International Association for Cryptologic Research

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2013-03-15
06:17 [Pub][ePrint]

Data integrity and storage efficiency are two important requirements for cloud storage. Proof of Retrievability (POR) and Proof of Data Possession (PDP) techniques assure data integrity for cloud storage. Proof of Ownership (POW) improves storage efficiency by securely removing unnecessarily duplicated data on the storage server. However, trivial combination of the two techniques, in order to achieve both data integrity and storage efficiency, results in non-trivial duplication of metadata (i.e., authentication tags), which contradicts the objectives of POW. Recent attempts to this problem introduce tremendous computational and communication costs and have been proven not secure. It calls for a new solution to support efficient and secure data integrity auditing with storage deduplication for cloud storage. In this paper we solve this open problem with a novel scheme based on techniques including polynomial-based authentication tags and homomorphic linear authenticators. Our design allows deduplication of both files and their corresponding authentication tags. Data integrity auditing and storage deduplication are achieved simultaneously. Our proposed scheme is also characterized by constant realtime communication and computational cost on the user side. Public auditing and batch auditing are both supported. Hence, our proposed scheme outperforms existing POR and PDP schemes while providing the additional functionality of deduplication. We prove the security of our proposed scheme based on the Computational Diffie-Hellman problem and the Strong Diffie-Hellman assumption. Numerical analysis and experimental results on Amazon AWS show that our scheme is efficient and scalable.

06:17 [Pub][ePrint]

TCS\\_SHA-3 is a family of four cryptographic hash functions that are covered by an US patent (US 2009/0262925). The digest sizes are 224, 256, 384 and 512 bits. The hash functions use bijective functions in place of the standard, compression functions. In this paper we describe first and second preimage attacks on the full hash functions. The second preimage attack requires negligible time and the first preimage attack requires $O(2^{36})$ time. In addition to these attacks, we also present a negligible-time second preimage attack on a strengthened variant of the TCS\\_SHA-3. All the attacks have negligible memory requirements.

06:17 [Pub][ePrint]

To against some known attacks to Secure Shell (SSH), I propose some fixes to SSH. The fixes include add a key producer function and revise the MAC.

06:17 [Pub][ePrint]

Securely deleting data from storage systems has become difficult

today. Most storage space is provided as a virtual resource and traverses

many layers between the user and the actual physical storage medium.

Operations to properly erase data and wipe out all its traces are

typically not foreseen. This paper introduces a cryptographic model

for policy-based secure deletion of data in storage systems, whose

security relies on the proper erasure of cryptographic keys.

Deletion operations are expressed in terms of a deletion policy that

describes data destruction through deletion attributes and

protection classes. A protection class is first applied to the

stored data. Later, a secure deletion operation takes attributes as

parameters and triggers the destruction of all data whose protection

class is deleted according to the policy. No stored data is ever

re-encrypted. A cryptographic construction is presented for

deletion policies given by directed acyclic graphs; it is built in a

modular way from exploiting that secure deletion schemes may be

composed with each other. Finally, the paper describes a prototype

implementation of a Linux filesystem with policy-based secure

deletion.

06:17 [Pub][ePrint]

Most of certificateless signature schemes without random oracles can not resist key replacement attack. To overcome this security weakness, Yu et al. recently propose a new certificateless signature scheme and claimed that their scheme is provably secure in the standard model. However, in this paper, we show their scheme is still insecure against key replacement attack where an adversary who replaces the public key of a signer can forge valid signatures on any messages for that signer without knowing the signer\'s partial secret key. Moreover, we show Yu et al.\'s certificateless signature scheme is vulnerable to malicious-but-passive\'\' KGC attack where a malicious KGC can forge valid signatures by embedding extra trapdoors in the system parameter.

06:17 [Pub][ePrint]

We investigate alternative suspicion functions for Tardos traitor tracing schemes. In the simple decoder approach (computation of a score for every user independently) we derive suspicion functions that optimize a performance indicator related to the sufficient code length $\\ell$ in the limit of large coalition size $c$. Our results hold for the Restricted-Digit Model as well as the Combined-Digit Model. The scores depend on information that is usually not available

to the tracer -- the attack strategy or the tallies of the symbols received by the colluders. We discuss how such results can be used in realistic contexts.

We study several combinations of coalition attack strategy vs. suspicion function optimized against some attack (another attack or the same). In many of these combinations the usual scaling $\\ell \\propto c^2$ is replaced by a lower power of $c$, e.g. $c^{3/2}$. We find that the interleaving strategy is an especially

powerful attack, and the suspicion function tailored against interleaving is effective against all considered attacks.

