International Association for Cryptologic Research

# IACR News Central

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2014-01-22
19:17 [Pub][ePrint]

In TPM2.0, a single signature primitive is proposed to sup-

port various signature schemes including Direct Anonymous Attestation

(DAA), U-Prove and Schnorr signature. This signature primitive is im-

plemented by several APIs. In this paper, we show these DAA-related

APIs can be used as a static Diffie-Hellman oracle thus the security

strength of these signature schemes can be weakened by 14-bit. We pro-

pose a novel property of DAA called forward anonymity and show how

to utilize these DAA-related APIs to break forward anonymity. Then we

propose new APIs which not only remove the Static Diffie-Hellman oracle

but also support the forward anonymity, thus significantly improve the

security of DAA and the other signature schemes supported by TPM2.0.

We prove the security of our new APIs under the discrete logarithm

assumption in the random oracle model. We prove that DAA satisfy for-

ward anonymity using the new APIs under the Decision Diffie-Hellman

assumption. Our new APIs are almost as efficient as the original APIs

in TPM2.0 specification and can support LRSW-DAA and SDH-DAA

together with U-Prove as the original APIs.

16:17 [Pub][ePrint]

The Fibonacci-to-Galois transformation is useful for reducing the propagation delay of feedback shift register-based stream ciphers and hash functions. In this paper, we extend it to handle Galois-to-Galois case as well as feedforward connections. This makes possible transforming Trivium stream cipher and increasing its keystream data rate by 27\\% without any penalty in area. The presented transformation might open new possibilities for cryptanalysis of Trivium, since it induces a class of stream ciphers which generate the same set of keystreams as Trivium, but have a different structure.

2014-01-21
16:17 [Pub][ePrint]

In this paper we study the problem that when a Boolean function can

be represented as the sum of two bent functions. This problem was

recently presented by N. Tokareva in studying the number of bent

functions. Firstly, many functions, such as

quadratic Boolean functions, Maiorana-MacFarland bent functions,

partial spread functions etc, are proved to be able to be

represented as the sum of two bent functions. Methods to construct

such functions from low dimension ones are also introduced. N.

Tokareva\'s main hypothesis is proved for $n\\leq 6$. Moreover,

two hypotheses which are equivalent to N. Tokareva\'s main hypothesis

are presented. These hypotheses may lead to new ideas or methods to

solve this problem. At last, necessary and sufficient conditions on

the problem when the sum of several bent functions is again a bent

function are given.

16:17 [Pub][ePrint]

Technological advancements in cloud computing due to increased connectivity and exponentially proliferating data has resulted in migration towards cloud architecture. Cloud computing is technology where the users\' can use high end services in form of software that reside on different servers and access data from all over the world. Cloud storage enables users to access and store their data anywhere. It also ensures optimal usage of the available resources. There is no need for the user to maintain the overhead of hardware and software costs. With a promising technology like this, it certainly abdicates users\' privacy, putting new security threats towards the certitude of data in cloud. The user relies entirely for his data protection on the cloud providers, making them solely responsible for safeguarding it. The security threats such as maintenance of data integrity, data hiding and data safety dominate our concerns when the issue of cloud security come up. The voluminous data and time consuming encryption calculations related to applying any encryption method have been proved as a hindrance in this field.

In this research paper, we have contemplated a design for cloud architecture which ensures secured movement of data at client and server end. We have used the non breakability of Elliptic curve cryptography for data encryption and Diffie Hellman Key Exchange mechanism for connection establishment. The proposed encryption mechanism uses the combination of linear and elliptical cryptography methods. It has three security checkpoints: authentication, key generation and encryption of data.

16:17 [Pub][ePrint]

Menezes--Qu--Vanstone key agreement (MQV) is intended to provide implicit key authentication (IKA) and several other security objectives. MQV is approved and specified in five standards.

This report focuses on the IKA of two-pass MQV, without key confirmation. Arguably, implicit key authentication is the most essential security objective in authenticated key agreement. The report examines various necessary or sufficient formal conditions under which MQV may provide IKA.

Incidentally, this report defines, relies on, and inter-relates various conditions on the key deriviation function and Diffie--Hellman groups. While it should be expected that most such definitions and results are already well-known, a reader interested in these topics may be interested in this report as a kind of review, even if they have no interest in MQV whatsoever.

