Making Existential-Unforgeable Signatures Strongly Unforgeable in the Quantum Random-Oracle Model
This provides a generic method to enhance signature security for quantum-resistant cryptography, addressing a practical need in cryptographic constructions.
The paper tackles the problem of transforming existential-unforgeable signature schemes into strongly unforgeable ones against quantum adversaries, showing that a known transformation works in the quantum random-oracle model and yields an efficient quantum-secure scheme based on lattice assumptions.
Strongly unforgeable signature schemes provide a more stringent security guarantee than the standard existential unforgeability. It requires that not only forging a signature on a new message is hard, it is infeasible as well to produce a new signature on a message for which the adversary has seen valid signatures before. Strongly unforgeable signatures are useful both in practice and as a building block in many cryptographic constructions. This work investigates a generic transformation that compiles any existential-unforgeable scheme into a strongly unforgeable one, which was proposed by Teranishi et al. and was proven in the classical random-oracle model. Our main contribution is showing that the transformation also works against quantum adversaries in the quantum random-oracle model. We develop proof techniques such as adaptively programming a quantum random-oracle in a new setting, which could be of independent interest. Applying the transformation to an existential-unforgeable signature scheme due to Cash et al., which can be shown to be quantum-secure assuming certain lattice problems are hard for quantum computers, we get an efficient quantum-secure strongly unforgeable signature scheme in the quantum random-oracle model.