## CryptoDB

### Yehuda Lindell

#### Publications

Year
Venue
Title
2021
JOFC
ECDSA is a standard digital signature scheme that is widely used in TLS, Bitcoin and elsewhere. Unlike other schemes like RSA, Schnorr signatures and more, it is particularly hard to construct efficient threshold signature protocols for ECDSA (and DSA). As a result, the best-known protocols today for secure distributed ECDSA require running heavy zero-knowledge proofs and computing many large-modulus exponentiations for every signing operation. In this paper, we consider the specific case of two parties (and thus no honest majority) and construct a protocol that is approximately two orders of magnitude faster than the previous best. Concretely, our protocol achieves good performance, with a single signing operation for curve P-256 taking approximately 37 ms between two standard machine types in Azure (utilizing a single core only). Our protocol is proven secure for sequential composition under standard assumptions using a game-based definition. In addition, we prove security by simulation under a plausible yet non-standard assumption regarding Paillier. We show that partial concurrency (where if one execution aborts, then all need to abort) can also be achieved.
2020
JOFC
A protocol for computing a functionality is secure if an adversary in this protocol cannot cause more harm than in an ideal computation, where parties give their inputs to a trusted party that returns the output of the functionality to all parties. In particular, in the ideal model, such computation is fair—if the corrupted parties get the output, then the honest parties get the output. Cleve (STOC 1986) proved that, in general, fairness is not possible without an honest majority. To overcome this impossibility, Gordon and Katz (Eurocrypt 2010) suggested a relaxed definition—1/ p -secure computation—which guarantees partial fairness. For two parties, they constructed 1/ p -secure protocols for functionalities for which the size of either their domain or their range is polynomial (in the security parameter). Gordon and Katz ask whether their results can be extended to multiparty protocols. We study 1/ p -secure protocols in the multiparty setting for general functionalities. Our main result is constructions of 1/ p -secure protocols that are resilient against any number of corrupted parties provided that the number of parties is constant and the size of the range of the functionality is at most polynomial (in the security parameter ${n}$ n ). If fewer than 2/3 of the parties are corrupted, the size of the domain of each party is constant, and the functionality is deterministic, then our protocols are efficient even when the number of parties is $\log \log {n}$ log log n . On the negative side, we show that when the number of parties is super-constant, 1/ p -secure protocols are not possible when the size of the domain of each party is polynomial. Thus, our feasibility results for 1/ p -secure computation are essentially tight. We further motivate our results by constructing protocols with stronger guarantees: If in the execution of the protocol there is a majority of honest parties, then our protocols provide full security. However, if only a minority of the parties are honest, then our protocols are 1/ p -secure. Thus, our protocols provide the best of both worlds, where the 1/ p -security is only a fall-back option if there is no honest majority.
2019
JOFC
Recently, there has been huge progress in the field of concretely efficient secure computation, even while providing security in the presence of malicious adversaries. This is especially the case in the two-party setting, where constant-round protocols exist that remain fast even over slow networks. However, in the multi-party setting, all concretely efficient fully secure protocols, such as SPDZ, require many rounds of communication. In this paper, we present a constant-round multi-party secure computation protocol that is fully secure in the presence of malicious adversaries and for any number of corrupted parties. Our construction is based on the constant-round protocol of Beaver et al. (the BMR protocol) and is the first version of that protocol that is concretely efficient for the dishonest majority case. Our protocol includes an online phase that is extremely fast and mainly consists of each party locally evaluating a garbled circuit. For the offline phase, we present both a generic construction (using any underlying MPC protocol) and a highly efficient instantiation based on the SPDZ protocol. Our estimates show the protocol to be considerably more efficient than previous fully secure multi-party protocols.
2018
JOFC
2018
JOFC
2018
JOFC
2018
CRYPTO
2018
CRYPTO
