Cost-Effective Authentic and Anonymous Data Sharing with Forward Security

COST-EFFECTIVE AUTHENTIC AND ANONYMOUS DATA SHARING WITH
FORWARD SECURITY
Abstract—Data sharing has never been easier with the advances of cloud
computing, and an accurate analysis on the shared data provides an array of
benefits to both the society and individuals. Data sharing with a large number of
participants must take into account several issues, including efficiency, data
integrity and privacy of data owner. Ring signature is a promising candidate to
construct an anonymous and authentic data sharing system. It allows a data owner
to anonymously authenticate his data which can be put into the cloud for storage or
analysis purpose. Yet the costly certificate verification in the traditional public key
infrastructure (PKI) setting becomes a bottleneck for this solution to be scalable.
Identity-based (ID-based) ring signature, which eliminates the process of
certificate verification, can be used instead. In this paper, we further enhance the
security of ID-based ring signature by providing forward security: If a secret key of
any user has been compromised, all previous generated signatures that include this
user still remain valid. This property is especially important to any large scale data
sharing system, as it is impossible to ask all data owners to reauthenticate their data
even if a secret key of one single user has been compromised. We provide a

concrete and efficient instantiation of our scheme, prove its security and provide an
implementation to show its practicality.
EXISTING SYSTEM:
Data Authenticity. In the situation of smart grid, the statistic energy usage data
would be misleading if it is forged by adversaries. While this issue alone can be
solved using well established cryptographic tools (e.g., message authentication
code or digital signatures), one may encounter additional difficulties when other
issues are taken into account, such as anonymity and efficiency;
_ Anonymity. Energy usage data contains vast information of consumers, from
which one can extract the number of persons in the home, the types of electric
utilities used in a specific time period, etc. Thus, it is critical to protect the
anonymity of consumers in such applications, and any failures to do so may lead to
the reluctance from the consumers to share data with others; and
_ Efficiency. The number of users in a data sharing system could be HUGE
(imagine a smart grid with a country size), and a practical system must reduce the
computation and communication cost as much as possible. Otherwise it would lead
to a waste of energy, which contradicts the goal of smart grid.

PROPOSED SYSTEM:
We propose a new notion called forward secure ID-based ring signature, which is
an essential tool for building cost-effective authentic and anonymous data sharing
system:
_ For the first time, we provide formal definitions on forward secure ID-based ring
signatures;
_ We present a concrete design of forward secure IDbased ring signature. No
previous ID-based ring signature schemes in the literature have the property of
forward security, and we are the first to provide this feature;
_ We prove the security of the proposed scheme in the random oracle model, under
the standard RSA assumption; and
_ Our implementation is practical, in the following ways:
1) It is in ID-based setting. The elimination of the costly certificate
verification process makes it scalable and especially suitable for big data analytic
environment.
2) The size of a secret key is just one integer.
3) Key update process only requires an exponentiation.
4) We do not require any pairing in any stage.

Module 1
Authentication in cloud computing
Module 2
Identity-Based Ring Signature
The aforementioned three issues remind us a cryptographic primitive “identity-
based ring signature”, an efficient solution on applications requiring data
authenticity and anonymity.
ID-Based Cryptosystem Identity-based (ID-based) cryptosystem, introduced by
Shamir, eliminated the need for verifying the validity of public key certificates, the
management of which is both time and cost consuming. In an ID-based
cryptosystem, the public key of each user is easily computable from a string
corresponding to this user’s publicly known identity (e.g., an email address, a
residential address, etc.). A private key generator (PKG) then computes private
keys from its master secret for users. This property avoids the need of certificates
(which are necessary in traditional public-key infrastructure) and associates an
implicit public key (user identity) to each user within the system. In order to verify
an ID-based signature, different from the traditional public key based signature,
one does not need to verify the certificate first. The elimination of the certificate

validation makes the whole verification process more efficient, which will lead to a
significant save in communication and computation when a large number of users
are involved (say, energy usage data sharing in smart-grid). Ring signature is a
group-oriented signature with privacy protection on signature producer. A user can
sign anonymously on behalf of a group on his own choice, while group members
can be totally unaware of being conscripted in the group. Any verifier can be
convinced that a message has been signed by one of the members in this group
(also called the Rings), but the actual identity of the signer is hidden. Ring
signatures could be used for whistle blowing, anonymous membership
authentication for ad hoc groups and many other applications which do not want
complicated group formation stage but require signer anonymity. There have been
many different schemes proposed since the first appearance of ring signature in
1994 and the formal introduction in 2001.
Module 3
Notions of Security
The security of IDFSRS consists of two aspects: forward security and anonymity.
Before giving their definition, we consider the following oracles which together
model the ability of the adversaries in breaking the security of IDFSRS.

