Trust-Aware Anonymous and Efficient Routing for
Mobile Ad-Hoc Networks
Min-Hua Shao and Shin-Jia Huang
Department of Management Information Systems, National Pingtung University of Science &
Technology, 1 Hseuh Fu Road, Nei Pu, Pingtung, Taiwan 91201
Abstract. Anonymous routing is a value-added technique used in mobile ad
hoc networks for the purposes of security and privacy concerns. It has inspired
lot of research interest, but very few measures exist to trust-integrated coopera-
tion for reliable routing. This paper proposes an optimistic routing protocol for
the betterment of collaborative trust-based anonymous routing in MANET. The
key features of our scheme are including of accomplishment of anonymity-
related goals, trust-aware anonymous routing, effective pseudonym manage-
ment and lightweight overhead in computation, communication and storage.
1 Introduction
Routing security is a paramount concern in MANET and solutions to the routing
security have been addressed. In which, anonymous routing is used for the purpose of
security and privacy concerns. Anonymity protection in MANET is one of the coun-
termeasures against the mounting intrusions and attacks, such as traffic analysis,
spoofing, and denial of service attacks. As discussed in [5,6,7], the following set of
anonymity properties investigated into the requirements for MANET are incorporated
and extended: (1) Identity privacy: No one but the communicating parties can know
themselves (the identities of the source and the destination); and further, a node for-
warding packets cannot be identified by its neighbors. The former is also named as
source anonymity and the latter is called as sender and recipient anonymity. (2)
Route/path anonymity: Anyone, either en route or out of the route, cannot infer the
identities of intermediaries on a path. (3) Topology/location privacy: No one can
deduce the arrangement or mapping of the elements (links, nodes, distance, etc.) of a
network, from routing information in the packets.
In academic literature, there is often the use of onion routing approach to achieve
anonymity goals. ANODR proposed by Kong and Hong [2] is one of the leading
proposals to tackle route anonymity and location privacy. The design of ANODR is
based on broadcast with trapdoor information. Zhu et al. [7] indicated that their work
has more or less weakness and/or security flaws with result that they cannot provide
the features and security as claimed. Due to the betterment of privacy and anonymity
protection, a solution on anonymity, especially identity anonymity and strong location
privacy, is given in Zhu et al.’s work. More recent studies have focus on efficient
anonymous routing schemes in MANET. AnonDSR [4], ARM [3] and Discount-
Shao M. and Huang S. (2008).
Trust-Aware Anonymous and Efficient Routing for Mobile Ad-Hoc Networks.
In Proceedings of the 6th International Workshop on Security in Information Systems, pages 132-137
DOI: 10.5220/0001731201320137
Copyright
c
 SciTePress

ANODR [6] are examples. Previous research efforts yielded elegant but typically
inefficient solutions to the purpose of trust-aware anonymity. Each mobile node can
conduct an anonymous communication with each other in concert with trustworthy
intermediaries. In this paper, we propose a trust-based anonymous routing scheme for
MANET. In which, the communicating parties can select the most reliable route
based on trust management system and feedback the connection experience to the
system. The security works about these are essentially different approaches to achieve
the same purpose. Besides, an efficient routing protocol that has both strong security
and high network performance is considered.
2 Notation
The model and all cryptographic symbols for operations are summarized below. (1) S,
D, N
x
: S is the source node, D is the destination node, and N
x
is the intermediate nodes.
(2) ID
x
: The real identity of node x. (3) F
x
: The flag is used to indicate the type of a
packet, including of F
RREQ
, F
RREP
, and F
DATA
. (4) Seq: In addition to replay attacks, it
can uniquely identify the particular message when taken in conjunction with the pre-
ceding node’s one-time pseudonym. (5)
ii
qr , : Random numbers generated by node i
are used for the generation of one-time pseudonym. (6)
)(
⋅
SD
K : A symmetric encryp-
tion function with the shared secret key K
SD
between S and D. (7) ),( skpk : A one-
time public-private key pair is used for the purpose of anonymity. (8)
}{⋅pk : An
asymmetric encryption function using the public key
pk . (9) )(
⋅
=
Hh
x
: A collision
resistant one-way hash function
)(
⋅
H and its result h
x
is computed by node x.
