*12:17* [Pub][ePrint]
New Quadratic Bent Functions in Polynomial Forms with Coefficients in Extension Fields, by Chunming Tang, Yanfeng Qi, Maozhi Xu
In this paper, we first discuss the bentness of a large class of quadratic Boolean functions in polynomial form$f(x)=\\sum_{i=1}^{\\frac{n}{2}-1}Tr^n_1(c_ix^{1+2^i})+ Tr_1^{n/2}(c_{n/2}x^{1+2^{n/2}})$, where

$c_i\\in GF(2^n)$ for $1\\leq i \\leq \\frac{n}{2}-1$ and $c_{n/2}\\in GF(2^{n/2})$.

The bentness of these functions can be connected with linearized permutation

polynomials. Hence, methods for constructing quadratic bent functions are given. Further, we consider a subclass of quadratic Boolean functions of the form

$f(x)=\\sum_{i=1}^{\\frac{m}{2}-1}Tr^n_1(c_ix^{1+2^{ei}})+

Tr_1^{n/2}(c_{m/2}x^{1+2^{n/2}})$ , where $c_i\\in GF(2^e)$, $n=em$ and $m$ is even. The bentness of these functions are characterized and some methods for constructing new quadratic bent functions are given. Finally, for a special case: $m=2^{v_0}p^r$ and

$gcd(e,p-1)=1$, we present the enumeration of quadratic bent functions.

*12:17* [Pub][ePrint]
Attribute-Based Server-Aided Verfication Signature, by Zhiwei Wang and Ruirui Xie and Wei Zhang and Liwen He and Guozi Sun and Wei Chen
Attribute based signature (ABS) is a novel cryptographic primitive, which enables a party can sign messages for any predicate satisfy by their attributes. However, heavy computational cost is required during the verification procedure in most existing ABS schemes, which may needs many pairing operations. Pairing are costly operation when compared to exponentiation in the base group. As a result, this presents a greatly challenge for resource-limited users, such as smart cards and wireless sensor. In other words, verification can hardly be done in these devices if attribute based signature is employed. We solve thisproblem by proposing a new notion called \\emph{Attribute-Based Server-Aided Verification Signature}. It is similar to normal ABS scheme, but it further enables the verifier to verify the signature with the assistance of an external server. In this paper, we provide the security definition of Attribute-Based Server-Aided Verification Signature, and design a concrete server-aided verification protocol for Li et al.\'s attribute based signature. We also prove that our protocol is secure with random oracles.

*12:17* [Pub][ePrint]
Practical Secure Logging: Seekable Sequential Key Generators, by Giorgia Azzurra Marson and Bertram Poettering
In computer forensics, log files are indispensable resources that support auditors in identifying and understanding system threats and security breaches. If such logs are recorded locally, i.e., stored on the monitored machine itself, the problem of log authentication arises: if a system intrusion takes place, the intruder might be able to manipulate the log entries and cover her traces. Mechanisms that cryptographically protect collected log messages from manipulation should ideally have two properties: they should be *forward-secure* (the adversary gets no advantage from learning current keys when aiming at forging past log entries), and they should be *seekable* (the auditor can verify the integrity of log entries in any order or access pattern, at virtually no computational cost).We propose a new cryptographic primitive, a *seekable sequential key generator* (SSKG), that combines these two properties and has direct application in secure logging. We rigorously formalize the required security properties and give a provably-secure construction based on the integer factorization problem. We further optimize the scheme in various ways, preparing it for real-world deployment. As a byproduct, we develop the notion of a *shortcut one-way permutation* (SCP), which might be of independent interest.

Our work is highly relevant in practice. Indeed, our SSKG implementation has become part of the logging service of the systemd system manager, a core component of many modern commercial Linux-based operating systems.