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07:17 [Pub][ePrint] Weakness of F_{3^{6*1429}} and F_{2^{4*3041}} for Discrete Logarithm Cryptography, by Gora Adj and Alfred Menezes and Thomaz Oliveira and Francisco Rodriguez-Henriquez

  In 2013, Joux and then Barbulsecu et al. presented new algorithms for computing discrete logarithms in finite fields of small characteristic. Shortly thereafter, Adj et al. presented a concrete analysis showing that, when combined with some steps from classical algorithms, the new algorithms render the finite field F_{3^{6*509}} weak for pairing-based cryptography. Granger and Zumbragel then presented a modification of the new algorithms that extends their effectiveness to a wider range of fields.

In this paper, we study the effectiveness of the new algorithms combined with a carefully crafted descent strategy for the fields F_{3^{6*1429}} and F_{2^{4*3041}}. The intractability of the discrete logarithm problem in these fields is necessary for the security of pairings derived from supersingular curves with embedding degree 6 and 4 defined, respectively, over F_{3^{1429}} and F_{2^{3041}}; these curves were believed to enjoy a security level of 192 bits against attacks by Coppersmith\'s algorithm. Our analysis shows that these pairings offer security levels of at most 91 and 129 bits, respectively, leading us to conclude that they are dead for pairing-based cryptography.

07:17 [Pub][ePrint] Multi-Input Functional Encryption, by Shafi Goldwasser and Vipul Goyal and Abhishek Jain and Amit Sahai

  We introduce the problem of Multi-Input Functional Encryption, where a secret key SK_f can correspond to an n-ary function f that takes multiple ciphertexts as input. Multi-input functional encryption is a general tool for computing on encrypting data which allows for mining aggregate information from several different data sources (rather than just a single source as in single input functional encryption). We show wide applications of this primitive to running SQL queries over encrypted database, non-interactive differentially private data release, delegation of computation, etc.

We formulate both indistinguishability-based and simulation-based definitions of security for this notion, and show close connections with indistinguishability and virtual black-box definitions of obfuscation. Assuming indistinguishability obfuscation for circuits, we present constructions achieving indistinguishability security for a large class of settings. We show how to modify this construction to achieve simulation-based security as well, in those settings where simulation security is possible. Assuming differing-inputs obfuscation [Barak et al., FOCS\'01], we also provide a construction with similar security guarantees as above, but where the keys and ciphertexts are compact.

07:17 [Pub][ePrint] Modified Alternating Step Generators, by Robert Wicik and Tomasz Rachwalik

  Irregular clocking of feedback shift registers is a popular technique to improve parameters of keystream generators in stream ciphers. Another technique is to implement nonlinear functions. We join these techniques and propose Modified Alternating Step Generators built with linear and nonlinear feedback shift registers. Adequate nonlinear Boolean functions are used as feedbacks or as filtering functions of shift registers in order to increase complexity of sequences produced by individual registers and the whole generator. We investigate basic parameters of proposed keystream generators, such as period, linear complexity and randomness.

07:17 [Pub][ePrint] Functional Encryption for Randomized Functionalities, by Vipul Goyal and Abhishek Jain and Venkata Koppula and Amit Sahai

  In this work, we present the first definitions and constructions for functional encryption supporting randomized functionalities. The setting of randomized functionalities require us to revisit functional encryption definitions by, for the first time, explicitly adding security requirements for dishonest encryptors, to ensure that they cannot improperly tamper with the randomness that will be used for computing outputs. Our constructions are built using indistinguishability obfuscation.

07:17 [Pub][ePrint] Stamp \\& Extend -- Instant but Undeniable Timestamping based on Lazy Trees, by {\\L}ukasz Krzywiecki and Przemys{\\l}aw Kubiak and Miros{\\l}aw Kuty{\\l}owski

  We present a Stamp\\&Extend time-stamping scheme based on linking via modified creation of Schnorr signatures.

The scheme is based on lazy construction of a tree of signatures.

Stamp\\&Extend returns a timestamp immediately after the request, unlike the schemes based on the concept of timestamping rounds.

