Quantum Hardcore Functions by Complexity-Theoretical Quantum List Decoding

  • Authors:
  • Akinori Kawachi;Tomoyuki Yamakami

  • Affiliations:
  • kawachi@is.titech.ac.jp;TomoyukiYamakami@gmail.com

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 2010

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Abstract

Hardcore functions have been used as a technical tool to construct secure cryptographic systems; however, little is known on their quantum counterpart, called quantum hardcore functions. With a new insight into fundamental properties of quantum hardcores, we present three new quantum hardcore functions for any (strong) quantum one-way function. We also give a “quantum” solution to Damgård's question [Advances in Cryptology, Lecture Notes in Comput. Sci. 403, Springer, Berlin, 1990, pp. 163-172] on a classical hardcore property of his pseudorandom generator by proving its quantum hardcore property. Our major technical tool is the new notion of quantum list-decoding of “classical” error-correcting codes (rather than “quantum” error-correcting codes), which is defined on the platform of computational complexity theory and computational cryptography (rather than information theory). In particular, we give a simple but powerful criterion that makes a polynomial-time computable classical block code (seen as a function) a quantum hardcore for all quantum one-way functions. On their own interest, we construct efficient quantum list-decoding algorithms for classical block codes whose associated quantum states (called codeword states) form a nearly phase-orthogonal basis.