A new secret handshakes scheme with dynamic matching based on zss

International Journal of Network Security & Its Applications (IJNSA) Vol.7, No.1, January 2015
DOI:10.5121/ijnsa.2015.7106 67
A NEW SECRET HANDSHAKES SCHEME WITH
DYNAMIC MATCHING BASED ON ZSS
Preeti Kulshrestha and Arun Kumar Pal
Department of Mathematics, Statistics & Computer Science
G.B. Pant University of Agriculture and Technology
Pant Nagar, India
ABSTRACT
Balfanz et al. in 2003, introduced the primitive secret handshakes (SH) as a two party protocol together with a
notion of roles and implements it using pairing based cryptography, the scheme allows two parties to make a
match (authentication & verification) and derive a shared common session key if and only if they belong to
same group. If the parties do not belong to the same group, they cannot make any conclusion about the veracity
of other’s affiliation. Ateniese et al. in 2007 presented a SH with dynamic matching in which each party can
specify both the group and the role the other must have in order to complete a successful handshake. This paper
presents a new SH scheme with dynamic matching which is computationally comparable with the scheme of
Ateniese et al. The proposed scheme is inspired on an identity based authenticated key agreement proposed by
McCullagh et al. and uses ZSS signature. The paper also gives security proofs for the new scheme in the
random oracle.
KEYWORDS
Secret Handshakes, Authentication, Dynamic Matching, Pairing based Cryptography, Bilinear Pairing, ZSS
Signature.
1. INTRODUCTION
The secret handshakes (SH) are an important research subject in the field of privacy-preserving
authentication protocols. It is a cryptographic protocol introduced by Balfanz et al. [2] in 2003, which
allows two members of a specific group to authenticate themselves secretly in the sense that each
party reveals his affiliation to the other only if the other party is also a member of the same group.
They also introduced the SH with roles, so that a group member A can specify a role another group
member B must have in order to successfully complete the handshake. As in secret handshakes group
members can play different roles within a group, and can authenticate themselves in these roles. For
example, a CBI agent A wants to discover and communicates with other agent B, but they don’t want
to reveal their affiliations to non-agents. If B is not a CBI agent, then the protocol should not help B in
determining whether A is a CBI agent or not, and vice versa. In other words, the SH scheme enables
two members who belong to same group G to authenticate each other in a way that hides their
affiliation from all others.