09:48 [Event][New]

Submission: 16 March 2014
Notification: 23 May 2014
From September 25 to September 26
Location: Aveiro, Portugal

2014-01-20
10:17 [Pub][ePrint]

Random number generators have direct applications in information security, online

gaming, gambling, and computer science in general. True random number generators

need an entropy source which is a physical source with inherent uncertainty, to ensure

unpredictability of the output. In this paper we propose a new indirect approach to

collecting entropy using human errors in the game play of a user against a computer. We

argue that these errors are due to a large set of factors and provide a good source of

randomness. To show the viability of this proposal, we design and implement a game,

conduct a user study in which we collect user input in the game, and extract randomness

from it. We measure the rate and the quality of the resulting randomness that clearly

show effectiveness of the approach. Our work opens a new direction for construction of

entropy sources that can be incorporated into a large class of video games.

10:17 [Pub][ePrint]

Recently, Fan et al. proposed a user efficient recoverable off-line e-cash scheme with fast anonymity revoking. They claimed that their scheme could achieve security requirements of an e-cash system such as, anonymity, unlinkability, double spending checking, anonymity control, and rapid anonymity revoking on double spending. They further formally prove the unlinkability and the un-forgeability security features. However, after crypto-analysis, we found that the scheme cannot attain the two proven security features, anonymity and unlinkability. We, therefore, modify it to comprise the two desired requirements which are very important in an e-cash system.

10:17 [Pub][ePrint]

The paper is about methodology to detect and demonstrate impossible differentials in a block cipher. We were inspired by the shrinking technique proposed by Biham et al. in 1999 which recovered properties of scalable block cipher structures from numerical search on scaled down variants. Attempt to bind all concepts and techniques of impossible differentials together reveals a view of the search for impossible differentials that can benefit from the computational power of a computer. We demonstrate on generalized Feistel networks with internal permutations an additional clustering layer on top of shrinking which let us merge numerical data into relevant human-readable information to be used in an actual proof. After that, we show how initial analysis of scaled down TEA-like schemes leaks the relevant part of the design and the length and ends of the impossible differentials. We use that initial profiling to numerically discover 4 15-round impossible differentials (beating the current 13-round) and thousands of shorter ones.

2014-01-17
13:17 [Pub][ePrint]

Even as data and analytics driven applications are becoming increasingly popular, retrieving data from shared databases poses a threat to the privacy of their users. For example, investors/patients retrieving records about interested stocks/diseases from a stock/medical database leaks sensitive information to the database server. PIR (Private Information Retrieval) is a promising security primitive to protect the privacy of users\' interests. PIR allows the retrieval of a data record from a database without letting the database server know which record is being retrieved. The privacy guarantees could either be information theoretic or computational. Ever since the first PIR schemes were proposed, a lot of work has been done to reduce the communication cost in the information-theoretic settings - particularly the question communication cost, i.e., the traffic from the user to the database server. The answer communication cost (the traffic from the database server to the user) has however barely been improved. When question communication cost is much lower than the record length, reducing question communication cost has marginal benefit on lowering overall communication cost. In contrast, reducing answer cost becomes very important. In this paper we propose ramp secret sharing based mechanisms that reduce the answer communication cost in information-theoretic PIR. We have designed four information-theoretic PIR schemes, using three ramp secret sharing approaches, achieving answer communication cost close to the cost of non-private information retrieval. Evaluation shows that our PIR schemes can achieve lower communication cost and the same level of privacy compared with existing schemes. Our PIR schemes\' usages are demonstrated for realistic settings of outsourced data sharing and P2P content delivery scenarios. Thus, our approach makes PIR a viable communication efficient technique to protect user interest privacy.

10:17 [Pub][ePrint]

In this paper, we propose a new algorithm for solving the approximate common divisors problems, which is based on LLL reduction algorithm of certain special lattice and linear equation solving algorithm over integers. Through both theoretical argument and experimental data, we show that our new algorithm is a polynomial time algorithm under reasonable assumptions on the parameters. We use our algorithm to solve concrete problems that no other algorithm could solve before. Further more, we show that our algorithm can break

the fully homomorphic encryption schemes, which are based on the approximate common divisors problem, in polynomial time in terms of the system parameter $\\lambda$.