(10)
)(⋅=
XX
KK
Hh
: Keyed hash function using the secret key K
x
.
3 The Proposed Scheme
We assume that a shared secret key K
SD
existed in between S and D. Node S needs to
maintain a list of pairs
),(
sii
KID for correspondent nodes. The permanent identity of
every node in the network is known by communicating nodes. The proposed protocol
consists of the anonymous route discovery and the data transmission.
3.1 Trust-aware Anonymous Route Discovery Protocol
The anonymous route discovery process is initiated whenever source node S needs to
communicate with destination node D in secret. In which, the reverse path formation
is along with broadcasting a route request (RREQ) packet from S to neighbors, as
well as the forward path setup will accompany the transmission of the eventual route
reply (RREP) packet from D to neighbors. Specifically, every node is in possession of
three identities for one link, including the real identity and two pseudonyms used in
the reverse path and in the forward path respectively.
133

A. RREQ Phase
Step 1.
〉〈→
sssSDKRREQ
hIDpkskseqrKpkhSeqFS
SD
},{),,,(,,,,:*
S generates the masked identity of D by computing
)(
DKK
IDHh
SDSD
=
of D’s real
identity with K
SD
. Then, S randomly selects one-time key pair ),( skpk for the estab-
lishment of a protected path onion
}{
s
IDpk . Random number
s
r is created for the
purpose of pseudonym and also works as a message ID for the validation of the reply
RREP later. Accordingly,
s
r must be unique until the termination of its corresponding
RREQ. Due to anonymity, S produces its pseudonym
),(
sss
rIDHh
=
and then S com-
putes
),,( skseqrK
sSD
that is intended for D, maintains the associated data in the route
table, and broadcasts the RREQ packet to its own neighbors.
Step 2.
〉〈→
xxxssSDKRREQx
hrIDIDpkpkskseqrKpkhSeqFN
SD
},,}{{),,,(,,,,:*
〉〈→
〉〈→
++++++
++++
nxnxnxxxxxssSDKRREQnx
xxxxxssSDKRREQx
hrIDrIDrIDIDpkpkpkpkskseqrKpkhSeqFN
hrIDrIDIDpkpkpkskseqrKpkhSeqFN
SD
SD
},,}...},},}{{{{...{),,,(,,,,:*
},,},}({{),,,(,,,,:*
11
1111
Upon receiving the packet, node
x
N firstly checks whether it is the concerned node.
It calculates )(
xKK
IDHh
ixix
= for each correspondent node i in the list of
pairs
),(
ixi
KID . Here, we assume that
x
N is one of intermediate nodes. When the
verification doesn’t hold, it uses the pair
),(
1−+nx
hseq as a key to search its route table.
If a match is found,
x
N drops the redundant RREQ and does not rebroadcast it. Other-
wise,
x
ID and
x
r randomly generated are appended to the cryptographic on-
ion
},}{{
xxs
rIDIDpkpk
by using
pk
.
x
N computes its pseudonym
),,(
xxsx
rIDhHh = and replaces
s
h with
x
h as a forwarder. Lastly,
x
N keeps the rout-
ing information in the table and rebroadcasts the RREQ. The variation of the RREQ
packet among intermediate nodes is depicted in the step 2.
Step 3. D receives the RREQ packet.
