*15:17* [Pub][ePrint]
Malleable Signatures: Complex Unary Transformations and Delegatable Anonymous Credentials, by Melissa Chase and Markulf Kohlweiss and Anna Lysyanskaya and Sarah Meiklejohn
A signature scheme is malleable if, on input a message m and a signature $\\sigma$, it is possible to efficiently compute a signature $\\sigma\'$ on a related message $m\' = T(m)$, for a transformation T that is allowable with respect to this signature scheme. Previous work considered various useful flavors of allowable transformations, such as quoting and sanitizing messages. In this paper, we explore a connection between malleable signatures and anonymous credentials, and give the following contributions:-We define and construct malleable signatures for a broad category of allowable transformation classes, with security properties that are stronger than those that have been achieved previously. Our construction of malleable signatures is generically based on malleable zero-knowledge proofs, and we show how to instantiate it under the Decision Linear assumption.

-We construct delegatable anonymous credentials from signatures that are malleable with respect to an appropriate class of transformations; we also show that our construction of malleable signatures works for this class of transformations. The resulting concrete instantiation is the first to achieve security under a standard assumption (Decision Linear) while also scaling linearly with the number of delegations.

*15:17* [Pub][ePrint]
Practical Multilinear Maps over the Integers, by Jean-Sebastien Coron and Tancrede Lepoint and Mehdi Tibouchi
Extending bilinear elliptic curve pairings to multilinear maps is a long-standing open problem. The first plausible construction of such multilinear maps has recently been described by Garg, Gentry and Halevi, based on ideal lattices. In this paper we describe adifferent construction that works over the integers instead of ideal lattices, similar to the DGHV fully homomorphic encryption scheme. We also describe a different technique for proving the full randomization of encodings: instead of Gaussian linear sums, we apply the classical leftover hash lemma over a quotient lattice. We show that our construction is relatively practical: for reasonable security parameters a one-round 7-party Diffie-Hellman key exchange requires about $25$ seconds per party.

*00:17* [Pub][ePrint]
Cryptanalysis of Some Double-Block-Length Hash Modes of Block Ciphers with $n$-Bit Block and $n$-Bit Key, by Deukjo Hong and Daesung Kwon
In this paper, we make attacks on DBL (Double-Block-Length) hash modes of block ciphers with n-bit key and n-bit block. Our preimage attack on MDC-4 scheme requires the time complexity $2^{3n/2}$, whichis significantly improved compared to the previous results. Our collision attack on the hash function of MJH scheme has time complexity less than $2^{124}$ for n = 128. Our preimage attack on the compression functions of MJH scheme find a preimage with time complexity of $2^n$. It is converted to a preimage attack on the hash function with time complexity of $2^{3n/2+1}$. Our preimage attack on the compression functions of MJH scheme find a preimage with time complexity of $2^{3n/2}$. It is converted to a second-preimage attack on the hash function with time complexity of $2^{7n/4+1}$. These attacks are helpful for understanding the security of the hash modes together with their security proofs.

*00:17* [Pub][ePrint]
Machine-Generated Algorithms, Proofs and Software for the Batch Verification of Digital Signature Schemes, by Joseph A. Akinyele and Matthew Green and Susan Hohenberger and Matthew W. Pagano
As devices everywhere increasingly communicate with each other, many security applications will require low-bandwidth signatures that can be processed quickly. Pairing-based signatures can be very short, but are often costly to verify. Fortunately, they also tend to have efficient batch verification algorithms. Finding these batching algorithms by hand, however, can be tedious and error prone.We address this by presenting AutoBatch, an automated tool for generating batch verification code in either Python or C++ from a high level representation of a signature scheme. AutoBatch outputs both software and, for transparency, a LaTeX file describing the batching algorithm and arguing that it preserves the unforgeability of the original scheme.

We tested AutoBatch on over a dozen pairing-based schemes to demonstrate that a computer could find competitive batching solutions in a reasonable amount of time. Indeed, it proved highly competitive. In particular, it found an algorithm that is significantly faster than a batching algorithm from Eurocrypt 2010. Another novel contribution is that it handles cross-scheme batching, where it searches for a common algebraic structure between two distinct schemes and attempts to batch them together.

In this work, we expand upon an extended abstract on AutoBatch appearing in ACM CCS 2012 in a number of ways. We add a new loop-unrolling technique and show that it helps cut the batch verification cost of one scheme by roughly half. We describe our pruning and search algorithms in greater detail, including pseudocode and diagrams. All experiments were also re-run using the RELIC pairing library. We compare those results to our earlier results using the MIRACL library, and discuss why RELIC outperforms MIRACL in all but two cases. Automated proofs of several new batching algorithms are also included.

AutoBatch is a useful tool for cryptographic designers and implementors, and to our knowledge, it is the first attempt to outsource to machines the design, proof writing and implementation of signature batch verification schemes.

*00:17* [Pub][ePrint]
Distinguishing Attacks on RC4 and A New Improvement of the Cipher, by Jing Lv and Bin Zhang and Dongdai Lin
RC4, designed by Rivest in 1987, is the most widely deployed stream cipher in practical applications. In this paper, two new class of statistical biases inherent in RC4 are depicted and it is shown that the RC4 keystream is distinguishable from random no matter how many initial bytes have been dumped.RC4A, proposed by Paul and Preneel at FSE 2004 to strengthen the security of RC4, is also found to be vulnerable to similar attacks. Instead, a new pseudorandom bit generator RC4B is proposed, which is believed to provide better immunity against the known attacks.

*00:17* [Pub][ePrint]
A generic construction for voting correctness at minimum cost - Application to Helios, by Veronique Cortier and David Galindo and Stephane Glondu and Malika Izabachene
Most voting schemes aim at providing verifiability: voters should be able to check that their ballots did contribute to the outcome (individual verifiability) and that the tallying authorities did their job properly (universal verifiability). Surprisingly, verifiability still does not answer a very simple and natural question: how can I be sure that the published result corresponds to the (sum of) intended votes of the voters? This property is called correctness by Juels, Catalano, and Jakobsson. Actually, even a prominent voting system like Helios does not achieve correctness in the case of a dishonest bulletin board, since it may add ballots.We generalize the aforementioned definition of correctness to account for a malicious bulletin board (full correctness) and we provide a generic construction that transforms a correct voting scheme into a fully correct voting scheme. This construction simply requires to send credentials to the voters, with no additional infrastructure. We further provide a simple and natural criteria that implies voting correctness, which can then be turned into full correctness due to our construction. As an application, we build a variant of Helios that is both fully correct, verifiable and private.

Real-world elections often require threshold cryptosystems so that any t out of l trustees can proceed to tallying. We describe a fully distributed (with no dealer) threshold cryptosystem suitable for Helios (in particular, suitable to partial decryption). In doing so we happen to revisit the seminal multi-authority election system from Cramer, Gennaro and Schoenmakers. Altogether, we provide the first proof of privacy, verifiability and correctness for a fully distributed Helios voting scheme (and its enhanced version with credentials), together with its detailed description. This also implies, to our knowledge, the first formal proofs of privacy, verifiability and correctness for the scheme by Cramer et al. Last but not least, we provide an open source implementation of our variant of Helios.