International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Alexander Russell

Affiliation: University of Connecticut

Publications

Year
Venue
Title
2019
PKC
Let a Non-barking Watchdog Bite: Cliptographic Signatures with an Offline Watchdog
We study how to construct secure digital signature schemes in the presence of kleptographic attacks. Our work utilizes an offline watchdog to clip the power of subversions via only one-time black-box testing of the implementation. Previous results essentially rely on an online watchdog which requires the collection of all communicating transcripts (or active re-randomization of messages).We first give a simple but generic construction, without random oracles, in the partial-subversion model in which key generation and signing algorithms can be subverted. Then, we give the first digital signature scheme in the complete-subversion model in which all cryptographic algorithms can be subverted. This construction is based on the full-domain hash. Along the way, we enhance the recent result of Russell et al.  (CRYPTO 2018) about correcting a subverted random oracle.
2018
EUROCRYPT
2018
CRYPTO
Correcting Subverted Random Oracles 📺
The random oracle methodology has proven to be a powerful tool for designing and reasoning about cryptographic schemes, and can often act as an effective bridge between theory and practice. In this paper, we focus on the basic problem of correcting faulty—or adversarially corrupted—random oracles, so that they can be confidently applied for such cryptographic purposes.We prove that a simple construction can transform a “subverted” random oracle—which disagrees with the original one at a negligible fraction of inputs—into a construction that is indifferentiable from a random function. Our results permit future designers of cryptographic primitives in typical kleptographic settings (i.e., with adversaries who may subvert the implementation of cryptographic algorithms but undetectable via blackbox testing) to use random oracles as a trusted black box, in spite of not trusting the implementation. Our analysis relies on a general rejection re-sampling lemma which is a tool of possible independent interest.
2017
EUROCRYPT
2017
CRYPTO
2016
ASIACRYPT
2015
EPRINT
2015
EPRINT
2014
JOFC
2011
CRYPTO
2002
EUROCRYPT
2001
EPRINT
Efficient Encryption for Rich Message Spaces Under General Assumptions
Alexander Russell Hong Wang
We present a new family of public-key encryption schemes which combine modest computational demands with provable security guarantees under only general assumptions. The schemes may be realized with any one-way trapdoor permutation, and provide a notion of security corresponding to semantic security under the condition that the message space has sufficient entropy. Furthermore, these schemes can be implemented with very few applications of the underlying one-way permutation: schemes which provide security for message spaces in $\{0,1\}^n$ with minimum entropy $n - \ell$ can be realized with $\ell + w(k)\log k$ applications of the underlying one-way trapdoor permutation. Here $k$ is the security parameter and $w(k)$ is any function which tends to infinity. In comparison, extant systems offering full semantic security require roughly $n$ applications of the underlying one-way trapdoor permutation. Finally, we give a simplified proof of a fundamental ``elision lemma'' of Goldwasser and Micali.
2001
JOFC
1995
JOFC
1992
CRYPTO