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Electronic Colloquium on Computational Complexity

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Reports tagged with cryptography:
TR94-007 | 12th December 1994
Oded Goldreich, Rafail Ostrovsky, Erez Petrank

Computational Complexity and Knowledge Complexity

We study the computational complexity of languages which have
interactive proofs of logarithmic knowledge complexity. We show that
all such languages can be recognized in ${\cal BPP}^{\cal NP}$. Prior
to this work, for languages with greater-than-zero knowledge
complexity (and specifically, even for knowledge complexity 1) only
trivial computational complexity bounds ... more >>>

TR95-029 | 15th June 1995
Oded Goldreich, Leonid Levin, Noam Nisan

On Constructing 1-1 One-Way Functions

We show how to construct length-preserving 1-1 one-way
functions based on popular intractability assumptions (e.g., RSA, DLP).
Such 1-1 functions should not
be confused with (infinite) families of (finite) one-way permutations.
What we want and obtain is a single (infinite) 1-1 one-way function.

more >>>

TR95-038 | 2nd July 1995
Joe Kilian, Erez Petrank

An Efficient Non-Interactive Zero-Knowledge Proof System for NP with General Assumptions

We consider noninteractive zero-knowledge proofs in the shared random
string model proposed by Blum, Feldman and Micali \cite{bfm}. Until
recently there was a sizable polynomial gap between the most
efficient noninteractive proofs for {\sf NP} based on general
complexity assumptions \cite{fls} versus those based on specific
algebraic assumptions \cite{Da}. ... more >>>

TR96-042 | 26th July 1996
Oded Goldreich, Shai Halevi

Collision-Free Hashing from Lattice Problems

Recently Ajtai described a construction of one-way functions whose
security is equivalent to the difficulty of some well known approximation
problems in lattices. We show that essentially the same
construction can also be used to obtain collision-free hashing.

more >>>

TR97-018 | 8th May 1997
Oded Goldreich, Shai Halevi

Eliminating Decryption Errors in the Ajtai-Dwork Cryptosystem.

Following Ajtai's lead, Ajtai and Dwork have recently introduced a
public-key encryption scheme which is secure under the assumption
that a certain computational problem on lattices is hard on the
worst-case. Their encryption method may cause decryption errors,
though with small probability (i.e., inversely proportional to the
more >>>

TR97-061 | 12th November 1997
Eli Biham, Dan Boneh, Omer Reingold

Generalized Diffie-Hellman Modulo a Composite is not Weaker than Factoring

The Diffie-Hellman key-exchange protocol may naturally be
extended to k>2 parties. This gives rise to the generalized
Diffie-Hellman assumption (GDH-Assumption).
Naor and Reingold have recently shown an efficient construction
of pseudo-random functions and reduced the security of their
construction to the GDH-Assumption.
In this note, we ... more >>>

TR98-010 | 22nd January 1998
Phong Nguyen, Jacques Stern

A Converse to the Ajtai-Dwork Security Proof and its Cryptographic Implications

Revisions: 1

Recently, Ajtai discovered a fascinating connection
between the worst-case complexity and the average-case
complexity of some well-known lattice problems.
Later, Ajtai and Dwork proposed a cryptosystem inspired
by Ajtai's work, provably secure if a particular lattice
problem is difficult. We show that there is a converse
to the ... more >>>

TR00-003 | 26th November 1999
Matthias Krause, Hans Ulrich Simon

Determining the Optimal Contrast for Secret Sharing Schemes in Visual Cryptography

This paper shows that the largest possible contrast C(k,n)
in a k-out-of-n secret sharing scheme is approximately
4^(-(k-1)). More precisely, we show that
4^(-(k-1)) <= C_{k,n} <= 4^(-(k-1))}n^k/(n(n-1)...(n-(k-1))).
This implies that the largest possible contrast equals
4^(-(k-1)) in the limit when n approaches ... more >>>

TR00-014 | 16th February 2000
Matthias Krause, Stefan Lucks

On Learning versus Distinguishing and the Minimal Hardware Complexity of Pseudorandom Function Generators

A set $F$ of $n$-ary Boolean functions is called a pseudorandom function generator
(PRFG) if communicating
with a randomly chosen secret function from $F$ cannot be
efficiently distinguished from communicating with a truly random function.
We ask for the minimal hardware complexity of a PRFG. This question ... more >>>