06:17 [Pub][ePrint]

One of the main tools to construct secure two-party computation protocols are Yao garbled circuits. Using the cut-and-choose technique, one can get reasonably efficient Yao-based protocols with security against malicious adversaries. At TCC 2009, Nielsen and Orlandi suggested to apply cut-and-choose at the gate level, while previously cut-and-choose was applied on the circuit as a whole. This appealing idea allows for a speed up with practical significance (in the order of the logarithm of the size of the circuit) and has become known as the LEGO\'\' construction. Unfortunately the construction by Nielsen and Orlandi is based on a specific number-theoretic assumption and requires public-key operations per gate of the circuit.

The main technical contribution of this work is a new XOR-homomorphic commitment scheme based on oblivious transfer, that we use to cope with the problem of connecting the gates in the LEGO construction. Our new protocol has the following advantages:

\\begin{enumerate}

\\item

It maintains the efficiency of the LEGO cut-and-choose.

\\item

After a number of seed oblivious transfers linear in the security parameter, the construction uses only primitives from Minicrypt (i.e., private-key cryptography) per gate in the circuit (hence the name MiniLEGO).

\\item

On the contrary of original LEGO, MiniLEGO is compatible with all known optimization for Yao garbled gates (row reduction, free-XORs, point-and-permute).

\\end{enumerate}

2013-03-14
03:17 [Pub][ePrint]

This paper explores the potential for using genus~2 curves over quadratic extension fields in cryptography, motivated by the fact that they allow for an 8-dimensional scalar decomposition when using a combination of the GLV/GLS algorithms. Besides lowering the number of doublings required in a scalar multiplication, this approach has the advantage of performing arithmetic operations in a 64-bit ground field, making it an attractive candidate for embedded devices. We found cryptographically secure genus 2 curves which, although susceptible to index calculus attacks, aim for the standardized 112-bit security level. Our implementation results on both high-end architectures (Ivy Bridge) and low-end ARM platforms (Cortex-A8) highlight the practical benefits of this approach.

2013-03-13
11:24 [Job][New]

The Information Security Group (ISG) at Royal Holloway, University of London is looking for outstanding young graduates to fill 10 well-funded doctoral studentships in Cyber Security starting in October 2013.

The ISG is one of the largest and longest-established academic research groups working in cyber security, with a community of 15 academic staff, 10 postdocs and 40 PhD students. The ISG has a wide range of research interests related to cyber security, including the basic components of security services, such as cryptographic algorithms and trusted hardware; management of cryptographic keys; the correctness of the design and implementation of security protocols; the design of security services for embedded systems, business information systems, telecommunications networks and critical infrastructure; the detection and analysis of malware; and the study of economics, psychology, organizational theory, design theory and sociology in the context of information and cyber security.

We will consider applications from candidates with undergraduate and master\\\'s qualifications in a wide range of disciplines, including, but not limited to, mathematics, computer science, and electrical and electronic engineering. Funding is provided by the EPSRC (the UK Engineering and Physical Sciences Research Council), so full studentships are available to UK residents only (see http://www.epsrc.ac.uk/skills/students/help/Pages/eligibility.aspx for further details).

Further details of the research interests of the ISG can be found at http://www.isg.rhul.ac.uk/bin/staff-dir.php. Informal enquiries about the studentships can be made to Dr Carlos Cid, Prof. Jason Crampton, Prof. Keith Martin or Prof. Kenny Paterson ({carlos.cid,jason.crampton,keith.martin,kenny.paterson}@rhul.ac.uk). Further information about applying for the PhD programme at Royal Holloway is available at http://www.rhul.ac.uk/studyhere/research

06:17 [Pub][ePrint]

In this paper we present a new method of choosing primitive elements for Brezing-Weng families of pairing friendly elliptic curves with small rho-value, and we improve on previously-known best rho-values of families for the cases k=16, 22, 28 and 46. Our construction uses fixed discriminants.

06:17 [Pub][ePrint]

We present a runtime environment for executing secure programs via a multi-party computation protocol in the preprocessing model. The runtime environment is general and allows arbitrary reactive computations to be performed. A particularly novel aspect is that it automatically determines the minimum number of rounds needed for a computation, and uses this to minimize the overall cost of the computation. Various experiments are reported on, on various non-trivial functionalities. We show how, by utilizing the ability of modern processors to execute multiple threads at a time, one can obtain various tradeoffs between latency and throughput.