229 research outputs found
The Random Oracle Methodology, Revisited
We take a critical look at the relationship between the security of
cryptographic schemes in the Random Oracle Model, and the security of the
schemes that result from implementing the random oracle by so called
"cryptographic hash functions". The main result of this paper is a negative
one: There exist signature and encryption schemes that are secure in the Random
Oracle Model, but for which any implementation of the random oracle results in
insecure schemes.
In the process of devising the above schemes, we consider possible
definitions for the notion of a "good implementation" of a random oracle,
pointing out limitations and challenges.Comment: 31 page
EasyUC: using EasyCrypt to mechanize proofs of universally composable security
We present a methodology for using the EasyCrypt proof assistant (originally designed for mechanizing the generation of proofs of game-based security of cryptographic schemes and protocols) to mechanize proofs of security of cryptographic protocols within the universally composable (UC) security framework. This allows, for the first time, the mechanization and formal verification of the entire sequence of steps needed for proving simulation-based security in a modular way: Specifying a protocol and the desired ideal functionality; Constructing a simulator and demonstrating its validity, via reduction to hard computational problems; Invoking the universal composition operation and demonstrating that it indeed preserves security. We demonstrate our methodology on a simple example: stating and proving the security of secure message communication via a one-time pad, where the key comes from a Diffie-Hellman key-exchange, assuming ideally authenticated communication. We first put together EasyCrypt-verified proofs that: (a) the Diffie-Hellman protocol UC-realizes an ideal key-exchange functionality, assuming hardness of the Decisional Diffie-Hellman problem, and (b) one-time-pad encryption, with a key obtained using ideal key-exchange, UC-realizes an ideal secure-communication functionality. We then mechanically combine the two proofs into an EasyCrypt-verified proof that the composed protocol realizes the same ideal secure-communication functionality. Although formulating a methodology that is both sound and workable has proven to be a complex task, we are hopeful that it will prove to be the basis for mechanized UC security analyses for significantly more complex protocols and tasks.Accepted manuscrip
08491 Abstracts Collection -- Theoretical Foundations of Practical Information Security
From 30.11. to 05.12.2008, the Dagstuhl Seminar 08491 ``Theoretical Foundations of Practical Information Security \u27\u27 was held in Schloss Dagstuhl~--~Leibniz Center for Informatics.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
The random oracle methodology, revisited
We take a critical look at the relationship between the security of cryptographic schemes in the Random Oracle Model, and the security of the schemes that result from implementing the random oracle by so called “cryptographic hash functions”. The main result of this paper is a negative one: There exist signature and encryption schemes that are secure in the Random Oracle Model, but for which any implementation of the random oracle results in insecure schemes. In the process of devising the above schemes, we consider possible definitions for the notion of a “good implementation” of a random oracle, pointing out limitations and challengesAccepted manuscrip
08491 Executive Summary -- Theoretical Foundations of Practical Information Security
Designing, building, and operating secure information processing
systems is a complex task, and the only scientific way to address the
diverse challenges arising throughout the life-cycle of security
criticial systems is to consolidate and increase the knowledge of the
theoretical foundations of practical security problems. To this aim,
the mutual exchange of ideas across individual security research
communities can be extraordinary beneficial. Accordingly, the
motivation of this Dagstuhl seminar was the integration of different
research areas with the common goal of providing an integral
theoretical basis that is needed for the design of secure information
processing systems
Universally Composable Signatures, Certification and Authentication
Recently some efforts were made towards capturing the security requirements from digital signature schemes as an ideal functionality within a
composable security framework. This modeling of digital signatures
potentially has some significant analytical advantages (such as enabling component-wise analysis of complex systems that use signature schemes, as well as symbolic and automatable analysis of such systems). However, it turns out that
formulating ideal functionalities that capture the properties
expected from signature schemes in a way that is both sound and
enjoys the above advantages is not a trivial task.
This work has several contributions. We first correct some flaws in the definition of the ideal signature functionality of Canetti, 2001, andsubsequent formulations. Next we provide a minimal
formalization of ``ideal certification authorities\u27\u27 and
show how authenticated communication can be obtained using ideal signatures and an ideal certification authority. This is done while guaranteeing full modularity (i.e., each component is analyzed as stand-alone), and in an unconditional and errorless way.
This opens the door to symbolic and
automated analysis of protocols for these tasks, in a way that is
both modular and cryptographically sound
On the Computational Hardness Needed for Quantum Cryptography
In the classical model of computation, it is well established that one-way functions (OWF) are minimal for computational cryptography: They are essential for almost any cryptographic application that cannot be realized with respect to computationally unbounded adversaries. In the quantum setting, however, OWFs appear not to be essential (Kretschmer 2021; Ananth et al., Morimae and Yamakawa 2022), and the question of whether such a minimal primitive exists remains open.
We consider EFI pairs - efficiently samplable, statistically far but computationally indistinguishable pairs of (mixed) quantum states. Building on the work of Yan (2022), which shows equivalence between EFI pairs and statistical commitment schemes, we show that EFI pairs are necessary for a large class of quantum-cryptographic applications. Specifically, we construct EFI pairs from minimalistic versions of commitments schemes, oblivious transfer, and general secure multiparty computation, as well as from QCZK proofs from essentially any non-trivial language. We also construct quantum computational zero knowledge (QCZK) proofs for all of QIP from any EFI pair.
This suggests that, for much of quantum cryptography, EFI pairs play a similar role to that played by OWFs in the classical setting: they are simple to describe, essential, and also serve as a linchpin for demonstrating equivalence between primitives
Universally composable end-to-end secure messaging
CNS-1718135 - National Science Foundation; CNS-1801564 - National Science Foundation; CNS-1931714 - National Science Foundation; CNS-1915763 - National Science Foundation; HR00112020021 - Department of Defense/DARPA; 000000000000000000000000000000000000000000000000000000037211 - SRI Internationalhttps://eprint.iacr.org/2022/376.pdfAccepted manuscrip
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