Arrow Research search

Author name cluster

Yevgeniy Dodis

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

18 papers
1 author row

Possible papers

18

FOCS Conference 2024 Conference Paper

How to Simulate Random Oracles with Auxiliary Input

  • Yevgeniy Dodis
  • Aayush Jain
  • Huijia Lin
  • Ji Luo 0002
  • Daniel Wichs

The random oracle model (ROM) allows us to opti-mistically reason about security properties of cryptographic hash functions, and has been hugely influential in designing practical cryptosystems. But it is overly optimistic against non-uniform adversaries, and often suggests security properties and security levels unachievable by any real hash function. To reconcile with this discrepancy, Unruh [CRYPTO '07] proposed the auxiliary-input random oracle model (AI-ROM), where a non-uniform attacker additionally gets a bounded amount of advice about the random oracle. Proving security in the AI-ROM is often much more difficult, but a series of works starting with Unruh provided useful technical tools to do so. Although these tools lead to good results in the information-theoretic setting, they are unsatisfactory in the computational setting, where the random oracle is used alongside other computational hardness assumptions. At the most basic level, we did not even know whether it is possible to efficiently simulate random oracle queries given auxiliary input, which has remained as an explicit open problem since the work of Unruh. In this work, we resolve the above open problem and show how to efficiently simulate auxiliary-input random oracles. Moreover, the simulation has low concrete overhead, leading to small losses in exact security. We use it to prove the security of a broad class of computational schemes in the AI-ROM, including the first non-interactive zero-knowledge (NIZK) scheme in the AI-ROM. As a tool of independent interest, we develop a new notion of ultra-secure pseudorandom functions with fast RAM evaluation, which can achieve $2^{\lambda}$ security while having sublinear $\mathrm{o}(\lambda)$ evaluation time.

Details

STOC Conference 2015 Conference Paper

Non-malleable Reductions and Applications

  • Divesh Aggarwal
  • Yevgeniy Dodis
  • Tomasz Kazana
  • Maciej Obremski

Non-malleable codes, introduced by Dziembowski, Pietrzak and Wichs [DPW10], provide a useful message integrity guarantee in situations where traditional error-correction (and even error-detection) is impossible; for example, when the attacker can completely overwrite the encoded message. Informally, a code is non-malleable if the message contained in a modified codeword is either the original message, or a completely "unrelated value". Although such codes do not exist if the family of "tampering functions" cF allowed to modify the original codeword is completely unrestricted, they are known to exist for many broad tampering families cF. The family which received the most attention [DPW10,LL12,DKO13,ADL14,CG14a,CG14b] is the family of tampering functions in the so called (2-part) split-state model: here the message x is encoded into two shares L and R, and the attacker is allowed to arbitrarily tamper with each L and R individually. Despite this attention, the following problem remained open: Build efficient, information-theoretically secure non-malleable codes in the split-state model with constant encoding rate: |L|=|R|=O(|x|).

Details

STOC Conference 2014 Conference Paper

Non-malleable codes from additive combinatorics

  • Divesh Aggarwal
  • Yevgeniy Dodis
  • Shachar Lovett

Non-malleable codes provide a useful and meaningful security guarantee in situations where traditional errorcorrection (and even error-detection) is impossible; for example, when the attacker can completely overwrite the encoded message. Informally, a code is non-malleable if the message contained in a modified codeword is either the original message, or a completely unrelated value. Although such codes do not exist if the family of "tampering functions" F is completely unrestricted, they are known to exist for many broad tampering families F . One such natural family is the family of tampering functions in the so called split-state model. Here the message m is encoded into two shares L and R , and the attacker is allowed to arbitrarily tamper with L and R individually . The split-state tampering arises in many realistic applications, such as the design of non-malleable secret sharing schemes , motivating the question of designing efficient non-malleable codes in this model.

