Tim Ruffing

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The decentralized currency network Bitcoin is emerging as a potential new way of performing financial transactions across the globe. Its use of pseudonyms towards protecting users' privacy has been an attractive feature to many of its adopters. Nevertheless, due to the inherent public nature of the Bitcoin transaction ledger, users' privacy is severely(More)
Dolev-Yao models of cryptographic operations constitute the foundation of many successful verification tools for security protocols, such as the protocol verifier ProVerif. Research over the past decade has shown that many of these symbolic abstractions are computationally sound, i.e., the absence of attacks against the abstraction entails the security of(More)
We show that equivocation, i.e., making conflicting statements to others in a distributed protocol, can be monetarily disincentivized by the use of crypto-currencies such as Bitcoin. To this end, we design completely decentralized non-equivocation contracts, which make it possible to penalize an equivocating party by the loss of its money. At the core of(More)
Public-key steganography has been proposed for several censorship-resistance systems. However, distribution of the employed public keys presents an availability, scalability, and security challenge in many of those. To mitigate this problem, we introduce the notion of identity-based steganography. In particular, we define identity-based steganographic(More)
Cryptographic protocols are commonly designed and their security proven under the assumption that the protocol parties have access to perfect (uniform) randomness. Physical randomness sources deployed in practical implementations of these protocols often fall short in meeting this assumption, but instead provide only a steady stream of bits with certain(More)
We present a generic computational soundness result for interactive cryptographic primitives. Our abstraction of interactive primitives leverages the Universal Composability (UC) framework, and thereby offers strong composability properties for our computational soundness result: given a computationally sound Dolev-Yao model for non-interactive primitives,(More)
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