Online users' behaviours and behavioural intentions with reference to live streaming : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Albany, New Zealand. EMBARGOED until 26 March 2023.

Embargoed until 26 March 2023Live streaming, as a new medium, allows users to participate in real-time interaction. It has attracted a large number of online users, and become a new social commerce venue and lucrative business, especially in China where the live streaming industry is growing explosively and is the largest in the world. This thesis aims to comprehensively investigate users’ behaviours and behavioural intentions in live streaming through both qualitative and quantitative approaches using the Chinese live streaming as an example. This thesis contains four studies to investigate from both streamers’ and viewers’ aspects. Firstly, we conducted two qualitative studies to investigate users’ online behaviours in the social commerce practice in live streaming by exploring how streamers attract viewers (Chapter 2) and encourage gifting (Chapter 3). Novel multiple triangulation was used, including data source triangulation and methodological triangulation. Through multiple triangulation, three behaviours for viewer attraction and four behaviours for gifting encouragement were identified. These two chapters help to comprehensively understand streamers’ online behaviours in this new form of social commerce. Next, we conducted two quantitative studies to explore why viewers continue to watch streams (Chapters 4 and 5). Based on expectation-confirmation theory (ECT), in Chapter 4, we modified the post-acceptance model of information system continuance and re-defined the constructs in a structural equation model of predictors of continuance intention of watching live streams. Chapter 4 successfully connects intention and continuance intention of watching, and integrates disparate understandings of viewers’ watching behaviours. To solve the deficiencies identified in current ECT-based models and further increase the explanation of variance in continuance intention of watching, in Chapter 5, we proposed a value-based continuance intention model (V-ECM), which theoretically extends ECT-based studies by including a process of overall practical assessment between users’ perceived benefits and perceived sacrifices. V-ECM appears to be a better model for explaining users’ continuance intention in the stream-watching context. Also, V-ECM could be used broadly in online and/or technology-related fields. Overall, this thesis comprehensively investigates both streamers’ and viewers’ behaviours and behavioural intentions in live streaming. Insights from this thesis can improve the design, functions and marketing within live streaming platforms. Also, this thesis provides strong foundations for further online behaviour studies, for example, stream-watching addiction

Green Cryptanalysis: Meet-in-the-Middle Key-Recovery for the Full KASUMI Cipher

KASUMI is a block cipher with eight Feistel rounds and a key of up to 128 bits. Proposed more than 10 years ago, the confidentiality and integrity of 3G mobile communications systems depend on the security of KASUMI. In the practically interesting single key setting that we are aiming for in this work, no attack is known. For the full 8-round KASUMI we show for the first time a wide variety of results with data complexities between $2^{32}$ chosen plaintexts and as few as 2 texts, while the speed-ups over brute force are between a factor 4 and 6. For use-cases of KASUMI in 2G networks, relying on a 64-bit master key, we describe key recovery methods with extremely low data complexity and speed-ups between a factor 2 and 3 for essentially any desired success probability. The latter results are the first of this type of cryptanalysis that could result in practically realizable cost and energy savings for key recovery efforts. By also analyzing an earlier version of the KASUMI-64 design that had a different mapping from the 64-bit master key to the 128-bit cipher key, we shed some light on a high-level key schedule design issue that may be of independent interest

Compact Lattice Gadget and Its Applications to Hash-and-Sign Signatures

Lattice gadgets and the associated algorithms are the essential building blocks of lattice-based cryptography. In the past decade, they have been applied to build versatile and powerful cryptosystems. However, the practical optimizations and designs of gadget-based schemes generally lag their theoretical constructions. For example, the gadget-based signatures have elegant design and capability of extending to more advanced primitives, but they are far less efficient than other lattice-based signatures. This work aims to improve the practicality of gadget-based cryptosystems, with a focus on hash-and-sign signatures. To this end, we develop a compact gadget framework in which the used gadget is a square matrix instead of the short and fat one used in previous constructions. To work with this compact gadget, we devise a specialized gadget sampler, called semi-random sampler, to compute the approximate preimage. It first deterministically computes the error and then randomly samples the preimage. We show that for uniformly random targets, the preimage and error distributions are simulatable without knowing the trapdoor. This ensures the security of the signature applications. Compared to the Gaussian-distributed errors in previous algorithms, the deterministic errors have a smaller size, which lead to a substantial gain in security and enables a practically working instantiation. As the applications, we present two practically efficient gadget-based signature schemes based on NTRU and Ring-LWE respectively. The NTRU-based scheme offers comparable efficiency to Falcon and Mitaka and a simple implementation without the need of generating the NTRU trapdoor. The LWE-based scheme also achieves a desirable overall performance. It not only greatly outperforms the state-of-the-art LWE-based hash-and-sign signatures, but also has an even smaller size than the LWE-based Fiat-Shamir signature scheme Dilithium. These results fill the long-term gap in practical gadget-based signatures

Improved Meet-in-the-Middle Attacks on AES-192 and PRINCE

This paper studies key-recovery attacks on AES-192 and PRINCE under single-key model by methodology of meet-in-the-middle attack. A new technique named key-dependent sieve is proposed to further reduce the memory complexity of Demirci et al.\u27s attack at EUROCRYPT 2013, which helps us to achieve 9-round attack on AES-192 by using a 5-round distinguisher; the data, time and memory complexities are 2^{121} chosen plaintexts, 2^{185} encryptions and 2^{185} 128- bit memories, respectively. The new technique is also applied to attack block cipher PRINCE. Instead of 6-round results in the previous cryptanalysis, we rst present attacks on 8-round (out of 12) PRINCEcore and PRINCE with about 2^{53} and 2^{60} encryptions, respectively. Furthermore, we construct an interesting 7-round distinguisher and extend the attack to 9-round PRINCE; the attack needs about 2^{57} chosen plaintexts, 2^{64} encryptions and 2^{57.3} 64-bit memories

New Pseudo-Near-Collision Attack on Reduced-Round of Hamsi-256

Hamsi-256 is designed by Özgül Kücük and it has been a candidate Hash function for the second round of SHA-3. The compression function of Hamsi-256 maps a 256-bit chaining value and a 32-bit message to a new 256-bit chaining value. As hashing a message, Hamsi-256 operates 3-round except for the last message it operates 6-round. In this paper, we will give the pseudo-near-collision for 5-round Hamsi-256. By the message modifying, the pseudo-near-collision for 3, 4 and 5 rounds can be found with $2^5$, $2^{32}$ and $2^{125}$ compression function computations respectively

Practical-time Attack on the Full MMB Block Cipher

Modular Multiplication based Block Cipher (MMB) is a block cipher designed by Daemen \emph{et al.} as an alternative to the IDEA block cipher. In this paper, we give a practical-time attack on the full MMB with adaptive chosen plaintexts and ciphertexts. By the constructive sandwich distinguisher for 5 of the 6 rounds of MMB with amazingly high probability 1, we give the key recovery attack on the full MMB with data complexity $2^{40}$ and time complexity $2^{13.4}$ MMB encryptions. Then a rectangle-like sandwich attack on the full MMB is presented, with $2^{66.5}$ chosen plaintexts, $2^{64}$ MMB encryptions and $2^{70.5}$ memory bytes. By the way, we show an improved differential attack on the full MMB with data complexity of $2^{96}$ chosen plaintexts and ciphertexts, time complexity $2^{64}$ encryptions and $2^{66}$ bytes of memory