68
2. Related Work
The secret handshakes scheme by Balfanz adapts the non interactive key agreement protocol of Sakai
et al. [12] based on bilinear maps. The scheme is secure under the BDH assumption. It uses one time
credentials to achieve the unlinkability, which means that each user must store a large number of
credentials. In 2004 Castelluccia et al. [3] constructed two party secret handshakes scheme with one
group by using CA-Oblivious encryption. This solution is secure under CDH assumption. Both these
schemes are secure in the random oracle model.
Ateniese et al. [1] introduced SH with dynamic matching which is the first efficient unlinkable SH
scheme, allowing to verify the presence of properties different from the user’s own. Their scheme
treats a set of members with identical attribute as an entity instead of different individual. It is
essentially a group key agreement scheme between different sub-group members in a large group
environment. Property credentials are issued by a certification authority (CA). This scheme is
somewhat in between SH and secures matchmaking protocol.
Sorniotti et al. [13] also proposed a similar concept of dynamic controlled matching allowing an
authorized prover to convince an authorized verifier that she owns a property. Both schemes allow
more flexible types of secret handshakes. Users holding credentials for different properties can
conduct successful secret handshakes; if credentials match the other user’s matching references. The
difference between the two schemes is the control that the CA retains over the matching ability.
However, neither of them supports revocation of credentials. Sorniotti and Molva [14] presented an
SH scheme with revocation which allows a user to prove to a verifier possession of a credential.
Credentials can be revoked simply by publishing a value in a revocation list.
Lu et al. [9] introduced secure same symptom based SH scheme which allows a patient to securely
share a PHI (Patient Health Information) and conduct extensive simulations to evaluate its efficiency
in terms of PHI reporting delay. Ryu et al. [11] introduced unlinkable SH for anonymous
communications allowing two arbitrary communication parties with the same role in either one single
group or multiple groups to privately authenticate each other. Recently Kulshrestha et al. [8] points
out that Ryu et al. scheme is insecure to key compromise impersonation attack. Wen et al. [17]
proposed an unlinkable SH with fuzzy matching for social network, it supports more flexible
threshold based appropriate matching under the multiple groups environment which is not limited to
authenticate between members from the same group and which is secure under the decisional bilinear
Diffie -Hellman assumption.
Vergnaud [16] constructed a SH scheme using RSA signature and Zhou et al. [24] constructed a SH
scheme using ElGamal and DSA signature. Both the schemes rely on random oracles for their security
and uses one time credential to insure that handshake protocol performed by the same party cannot be
linked. Xu -Yung [20] proposed SH scheme that achieves unlinkability with reusable credentials.
They introduced the concept of k-anonymous secret handshakes where k is an adjustable parameter
indicating the desired anonymity assurance. Huang -Cao [5] in 2009 proposed an efficient unlinkable
secret handshakes scheme and claimed that scheme achieves affiliation hiding and unlinkability.
However Su [15] and Youn -Park [22] proved that Huang -Cao scheme has a design flaw and is
insecure.
Gu -Xue [4] in 2011 proposed an improved secret handshakes scheme with unlinkability based on the
Huang -Cao scheme. Yoon [21] in 2011 points out that Gu -Xue scheme is insecure to key
compromise impersonation attack and cannot provide master key forward secrecy. Jarecki and Liu [6]
proposed a practical unlinkable secret handshakes scheme that supports both traceability and
revocation with reusable credentials. Resorting to group signature with message recovery, Kawai et
al. [7] proposed a conditional unlinkable secret handshakes scheme. Wen et al. [19] proposed a new
generic framework for constructing two-party secret handshakes schemes from ID-based message
recovery signatures. Inspired by Kawai et al. scheme [7], Wen et al. [18] also proposed unlinkable
secret handshakes from message recovery signature.

69
In this paper we propose a new SH scheme with dynamic matching from bilinear pairing. Our scheme
is constructed from Bilinear Inverse Diffie- Hellman. Our proposed SH scheme is constructed using
Ateniese et al. [1]. Our scheme is based on ZSS signature [23] and is inspired by identity based
authenticated key agreement by McCullagh et al. [10]. We also give security proofs for the new
scheme in the random oracle model.
Organization:
The remainder of this paper is organized as follows. Section 3 recalls the preliminaries related to our
work. Section 4 describes definitions and security requirements of a secret handshakes scheme. In
Section 5 we give our secret handshakes scheme with dynamic matching based on ZSS signature.
Section 6 gives the security analysis of our proposed scheme. In section 7 we discuss efficiency
issues. Finally we draw our conclusion in Section 8.
3. Preliminaries
3.1 Bilinear Pairing:
Let and be two cyclic groups of the same large prime order . is denoted as an additive
group and as a multiplicative group. Let denote a generator of .
A Bilinear Pairing is a function ∶ × → with the following properties:
(1) [Bilinearity] for ∈ and , ∈ ∗
, ( , ) = ( , ) .
(2) [Non-degeneracy] ( , ) ≠ 1.
(3) [Computability] e can be efficiently computed in polynomial time.
3.2 Some Mathematical problems in , are described as follows:
 Computational Diffie-Hellman (CDH) problem: The CDH problem is to compute abP when
given P, aP and bP for some , ∈ ∗
.
 Inverse Computational Diffie-Hellman (ICDH) problem: The ICDH problem is to compute a−1
P
when given P and aP for some ∈ ∗
.
 Modified Inverse Computational Diffie-Hellman (mICDH) problem: The mICDH problem is to
compute ( + ) when given bP, P, aP and (a+b)P for some , ∈ ∗
.
 Bilinear Diffie Hellman Problem (BDH): The BDH problem is to compute ( , ) when
given , , and for some , , ∈ ∗
.
 Bilinear Inverse Diffie Hellman Problem (BIDH): The BIDH problem is to compute ( , )
when given , and for some , ∈ ∗
.
 Modified Bilinear Inverse Diffie- Hellman (mBIDH) Problem: The mBIDH problem is to
compute ( , )( )
when given , , and for some , , ∈ ∗
.

