
benefits in the system.
In Section II the paper describes the proposals of different
research papers especially about the present technologies and
their architectures. It mainly describes about the security
issues involved as the matter of privacy concerns and their
implemtation to overcome those security issues. In Section
III the paper introduces and describes the important entities
along with its functionality. Section IV describes the com-
munication model between the entities described in before
section.It briefly exlains how the registration process takes
place with diffie-hellman protocol, energy inormation and its
billing information respectively. In section V the proposed
scheme is described briefly in preserving the electric vehicles
identity and session key generation. In section VI the paper
concludes the proposed scheme and describes the future scope
to it.
II. LITERATURE REVIEW
In 2014, Huei-Ru Tseng proposed a threshold based privacy
preserving key management scheme for V2G networks, which
makes use of threshold based secret sharing and symmetric
key technique to protect the identities of the EV owners and
establish shared session key between aggregator and vehicle
which achieves the property of identity privacy, confidentiality
and known key security [1].Aggregator acts according to the
requirement of electricity sent by SGCC . To fullfill these
requirements aggregator sends the messages to the EVs within
its range. In this scheme the identity of the Electric Vehicle
will be disclosed to the Smart Grid Control Center where
there raises an issue of privacy. In 2013, Hasen Nicanfar [2]
proposed EV and station utilizes pseudonym of the EV, where
only the Smart Grid Server (SGS) can map the identity of the
EVs by providing the identity management which have control
over EVs identity. In 2014, Rottondi [3] proposed Enabling
Privacy in Vehicle-to-Grid Interactions for Battery Recharging,
where the ID’s of Electric vehicles are anonymized with the
help of anonymizer and then the anonymized ID will be sent
to AG.AG uses ”Shamir secret sharing Scheme” [4] where a

2. set of aggregators will collaboratively schedule the charge and
discharge of the EV’s with psedonyms before forwarding the
messages to the Aggregator.
In 2014, Andrew Paverd [5] the adversary system achieves
the security goals but it couldn’t achieve the privacy goals
because of the external entities which are not trustworthy.
In order to address this issue the author came up with an
enhanced consumer privacy to the smart grid where Trust-
worthy Remote Entity establishes trust worthy relationship
with the consumer and energy provider. In this paper, we
propose a ”Role of Trusted Third Party in Preserving the
Electric Vehicle Identity”. The proposed scheme achieves the
properties of [1] and secure communication between EV and
SGCC relying on Trusted Third Party where TTP is the middle
man between the EV and SGCC for secure communication.
The EV communicates with the AG and SCGG through its
pseudo identity generated by the Trusted Third Party without
revealing its actual identity for the power usage in smart
grid. The EVs get registered with the Trusted Third Party and
shares a key pair for further communication. By introducing
the Trusted Third Party we ensure the privacy of the EV
owners for secure communication. In our paper, the EV
owner communicates with the TTP using Diffie-Hellman Key
exchange and generates a secret key. This secret is further used
for session establishment in the system.
III. ENTITIES
For better and stable bi-directional communication, there are
five key entities which plays pivot role as described below.
1) Electric Vehicles (EVs)
2) Road Side Units (RSUs)
3) Trusted Third Party (TTP)
4) Aggregator (AG)
5) Smart Grid Control Center (SGCC)
Fig. 1. Communication Model
A. Electric Vehicles (EVs)
Electric vehicles (EVs) are equipped with software and
hardware with two way grid power interface and wireless
connectivity.The EVs are charged through electricity from
power grid or through self contained generator which converts
the fuel into the required elctricity to run the vehicle providing
comfort levels of operations.In our model we introduce new
set of communicating patterns to enable privacy and secu-
rity.Initially, EVs should get registered with the Trusted Third
Parties (TTP) with the help of unique ID of electic vehicle
(Drivers License or Number Plate).In demand response ser-
vices, the role of the electric vehicle is to act according to the
requirement of electricity. In this process, they communicate
with Road Side Units (RSUs) to get the time stamp. With the
help of this timestamp EVs communicate with the aggregator
and generates a session key if the timestamp is fresh.
