Spontaneous anonymous group cryptography and its applications.

Fung Kar-Yin.Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.Includes bibliographical references (leaves 72-81).Abstracts in English and Chinese.Abstract --- p.iAcknowledgement --- p.iiiChapter 1 --- Introduction --- p.1Chapter 1.1 --- Development of Cryptography --- p.1Chapter 1.2 --- Group Cryptography --- p.3Chapter 1.3 --- Spontaneous Anonymous Group Signature --- p.4Chapter 1.4 --- Blind Signature --- p.5Chapter 1.5 --- Blind SAG Signature --- p.6Chapter 1.6 --- Organization of This Thesis --- p.6Chapter 2 --- Background Study --- p.7Chapter 2.1 --- Six Primitives in Cryptography --- p.7Chapter 2.1.1 --- Symmetric Encryption --- p.8Chapter 2.1.2 --- Asymmetric Encryption --- p.8Chapter 2.1.3 --- Digital Signature --- p.9Chapter 2.1.4 --- Hash Function --- p.9Chapter 2.1.5 --- Digital Certificate --- p.10Chapter 2.1.6 --- Proof of Knowledge --- p.10Chapter 2.2 --- Euler Totient Function --- p.11Chapter 2.3 --- One-Way Function --- p.12Chapter 2.3.1 --- One-Way Trapdoor Function --- p.13Chapter 2.3.2 --- Discrete Logarithm Problem --- p.13Chapter 2.3.3 --- RSA Problem --- p.14Chapter 2.3.4 --- Integer Factorization Problem --- p.15Chapter 2.3.5 --- Quadratic Residuosity Problem --- p.15Chapter 2.3.6 --- Schnorr's ROS assumption --- p.16Chapter 2.4 --- Bilinear Pairing --- p.16Chapter 2.4.1 --- Weil Pairing --- p.18Chapter 2.4.2 --- Tate Pairing --- p.18Chapter 2.5 --- Gap Diffie-Hellman Group --- p.19Chapter 2.5.1 --- GDH --- p.19Chapter 2.5.2 --- Co-GDH --- p.20Chapter 2.6 --- Random Oracle Model --- p.21Chapter 2.6.1 --- Random Permutation --- p.23Chapter 2.6.2 --- Lunchtime Attack --- p.23Chapter 2.6.3 --- Back Patch --- p.23Chapter 2.6.4 --- Rewind Simulation --- p.24Chapter 2.7 --- Generic Group Model --- p.24Chapter 3 --- Digital and Threshold Signatures --- p.26Chapter 3.1 --- Introduction --- p.26Chapter 3.2 --- Notion of Attacks and Security in Signature --- p.28Chapter 3.2.1 --- Types of Signatures --- p.29Chapter 3.3 --- Threshold Signature --- p.31Chapter 3.4 --- Properties in Threshold Signatures --- p.31Chapter 4 --- Blind Signature --- p.33Chapter 4.1 --- Introduction --- p.33Chapter 4.1.1 --- Security Requirements --- p.35Chapter 4.2 --- Transferred Proof of Knowledge --- p.36Chapter 4.3 --- RSA Based Schemes --- p.37Chapter 4.3.1 --- Chaum's RSA Scheme --- p.37Chapter 4.3.2 --- Abe's RSA Scheme --- p.38Chapter 4.4 --- Discrete Logarithm Based Schemes --- p.39Chapter 4.4.1 --- Schnorr Blind Signature --- p.39Chapter 4.4.2 --- Okamoto-Schnorr Blind Signature --- p.40Chapter 4.5 --- Bilinear Mapping Based Schemes --- p.40Chapter 5 --- Spontaneous Anonymous Group Signature --- p.42Chapter 5.1 --- Introduction --- p.42Chapter 5.2 --- Cramer-Damgard-Schoemaker (CDS) SAG Signature --- p.44Chapter 5.2.1 --- (1´ةn)-CDS type SAG Signature --- p.44Chapter 5.2.2 --- "(t, n)-CDS type SAG Signature" --- p.45Chapter 5.3 --- Ring-type SAG Signature Schemes --- p.46Chapter 5.3.1 --- Rivest-Shamir-Tauman --- p.46Chapter 5.3.2 --- Abe's 1-out-of-n Ring Signature --- p.49Chapter 5.4 --- Discussions --- p.51Chapter 6 --- Blind SAG Signature --- p.53Chapter 6.1 --- Introduction --- p.53Chapter 6.2 --- Security Definitions --- p.54Chapter 6.2.1 --- Security Model --- p.55Chapter 6.3 --- "(1,n)-Ring Structured Blind SAG Signature" --- p.57Chapter 6.3.1 --- Signing Protocol --- p.58Chapter 6.3.2 --- Verification Algorithm --- p.58Chapter 6.4 --- CDS-type Blind SAG Signature --- p.59Chapter 6.4.1 --- "(l,n)-CDS-type" --- p.59Chapter 6.5 --- "(t,n)-CDS-type" --- p.60Chapter 6.5.1 --- Signing Protocol --- p.61Chapter 6.5.2 --- Verification Algorithm --- p.61Chapter 6.6 --- Security Analysis --- p.62Chapter 6.7 --- Applications to Credential System --- p.67Chapter 7 --- Conclusion --- p.69A --- p.71Bibliography --- p.8