70
3.3 ZSS Signature:
ZSS Signature was proposed by Zhang et al. [23] in 2004. The signature scheme consists of four
algorithms a parameter generation algorithm ParamGen, a key generation algorithm KeyGen, a
signature generation algorithm Sign and a signature verification algorithm Ver.
Signature scheme is as follows:
ParamGen:
Given a security parameter the algorithm generates the system parameter 〈 , , , , , 〉 where
and are the two cyclic groups of same order q, and P is a generator of , e is the bilinear map and
∶ {0,1}∗
→ ∗
is the cryptographic hash function.
KeyGen:
Randomly selects ∈ ∗
as the secret key and computes = as the public key.
Sign:
Given a secret key , and a message m, computes the signature = ( )
.
Ver:
Given a public key , a message m, and a signature S, verifies if
( ( ) + , ) = ( , ).
The verification works because
( ( ) + , ) = ( ( ) + , ( ( ) + ) ) = ( , ).
4. Secret Handshakes (SH) Scheme
In SH scheme there exists three entities for a group G, a user who may or may not be a member of G,
a user who belongs to the group and a group administrator (GA) who creates and adds members into
the group, and issues certificate in a form of secret key to members.
A secret handshakes scheme consists of the following algorithms:
Create Group:
This is an algorithm run by a group administrator GA, which takes params as input and generates a
key pair (group public key) and (group secret key).
Add User:
This is an algorithm between a user U and the GA of some group. It takes params and GA’s secret
as input and output a public key and secret key for U and makes U a valid member of the
group.

71
Handshake:
This is the authentication protocol. It is executed between users A and B, who want to authenticate
each other on the public inputs , and params. The private input of each party is their secret
credential and the output of the protocol for either party is either ‘reject’ or ‘accept’ (A and B belong
to the same group if and only if the output is ‘accept’). At the end of the protocol, if A’s requirements
for B are matched by B’s credentials and B’s requirements for A are matched by A’s credentials, A and
B authenticate by sharing a common key otherwise such authentication fails.
A secret handshakes scheme must have the following security properties:
Completeness/ Correctness:
If two honest members A, B belonging to the same group and run handshake protocol with valid
credentials of their and group public keys, then both members always output “accept”.
Impersonator Resistance:
An adversary not satisfying the rules of the handshake protocol is unable to successfully authenticate
to an honest member.
Detector Resistance:
An adversary not satisfying the rules of the handshake protocol cannot decide whether some honest
party satisfies the rule or not.
Unlinkability:
It is not feasible to tell whether two execution of the handshake protocol were performed by the same
party or not, even if both them were successful.
5. Proposed Scheme
In this section we propose a secret handshakes scheme with dynamic matching based on of ZSS
signature [23]. Our scheme uses same technique as Ateniese et al. [1].
Create Group:
The GA inputs a security parameter k into BDH parameter generator which returns
Params: 〈 , , , , , , 〉 as defined in section 3.
Add User:
For a user U, GA computes = ( ∥ ) where group is the group identity of the
user U and is its role. It then issues public key as = ( + ) and
secret key as = ( + ) .
Handshake:
Suppose A with secret on the identity and role and B with secret on the identity
and role engage in a handshake protocol. They should successfully complete the
protocol if the group and the role specified by A for B matches B’s credentials and group and role
specified by B for A matches A’s credentials.

