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We study the round complexity of various cryptographic protocols. Our main result is a tight lower bound on the round complexity of any fully-black-box construction of a statistically-hiding commitment scheme from one-way permutations, and even from trapdoor permutations. This lower bound matches the round complexity of the statistically-hiding commitment… (More)

- Stefan Wolf, Prof, Ivan Damgård, Don Beaver, Hugue Blier, Gilles Brassard +49 others

2007 ii Acknowledgments First of all, I would like to thank Stefan Wolf who has been a great advisor. Many results in this thesis are the outcome of endless discussions with him. I also want to thank Ivan Damgård for co-refereeing this thesis. I would also like to thank all the people I was able to work with or talk to about my research during the last few… (More)

We construct the rst public-key encryption scheme that is proven secure (in the standard model, under standard assumptions) even when the attacker gets access to encryptions of arbitrary ecient functions of the secret key. Specically, under either the DDH or LWE assumption , and for arbitrary but xed polynomials L and N , we obtain a public-key encryption… (More)

We give a construction of statistically-hiding commitment schemes (ones where the hiding propertyholds information theoretically), based on the minimal cryptographic assumption that one-way functions exist. Our construction employs two-phase commitment schemes, recently constructed by Nguyen, Ong and Vadhan (FOCS '06), and universal one-way hash functions… (More)

We consider two of the most fundamental theorems in Cryptography. The first, due to Håstad et al. [HILL99], is that pseudorandom generators can be constructed from any one-way function. The second due to Yao [Yao82] states that the existence of weak one-way functions (i.e. functions on which every efficient algorithm fails to invert with some noticeable… (More)

We give a construction of statistically hiding commitment schemes (those in which the hiding property holds against even computationally unbounded adversaries) under the minimal complexity assumption that one-way functions exist. Consequently, one-way functions suffice to give statistical zero-knowledge arguments for any NP statement (whereby even a… (More)

A common method for increasing the usability and uplifting the security of pseudorandom function families (PRFs) is to " hash " the inputs into a smaller domain before applying the PRF. This approach, known as " Levin's trick " , is used to achieve " PRF domain extension " (using a short, e.g., fixed, input length PRF to get a variable-length PRF), and more… (More)

In their seminal work, Impagliazzo and Rudich (STOC’89) showed that no key-agreement protocol exists in the random-oracle model, yielding that key agreement cannot be black-box reduced to one-way functions. In this work, we generalize their result, showing that, to a large extent, no-private-input, semi-honest, two-party functionalities that can be securely… (More)

In a multiparty <i>fair</i> coin-flipping protocol, the parties output a common (close to) unbiased bit, even when some corrupted parties try to bias the output. Cleve [STOC 1986] has shown that in the case of dishonest majority (i.e., at least half of the parties can be corrupted), in <i>any m</i>-round coin-flipping protocol, the corrupted parties can… (More)

We study the possibility of constructing encryption schemes secure under messages that are chosen depending on the key k of the encryption scheme itself. We give the following separation results that hold both in the private and in the public key settings: – Let H be the family of poly(n)-wise independent hash-functions. There exists no fully-black-box… (More)