Identity based cryptography from pairings.

Yuen Tsz Hon.Thesis (M.Phil.)--Chinese University of Hong Kong, 2006.Includes bibliographical references (leaves 109-122).Abstracts in English and Chinese.Abstract --- p.iAcknowledgement --- p.iiiList of Notations --- p.viiiChapter 1 --- Introduction --- p.1Chapter 1.1 --- Identity Based Cryptography --- p.3Chapter 1.2 --- Hierarchical Identity Based Cryptosystem --- p.4Chapter 1.3 --- Our contributions --- p.5Chapter 1.4 --- Publications --- p.5Chapter 1.4.1 --- Publications Produced from This Thesis --- p.5Chapter 1.4.2 --- Publications During Author's Study in the Degree --- p.6Chapter 1.5 --- Thesis Organization --- p.6Chapter 2 --- Background --- p.8Chapter 2.1 --- Complexity Theory --- p.8Chapter 2.1.1 --- Order Notation --- p.8Chapter 2.1.2 --- Algorithms and Protocols --- p.9Chapter 2.1.3 --- Relations and Languages --- p.11Chapter 2.2 --- Algebra and Number Theory --- p.12Chapter 2.2.1 --- Groups --- p.12Chapter 2.2.2 --- Elliptic Curve --- p.13Chapter 2.2.3 --- Pairings --- p.14Chapter 2.3 --- Intractability Assumptions --- p.15Chapter 2.4 --- Cryptographic Primitives --- p.18Chapter 2.4.1 --- Public Key Encryption --- p.18Chapter 2.4.2 --- Digital Signature --- p.19Chapter 2.4.3 --- Zero Knowledge --- p.21Chapter 2.5 --- Hash Functions --- p.23Chapter 2.6 --- Random Oracle Model --- p.24Chapter 3 --- Literature Review --- p.26Chapter 3.1 --- Identity Based Signatures --- p.26Chapter 3.2 --- Identity Based Encryption --- p.27Chapter 3.3 --- Identity Based Signcryption --- p.27Chapter 3.4 --- Identity Based Blind Signatures --- p.28Chapter 3.5 --- Identity Based Group Signatures --- p.28Chapter 3.6 --- Hierarchical Identity Based Cryptography --- p.29Chapter 4 --- Blind Identity Based Signcryption --- p.30Chapter 4.1 --- Schnorr's ROS problem --- p.31Chapter 4.2 --- BIBSC and Enhanced IBSC Security Model --- p.32Chapter 4.2.1 --- Enhanced IBSC Security Model --- p.33Chapter 4.2.2 --- BIBSC Security Model --- p.36Chapter 4.3 --- Efficient and Secure BIBSC and IBSC Schemes --- p.38Chapter 4.3.1 --- Efficient and Secure IBSC Scheme --- p.38Chapter 4.3.2 --- The First BIBSC Scheme --- p.43Chapter 4.4 --- Generic Group and Pairing Model --- p.47Chapter 4.5 --- Comparisons --- p.52Chapter 4.5.1 --- Comment for IND-B --- p.52Chapter 4.5.2 --- Comment for IND-C --- p.54Chapter 4.5.3 --- Comment for EU --- p.55Chapter 4.6 --- Additional Functionality of Our Scheme --- p.56Chapter 4.6.1 --- TA Compatibility --- p.56Chapter 4.6.2 --- Forward Secrecy --- p.57Chapter 4.7 --- Chapter Conclusion --- p.57Chapter 5 --- Identity Based Group Signatures --- p.59Chapter 5.1 --- New Intractability Assumption --- p.61Chapter 5.2 --- Security Model --- p.62Chapter 5.2.1 --- Syntax --- p.63Chapter 5.2.2 --- Security Notions --- p.64Chapter 5.3 --- Constructions --- p.68Chapter 5.3.1 --- Generic Construction --- p.68Chapter 5.3.2 --- An Instantiation: IBGS-SDH --- p.69Chapter 5.4 --- Security Theorems --- p.73Chapter 5.5 --- Discussions --- p.81Chapter 5.5.1 --- Other Instantiations --- p.81Chapter 5.5.2 --- Short Ring Signatures --- p.82Chapter 5.6 --- Chapter Conclusion --- p.82Chapter 6 --- Hierarchical IBS without Random Oracles --- p.83Chapter 6.1 --- New Intractability Assumption --- p.87Chapter 6.2 --- Security Model: HIBS and HIBSC --- p.89Chapter 6.2.1 --- HIBS Security Model --- p.89Chapter 6.2.2 --- Hierarchical Identity Based Signcryption (HIBSC) --- p.92Chapter 6.3 --- Efficient Instantiation of HIBS --- p.95Chapter 6.3.1 --- Security Analysis --- p.96Chapter 6.3.2 --- Ordinary Signature from HIBS --- p.101Chapter 6.4 --- Plausibility Arguments for the Intractability of the OrcYW Assumption --- p.102Chapter 6.5 --- Efficient HIBSC without Random Oracles --- p.103Chapter 6.5.1 --- Generic Composition from HIBE and HIBS --- p.104Chapter 6.5.2 --- Concrete Instantiation --- p.105Chapter 6.6 --- Chapter Conclusion --- p.107Chapter 7 --- Conclusion --- p.108Bibliography --- p.10