Details

FOCS Conference 2011 Conference Paper

Privacy Amplification and Non-malleable Extractors via Character Sums

  • Yevgeniy Dodis
  • Xin Li 0006
  • Trevor D. Wooley
  • David Zuckerman

In studying how to communicate over a public channel with an active adversary, Dodis and Wichs introduced the notion of a non-malleable extractor. A non-malleable extractor dramatically strengthens the notion of a strong ex- tractor. A strong extractor takes two inputs, a weakly-random x and a uniformly random seed y, and outputs a string which appears uniform, even given y. For a non-malleable extractor nmExt, the output nmExt(x, y) should appear uniform given y as well as nmExt(x, A(y)), where A is an arbitrary function with A(y) ≠ y. We show that an extractor introduced by Chor and Goldreich is non-malleable when the entropy rate is above half. It outputs a linear number of bits when the entropy rate is 1/2 + α, for any α >; 0. Previously, no nontrivial parameters were known for any non-malleable extractor. To achieve a polynomial running time when outputting many bits, we rely on a widely-believed conjecture about the distribution of prime numbers in arithmetic progressions. Our analysis involves a character sum estimate, which may be of independent interest. Using our non-malleable extractor, we obtain protocols for "privacy amplification": key agreement between two parties who share a weakly-random secret. Our protocols work in the presence of an active adversary with unlimited computational power, and have asymptotically optimal entropy loss. When the secret has entropy rate greater than 1/2, the protocol fol- lows from a result of Dodis and Wichs, and takes two rounds. When the secret has entropy rate δ for any constant δ >; 0, our new protocol takes a constant (polynomial in 1/δ) number of rounds. Our protocols run in polynomial time under the above well-known conjecture about primes.

Details

FOCS Conference 2011 Conference Paper

Storing Secrets on Continually Leaky Devices

  • Yevgeniy Dodis
  • Allison Bishop Lewko
  • Brent Waters
  • Daniel Wichs

We consider the question of how to store a value secretly on devices that continually leak information about their internal state to an external attacker. If the secret value is stored on a single device from which it is efficiently retrievable, and the attacker can leak even a single predicate of the internal state of that device, then she may learn some information about the secret value itself. Therefore, we consider a setting where the secret value is shared between multiple devices (or multiple components of a single device), each of which continually leaks arbitrary adaptively chosen predicates its individual state. Since leakage is continual, each device must also continually update its state so that an attacker cannot just leak it entirely one bit at a time. In our model, the devices update their state individually and asynchronously, without any communication between them. The update process is necessarily randomized, and its randomness can leak as well. As our main result, we construct a sharing scheme for two devices, where a constant fraction of the internal state of each device can leak in between and during updates. Our scheme has the structure of a public-key encryption, where one share is a secret key and the other is a ciphertext. As a contribution of independent interest, we also get public-key encryption in the continual leakage model, introduced by Brakerski et al. and Dodis et al. (FOCS '10). This scheme tolerates continual leakage on the secret key and the updates, and simplifies the recent construction of Lewko, Lewko and Waters (STOC '11). For our main result, we show how to update the ciphertexts of the encryption scheme so that the message remains hidden even if an attacker interleaves leakage on secret key and ciphertext shares. The security of our scheme is based on the linear assumption in prime-order bilinear groups. We also provide an extension to general access structures realizable by linear secret sharing schemes across many devices. The main advantage of this extension is that the state of some devices can be compromised entirely, while that of the all remaining devices is susceptible to continual leakage. Lastly, we show impossibility of information theoretic sharing schemes in our model, where continually leaky devices update their state individually.

Details

FOCS Conference 2010 Conference Paper

Cryptography against Continuous Memory Attacks

  • Yevgeniy Dodis
  • Kristiyan Haralambiev
  • Adriana López-Alt
  • Daniel Wichs

We say that a cryptographic scheme is Continuous Leakage-Resilient (CLR), if it allows users to refresh their secret keys, using only fresh local randomness, such that: 1. The scheme remains functional after any number of key refreshes, although the public key never changes. Thus, the “outside world'' is neither affected by these key refreshes, nor needs to know about their frequency. 2. The scheme remains secure even if the adversary can continuously leak arbitrary information about the current secret-key, as long as the amount of leaked information is bounded in between any two successive key refreshes. There is no bound on the total amount of information that can be leaked during the lifetime of the system. In this work, we construct a variety of practical CLR schemes, including CLR one-way relations, CLR signatures, CLR identification schemes, and CLR authenticated key agreement protocols. For each of the above, we give general constructions, and then show how to instantiate them efficiently using a well established assumption on bilinear groups, called the K-Linear assumption (for any constant K greater than or equal to 1). Our constructions are highly modular, and we develop many interesting techniques and building-blocks along the way, including: leakage-indistinguishable re-randomizable relations, homomorphic NIZKs, and leakage-of-cipher text non-malleable encryption schemes.