_ Extration Oracle (EO). On input an identity IDi and a time period t, the
corresponding secret key ski;t 2 D for that time period is returned.
_ Signing Oracle (SO). On input a time period t, a group size n, a set L of n user
identities, a message m2M, a valid signature s is returned. Now we are ready to
define the security of IDFSRS:
1) Forward Security. Forward security of IDFSRS scheme is defined in
the following game between the simulator S and the adversary A in which A is
given access to oracles EO and SO:
a) S generates and gives A the system parameters param.
b) A may query the oracles according to any adaptive strategy.
c) A chooses a time t_, a group size n_ 2 N, a set L_ of n_
identities and a message m_ 2M.
d) A may continue to query the oracles according to any
adaptive strategy.
e) A outputs a signature s_t
_ Verifyðt_;L_;m_; s_t_Þ ¼ valid.
_ None of the identities in L_ has been queried to EO with time t _ t_ as the time
input parameter. (Unlimited query to EO with time t > t_ to be the time input
parameter.)

_ ðt_;L_;m_Þ are not queried to SO. We denote Advfs A ð_Þ the probability of A
winning the game.
Module 4
Key Exposure in Big Data Sharing System
The issue of key exposure is more severe in a ring signature scheme: if a ring
member’s secret key is exposed, the adversary can produce valid ring signatures of
any documents on behalf of that group. Even worse, the “group” can be defined by
the adversary at will due to the spontaneity property of ring signature: The
adversary only needs to include the compromised user in the “group” of his choice.
As a result, the exposure of one user’s secret key renders all previously obtained
ring signatures invalid (if that user is one of the ring members), since one cannot
distinguish whether a ring signature is generated prior to the key exposure or by
which user. Therefore, forward security is a necessary requirement that a big data
sharing system must meet. Otherwise, it will lead to a huge waste of time and
resource. While there are various designs of forward-secure digital signatures,
adding forward security on ring signatures turns out to be difficult. As far as the

authors know, there are only two forward secure ring signature schemes. However,
they are both in the traditional public key setting where signature verification
involves expensive certificate check for every ring member. This is far below
satisfactory if the size of the ring is huge, such as the users of a smart grid. To
summarize, the design of ID-based ring signature with forward security, which is
the fundamental tool for realizing cost-effective authentic and anonymous data
sharing, is still an open problem.
Module 5
Id-based forward secure
Ring signature scheme This section is devoted to the description and analysis of
our proposed ID-based forward secure ring signature scheme.
The Design We assume that the identities and user secret keys are valid into T
periods and makes the time intervals public. We also set the message spaceM ¼ f0;
1.
CONCLUSION

Motivated by the practical needs in data sharing, we proposed a new notion called
forward secure ID-based ring signature. It allows an ID-based ring signature
scheme to have forward security. It is the first in the literature to have this feature
for ring signature in ID-based setting. Our scheme provides unconditional
anonymity and can be proven forward- secure unforgeable in the random oracle
model, assuming RSA problem is hard. Our scheme is very efficient and does not
require any pairing operations. The size of user secret key is just one integer, while
the key update process only requires an exponentiation. We believe our scheme
will be very useful in many other practical applications, especially to those require
user privacy and authentication, such as ad-hoc network, e-commerce activities
and smart grid. Our current scheme relies on the random oracle assumption to
prove its security. We consider a provably secure scheme with the same features in
the standard model as an open problem and our future research work
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[2] R. Anderson, “Two remarks on public-key cryptology,” Manuscript, Sep. 2000.
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Cost-Effective Authentic and Anonymous Data Sharing with Forward Security

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Cost-Effective Authentic and Anonymous Data Sharing with Forward Security