Despite the fact that all timestamps are linearly linked, verification of a timestamp requires a logarithmic number of steps with respect to the chain length.

An extra feature of the scheme is that any attempt to forge a timestamp by the Time Stamping Authority (TSA) results in revealing its secret key, providing an undeniable cryptographic evidence of misbehavior of TSA.

Breaking Stamp\\&Extend requires not only breaking Schnorr signatures,

but to some extend also breaking Pedersen commitments.

07:17 [Pub][ePrint] Constructing Differentially 4-uniform Permutations over GF(2^{2k}) from the Inverse Function Revisited, by Yongqiang Li and Mingsheng Wang and Yuyin Yu

  Constructing S-boxes with low differential uniformity and high

nonlinearity is of cardinal significance in cryptography. In the

present paper, we show that numerous differentially 4-uniform

permutations over GF(2^{2k}) can be constructed by composing

the inverse function and cycles over GF(2^{2k}). Two sufficient

conditions are given, which ensure that the differential uniformity

of the corresponding compositions equals 4. A lower bound on

nonlinearity is also given for permutations constructed with the

method in the present paper. Moreover, up to CCZ-equivalence, a new

differentially 4-uniform permutation with the best known

nonlinearity over GF(2^{2k}) with $k$ odd is constructed. For

some special cycles, necessary and sufficient conditions are given

such that the corresponding compositions are differentially


13:47 [Event][New] LATINCRYPT 2014: Third International Conference on Cryptology and Information Security

  Submission: 5 July 2014
Notification: 23 August 2014
From September 17 to September 19
Location: Florian´┐Żpolis, Brazil
More Information:

08:54 [Event][New] IWSEC 2013: The 8th International Workshop on Security (Poster Session)

  Submission: 15 November 2013
Notification: 16 November 2013
From November 18 to November 20
Location: Okinawa, Japan
More Information:

08:50 [Job][New] Security Engineer, CloudFlare Inc., San Francisco, CA, USA, the Northern Hemisphere


CloudFlare is looking for a talented security engineer to join our team. We are working on a number of ambitious projects to secure the web and protect our customers from threats of all sorts. The role of security engineer at CloudFlare is more that of a builder than a breaker. You will have to approach problems with creativity and flexibility and be able to identify and use the best tools for the job or build better ones from scratch. At CloudFlare, we are serious about protecting our customers and advancing the state of the art in computer security.


Strong systems-level programming skills?

Deep understanding of networking protocols (TCP/IP, SSL/TLS, DNS)

Experience with cryptographic libraries and APIs

Expert in C/C++ and performance analysis

Proficiency in Go and/or Lua or willingness to learn

Strong understanding of security concepts (key management, access control, authentication)

Understanding of Linux internals

Interest in advancements in security and cryptography

Bonus Points:

Contributions to the open source community

Experience implementing production-grade cryptographic algorithms

Knowledge or expertise in White-box cryptography

Experience with DNSSEC

Familiarity with compilers or code generation tools

Experience with cryptographic hardware (TPM, HSM, etc.)

Healthy sense of paranoia

08:48 [Job][New] Ph.D. Scholarships, University of Salerno, Italy

  to appear

07:17 [Pub][ePrint] Deep Attacks of a Certificateless Signature Scheme, by Bo Yang and Zhao Yang and Zibi Xiao and Shougui Li

  Certificateless public key cryptography is an attractive paradigm since it eliminates the use of certificates in traditional public key cryptography and alleviates the inherent key escrow problem in identity-based cryptography. Recently, Xiong et al. proposed a certificateless signature scheme and proved that their scheme is existentially unforgeable against adaptive chosen message attack under the random oracle model. He et al. pointed out that Xiong et al.\'s scheme is insecure against the Type II adversary. But, their forged signatures are not random, and their improved scheme has the same security defects as Xiong et al.\'s scheme. In this paper, we present two malicious-but-passive KGC attack methods on Xiong et al.\'s scheme and our results show that their scheme is insecure against malicious-but-passive KGC attack.