Abstract-Existing software-based data erasure programs can be summarized as following the same one-bit-return protocol: the deletion program performs data erasure and returns either success or failure. However, such a one-bit-return protocol turns the data deletion system into a black box -the user has to trust the outcome but cannot easily verify it. This is especially problematic when the deletion program is encapsulated within a Trusted Platform Module (TPM), and the user has no access to the code inside. In this paper, we present a cryptographic solution that aims to make the data deletion process more transparent and verifiable. In contrast to the conventional black/white assumptions about TPM (i.e., either completely trust or distrust), we introduce a third assumption that sits in between: namely, "trust-but-verify". Our solution enables a user to verify the correct implementation of two important operations inside a TPM without accessing its source code: i.e., the correct encryption of data and the faithful deletion of the key. Finally, we present a proof-of-concept implementation of the SSE system on a resource-constrained Java card to demonstrate its practical feasibility. To our knowledge, this is the first systematic solution to the secure data deletion problem based on a "trust-but-verify" paradigm, together with a concrete prototype implementation.

Dragonfly is a password authenticated key exchange protocol that has been submitted to the Internet Engineering Task Force as a candidate standard for general internet use. We analyzed the security of this protocol and devised an attack that is capable of extracting both the session key and password from an honest party. This attack was then implemented and experiments were performed to determine the time-scale required to successfully complete the attack.

Bitcoin has, since 2009, become an increasingly popular online currency, in large part because it resists regulation and provides anonymity. We discuss how Bitcoin has become both a highly useful tool for criminals and a lucrative target for crime, and argue that this arises from the same essential ideological and design choices that have driven Bitcoin's success to date. In this paper, we survey the landscape of Bitcoinrelated crime, such as dark markets and bitcoin theft, and speculate about possible future possibilities, including tax evasion and money laundering. AbstractBitcoin has, since 2009, become an increasingly popular online currency, in large part because it resists regulation and provides anonymity. We discuss how Bitcoin has become both a highly useful tool for criminals and a lucrative target for crime, and argue that this arises from the same essential ideological and design choices that have driven Bitcoin's success to date. In this paper, we survey the landscape of Bitcoin-related crime, such as dark markets and bitcoin theft, and speculate about possible future possibilities, including tax evasion and money laundering. Abstract. Bitcoin has, since 2009, become an increasingly popular online currency, in large part because it resists regulation and provides anonymity. We discuss how Bitcoin has become both a highly useful tool for criminals and a lucrative target for crime, and argue that this arises from the same essential ideological and design choices that have driven Bitcoin's success to date. In this paper, we survey the landscape of Bitcoin-related crime, such as dark markets and bitcoin theft, and speculate about possible future possibilities, including tax evasion and money laundering. About the authors

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Verifiable electronic voting has been extensively researched for over twenty years, but few protocols have achieved real-life deployment. A key impediment, we argue, is caused by the existing protocols' universal reliance on the probity of the tallying authorities. This might seem surprising to many people as dependence on tallying authorities has been a de facto standard in the field. However, this dependence is actually a legacy inherited from traditional physical voting, one that has proved problematic in the electronic context. In this paper, we propose a radically new concept called "self-enforcing electronic voting", which refers to voting systems that are free from reliance on any tallying authority. This proposal goes significantly further than all existing or proposed e-voting systems. We explain the feasibility of this new approach, with a theoretical definition of the system properties, a concrete engineering design, a practical implementation, and real-world trial experiments. We also highlight some open issues for further research.

Bitcoin is designed to protect user anonymity (or pseudonymity) in a financial transaction, and has been increasingly adopted by major ecommerce websites such as Dell, PayPal and Expedia. While the anonymity of Bitcoin transactions has been extensively studied, little attention has been paid to the security of post-transaction correspondence. In a commercial application, the merchant and the user often need to engage in follow-up correspondence after a Bitcoin transaction is completed, e.g., to acknowledge the receipt of payment, to confirm the billing address, to arrange the product delivery, to discuss refund and so on. Currently, such follow-up correspondence is typically done in plaintext via email with no guarantee on confidentiality. Obviously, leakage of sensitive data from the correspondence (e.g., billing address) can trivially compromise the anonymity of Bitcoin users. In this paper, we initiate the first study on how to realise end-to-end secure communication between Bitcoin users in a post-transaction scenario without requiring any trusted third party or additional authentication credentials. This is an important new area that has not been covered by any IEEE or ISO/IEC security standard, as none of the existing PKI-based or password-based AKE schemes are suitable for the purpose. Instead, our idea is to leverage the Bitcoin's append-only ledger as an additional layer of authentication between previously confirmed transactions. This naturally leads to a new category of AKE protocols that bootstrap trust entirely from the block chain. We call this new category "Bitcoin-based AKE" and present two concrete protocols: one is non-interactive with no forward secrecy, while the other is interactive with additional guarantee of forward secrecy. Finally, we present proof-of-concept prototypes for both protocols with experimental results to demonstrate their practical feasibility.Blockchain contains (rA, sA) and (rB, sB) from TA and TB Alice (A, dA) Bob (B, dB) 1. kA = (H(TA) + dArA)s −1

This paper shows several security weaknesses of a Multi-Factor Authenticated Key Exchange (MK-AKE) protocol, proposed by Pointcheval and Zimmer at ACNS'08. The Pointcheval-Zimmer scheme was designed to combine three authentication factors in one system, including a password, a secure token (that stores a private key) and biometrics. In a formal model, Pointcheval and Zimmer formally proved that an attacker had to break all three factors to win. However, the formal model only considers the threat that an attacker may impersonate the client; it however does not discuss what will happen if the attacker impersonates the server. We fill the gap by analyzing the case of the server impersonation, which is a realistic threat in practice. We assume that an attacker has already compromised the password, and we then present two further attacks: in the first attack, an attacker is able to steal a fresh biometric sample from the victim without being noticed; in the second attack, he can discover the victim's private key based on the Chinese Remainder theorem. Both attacks have been experimentally verified. In summary, an attacker actually only needs to compromise a single password factor in order to break the entire system. We also discuss the deficiencies in the Pointcheval-Zimmer formal model and countermeasures to our attacks.

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