Electronic money and the derived applications: anonymous micropayment, receipt-free electronic voting and anonymous internet access.

by Chan Yuen Yan.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.Includes bibliographical references (leaves 91-[97]).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Transition to a New Monetary System --- p.3Chapter 1.2 --- Security and Cryptography --- p.3Chapter 1.3 --- Electronic Cash: More than an Electronic Medium of Transaction --- p.4Chapter 1.4 --- Organisation of the Thesis --- p.5Chapter 2 --- Cryptographic Primitives --- p.7Chapter 2.1 --- One-way Hash Functions --- p.7Chapter 2.2 --- The Bit Commitment Protocol --- p.8Chapter 2.3 --- Secret Splitting --- p.8Chapter 2.4 --- Encryption / Decryption --- p.9Chapter 2.4.1 --- Symmetric Encryption --- p.10Chapter 2.4.2 --- Asymmetric Encryption --- p.10Chapter 2.5 --- The RSA Public Key Cryptosystem --- p.11Chapter 2.6 --- Blind Signature --- p.12Chapter 2.7 --- Cut-and-choose procotol --- p.13Chapter 2.8 --- The Elliptic Curve Cryptosystem (ECC) --- p.14Chapter 2.8.1 --- The Elliptic Curve Discrete Logarithm Problem --- p.15Chapter 2.8.2 --- Cryptographic Applications Implemented by ECC --- p.15Chapter 2.8.3 --- Analog of Diffie-Hellman Key Exchange --- p.15Chapter 2.8.4 --- Data Encryption [11] --- p.16Chapter 2.8.5 --- The ECC Digital Signature --- p.17Chapter 3 --- What is Money? --- p.18Chapter 3.1 --- Money --- p.18Chapter 3.1.1 --- The History of Money [17] --- p.19Chapter 3.1.2 --- Functions of Money --- p.20Chapter 3.2 --- Existing Payment Systems --- p.22Chapter 3.2.1 --- Cash Payments --- p.22Chapter 3.2.2 --- Payment through Banks --- p.22Chapter 3.2.3 --- Using Payment Cards --- p.23Chapter 4 --- Electronic Cash --- p.24Chapter 4.1 --- The Basic Requirements --- p.24Chapter 4.2 --- Basic Model of Electronic Cash --- p.25Chapter 4.2.1 --- Basic Protocol --- p.26Chapter 4.2.2 --- Modified Protocol --- p.27Chapter 4.2.3 --- Double Spending Prevention --- p.30Chapter 4.3 --- Examples of Electronic Cash --- p.31Chapter 4.3.1 --- eCash --- p.31Chapter 4.3.2 --- CAFE --- p.31Chapter 4.3.3 --- NetCash --- p.32Chapter 4.3.4 --- CyberCash --- p.32Chapter 4.3.5 --- Mondex --- p.33Chapter 4.4 --- Limitations of Electronic Cash --- p.33Chapter 5 --- Micropayments --- p.35Chapter 5.1 --- Basic Model of Micropayments --- p.36Chapter 5.1.1 --- Micropayments generation --- p.37Chapter 5.1.2 --- Spending --- p.37Chapter 5.1.3 --- Redemption --- p.38Chapter 5.2 --- Examples of Micropayments --- p.39Chapter 5.2.1 --- Pay Word --- p.39Chapter 5.2.2 --- MicroMint --- p.40Chapter 5.2.3 --- Millicent --- p.41Chapter 5.3 --- Limitations of Micropayments --- p.41Chapter 5.4 --- Digital Money - More then a Medium of Transaction --- p.42Chapter 6 --- Anonymous Micropayment Tickets --- p.45Chapter 6.1 --- Introduction --- p.45Chapter 6.2 --- Overview of the Systems --- p.46Chapter 6.3 --- Elliptic Curve Digital Signature --- p.48Chapter 6.4 --- The Micropayment Ticket Protocol --- p.49Chapter 6.4.1 --- The Micropayment Ticket --- p.50Chapter 6.4.2 --- Payment --- p.51Chapter 6.4.3 --- Redemption --- p.52Chapter 6.4.4 --- Double Spending --- p.52Chapter 6.5 --- Security Analysis --- p.52Chapter 6.5.1 --- Conditional Anonymity --- p.53Chapter 6.5.2 --- Lost Tickets --- p.53Chapter 6.5.3 --- Double Spending --- p.53Chapter 6.5.4 --- Collusion with Vendors --- p.53Chapter 6.6 --- Efficiency Analysis --- p.55Chapter 6.7 --- Conclusion --- p.56Chapter 7 --- Anonymous Electronic Voting Systems --- p.57Chapter 7.1 --- Introduction --- p.57Chapter 7.2 --- The Proposed Electronic Voting System --- p.58Chapter 7.2.1 --- The Proposed Election Model --- p.58Chapter 7.3 --- Two Cryptographic Protocols --- p.60Chapter 7.3.1 --- Protocol One - The Anonymous Authentication Protocol --- p.61Chapter 7.3.2 --- Protocol Two - Anonymous Commitment --- p.64Chapter 7.4 --- The Electronic Voting Protocol --- p.65Chapter 7.4.1 --- The Registration Phase --- p.66Chapter 7.4.2 --- The Polling Phase --- p.66Chapter 7.4.3 --- Vote-Opening Phase --- p.67Chapter 7.5 --- Security Analysis --- p.68Chapter 7.5.1 --- Basic Security Requirements --- p.68Chapter 7.5.2 --- Receipt-freeness --- p.71Chapter 7.5.3 --- Non-transferability of Voting Right --- p.72Chapter 7.6 --- Conclusion --- p.72Chapter 8 --- Anonymous Internet Access --- p.74Chapter 8.1 --- Introduction --- p.74Chapter 8.2 --- Privacy Issues of Internet Access Services --- p.75Chapter 8.2.1 --- Present Privacy Laws and Policies --- p.75Chapter 8.2.2 --- Present Anonymous Internet Services Solutions --- p.76Chapter 8.2.3 --- Conditional Anonymous Internet Access Services --- p.76Chapter 8.3 --- The Protocol --- p.77Chapter 8.3.1 --- ISP issues a new pass to Alice using blind signature [1] scheme --- p.77Chapter 8.3.2 --- Account Operations --- p.78Chapter 8.4 --- Modified Version with Key Escrow on User Identity --- p.79Chapter 8.4.1 --- Getting a new pass --- p.79Chapter 8.4.2 --- Account operations --- p.82Chapter 8.4.3 --- Identity revocation --- p.83Chapter 8.5 --- Security Analysis --- p.83Chapter 8.5.1 --- Anonymity --- p.83Chapter 8.5.2 --- Masquerade --- p.84Chapter 8.5.3 --- Alice cheats --- p.84Chapter 8.5.4 --- Stolen pass --- p.84Chapter 8.6 --- Efficiency --- p.85Chapter 8.6.1 --- Random number generation --- p.85Chapter 8.6.2 --- Signing on the pass --- p.86Chapter 8.6.3 --- Pass validation --- p.86Chapter 8.6.4 --- Identity recovery --- p.87Chapter 8.7 --- Conclusion --- p.87Chapter 9 --- Conclusion --- p.88Bibliography --- p.9