TR00-040 | 19th May 2000
Maria Isabel Gonzalez Vasco, Igor E. Shparlinski

Security of the Most Significant Bits of the Shamir Message Passing Scheme

Boneh and Venkatesan have recently proposed a polynomial time
algorithm for recovering a ``hidden'' element $\alpha$ of a
finite field $\F_p$ of $p$ elements from rather short
strings of the most significant bits of the remainder
mo\-du\-lo $p$ of $\alpha t$ for several values of $t$ selected uniformly
at random ... more >>>

TR00-045 | 23rd June 2000
Maria Isabel Gonzalez Vasco, Igor E. Shparlinski

On the Security of Diffie--Hellman Bits

Boneh and Venkatesan have recently proposed a polynomial time
algorithm for recovering a ``hidden'' element $\alpha$ of a
finite field $\F_p$ of $p$ elements from rather short
strings of the most significant bits of the remainder
mo\-du\-lo $p$ of $\alpha t$ for several values of $t$ selected
uniformly at ... more >>>

TR01-057 | 15th August 2001
Boaz Barak, Oded Goldreich, Russell Impagliazzo, Steven Rudich, Amit Sahai, Salil Vadhan, Ke Yang

On the (Im)possibility of Obfuscating Programs

Informally, an <i>obfuscator</i> <b>O</b> is an (efficient, probabilistic)
"compiler" that takes as input a program (or circuit) <b>P</b> and
produces a new program <b>O(P)</b> that has the same functionality as <b>P</b>
yet is "unintelligible" in some sense. Obfuscators, if they exist,
would have a wide variety of cryptographic ... more >>>

TR01-064 | 10th September 2001
Moni Naor, Omer Reingold, Alon Rosen

Pseudo-Random Functions and Factoring

Factoring integers is the most established problem on which
cryptographic primitives are based. This work presents an efficient
construction of {\em pseudorandom functions} whose security is based
on the intractability of factoring. In particular, we are able to
construct efficient length-preserving pseudorandom functions where
each evaluation requires only a ... more >>>

TR02-047 | 3rd August 2002
Oded Goldreich

The GGM Construction does NOT yield Correlation Intractable Function Ensembles.

We consider the function ensembles emerging from the
construction of Goldreich, Goldwasser and Micali (GGM),
when applied to an arbitrary pseudoramdon generator.
We show that, in general, such functions
fail to yield correlation intractable ensembles.
Specifically, it may happen that, given a description of such a ... more >>>

TR03-009 | 3rd February 2003
Markus Bläser, Andreas Jakoby, Maciej Liskiewicz, Bodo Manthey

Private Computation --- $k$-connected versus $1$-connected Networks

Revisions: 1

We study the role of connectivity of communication networks in private
computations under information theoretic settings. It will be shown that
some functions can be computed by private protocols even if the
underlying network is 1-connected but not 2-connected. Then we give a
complete characterisation of non-degenerate functions that can ... more >>>

TR03-015 | 20th March 2003
Yael Tauman

On the (In)security of the Fiat-Shamir Paradigm

In 1986, Fiat and Shamir suggested a general method for transforming secure 3-round public-coin identification schemes into digital signature schemes. The significant contribution of this method is a means for designing efficient digital signatures, while hopefully achieving security against chosen message attacks. All other known constructions which achieve such security ... more >>>

TR03-066 | 2nd September 2003
Daniele Micciancio

Almost perfect lattices, the covering radius problem, and applications to Ajtai's connection factor

Lattices have received considerable attention as a potential source of computational hardness to be used in cryptography, after a breakthrough result of Ajtai (STOC 1996) connecting the average-case and worst-case complexity of various lattice problems. The purpose of this paper is twofold. On the expository side, we present a rigorous ... more >>>

TR03-071 | 18th August 2003
Markus Bläser, Andreas Jakoby, Maciej Liskiewicz, Bodo Manthey

Privacy in Non-Private Environments

Revisions: 1

We study private computations in information-theoretical settings on
networks that are not 2-connected. Non-2-connected networks are
``non-private'' in the sense that most functions cannot privately be
computed on such networks. We relax the notion of privacy by
introducing lossy private protocols, which generalize private
protocols. We measure the information each ... more >>>

TR04-063 | 23rd July 2004
Yehuda Lindell, Benny Pinkas

A Proof of Yao's Protocol for Secure Two-Party Computation

Revisions: 1

In the mid 1980's, Yao presented a constant-round protocol for
securely computing any two-party functionality in the presence of
semi-honest adversaries (FOCS 1986). In this paper, we provide a
complete description of Yao's protocol, along with a rigorous
proof of security. Despite the importance of Yao's protocol to the
field ... more >>>