B. Road Side Units (RSUs)
Road side Units are the communicating nodes with the EVs
in Dedicated Short-range Communications(DSRC) of about
1000m range.RSUs provide connecting support to the vehi-
cles passing through them, these are typically computational
devices located by side of the roads. EVs communicate with
RSUs to obtain timestamp.Once the EV receives the timestamp
from the RSU, it checks whether the timestamp is free or being
used by another vehicle. It communicates with the Aggregator
only if it has a fresh timestamp.
C. Trusted Third Party (TTP)
Generally, TTP is an independent entity which uses Trusted
Computing (TC) technologies and provides trust worthy com-
munication from both the ends. In this enhanced architecture
Trusted Third Party acts as middleman between the Smart
Grid Control Center (SGCC), Aggregator (AG) and Electric
Vehicle (EVs). Electric Vehicle communicates with the Trusted
Third Party and exchange its ID with Diffie-Helman Key
Exchange and generates a secret key which is furthur used for
session establishment. With the help of this, Electric vehicle
can charge/dis-charge directly once if it registered initially.
D. Aggregator (AG)
The aggregator acts as middle man between Smart Grid
Control Center (SGCC) and Electric Vehicles (EVs). SGCC
sends the electric requirement to AG, which then sends
broadcast messages to the EVs near the range. EVs receive
these broadcast message and decided to respond to AG if
the EVs has enough amount of electricity within them. EVs
generates a session key with AG and communicate within the
secure channel depending on the requirement sent by SGCC.
Depending on all the strategies, EVs within the communication
range of AG will decide to charge or discharge.
E. Smart Grid Control Center (SGCC)
Smart Grid Control Center (SGCC) is the energy supplier
and keeps the records of EVs and their billing informations ac-
cordingly. SGCC communicates with Aggregator and Trusted

3. Third Party. SGCC sends the electricity requirement to the
Aggregator. The aggregator inturn communicates with the EVs
by sending broadcast messages within its range. EVs decides
to respond to the aggregator and communicates by using secret
key generated by TTP. SGCC is responsible for generating
IDs for AG and Bill generation. SGCC communicates with
TTP regarding billing information i.e. the amount of power
charged/di-scharged of the EVs.
IV. COMMUNICATION MODEL
Electric Vehicles (EVs) communicate with AG with the
help of RSUs. In Figure 1, EVs should first get registered
with TTP. The role of SGCC is to forward the electricity
requirement to AG.AG will pass the message to EVs within
its range depending on the requirement sent by SGCC. EVs
firstly communicate with RSUs when passing through the
roads, RSUs sends the passage and adds Timestamp to it
and sends back to EV. EVs checks for the freshness of
Timestamp and establish a session with AG if the Timestamp
is fresh.Depending on the electricity requirement the EVs
charge/discharge the power.
A. Registration Process
EVs communicate with TTP with help of” Diffe-Hellman
protocol” [6] and get registered with TTP and recieve a pseudo
random key which is generated by TTP, so that even if EVs
comes for the next time, it can directly recognise the EVs
identity without sharing its ID by using Pseudo random key
which is generated by TTP. If it fails to match the ID and
Pseudo random key it disables the communication over the
network when any unauthorized user tries to communicate
with AG. The flow of registration process is explained in detail
with flowchart in fig2.
B. Energy Information
AG moniters the EVs for every time interval which is
predifined by the system (15 or 30 mins). AG contains
information of every individual EV in the form of a table.
The table consists of four columns which are Initial State
of Charge (ISC in Percentage), Required Amount of Charge
(RAC in Percentage), charging Rate of EV and the Departure
Time (DT). Initial state of charge contains the information
about the current battery level of EV when it comes to
charge. Required amount of charge (RAC) column contains
the total amount of battery level at the time of departure.
Departure times says that the time of departure and Charging
rate of EV.The measurement is in milli Amps per unit of
charge. From the above information we can find the amount
of Energy consumed by EV.