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The protocol proceeds as follows:
1. A chooses unique random nonce ∈ ∗
and sends
= ( | ) + ,
where is the role and is the group identity that B must have in order to complete
the handshake.
2. Similarly, B chooses unique random nonce ∈ ∗
and sends
= ( | ) + ,
where is the role and is the group identity that A must have in order to complete
the handshake.
3. Using the knowledge of x and what A just received from B, A computes the following key:
= ( , ) and = ( , ).
4. Using the knowledge of and what B just received from A, B computes the following key:
= ( , ) and = ( , ) .
If = , = , = , and = , then at the end of the
handshake both A and B share a secret key = ( , ) .
Correctness:
If the participants satisfy the rules of the handshakes protocol, they will successfully share a common
key. For correctness of scheme we show that the shared key that A and B computes the same.
For A we have
= ( , ) = ( ∥ ) + , ( ( ∥ ) + ) ) ,
if = , and = , then
= ( , ) .
Similarly for user B
= ( , ) = ( ∥ ) + , ( ( ∥ ) + ) ) ,
if = , and = , then
= ( , ) .
6. Security
An adversary A who can forge a valid ZSS signature can surely attack the SH protocol just as an
honest member. Hence the probability to attack SH scheme cannot be smaller than the probability to
forge a valid ZSS signature.

73
Group Member Impersonation:
For an adversary A we define a member impersonation game, during which A is allowed to corrupt
users of her choice, but not GA.
Create:
Adversary A setup a new oracle in the system that has public key and secret key for some users. We
denote by the users that A controls.
Selects:
Adversary A selects a target user such that ∉ with whom she would like to communicate
and wants to detect a target role under which she wants to detect a target user .
Interaction:
Adversary A interacts with where ∉ in which case may be assumed that he interacts with
legitimate user. Since in this scheme during the handshake sends only
( ( ∥ )) + , ∈ ∗
, where ∥ is the expected identity of the
other end, this message can be generated by anyone. A can impersonate , if cannot distinguish
between A’s message and the real execution of the handshake protocol.
Challenge:
We claim that at the end of the interaction A cannot compute the same key that obtains because for
calculating the shared key she must possess the secret key which corresponds to the same identity or
requirement that want, because even knowing the public key or requirement send by ,
( + ) the probability to calculate the secret key ( + ) which correspond to a specific
identity is negligible.
= [ ] < is negligible.
Impersonation Resistance:
If A never corrupts a member of the target group with role then ∩ , = ∅. The secret
handshakes scheme is said to ensure impersonation resistance if is negligible for all A.
Group Member Detection:
For an adversary A we define a member detection game, in which A can corrupt users of her choice,
the goal of A to learns, how to identify member of a certain group.
Create:
Adversary A setup a new oracle in the system that has public key and secret key for some users. We
denote by the users that A controls.

74
Select:
and wants to detect a target role under which she wants to detect a target user .
Challenge:
An adversary A unable to distinguish between and simulator R because in our proposed scheme
during the handshake sends only ( ( ∥ )) + , ∈ ∗
, where
∥ is the expected identity of the other end. This message can be generated by anyone.
Therefore A cannot determine whether it was sent by or a simulator R either A interacts with or
a simulator R. Specifically, to answer a query the oracle flips a fair coin ∈ {0,1}; if the answer is 0,
it outputs the target user , and if the answer is 1, it outputs a random simulator. A then must decide
whether C is 0 or 1; call this prediction . A’s advantage in distinguish the target user and random
simulator in this game, is given by
= | [ = ] − |.
Detection Resistance:
Let be the group to which belongs with role in and suppose A never corrupts member of
with role the secret handshake scheme is said to ensure detection resistance if ∩ , = ∅.
Then is negligible for all A.
Unlinkability:
The property of unlinkability requires that it should be computationally hard for an adversary to link
transmitted message by the same party. For an adversary A we define a linking game, during which A
is allowed to corrupt users of her choice, but not GA.
Create:
Adversary A setup a new oracle in the system that has secret key for some users. We denote by
the users that A controls.
Interaction:
Adversary A interacts with users of her choice and obtains secrets for some users .
Selects:
and engage in handshake protocols with .
Challenge:
Given a transmitted messages X and Y for secret handshakes, the only way for an adversary to
distinguish the messages by the same or different parties is to compute a type of shared secrets
= ( , ).

