We examine the diffusion layers of some block ciphers referred to as substitution‐permutation networks. We investigate the practical and provable security of these diffusion layers against differential and linear cryptanalysis. First, in terms of practical security, we show that the minimum number of differentially active S‐boxes and that of linearly active S‐boxes are generally not identical and propose some special conditions in which those are identical. We also study the optimal diffusion effect for some diffusion layers according to their constraints. Second, we obtain the results that the consecutive two rounds of SPN structure provide provable security against differential and linear cryptanalysis, i.e., we prove that the probability of each differential (resp. linear hull) of the consecutive two rounds of SPN structure with a maximal diffusion layer is bounded by pn (resp. qn) and that of each differential (resp. linear hull) of the SDS function with a semi‐maximal diffusion layer is bounded by pn‐1 (resp. qn‐1), where p and q are maximum differential and linear probabilities of the substitution layer, respectively.

A one-time password (OTP) is a password that is valid for only one login session or transaction, in IT systems or digital devices. This is one of the human-centered security services and is commonly used for multi-factor authentication. This is very similar to generating pseudo-random bit streams in cryptography. However, it is only part of what is used as OTP in the bit stream. Therefore, the OTP mechanism requires an algorithm to extract portions. It is also necessary to convert hexadecimal to decimal so that the values of the bit strings are familiar to human. In this paper, we classify three algorithms for extracting the final data from the pseudo random bit sequence. We also analyze the fact that a vulnerability occurs during the extraction process, resulting in a high frequency of certain numbers; even if cryptographically secure generation algorithms are used.

Abstract. Within the security architecture of the 3GPP system there is a standardised encryption mode f 8 based on the block cipher KASUMI. In this work we examine the pseudorandomness of the block cipher KA-SUMI and the provable security of f 8. First we show that the three round KASUMI is not a pseudorandom permutation ensemble but the four round KASUMI is a pseudorandom permutation ensemble under the adaptive distinguisher model by investigating the properties of the round functions in a clear way. Second we provide the upper bound on the security of f 8 mode under the reasonable assumption from the first result by means of the left-or-right security notion.

In this paper, we briefly describe an underwater media access control protocol based on the request to send/clear to send mechanism with security algorithms, which is proposed to provide data confidentiality, authenticity, and replay attack protection. The protocol includes the counter with cipher block chaining-message authentication code (CBC-MAC) for underwater (CCM-UW) mode that is the modified form of the counter with CBC-MAC (CCM*) mode for underwater acoustic communication, based on the advanced encryption standard/agency, research and institute, academy block cipher algorithm. CCM-UW security mechanism is suitable for underwater acoustic sensor networks (UWASNs) and offers six different security levels with different security strength, energy & Soo-Hyun Park consumption and transmission time. The results in the paper show that the protocol is not impracticable for UWASNs since it is energy efficient and saves transmission time.Keywords CCM-UW (counter with CBC-MAC for underwater) Á CCM* (counter with CBC-MAC) Á Media access control (MAC) Á RTS (request to send) Á CTS (clear to send) Á UWASNs (underwater acoustic sensor networks) Á AES (advanced encryption standard) Á ARIA (agency, research and institute, academy)

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