157 citations · 815 across the 35 of their papers we have counts for
37 papers
On The Simplest Quantum-Secure Block Cipher
Gorjan Alagic, Joseph Carolan, Christian Majenz +1
Pseudorandom permutations are ubiquitous in theoretical and applied cryptography. PRPs that offer security even against adversaries making quantum queries are of increasing interes…
Compressed Permutation Oracles Revisited
Joseph Carolan, Christian Majenz
The compressed permutation oracle has been used to analyze the quantum security of a number of cryptographic constructions which resisted prior techniques. However, these analyses…
Security of the Fischlin Transform in Quantum Random Oracle Model
Christian Majenz, Jaya Sharma
The Fischlin transform yields non-interactive zero-knowledge proofs with straight-line extractability in the classical random oracle model. This is done by forcing a prover to gene…
Quantum Oracle Distribution Switching and Applications to Falcon and Ring Signatures
Marvin Beckmann, Christian Majenz
Motivated by digital signature algorithms ranging from Falcon to fully-anonymous ring signatures used in Signal-style key exchange, such as Gandalf, we revisit a fundamental proble…
Post-Quantum Security of Block Cipher Constructions
Gorjan Alagic, Chen Bai, Christian Majenz +1
Block ciphers are versatile cryptographic ingredients that are used in a wide range of applications ranging from secure Internet communications to disk encryption. While post-quant…
The Sponge is Quantum Indifferentiable
Gorjan Alagic, Joseph Carolan, Christian Majenz +1
The sponge is a cryptographic construction that turns a public permutation into a hash function. When instantiated with the Keccak permutation, the sponge forms the NIST SHA-3 stan…
Permutation Superposition Oracles for Quantum Query Lower Bounds
Christian Majenz, Giulio Malavolta, Michael Walter
We propose a generalization of Zhandry's compressed oracle method to random permutations, where an algorithm can query both the permutation and its inverse. We show how to use the…
Failing gracefully: Decryption failures and the Fujisaki-Okamoto transform
Kathrin Hövelmanns, Andreas Hülsing, Christian Majenz
In known security reductions for the Fujisaki-Okamoto transformation, decryption failures are handled via a reduction solving the rather unnatural task of finding failing plaintext…
Efficient NIZKs and Signatures from Commit-and-Open Protocols in the QROM
Jelle Don, Serge Fehr, Christian Majenz +1
Commit-and-open Sigma-protocols are a popular class of protocols for constructing non-interactive zero-knowledge arguments and digital-signature schemes via the Fiat-Shamir transfo…
Post-Quantum Security of the Even-Mansour Cipher
Gorjan Alagic, Chen Bai, Jonathan Katz +1
The Even-Mansour cipher is a simple method for constructing a (keyed) pseudorandom permutation from a public random permutation~. It is secur…
Local simultaneous state discrimination
Christian Majenz, Maris Ozols, Christian Schaffner +1
Quantum state discrimination is one of the most fundamental problems studied in quantum information theory. Applications range from channel coding to metrology and cryptography. In…
A Guide for New Program Committee Members at Theoretical Computer Science Conferences
Yfke Dulek, Stacey Jeffery, Christian Majenz +3
In theoretical computer science, conferences play an important role in the scientific process. The decisions whether to accept or reject articles is taken by the program committee…
Limitations on Uncloneable Encryption and Simultaneous One-Way-to-Hiding
Christian Majenz, Christian Schaffner, Mehrdad Tahmasbi
We study uncloneable quantum encryption schemes for classical messages as recently proposed by Broadbent and Lord. We focus on the information-theoretic setting and give several li…
Quantum-access security of the Winternitz one-time signature scheme
Christian Majenz, Chanelle Matadah Manfouo, Maris Ozols
Quantum-access security, where an attacker is granted superposition access to secret-keyed functionalities, is a fundamental security model and its study has inspired results in po…
Online-Extractability in the Quantum Random-Oracle Model
Jelle Don, Serge Fehr, Christian Majenz +1
We show the following generic result. Whenever a quantum query algorithm in the quantum random-oracle model outputs a classical value that is promised to be in some tight relat…
Tight adaptive reprogramming in the QROM
Alex B. Grilo, Kathrin Hövelmanns, Andreas Hülsing +1
The random oracle model (ROM) enjoys widespread popularity, mostly because it tends to allow for tight and conceptually simple proofs where provable security in the standard model…
Quantum copy-protection of compute-and-compare programs in the quantum random oracle model
Andrea Coladangelo, Christian Majenz, Alexander Poremba
Copy-protection allows a software distributor to encode a program in such a way that it can be evaluated on any input, yet it cannot be "pirated" - a notion that is impossible to a…
The Measure-and-Reprogram Technique 2.0: Multi-Round Fiat-Shamir and More
Jelle Don, Serge Fehr, Christian Majenz
We revisit recent works by Don, Fehr, Majenz and Schaffner and by Liu and Zhandry on the security of the Fiat-Shamir transformation of -protocols in the quantum random oracle mo…
Weak approximate unitary designs and applications to quantum encryption
Cécilia Lancien, Christian Majenz
Unitary -designs are the bread and butter of quantum information theory and beyond. An important issue in practice is that of efficiently constructing good approximations of suc…
Efficient simulation of random states and random unitaries
Gorjan Alagic, Christian Majenz, Alexander Russell
We consider the problem of efficiently simulating random quantum states and random unitary operators, in a manner which is convincing to unbounded adversaries with black-box oracle…
Secure Multi-party Quantum Computation with a Dishonest Majority
Yfke Dulek, Alex B. Grilo, Stacey Jeffery +2
The cryptographic task of secure multi-party (classical) computation has received a lot of attention in the last decades. Even in the extreme case where a computation is performed…
Non-malleability for quantum public-key encryption
Christian Majenz, Christian Schaffner, Jeroen van Wier
Non-malleability is an important security property for public-key encryption (PKE). Its significance is due to the fundamental unachievability of integrity and authenticity guarant…
Quantum Lazy Sampling and Game-Playing Proofs for Quantum Indifferentiability
Jan Czajkowski, Christian Majenz, Christian Schaffner +1
Game-playing proofs constitute a powerful framework for non-quantum cryptographic security arguments, most notably applied in the context of indifferentiability. An essential ingre…
Security of the Fiat-Shamir Transformation in the Quantum Random-Oracle Model
Jelle Don, Serge Fehr, Christian Majenz +1
The famous Fiat-Shamir transformation turns any public-coin three-round interactive proof, i.e., any so-called sigma-protocol, into a non-interactive proof in the random-oracle mod…