Abstract. The paper proposes efficient solutions to two long standing open problems related to secret sharing schemes in multilevel (or hierarchical) and compartmented access structures. The secret sharing scheme in multilevel access structures uses a sequence of related Shamir threshold schemes with overlapping shares and the secret. The secret sharing scheme in compartmented access structures applies Shamir schemes first to recover partial secrets and second to combine them into the requested secret. Both schemes described in the paper are ideal and perfect.

Detection of cheating and identification of cheaters in threshold schemes has been well studied, and several solid solutions have been provided in the literature. This paper analyses Harn and Lin's recent work on cheating detection and identification of cheaters in Shamir's threshold scheme. We will show that, in a broad area, Harn-Lin's scheme fails to detect cheating and even if the cheating is detected cannot identify the cheaters. In particular, in a typical Shamir (t, n)-threshold scheme, where n = 2t − 1 and up to t − 1 of participants are corrupted, their scheme neither can detect nor can identify the cheaters. Moreover, for moderate size of groups their proposed cheaters identification scheme is not practical.

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A Continuous Double Auction (CDA) allows many buyers and sellers to continuously submit bids for the purchase and sale of a commodity (e.g., online share trading). Protocols protecting privacy in this type of powerful market mechanism are essential. However, until recently the security of CDAs has been given limited coverage. This paper describes a new scheme for conducting an anonymous and secure CDA. We show that any existing secure group signature scheme can be used to implement a CDA which has the following characteristics: unforgeability, anonymity, unlinkability, exculpability, coalitionresistance, verifiability, robustness and traceability. Furthermore, bidders can be added to and removed from the auction without affecting the process of the auction. Our scheme is more flexible than the only existing secure CDA scheme, which in contrast provides only a limited subset of these characteristics.

Phishing is an online scam used to dupe people out of their personal information for the purpose of defrauding them. This paper presents a conceptual design for removing phishing pages that have been uploaded on a website, potentially without knowledge of the website owner or host server. Initially the system is alerted to the presence of a phishing page upon receiving the Phisher's solicitation e-mail. Next the system retrieves the location, IP address and contact information of the host server using a tracking program. Finally, the system sends notification to the Administrator about the phishing page on its server. It is then up to the host server Administrator to remove the phishing page from its server, or face the possibility of criminals continuing to use their site. This approach acts as the basis for further development into proactively (or aggressively) attacking Phishers directly, rather than being a reactionary approach that is common to most email filters and anti-virus software.

Abstract. Classical results in unconditionally secure multi-party computation (MPC) protocols with a passive adversary indicate that every n-variate function can be computed by n participants, such that no set of size t < n/2 participants learns any additional information other than what they could derive from their private inputs and the output of the protocol. We study unconditionally secure MPC protocols in the presence of a passive adversary in the trusted setup ('semi-ideal') model, in which the participants are supplied with some auxiliary information (which is random and independent from the participant inputs) ahead of the protocol execution (such information can be purchased as a "commodity" well before a run of the protocol). We present a new MPC protocol in the trusted setup model, which allows the adversary to corrupt an arbitrary number t < n of participants. Our protocol makes use of a novel subprotocol for converting an additive secret sharing over a field to a multiplicative secret sharing, and can be used to securely evaluate any n-variate polynomial G over a field F , with inputs restricted to non-zero elements of F . The communication complexity of our protocol is O(ℓ · n 2 ) field elements, where ℓ is the number of non-linear monomials in G. Previous protocols in the trusted setup model require communication proportional to the number of multiplications in an arithmetic circuit for G; thus, our protocol may offer savings over previous protocols for functions with a small number of monomials but a large number of multiplications.

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