



@article {2307,
	title = {Can you sign a quantum state?},
	journal = {v4: version for publication in Quantum, v5: CC license},
	year = {2021},
	month = {12/6/2021},
	abstract = {<p>Cryptography with quantum states exhibits a number of surprising and counterintuitive features. In a 2002 work, Barnum et al. argued informally that these strange features should imply that digital signatures for quantum states are impossible (Barnum et al., FOCS 2002). In this work, we perform the first rigorous study of the problem of signing quantum states. We first show that the intuition of Barnum et al. was correct, by proving an impossibility result which rules out even very weak forms of signing quantum states. Essentially, we show that any non-trivial combination of correctness and security requirements results in negligible security. This rules out all quantum signature schemes except those which simply measure the state and then sign the outcome using a classical scheme. In other words, only classical signature schemes exist. We then show a positive result: it is possible to sign quantum states, provided that they are also encrypted with the public key of the intended recipient. Following classical nomenclature, we call this notion quantum signcryption. Classically, signcryption is only interesting if it provides superior efficiency to simultaneous encryption and signing. Our results imply that, quantumly, it is far more interesting: by the laws of quantum mechanics, it is the only signing method available. We develop security definitions for quantum signcryption, ranging from a simple one-time two-user setting, to a chosen-ciphertext-secure many-time multi-user setting. We also give secure constructions based on post-quantum public-key primitives. Along the way, we show that a natural hybrid method of combining classical and quantum schemes can be used to \&quot;upgrade\&quot; a secure classical scheme to the fully-quantum setting, in a wide range of cryptographic settings including signcryption, authenticated encryption, and chosen-ciphertext security.</p>},
	url = {https://arxiv.org/abs/1811.11858},
	author = {Gorjan Alagic and Tommaso Gagliardoni and Christian Majenz}
}
@conference {1712,
	title = {Computational Security of Quantum Encryption},
	booktitle = {Computational Security of Quantum Encryption. In: Nascimento A., Barreto P. (eds) Information Theoretic Security. },
	year = {2016},
	month = {2016/11/10},
	abstract = {<p>Quantum-mechanical devices have the potential to transform cryptography. Most research in this area has focused either on the information-theoretic advantages of quantum protocols or on the security of classical cryptographic schemes against quantum attacks. In this work, we initiate the study of another relevant topic: the encryption of quantum data in the computational setting. In this direction, we establish quantum versions of several fundamental classical results. First, we develop natural definitions for private-key and public-key encryption schemes for quantum data. We then define notions of semantic security and indistinguishability, and, in analogy with the classical work of Goldwasser and Micali, show that these notions are equivalent. Finally, we construct secure quantum encryption schemes from basic primitives. In particular, we show that quantum-secure one-way functions imply IND-CCA1-secure symmetric-key quantum encryption, and that quantum-secure trapdoor one-way permutations imply semantically-secure public-key quantum encryption.</p>},
	url = {https://link.springer.com/chapter/10.1007\%2F978-3-319-49175-2_3},
	author = {Gorjan Alagic and Anne Broadbent and Bill Fefferman and Tommaso Gagliardoni and Christian Schaffner and Michael St. Jules}
}
@article {1391,
	title = {Classical simulation of Yang-Baxter gates},
	journal = {9th Conference on the Theory of Quantum Computation, Communication and Cryptography (TQC 2014)},
	volume = {27},
	year = {2014},
	month = {2014/07/05},
	pages = {161-175},
	abstract = {  A unitary operator that satisfies the constant Yang-Baxter equation
immediately yields a unitary representation of the braid group B n for every $n
\ge 2$. If we view such an operator as a quantum-computational gate, then
topological braiding corresponds to a quantum circuit. A basic question is when
such a representation affords universal quantum computation. In this work, we
show how to classically simulate these circuits when the gate in question
belongs to certain families of solutions to the Yang-Baxter equation. These
include all of the qubit (i.e., $d = 2$) solutions, and some simple families
that include solutions for arbitrary $d \ge 2$. Our main tool is a
probabilistic classical algorithm for efficient simulation of a more general
class of quantum circuits. This algorithm may be of use outside the present
setting.
},
	doi = {10.4230/LIPIcs.TQC.2014.161},
	url = {http://arxiv.org/abs/1407.1361v1},
	author = {Gorjan Alagic and Aniruddha Bapat and Stephen P. Jordan}
}