Advances in cryptographic voting systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 241-254).Democracy depends on the proper administration of popular elections. Voters should receive assurance that their intent was correctly captured and that all eligible votes were correctly tallied. The election system as a whole should ensure that voter coercion is unlikely, even when voters are willing to be influenced. These conflicting requirements present a significant challenge: how can voters receive enough assurance to trust the election result, but not so much that they can prove to a potential coercer how they voted? This dissertation explores cryptographic techniques for implementing verifiable, secret-ballot elections. We present the power of cryptographic voting, in particular its ability to successfully achieve both verifiability and ballot secrecy, a combination that cannot be achieved by other means. We review a large portion of the literature on cryptographic voting. We propose three novel technical ideas: 1. a simple and inexpensive paper-base cryptographic voting system with some interesting advantages over existing techniques, 2. a theoretical model of incoercibility for human voters with their inherent limited computational ability, and a new ballot casting system that fits the new definition, and 3. a new theoretical construct for shuffling encrypted votes in full view of public observers.by Ben Adida.Ph.D

Kleptography and steganography in blockchains

Despite its vast proliferation, the blockchain technology is still evolving, and witnesses continuous technical innovations to address its numerous unresolved issues. An example of these issues is the excessive electrical power consumed by some consensus protocols. Besides, although various media reports have highlighted the existence of objectionable content in blockchains, this topic has not received sufficient research. Hence, this work investigates the threat and deterrence of arbitrary-content insertion in public blockchains, which poses a legal, moral, and technical challenge. In particular, the overall aim of this work is to thoroughly study the risk of manipulating the implementation of randomized cryptographic primitives in public blockchains to mount kleptographic attacks, establish steganographic communication, and store arbitrary content. As part of our study, we present three new kleptographic attacks on two of the most commonly used digital signatures: ring signature and ECDSA. We also demonstrate our kleptographic attacks on two real cryptocurrencies: Bytecoin and Monero. Moreover, we illustrate the plausibility of hijacking public blockchains to establish steganographic channels. Particularly, we design, implement, and evaluate the first blockchain-based broadcast communication tool on top of a real-world cryptocurrency. Furthermore, we explain the detrimental consequences of kleptography and steganography on the users and the future of the blockchain technology. Namely, we show that kleptography can be used to surreptitiously steal the users' secret signing keys, which are the most valuable and guarded secret in public blockchains. After losing their keys, users of cryptocurrencies will inevitably lose their funds. In addition, we clarify that steganography can be used to establish subliminal communication and secretly store arbitrary content in public blockchains, which turns them into cheap cyberlockers. Consequently, the participation in such blockchains, which are known to store unethical content, can be criminalized, hindering the future adoption of blockchains. After discussing the adverse effects of kleptographic and steganographic attacks on blockchains, we survey all of the existing techniques that can defend against these attacks. Finally, due to the shortcomings of the available techniques, we propose four countermeasures that ensure kleptography and steganography-resistant public blockchains. Our countermeasures include two new cryptographic primitives and a generic steganographyresistant blockchain framework (SRBF). This framework presents a universal solution that deters steganography and practically achieves the right to be forgotten (RtbF) in blockchains, which represents a regulatory challenge for current immutable blockchains