The check of the destination is similar to the beginning of step 2. Suppose that D
can find
SDiDiD
KDKK
hIDHh =
=
)( from the list of pairs ),(
iDi
KID and use the key
SD
K to
decrypt the ciphertext
),,( skseqrK
sSD
. A protected path },...,,,{
1 nxxxs
IDIDIDID
++
is
restored by peeling the onion off gradually with
sk . D uses the chain of (
i
ID ,
i
r ) for
all nodes en route to verify the authenticity of the pseudonym
nx
h
+
by computing
),)...),,),,),,((((...(
11 nxnxxxxxss
rIDrIDrIDrIDHHHH
++++
, and rejects the packet if the
verification is failed. This is used to ensure that the anonymous link on the reverse
path corresponds to the real link received. D maintains the route table. It is clear that
there may be more than one path received, if D has already received a RREQ with the
same pair
),(
nx
hseq
+
. After the reasonable waiting time is ended, D may select the
most trustable path or the shortest path from the table and make ready for the RREP.
134

B. RREP Phase
Step 1.
(
)
><→
+ DiiDSDnxRREP
hSeqIDchainrchainqKhSeqFD ,),(),(,,,,:*
Due to privacy concerns, the destination node D randomly generates a number q
and produces its pseudonym
),(
DDD
qIDHh
=
used in the forward path for the RREP.
The path information and other items
),,( seqqr
Ds
are encrypted by the shared
key
SD
K . The value },..,,,{)(
1 nxxxsi
rrrrrchain
++
= is the set of random number
i
r gener-
ated by all involved nodes, that is,
},,..,,,{)(
1 Dnxxxsi
IDIDIDIDIDIDchain
++
=
. D,
then, unicasts the RREP to its specific neighbor
nx
h
+
, that is, the next node of D in the
reverse path.
Step 2.
(
)
〉〈→
+−++ nxiiDSDnxRREPnx
hSeqIDchainrchainqKhSeqFN ,),(),(,,,,:*
1
(
)
() 〉〈→
〉〈→
++
xiiDSDsRREPx
xiiDSDxRREPx
hSeqIDchainrchainqKhSeqFN
hSeqIDchainrchainqKhSeqFN
,),(),(,,,,:*
,),(),(,,,,:*
11
The receiving node
nx
N
+
firstly compares
nx
h
+
with its identity for each pseudonym
in the route table and discards the packet if no match is found. Otherwise, if the pseu-
donym of next node in the reverse path is not filled with “null” in the matched entry,
node
nx
N
+
retrieves
nx
r
+
used in the RREQ from the route table and generates a new
pseudonym
nx
h
+
by computing ),,(
nxnxDnx
rIDhHh
+++
= in order to keep anonymity on
the forward path. The next node of
nx
N
+
in the forward path is
D
h . Afterwards, node
nx
N
+
replaces
D
h with
nx
h
+
and unicasts the RREP back to
1−+nx
h . The treatment of the
RREP among intermediate nodes is listed above.
Step 3. S receives the packet.
Assume that node S has the same pseudonym
s
h appeared in the route table and the
pseudonym of next node in the reverse path is filled with “null” in the matched entry.
The RREP travels back to the source. S retrieves the shared secret key
SD
K to obtain
the list of real identities on the path. In order to assure the validity of the forward path,
S compares the received item
x
h with the new one from the computation
of
),),,),...),,),,(((...((
11 xxxxnxnxDD
rIDrIDrIDqIDHHHH
++++
, and aborts if the verifica-
tion doesn’t hold. Otherwise,
x
h
is assigned to the pseudonym of next node in forward
path for the relevant entry of route table. Because of the end of the forward path, the
value of its pseudonym used in forward path is assigned with “null”. To this end, an
anonymous bi-direction link is built and trusted by the communicating parties.
3.2 Trust-aware Anonymous Data Transmission Protocol
After an anonymous route is establishment, the DATA transmission protocol will be
launched. Its format is as follows,
(
)
〉
〈
NextHopSDDATA
IDAnonSeqDATAKSeqF .,,,, . The
purpose and process of most fields in the DATA are similar to the RREQ and the
RREP. Specifically, the treatment of
NextHop
IDAnon.
is the key to fulfill data forward-
135

ing. Note that the distinction of data forwarding in the bi-direction link is marked “a”
for the forward path and “b” for the reverse path.