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In our proposed scheme during the handshake user send only, ( ( ∥ )) + ,
∈ ∗
, where ∥ is the expected identity of the other end. Specifically, to answer a
query the oracle flips a fair coin = {0,1}; if the answer is 0, it output a handshake protocol with the
same user, and if the answer is 1, it outputs a different member which is not corrupted by adversary.
A then must decide whether b is 0 or 1; call this prediction . A’s advantage in linking the target user
is given by
= | [ = ] − |.
If be the group to which belongs with role in and suppose A never corrupts member of
with role and a GA of then adversary A has at most negligible linking advantage.
6.1 Theorem:
The proposed SH scheme is a secure SH scheme with dynamic matching assuming that BIDH
assumption hold.
Proof:
All queries by the adversary A now pass through simulator S.
Create:
When A corrupts users by querying their private keys, S answer those queries as follows:
S chooses ∈ ∗
creates public keys as
= −
= +
and computes the private key as .
Select:
Once A declared the target user , simulator S answers as public key. Since S does not know , it
cannot calculate the correct private key for the user .
Interaction:
Simulator needs to send to A message for . S chooses for an unknown which is ( ), where
∈ ∗
. In response it will get a value from as the value . This is genuine value from and S
does not influence it.
Compute:
Now the key can be computed by ( , ) S must have non-negligible advantage in
calculating ( , ) , because S does not know private key of . S sets
= ( , ) . S can calculate ( , ) , since it know and calculate
= ( , ) . So S can solve BIDH as compute ( , ) = .

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Hence S can successfully break the BIDHP with non negligible probability .
7. Performance Analysis
In this section we compare our construction with Atenniese et al. [1] scheme in terms of computation
cost, assumptions and the security properties achieved in table. The following notations are used to
analyze the computational cost; M is used for multiplication, E for exponentiation, P for pairing. For
both scheme we show the computational cost per party in secret handshake phase. As shown in table-
1, computation cost of our scheme is as good as Atenniese et al. [1] schemes.
Table 1.
BDH,
SXD
H and
BIDH
stand for the Bilinear Diffie-Hellman, Symmetric External Diffie-Hellman and Bilinear Inverse Diffie-Hellman assumptions,
respectively.
8. Conclusion
In this paper, we have proposed a secret handshakes scheme with dynamic matching, in which each
party can specify both the group and the role the other must have in order to complete the handshake.
Our secret handshakes scheme is inspired by the McCullagh et al. identity based authenticated key
agreement protocol. We constructed the scheme using the technique of Ateniese et al. Our scheme is
based on ZSS signature and is secure under BIDH assumption. Since the credential in our scheme is a
short signature proposed by Zhang et al.[23], the proofs of completeness, IR and DR can be easily
deduced from Zhang et al. signature scheme[23].In terms of computation cost our scheme is as good
as Ateniese [1] et al. scheme though our construction is more simple.
ACKNOWLEDGEMENTS
The authors express sincere thanks to Professor Sunder Lal and Mr. Manmohan Singh Chauhan for
their help and encouragement.
REFERENCES
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77
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Authors
Preeti Kulshrestha is a Research Scholar
Statistics & Computer Science
Technology PantNagar, India. Sh
(Agra) University, India in 2008.
identity based cryptography and
Email Id: ibspreeti@gmail.com
Dr. Arun Kumar Pal is an
Mathematics, Statistics & Computer Science
and Technology PantNagar, India
RDBMS Soft Computing, Queuing Networ
Email Id: arun_pal1969@yahoo.co.in
is a Research Scholar in the Department of Mathematics,
omputer Science, G. B. Pant University of Agriculture and
She obtained her M.Phil. degree from Dr. B. R. A.
8. Her research interest includes secret handshakes,
and digital signature.
is an Associate Professor in the Department of
Statistics & Computer Science, G. B. Pant University of Agriculture
India. His research areas are Computer Network &
RDBMS Soft Computing, Queuing Network and cryptography.
arun_pal1969@yahoo.co.in
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