We present two new, highly efficient, protocols for securely generating a distributed RSA key pair in the two-party setting. One protocol is semi-honestly secure and the other maliciously secure. Both are constant round and do not rely on any specific number-theoretic assumptions and improve significantly over the state-of-the-art by allowing a slight leakage (which we show to not affect security).For our maliciously secure protocol our most significant improvement comes from executing most of the protocol in a “strong” semi-honest manner and then doing a single, light, zero-knowledge argument of correct execution. We introduce other significant improvements as well. One such improvement arrives in showing that certain, limited leakage does not compromise security, which allows us to use lightweight subprotocols. Another improvement, which may be of independent interest, comes in our approach for multiplying two large integers using OT, in the malicious setting, without being susceptible to a selective-failure attack.Finally, we implement our malicious protocol and show that its performance is an order of magnitude better than the best previous protocol, which provided only semi-honest security.
2018
PKC
In the setting of secure computation, a set of parties wish to compute a joint function of their private inputs without revealing anything but the output. Garbled circuits, first introduced by Yao, are a central tool in the construction of protocols for secure two-party computation (and other tasks like secure outsourced computation), and are the fastest known method for constant-round protocols. In this paper, we initiate a study of garbling multivalent-logic circuits, which are circuits whose wires may carry values from some finite/infinite set of values (rather than only $\mathsf {True}$True and $\mathsf {False}$False). In particular, we focus on the three-valued logic system of Kleene, in which the admissible values are $\mathsf {True}$True, $\mathsf {False}$False, and $\mathsf {Unknown}$Unknown. This logic system is used in practice in SQL where some of the values may be missing. Thus, efficient constant-round secure computation of SQL over a distributed database requires the ability to efficiently garble circuits over 3-valued logic. However, as we show, the two natural (naive) methods of garbling 3-valued logic are very expensive.In this paper, we present a general approach for garbling three-valued logic, which is based on first encoding the 3-value logic into Boolean logic, then using standard garbling techniques, and final decoding back into 3-value logic. Interestingly, we find that the specific encoding chosen can have a significant impact on efficiency. Accordingly, the aim is to find Boolean encodings of 3-value logic that enable efficient Boolean garbling (i.e., minimize the number of AND gates). We also show that Boolean AND gates can be garbled at the same cost of garbling XOR gates in the 3-value logic setting. Thus, it is unlikely that an analogue of free-XOR exists for 3-value logic garbling (since this would imply free-AND in the Boolean setting).
2017
EUROCRYPT
2017
CRYPTO
2017
ASIACRYPT
2017
TCC
2017
JOFC
2017
JOFC
2017
JOFC
2016
TCC
2016
JOFC
2015
JOFC
2015
TCC
2015
EUROCRYPT
2015
CRYPTO
2015
CRYPTO
2014
CRYPTO
2014
ASIACRYPT
2013
PKC
2013
TCC
2013
TCC
2013
CRYPTO
2013
ASIACRYPT
2013
ASIACRYPT
2013
JOFC
In this note, we show the existence of constant-round computational zero-knowledge proofs of knowledge for all $\mathcal {NP}$. The existence of constant-round zero-knowledge proofs was proven by Goldreich and Kahan (Journal of Cryptology, 1996), and the existence of constant-round zero-knowledge arguments of knowledge was proven by Feige and Shamir (CRYPTO, 1989). However, the existence of constant-round zero-knowledge proofs of knowledge for all $\mathcal {NP}$ is folklore, to the best of our knowledge, since no proof of this fact has been published.
2012
ASIACRYPT
2012
JOFC
Protocols for secure two-party computation enable a pair of parties to compute a function of their inputs while preserving security properties such as privacy, correctness and independence of inputs. Recently, a number of protocols have been proposed for the efficient construction of two-party computation secure in the presence of malicious adversaries (where security is proven under the standard simulation-based ideal/real model paradigm for defining security). In this paper, we present a protocol for this task that follows the methodology of using cut-and-choose to boost Yao’s protocol to be secure in the presence of malicious adversaries. Relying on specific assumptions (DDH), we construct a protocol that is significantly more efficient and far simpler than the protocol of Lindell and Pinkas (Eurocrypt 2007) that follows the same methodology. We provide an exact, concrete analysis of the efficiency of our scheme and demonstrate that (at least for not very small circuits) our protocol is more efficient than any other known today.
2011
JOFC
2011
TCC
2011
TCC
2011
CRYPTO
2011
CRYPTO
2011
CRYPTO
2011
CRYPTO
2011
EUROCRYPT
2011
JOFC
2011
JOFC
2011
JOFC
2010
JOFC
2010
JOFC
2009
TCC
2009
JOFC
2009
JOFC
2009
CRYPTO
2009
CRYPTO
2008
TCC
2008
JOFC
2008
JOFC
2007
EUROCRYPT
2007
TCC
2007
TCC
2006
CRYPTO
2006
JOFC
2006
JOFC
2006
JOFC
2005
CRYPTO
2005
EUROCRYPT
2005
TCC
2005
JOFC
2004
TCC
2003
EUROCRYPT
2003
EUROCRYPT
2003
EUROCRYPT
2003
JOFC
2002
JOFC
2001
CRYPTO
2001
CRYPTO
2000
CRYPTO

#### Program Committees

Eurocrypt 2018
Eurocrypt 2015
TCC 2014 (Program chair)
Crypto 2013
Eurocrypt 2012
PKC 2011
Crypto 2010
Crypto 2008
TCC 2008
Crypto 2006
TCC 2006
Crypto 2005
Eurocrypt 2004