*14:59* [PhD][New]
Constantin Catalin Dragan: Security of CRT-based Secret Sharing Schemes
Name: Constantin Catalin Dragan

Topic: Security of CRT-based Secret Sharing Schemes

Category: (no category)

Description: The Chinese Remainder Theorem (CRT) is a very useful tool in many areas of theoretical and practical cryptography. One of these areas is the theory of threshold secret sharing schemes. A *(t+1,n)*-threshold secret sharing scheme is a method of partitioning a secret among *n* users by providing each user with a share of the secret such that any *t+1* users can uniquely reconstruct the secret by pulling together their shares. Several threshold schemes based on CRT are known. These schemes use sequences of pairwise co-prime positive integers with special properties. The shares are obtained by dividing the secret or a secret-dependent quantity by the numbers in the sequence and collecting the remainders. The secret can be reconstructed by some sufficient number of shares by using CRT. It is well-known that the CRT-based threshold secret sharing schemes are not perfect (and, therefore, not ideal) but some of them are asymptotically perfect and asymptotically ideal and perfect zero-knowledge if sequences of consecutive primes are used for defining them.

\r\n\r\n\r\nIn this thesis we introduce *(k-)compact sequences of co-primes* and their applications to the security of CRT-based threshold secret sharing schemes is thorough investigated. Compact sequences of co-primes may be significantly denser than sequences of consecutive primes of the same length, and their use in the construction of CRT-based threshold secret sharing schemes may lead to better security properties. Concerning the asymptotic idealness property for CRT-based threshold schemes, we have shown there exists a necessary and sufficient condition for the Goldreich-Ron-Sudan (GRS) scheme and Asmuth-Bloom scheme if and only if *(1-)compact sequences of co-primes* are used. Moreover, the GRS and Asmuth-Bloom schemes based on *k*-compact sequences of co-primes are asymptotically perfect and perfect zero-knowledge. The Mignotte scheme is far from being asymptotically perfect [...]

*13:26* [Job][New]
Postdoctoral and Internship Positions, *MICROSOFT RESEARCH, Redmond, Washington USA*
Microsoft Research invites applications from graduate students and recent Ph.D.s for Postdoctoral and Internship positions in the Microsoft Research Cryptography Group. Number Theory candidates should have interest/experience in one or more of the following areas: algorithmic/arithmetic/algebraic number theory, elliptic and hyperelliptic curve cryptography, pairing-based cryptosystems, lattice-based cryptography. Cryptography candidates should have research interests in at least one of the following: protocols, security models, cryptanalysis, hash functions, applied or theoretical cryptography.Post-docs and interns will be in residence at Microsoft Research Redmond, the main campus of Microsoft\\\'s basic research division with over four hundred researchers in dozens of areas of computer science research. Researchers benefit from close proximity to Microsoft product units, collaborative relations and joint seminars with University of Washington, and an active research environment. For more information about MSR Redmond and the Cryptography group see: http://research.microsoft.com/aboutmsr/labs/redmond/ and http://research.microsoft.com/crypto/

The post-doctoral positions offer a competitive salary, benefits, and a relocation allowance. The term is for two years; the start date is July 1, 2014. Post-docs will report to Dr. Kristin Lauter, Research Manager for the MSR Crypto Group. Internships for graduate students will be for 10-12 weeks in Summer 2014, with flexible start date.

*19:17* [Pub][ePrint]
DAA-related APIs in TPM2.0 Revisited, by Li Xi
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]
When a Boolean Function can be Expressed as the Sum of two Bent Functions, by Longjiang Qu and Shaojing Fu and Qingping Dai and Chao Li
In this paper we study the problem that when a Boolean function canbe 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]
Data Security in Cloud Architecture Based on Diffie Hellman and Elliptical Curve Cryptography, by Neha tirthani and Ganesan
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.