Step 1a.
()
〉〈→
xSDDATA
hSeqDATAKSeqFS ,,,,*
Step 1b.
(
) 〉
〈
→
+nxSDDATA
hSeqDATAKSeqFD ,,,,*
Step 2a.
(
)
〉〈→
+1
,,,,:*
xSDDATAx
hSeqDATAKSeqFN
()
() 〉〈→
〉〈→
+
−++
DSDDATAnx
nxSDDATAx
hSeqDATAKSeqFN
hSeqDATAKSeqFN
,,,,:*
,,,,:*
11
Step 2b.
(
)
〉
〈
→
−++ 1
,,,,:*
nxSDDATAnx
hSeqDATAKSeqFN
(
)
()
〉〈→
〉〈→
+
+
sSDDATAnx
xSDDATAx
hSeqDATAKSeqFN
hSeqDATAKSeqFN
,,,,:*
,,,,:*
1
Step 3a. D receives the packet. Step 3b. S receives the packet.
4 Discussions
We firstly show how realization of privacy concerns is achieved in the proposed
scheme. Then, some features related to practicability and effectiveness are discussed.
Anonymous Analysis. The real identities of S and D are kept secret by the hash
operation
),(
sss
rIDHh
=
and ),(
DDD
qIDHh
=
. Similarly, the intermediaries en route
generate the one-time pseudonyms by using the same way to conceal their identities
from all nodes, except the communicating parties. This is for the purpose of trust-
aware routing. Every intermediary is in possession of two pseudonyms
i
h and
i
h on
the bi-direction link. A node receiving, sending, or forwarding packets cannot be
identified by its neighbors or inferred the identities of other nodes, either en route or
out of the route. No routing information about the exact location, the distance and the
true routing path of S and D is appeared in or deduced from the packets.
Trust-aware Anonymous Routing. An anonymous routing based on collabora-
tive effort of trust management systems is considered. In our scheme, D can know the
identities
},,..,,,{)(
1 Dnxxxsi
IDIDIDIDIDIDchain
++
= of the intermediaries en route
for all RREQ packets received. D can select the most reliable route from them ac-
cording to trust value and S may also abort the route if any untrusted node is involved.
S and D can feedback the communicating experience to trust systems.
Pseudonym Management. Our method of lowering the computational overhead
and identifier management is one-time identifier that mades up from
),)..),,((..(
iissi
rIDrIDHHh = and ),)..),,((..(
iiDDi
rIDqIDHHh = . They are generated as
receiving the RREQ and the RREP, rather than pre-establishment. It is effective to
achieve unlinkability and practicable to work in MANET with constrained capability.
Lightweight Overhead. The detection of the final destination is the key effect on
performance. In our scheme, a keyed-Hash Message Authentication Code
)(
DKK
IDHh
SDSD
=
is used in the RREQ in order to check whether D is reached. HAMC
should execute in approximately the same time as the embedded hash function. It’s
time complexity of matching computations is acceptable in MANET. The burden of
decryption operations has been only put on the communicating parties rather than on
nodes en route. The treatment is reasonable because they are willing to take on heavy
loading. In addition, terminating condition is required for reducing communication
136

overhead. The pair ),(
1−+nx
hseq uniquely identifies a RREQ, and the combinations of
related pseudonyms can determine the end of the RREP and the DATA.
5 Conclusions
Within the wireless networks an anonymous routing protocol toward security and
privacy concerns is very promising. This is a supplement to current MANET systems
and applications, which are much more vulnerable to malicious exploits than conven-
tional wired and the fixed backbone wireless networks. In this paper, we have shown
efficient solutions to trust-aware anonymity for the route discovery and hence for
subsequent data forwarding using the route. Considering many of early studies re-
move important performance optimizations, the proposed scheme can provide a better
tradeoff between security and performance.
Acknowledgements
This research was funded by the National Science Council of Taiwan under the con-
tract of NSC 96-2416-H-020-002-MY2.
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