TR04-102 | 20th October 2004
Thomas Holenstein

Key Agreement from Weak Bit Agreement

Assume that Alice and Bob, given an authentic channel, have a protocol where they end up with a bit S_A and S_B, respectively, such that with probability (1+eps)/2 these bits are equal. Further assume that conditioned on the event S_A = S_B no polynomial time bounded algorithm can predict the ... more >>>

TR05-110 | 3rd October 2005
Saurabh Sanghvi, Salil Vadhan

The Round Complexity of Two-Party Random Selection

We study the round complexity of two-party protocols for
generating a random $n$-bit string such that the output is
guaranteed to have bounded bias (according to some measure) even
if one of the two parties deviates from the protocol (even using
unlimited computational resources). Specifically, we require that
the output's ... more >>>

TR06-026 | 27th February 2006
Ronen Gradwohl, Salil Vadhan, David Zuckerman

Random Selection with an Adversarial Majority

We consider the problem of random selection, where $p$ players follow a protocol to jointly select a random element of a universe of size $n$. However, some of the players may be adversarial and collude to force the output to lie in a small subset of the universe. We describe ... more >>>

TR06-028 | 21st February 2006
Jonathan Katz, Chiu-Yuen Koo

On Expected Constant-Round Protocols for Byzantine Agreement

In a seminal paper, Feldman and Micali (STOC '88) show an n-party Byzantine agreement protocol tolerating t < n/3 malicious parties that runs in expected constant rounds. Here, we show an expected constant-round protocol for authenticated Byzantine agreement assuming honest majority (i.e., $t < n/2$), and relying only on the ... more >>>

TR06-056 | 27th April 2006
Salil Vadhan

An Unconditional Study of Computational Zero Knowledge

We prove a number of general theorems about ZK, the class of problems possessing (computational) zero-knowledge proofs. Our results are unconditional, in contrast to most previous works on ZK, which rely on the assumption that one-way functions exist.

We establish several new characterizations of ZK, and use these characterizations to ... more >>>

TR06-075 | 19th June 2006
Minh-Huyen Nguyen, Shien Jin Ong, Salil Vadhan

Statistical Zero-Knowledge Arguments for NP from Any One-Way Function

We show that every language in NP has a *statistical* zero-knowledge
argument system under the (minimal) complexity assumption that
one-way functions exist. In such protocols, even a computationally
unbounded verifier cannot learn anything other than the fact that the
assertion being proven is true, whereas a polynomial-time prover
cannot convince ... more >>>

TR07-096 | 8th October 2007
Lance Fortnow, Rahul Santhanam

Infeasibility of Instance Compression and Succinct PCPs for NP

We study the notion of "instance compressibility" of NP problems [Harnik-Naor06], closely related to the notion of kernelization in parameterized complexity theory [Downey-Fellows99, Flum-Grohe06, Niedermeier06]. A language $L$ in NP is instance compressible if there
is a polynomial-time computable function $f$ and a set $A$ such that
for each instance ... more >>>

TR08-050 | 12th March 2008
Manoj Prabhakaran, Mike Rosulek

Cryptographic Complexity of Multi-party Computation Problems: Classifications and Separations

We develop new tools to study the relative complexities of secure
multi-party computation tasks (functionalities) in the Universal
Composition framework. When one task can be securely realized using
another task as a black-box, we interpret this as a
qualitative, complexity-theoretic reduction between the two tasks.
Virtually all previous characterizations of ... more >>>

TR09-045 | 20th May 2009
Iftach Haitner, Omer Reingold, Salil Vadhan, Hoeteck Wee

Inaccessible Entropy

We put forth a new computational notion of entropy, which measures the
(in)feasibility of sampling high entropy strings that are consistent
with a given protocol. Specifically, we say that the i'th round of a
protocol (A, B) has _accessible entropy_ at most k, if no
polynomial-time strategy A^* can generate ... more >>>

TR09-062 | 28th July 2009
Daniele Venturi

Lecture Notes on Algorithmic Number Theory

The principal aim of this notes is to give a survey on the state of the art of algorithmic number theory, with particular focus on the theory of elliptic curves.
Computational security is the goal of modern cryptographic constructions: the security of modern criptographic schemes stems from the assumption ... more >>>

TR09-065 | 31st July 2009
Panagiotis Voulgaris, Daniele Micciancio

Faster exponential time algorithms for the shortest vector problem

We present new faster algorithms for the exact solution of the shortest vector problem in arbitrary lattices. Our main result shows that the shortest vector in any $n$-dimensional lattice can be found in time $2^{3.199 n}$ and space $2^{1.325 n}$.
This improves the best previously known algorithm by Ajtai, Kumar ... more >>>

