We present new, and mostly sharp, bounds on the maximum length of certain generalizations of Davenport-Schinzel sequences. Among the results are sharp bounds on order-s double DS sequences, for all s, sharp bounds on sequences avoiding catenated permutations (aka formation free sequences), and new lower bounds on sequences avoiding zig-zagging patterns.

In most of the existing identity-based key agreement schemes, it is usually assumed that either the communicated parties know each other’s identifier before the protocol starts or their identifiers are transferred along with the protocol messages. However, these schemes are not suitable for use in many real-world applications aimed to achieve unilateral identity privacy, which means that one co...

This paper presents some new unknown key-share attacks on STS-MAC, the version of the STS key agreement protocol which uses a MAC algorithm to provide key connrmation. Various methods are considered for preventing the attacks.

There are various services using mobile devices due to development of communication technology and mobile equipment, regardless of time and place. To secure usage of convenience and smart services, authentication between users’ devices and network is necessary. To achieve this, many researches have been studied about 3 rd Generation Partnership Project Authentication and Key Agreement (3GPP-AKA...

User anonymity is very important security technique in distributed computing environments that an illegal entity cannot determine any information concerning the user’s identity. In 2006, Kumar–Rajendra proposed a Secure Identification and Key agreement protocol with user Anonymity (SIKA). This paper demonstrates the vulnerability of the SIKA protocol and then presents an improvement to repair t...

For smooth varieties over finite fields, we prove that the shifted (aka derived) Witt groups of surfaces are finite and the higher GrothendieckWitt groups (aka Hermitian K-theory) of curves are finitely generated. For more general arithmetic schemes, we give conditional results, for example, finite generation of the motivic cohomology groups implies finite generation of the Grothendieck-Witt gr...

Multiple key agreement (MKA) protocols allow two parties to generate two or more session keys in one session, which will be used for future secure communications in public network. In recent years, many MKA protocols have been proposed. However, most of them do not consider ephemeral key compromise resilience, and some of them still exists security flaws. In this paper, we analyze the scheme pr...