A Note on the Bellare-Rivest Protocol for Translucent Cryptography

We remark that the Bellare-Rivest protocol for translucent cryptography [J. Cryptology (1999) 12: 117-139] can not truly enable the government to decrypt partial encrypted communications

Translucent Cryptography - An Alternative to Key Escrow, and its Implementation via Fractional Oblivious Transfer

We present an alternative to the controversial #key escrow" techniques for enabling lawenforcement and national security access to encrypted communications

Anonymous probabilistic payment in payment hub

Privacy protection and scalability are significant issues with blockchain. We propose an anonymous probabilistic payment under the general functionality for solving them. We consider the situation that several payers pay several payees through a tumbler. We have mediated the tumbler of the payment channel hub between payers and payees. Unlinkability means that the link, which payer pays which payee via the tumbler, is broken. A cryptographic puzzle plays a role in controlling the intermediation and execution of transactions. Masking the puzzle enables the payer and the payee to unlink their payments. The overview of the proposed protocol is similar to TumbleBit (NDSS 2017). We confirm the protocol realizes the ideal functionalities discussed in TumbleBit. The functionality required for our proposal is the hashed time lock contract that various cryptocurrencies use. This request is general, not restricted to any particular cryptocurrency. Our proposal includes a probabilistic payment. In probabilistic payment, one pays an ordinary mount with a certain probability. One pays a small amount as an expected value. One can run fewer transactions than a deterministic payment. It contributes scalability. We introduce a novel fractional oblivious transfer for probabilistic payment. We call it the ring fractional oblivious transfer (RFOT). RFOT is based on the ring learning with errors (RLWE) encryption. Our trick is based on the fact that an element of the ring is indistinguishable from the circular shifted element. We confirm that RFOT holds the properties of fractional hiding and binding presented in the DAM scheme (Eurocrypt 2017)

\u27Code\u27 and the Slow Erosion of Privacy

The notion of software code replacing legal code as a mechanism to control human behavior-- code as law --is often illustrated with examples in intellectual property and freedom of speech. This Article examines the neglected issue of the impact of code as law on privacy. To what extent is privacy-related code being used, either to undermine or to enhance privacy? On the basis of cases in the domains of law enforcement, national security, E-government, and commerce, it is concluded that technology rarely incorporates specific privacy-related norms. At the same time, however, technology very often does have clear effects on privacy, as it affects the reasonable expectation of privacy. Technology usually makes privacy violations easier. Particularly information technology is much more a technology of control than it is a technology of freedom. Privacy-enhancing technologies (PETs) have yet to be implemented on any serious scale. The consequent eroding effect of technology on privacy is a slow, hardly perceptible process. If one is to stop this almost natural process, a concerted effort is called for, possibly in the form of privacy impact assessments, enhanced control mechanisms, and awareness-raising

Abuse Resistant Law Enforcement Access Systems

The increasing deployment of end-to-end encrypted communications services has ignited a debate between technology firms and law enforcement agencies over the need for lawful access to encrypted communications. Unfortunately, existing solutions to this problem suffer from serious technical risks, such as the possibility of operator abuse and theft of escrow key material. In this work we investigate the problem of constructing law enforcement access systems that mitigate the possibility of unauthorized surveillance. We first define a set of desirable properties for an abuse-resistant law enforcement access system (ARLEAS), and motivate each of these properties. We then formalize these definitions in the Universal Composability framework, and present two main constructions that realize this definition. The first construction enables prospective access, allowing surveillance only if encryption occurs after a warrant has been issued and activated. The second, more powerful construction, allows retrospective access to communications that occurred prior to a warrant\u27s issuance. To illustrate the technical challenge of constructing the latter type of protocol, we conclude by investigating the minimal assumptions required to realize these systems

Imbalanced Cryptographic Protocols

Efficiency is paramount when designing cryptographic protocols, heavy mathematical operations often increase computation time, even for modern computers. Moreover, they produce large amounts of data that need to be sent through (often limited) network connections. Therefore, many research efforts are invested in improving efficiency, sometimes leading to imbalanced cryptographic protocols. We define three types of imbalanced protocols, computationally, communicationally, and functionally imbalanced protocols. Computationally imbalanced cryptographic protocols appear when optimizing a protocol for one party having significantly more computing power. In communicationally imbalanced cryptographic protocols the messages mainly flow from one party to the others. Finally, in functionally imbalanced cryptographic protocols the functional requirements of one party strongly differ from the other parties. We start our study by looking into laconic cryptography, which fits both the computational and communicational category. The emerging area of laconic cryptography involves the design of two-party protocols involving a sender and a receiver, where the receiver’s input is large. The key efficiency requirement is that the protocol communication complexity must be independent of the receiver’s input size. We show a new way to build laconic OT based on the new notion of Set Membership Encryption (SME) – a new member in the area of laconic cryptography. SME allows a sender to encrypt to one recipient from a universe of receivers, while using a small digest from a large subset of receivers. A recipient is only able to decrypt the message if and only if it is part of the large subset. As another example of a communicationally imbalanced protocol we will look at NIZKs. We consider the problem of proving in zero-knowledge the existence of exploits in executables compiled to run on real-world processors. Finally, we investigate the problem of constructing law enforcement access systems that mitigate the possibility of unauthorized surveillance, as a functionally imbalanced cryptographic protocol. We present two main constructions. The first construction enables prospective access, allowing surveillance only if encryption occurs after a warrant has been issued and activated. The second allows retrospective access to communications that occurred prior to a warrant’s issuance