TR09-127 | 25th November 2009
Brett Hemenway, Rafail Ostrovsky

Lossy Trapdoor Functions from Smooth Homomorphic Hash Proof Systems

Revisions: 2

In STOC '08, Peikert and Waters introduced a powerful new primitive called Lossy Trapdoor Functions (LTDFs). Since their introduction, lossy trapdoor functions have found many uses in cryptography. In the work of Peikert and Waters, lossy trapdoor functions were used to give an efficient construction of a chosen-ciphertext secure ... more >>>

TR10-020 | 19th February 2010
Vipul Goyal, Yuval Ishai, Mohammad Mahmoody, Amit Sahai

Interactive Locking, Zero-Knowledge PCPs, and Unconditional Cryptography

Motivated by the question of basing cryptographic protocols on stateless tamper-proof hardware tokens, we revisit the question of unconditional two-prover zero-knowledge proofs for $NP$. We show that such protocols exist in the {\em interactive PCP} model of Kalai and Raz (ICALP '08), where one of the provers is replaced by ... more >>>

TR10-127 | 9th August 2010
Brett Hemenway, Rafail Ostrovsky

Building Injective Trapdoor Functions From Oblivious Transfer

Revisions: 1

Injective one-way trapdoor functions are one of the most fundamental cryptographic primitives. In this work we give a novel construction of injective trapdoor functions based on oblivious transfer for long strings.

Our main result is to show that any 2-message statistically sender-private semi-honest oblivious transfer (OT) for ... more >>>

TR10-160 | 28th October 2010
Zeev Dvir, Dan Gutfreund, Guy Rothblum, Salil Vadhan

On Approximating the Entropy of Polynomial Mappings

We investigate the complexity of the following computational problem:

Polynomial Entropy Approximation (PEA):
Given a low-degree polynomial mapping
$p : F^n\rightarrow F^m$, where $F$ is a finite field, approximate the output entropy
$H(p(U_n))$, where $U_n$ is the uniform distribution on $F^n$ and $H$ may be any of several entropy measures.

... more >>>

TR11-141 | 2nd November 2011
Salil Vadhan, Colin Jia Zheng

Characterizing Pseudoentropy and Simplifying Pseudorandom Generator Constructions

Revisions: 3

We provide a characterization of pseudoentropy in terms of hardness of sampling: Let $(X,B)$ be jointly distributed random variables such that $B$ takes values in a polynomial-sized set. We show that $B$ is computationally indistinguishable from a random variable of higher Shannon entropy given $X$ if and only if there ... more >>>

TR13-118 | 2nd September 2013
Mahdi Cheraghchi, Venkatesan Guruswami

Capacity of Non-Malleable Codes

Non-malleable codes, introduced by Dziembowski, Pietrzak and Wichs (ICS 2010), encode messages $s$ in a manner so that tampering the codeword causes the decoder to either output $s$ or a message that is independent of $s$. While this is an impossible goal to achieve against unrestricted tampering functions, rather surprisingly ... more >>>

TR13-121 | 4th September 2013
Mahdi Cheraghchi, Venkatesan Guruswami

Non-Malleable Coding Against Bit-wise and Split-State Tampering

Revisions: 1

Non-malleable coding, introduced by Dziembowski, Pietrzak and Wichs (ICS 2010), aims for protecting the integrity of information against tampering attacks in situations where error-detection is impossible. Intuitively, information encoded by a non-malleable code either decodes to the original message or, in presence of any tampering, to an unrelated message. Non-malleable ... more >>>

TR15-027 | 25th February 2015
Benny Applebaum

Cryptographic Hardness of Random Local Functions -- Survey

Revisions: 1

Constant parallel-time cryptography allows to perform complex cryptographic tasks at an ultimate level of parallelism, namely, by local functions that each of their output bits depend on a constant number of input bits. A natural way to obtain local cryptographic constructions is to use \emph{random local functions} in which each ... more >>>

TR15-172 | 3rd November 2015
Benny Applebaum, Shachar Lovett

Algebraic Attacks against Random Local Functions and Their Countermeasures

Revisions: 1

Suppose that you have $n$ truly random bits $x=(x_1,\ldots,x_n)$ and you wish to use them to generate $m\gg n$ pseudorandom bits $y=(y_1,\ldots, y_m)$ using a local mapping, i.e., each $y_i$ should depend on at most $d=O(1)$ bits of $x$. In the polynomial regime of $m=n^s$, $s>1$, the only known solution, ... more >>>

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