End-to-End Encrypted Group Messaging with Insider Security

Our society has become heavily dependent on electronic communication, and preserving the integrity of this communication has never been more important. Cryptography is a tool that can help to protect the security and privacy of these communications. Secure messaging protocols like OTR and Signal typically employ end-to-end encryption technology to mitigate some of the most egregious adversarial attacks, such as mass surveillance. However, the secure messaging protocols deployed today suffer from two major omissions: they do not natively support group conversations with three or more participants, and they do not fully defend against participants that behave maliciously. Secure messaging tools typically implement group conversations by establishing pairwise instances of a two-party secure messaging protocol, which limits their scalability and makes them vulnerable to insider attacks by malicious members of the group. Insiders can often perform attacks such as rendering the group permanently unusable, causing the state of the group to diverge for the other participants, or covertly remaining in the group after appearing to leave. It is increasingly important to prevent these insider attacks as group conversations become larger, because there are more potentially malicious participants. This dissertation introduces several new protocols that can be used to build modern communication tools with strong security and privacy properties, including resistance to insider attacks. Firstly, the dissertation addresses a weakness in current two-party secure messaging tools: malicious participants can leak portions of a conversation alongside cryptographic proof of authorship, undermining confidentiality. The dissertation introduces two new authenticated key exchange protocols, DAKEZ and XZDH, with deniability properties that can prevent this type of attack when integrated into a secure messaging protocol. DAKEZ provides strong deniability in interactive settings such as instant messaging, while XZDH provides deniability for non-interactive settings such as mobile messaging. These protocols are accompanied by composable security proofs. Secondly, the dissertation introduces Safehouse, a new protocol that can be used to implement secure group messaging tools for a wide range of applications. Safehouse solves the difficult cryptographic problems at the core of secure group messaging protocol design: it securely establishes and manages a shared encryption key for the group and ephemeral signing keys for the participants. These keys can be used to build chat rooms, team communication servers, video conferencing tools, and more. Safehouse enables a server to detect and reject protocol deviations, while still providing end-to-end encryption. This allows an honest server to completely prevent insider attacks launched by malicious participants. A malicious server can still perform a denial-of-service attack that renders the group unavailable or "forks" the group into subgroups that can never communicate again, but other attacks are prevented, even if the server colludes with a malicious participant. In particular, an adversary controlling the server and one or more participants cannot cause honest participants' group states to diverge (even in subtle ways) without also permanently preventing them from communicating, nor can the adversary arrange to covertly remain in the group after all of the malicious participants under its control are removed from the group. Safehouse supports non-interactive communication, dynamic group membership, mass membership changes, an invitation system, and secure property storage, while offering a variety of configurable security properties including forward secrecy, post-compromise security, long-term identity authentication, strong deniability, and anonymity preservation. The dissertation includes a complete proof-of-concept implementation of Safehouse and a sample application with a graphical client. Two sub-protocols of independent interest are also introduced: a new cryptographic primitive that can encrypt multiple private keys to several sets of recipients in a publicly verifiable and repeatable manner, and a round-efficient interactive group key exchange protocol that can instantiate multiple shared key pairs with a configurable knowledge relationship

Attribute Based Cryptographic Enforcements for Security and Privacy in E-health Environments

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