Details

STOC Conference 2009 Conference Paper

Non-malleable extractors and symmetric key cryptography from weak secrets

  • Yevgeniy Dodis
  • Daniel Wichs

We study the question of basing symmetric key cryptography on weak secrets. In this setting, Alice and Bob share an n-bit secret W, which might not be uniformly random, but the adversary has at least k bits of uncertainty about it (formalized using conditional min-entropy). Since standard symmetric-key primitives require uniformly random secret keys, we would like to construct an authenticated key agreement protocol in which Alice and Bob use W to agree on a nearly uniform key R, by communicating over a public channel controlled by an active adversary Eve. We study this question in the information theoretic setting where the attacker is computationally unbounded. We show that single-round (i.e. one message) protocols do not work when k ≤ n/2, and require poor parameters even when n/2<k<<n . On the other hand, for arbitrary values of k, we design a communication efficient two-round (challenge-response) protocol extracting nearly k random bits. This dramatically improves the previous construction of Renner and Wolf [32], which requires Θ(λ + log(n)) rounds where λ is the security parameter. Our solution takes a new approach by studying and constructing "non-malleable" seeded randomness extractors -- if an attacker sees a random seed X and comes up with an arbitrarily related seed X', then we bound the relationship between R= Ext(W;X) and R' = Ext(W;X'). We also extend our two-round key agreement protocol to the "fuzzy" setting, where Alice and Bob share "close" (but not equal) secrets W A and W B , and to the Bounded Retrieval Model (BRM) where the size of the secret W is huge.

Details

STOC Conference 2009 Conference Paper

On cryptography with auxiliary input

  • Yevgeniy Dodis
  • Yael Tauman Kalai
  • Shachar Lovett

We study the question of designing cryptographic schemes which are secure even if an arbitrary function f(sk) of the secret key is leaked, as long as the secret key sk is still (exponentially) hard to compute from this auxiliary input. This setting of auxiliary input is more general than the more traditional setting, which assumes that some of information about the secret key sk may be leaked, but sk still has high min-entropy left. In particular, we deal with situations where f(sk) information-theoretically determines the entire secret key sk. As our main result, we construct CPA/CCA secure symmetric encryption schemes that remain secure with exponentially hard-to-invert auxiliary input. We give several applications of such schemes. * We construct an average-case obfuscator for the class of point functions, which remains secure with exponentially hard-to-invert auxiliary input, and is reusable. * We construct a reusable and robust extractor that remains secure with exponentially hard-to-invert auxiliary input. Our results rely on a new cryptographic assumption, Learning Subspace-with-Noise (LSN), which is related to the well known Learning Parity-with-Noise (LPN) assumption.

Details

STOC Conference 2005 Conference Paper

Correcting errors without leaking partial information

  • Yevgeniy Dodis
  • Adam Smith 0006

This paper explores what kinds of information two parties must communicate in order to correct errors which occur in a shared secret string W. Any bits they communicate must leak a significant amount of information about W --- that is, from the adversary's point of view, the entropy of W will drop significantly. Nevertheless, we construct schemes with which Alice and Bob can prevent an adversary from learning any useful information about W. Specifically, if the entropy of W is sufficiently high, then there is no function f(W) which the adversary can learn from the error-correction information with significant probability.This leads to several new results: (a) the design of noise-tolerant "perfectly one-way" hash functions in the sense of Canetti et al. [7], which in turn leads to obfuscation of proximity queries for high entropy secrets W; (b) private fuzzy extractors [11], which allow one to extract uniformly random bits from noisy and nonuniform data W, while also insuring that no sensitive information about W is leaked; and (c) noise tolerance and stateless key re-use in the Bounded Storage Model, resolving the main open problem of Ding [10].The heart of our constructions is the design of strong randomness extractors with the property that the source W can be recovered from the extracted randomness and any string W' which is close to W.

