Amit Behera

This work gives a comprehensive picture of the relationship between quantum public-key encryption with classical keys and ciphertexts and quantum-computable one-way functions. It proves a black-box separation by constructing, relative to a unitary, real, and self-inverse oracle, quantum public-key encryption and point-function obfuscation even though quantum-computable one-way functions do not exist. On the positive side, it constructs quantum public-key encryption from quantum indistinguishability obfuscation and efficiently verifiable one-way puzzles, assumptions potentially weaker than quantum-computable one-way functions.

This work gives a BB84-based quantum position-verification protocol that, in an idealized continuous-time model, is secure against any finite coalition of LOCC adversaries with arbitrary finite quantum storage and preshared entanglement. In discrete time, the protocol remains information-theoretically secure up to an adversarial resource bound that can exceed the honest parties' total communication and storage by any desired polynomial factor. This gap grows with clock precision, leading to an “I sleep, you work” paradigm.

This work introduces correlated-challenge security for single-decryptor encryption and unclonable puncturable obfuscation, allowing the two challenge instances to be arbitrarily correlated. It proves correlated security for existing constructions under standard cryptographic assumptions and obtains the first plain-model copy-protection schemes for point functions, k-point functions, and compute-and-compare programs, as well as identical-challenge copy-protection for general puncturable functionalities.

Quantum copy-protection compiles a classical program into a functionality-preserving quantum program that cannot be duplicated. Assuming indistinguishability obfuscation and Learning with Errors, this work constructs copy-protection for puncturable cryptographic functionalities and subclasses of evasive functionalities under a stronger security definition, using a new construction of unclonable puncturable obfuscation.

This work introduces ⊥-PRGs and ⊥-PRFs whose evaluations are pseudo-deterministic except for a recognizable abort. The main application is a quantum digital-signature scheme with classical public keys and signatures from logarithmic pseudorandom states; the paper also gives CPA-secure public-key encryption with tamper-resilient quantum public keys.

This paper gives a quantum-unitary oracle relative to which QEFID pairs exist but one-way state generators do not, separating QEFID and one-way puzzles from several efficiently verifiable Microcrypt primitives. It also proves a fully black-box separation of private-key quantum money from QEFID, supporting the view that efficient verification can make a quantum primitive qualitatively stronger.

This paper introduces unclonable puncturable obfuscation (UPO) and uses it as a common abstraction for public-key quantum money, copy-protection, unclonable encryption, and single-decryption encryption. It obtains generic copy-protection for puncturably secure functionalities and broad classes of evasive functions, and proposes candidate UPO constructions from cryptographic assumptions.

This work introduces pseudorandom states with proofs of destruction: measuring the state produces a secret-key-verifiable classical certificate that the state was destroyed. These states follow from any post-quantum one-way function and let several earlier applications—including encryption, MACs, one-time signatures, commitments, and private quantum coins—use only classical communication.

A tokenized MAC delegates limited signing authority through single-use quantum tokens, each capable of signing at most one document. This work gives an elementary BB84-based construction tolerating up to 14% noise—the first noise-tolerant TMAC—and proves existential unforgeability against adversaries with signing and verification oracles.

Quantum coins use identical money states rather than serial-numbered bills, offering users greater privacy. This work lifts any private quantum coin scheme into an almost-public scheme in which a new coin is verified against coins already held using projection onto the symmetric subspace, giving the first construction close to public quantum money with provable security from standard assumptions.