Energy Consumed = Initial State of Charge - Required
amount of Charge
Fig. 2. Registration Process
TABLE I
STATUS OF ELECTRIC VEHICLE
ISC DT RAC Charge rate of EV
25 20 75 x
25 15 65 x
30 25 90 x
C. Billing Information
As the Identity of EVs are only known to TTP, billing
information will be generated by SGCC and sent to TTP.
Aggregator sends the Energy information to SGCC through
a secure channel. AG communicates with Meta Data Man-
agement System (MDMS) for central processing. As a result,
TTP will forward the generated amount to EV through a secure
channel with the help of pre-shared key.
V. THE PROPOSED SCHEME
In this section, we present the role of Trusted Third Party
in preserving the Electric Vehicle Identity for V2G networks.
For secure communication between the entities in the model
we use encryption techniques and random ID generators.//
Let us assume that EV is registered with TTP and obtains
a pseudorandom identity PID using a secure symmetric
encryption algorithm for EVs original Identity [7]. The
notations used below are clearly mentioned and described in
Table II

4. TABLE II
NOTATIONS
Symbol Definition
SGCC Smart Grid Control Center
RSU Road Side Units
AG Aggregator
TTP Trusted Third Party
EV Electric Vehicle
EVi The ith Electric Vehicle
Pidi Pseudorandom identity of ith Electric Vehicle
Encx Ecure symmetric encryption algorithm [7]
IDi Identity of ith EV
SKiT Secret key of ith EV at time T
SKi Secret key of ith EV
H One way hash function
V Hash result value
Pidi = Encx(IDi)
With the pseudorandom identity PID, EV communicates
with the aggregator AG. The Aggregator doesn’t know about
the user, inorder to verify it crosschecks with the trusted third
party TTP. The TTP checks the user details associated with
PID in it’s database and sends the acknowledgment to the AG.
Fig. 3. Session Key Establishment
A. Session Key Generation
The SGCC sends the electricity requirement to the
aggregator.From aggregator, broadcast messages are sent to
the EVs about the electricity requirement within its range of
communication. Upon the message delivery to the EVs, the
EVs according to the requirement will respond and generates
the session key with the aggregator in either of the two ways
discussed below. The EVs are more concerned about the
privacy of their own identity, hence it ties up with the trusted
third party for a secret key generation and this secret key
is used in efficient way for secure communication without
revealing its original identity even though it has its own
pseudorandom identity.
1) EV with identity IDi communicates with RSU using its
PIDi and obtains the timestamp T.
2) Upon the mutual understanding between the EVs and
TTP, they come up with a secret key SKiT using
Diffie-Hellmen key exchange.
3) EVs uses the secret key as session key and establish a
session with the aggregator. The session key changes for
every T time interval and generates a new session key
using the same technique as mentioned. Where, T is a
positive integer.
Let us assume, a new secret key is generated every one
hour for the each electric vehicle ’i’ to charge/discharge.
At Time = T, the secret key is SKiT
The other alternate way to generate the session key is
by using the hash function which makes it impossible
for the malicious user to decrypt. This method also
follows same pattern as discussed in the above three
points. But here along with the secret key we append
the pseudorandom identity of EV and to that result we
apply the hash function. The generated hash function is
the appended value of the pseudorandom identity of EV
and secret key. The resulting value is used as session
key to communicate with the aggregator making it hard
to decrypt. The advantage in this method is we don’t
need to generate a new secret key for each time interval T.
V = H(PIDi + SKi)
VI. CONCLUSION
The traditional power grid is currently evolving into the
smart grid. Smart grid integrates the traditional power grid
with information and communication which empowers the
electrical utilities by constantly monitoring, controlling and
managing customers demands. Vehicle to Grid (V2G) is one
of the features provided by Smart Grid which has a vital
role where it’s components provide better ancillary services
to the customers. In this paper, we propose Role of Trusted
Third Part in Preserving the Electronic Vehicle Identity. In
this case, the IDs of Electric Vehicle will not be disclosed to
any of the other entities excluding Trusted Third Party. The
proposed scheme can achieve identity privacy, Communication
and Confidentiality.
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