Details

FOCS Conference 2004 Conference Paper

On the (Im)possibility of Cryptography with Imperfect Randomness

  • Yevgeniy Dodis
  • Shien Jin Ong
  • Manoj Prabhakaran 0001
  • Amit Sahai

We investigate the feasibility of a variety of cryptographic tasks with imperfect randomness. The kind of imperfect randomness we consider are entropy sources, such as those considered by Santha and Vazirani, Chor and Goldreich, and Zuckerman. We show the following: (1) certain cryptographic tasks like bit commitment, encryption, secret sharing, zero-knowledge, non-interactive zero-knowledge, and secure two-party computation for any non-trivial junction are impossible to realize if parties have access to entropy sources with slightly less-than-perfect entropy, i. e. , sources with imperfect randomness. These results are unconditional and do not rely on any un-proven assumption. (2) On the other hand, based on stronger variants of standard assumptions, secure signature schemes are possible with imperfect entropy sources. As another positive result, we show (without any unproven assumption) that interactive proofs can be made sound with respect to imperfect entropy sources.

Details

STOC Conference 2003 Conference Paper

Pricing network edges for heterogeneous selfish users

  • Richard Cole 0001
  • Yevgeniy Dodis
  • Tim Roughgarden

We study the negative consequences of selfish behavior in a congested network and economic means of influencing such behavior. We consider a model of selfish routing in which the latency experienced by network traffic on an edge of the network is a function of the edge congestion, and network users are assumed to selfishly route traffic on minimum-latency paths. The quality of a routing of traffic is measured by the sum of travel times (the total latency ).It is well known that the outcome of selfish routing (a Nash equilibrium ) does not minimize the total latency. An ancient strategy for improving the selfish solution is the principle of marginal cost pricing , which asserts that on each edge of the network, each network user on the edge should pay a tax offsetting the congestion effects caused by its presence. By pricing network edges according to this principle, the inefficiency of selfish routing can always be eradicated.This result, while fundamental, assumes a very strong homogeneity property: all network users are assumed to trade off time and money in an identical way. The guarantee also ignores both the algorithmic aspects of edge pricing and the unfortunate possibility that an efficient routing of traffic might only be achieved with exorbitant taxes. Motivated by these shortcomings, we extend this classical work on edge pricing in several different directions and prove the following results.We prove that the edges of a single-commodity network can always be priced so that an optimal routing of traffic arises as a Nash equilibrium, even for very general heterogeneous populations of network users.When there are only finitely many different types of network users and all edge latency functions are convex, we show how to compute such edge prices efficiently.We prove that an easy-to-check mathematical condition on the population of heterogeneous network users is both necessary and sufficient for the existence of edge prices that induce an optimal routing while requiring only moderate taxes.

Details

FOCS Conference 2002 Conference Paper

On the (non)Universality of the One-Time Pad

  • Yevgeniy Dodis
  • Joel Spencer

Randomization is vital in cryptography: secret keys should be randomly generated and most cryptographic primitives (e. g. , encryption) must be probabilistic. We initiate the quantitative study concerning feasibility of building secure cryptographic primitives using imperfect random sources. Specifically, we concentrate on symmetric-key encryption and message authentication, where the shared secret key comes from an imperfect random source instead of being assumed truly random. In each case, we compare the class of "cryptographic" sources for the task at hand with the classes of "extractable" and "simulatable" sources, where: (1) "cryptographic" refers to sources for which the corresponding symmetric-key primitive can be built; (2) "extractable" refers to a very narrow class of sources from which one can extract nearly perfect randomness; and (3) "simulatable" refers to a very general class of weak random sources which are known to suffice for BPP simulation. For both encryption and authentication, we show that the corresponding cryptographic sources lie strictly in between extractable and simulatable sources, which implies that "cryptographic usage" of randomness is more demanding than the corresponding "algorithmic usage", but still does not require perfect randomness. Interestingly, cryptographic sources for encryption and authentication are also quite different from each other, which suggests that there might not be an elegant way to describe imperfect sources sufficient for "general cryptographic use". We believe that our initial investigation in this new area will inspire a lot of further research.

Details
v2026.09.13