---
res:
  bibo_abstract:
  - "Verifiable Delay Functions (VDFs) introduced by Boneh et al. (CRYPTO'18) are
    functions that require a prescribed number of sequential steps T to evaluate,
    yet their output can be verified in time much faster than T. Since their introduction,
    VDFs have gained a lot of attention due to their applications in blockchain protocols,
    randomness beacons, timestamping and deniability. This thesis explores the theory
    and applications of VDFs, focusing on enhancing their soundness, efficiency and
    practicality.\r\n\r\nThe only practical VDFs known to date are based on repeated
    squaring in hidden order groups. Consider the function VDF(x,T)=x^(2^T).\r\nThe
    iterated squaring assumption states that, for a random group element x, the result
    of VDF cannot be computed significantly faster than performing T sequential squarings
    if the group order is unknown. To make the result verifiable a prover can compute
    a proof of exponentiation (PoE) \\pi. Given \\pi, the output of VDF can be verified
    in time much less than T.\r\n\r\nWe first present new constructions of statistically
    sound proofs of exponentiation, which are an important building block in the construction
    of SNARKs (Succinct Non-Interactive Argument of Knowledge). Statistical soundness
    means that the proofs remain secure against computationally unbounded adversaries,
    in particular, it remains secure even when the group order is known. We thereby
    address limitations in previous PoE protocols which either required (non-standard)
    hardness assumptions or a lot of parallel repetitions. Our construction significantly
    reduces the proof size of statistically sound PoEs that allow for a structured
    exponent, which leads to better efficiency of SNARKs and other applications.\r\n\r\nSecondly,
    we introduce improved batching techniques for PoEs, which allow multiple proofs
    to be aggregated and verified with minimal overhead. These protocols optimize
    communication and computation complexity in large-scale blockchain environments
    and enable scalable remote benchmarking of parallel computation resources.\r\n\r\nWe
    then construct VDFs with enhanced properties such as zero-knowledge and watermarkability.
    It was shown by Arun, Bonneau and Clark (ASIACRYPT'22) that these features enable
    new cryptographic primitives called short-lived proofs and signatures. The validity
    of such proofs and signatures expires after a predefined amount of time T, i.e.,
    they are deniable after time T. Our constructions improve upon the constructions
    by Arun, Bonneau and Clark in several dimensions (faster forging times, arguably
    weaker assumptions).\r\n\r\nFinally, we apply PoEs in the realm of primality testing,
    providing cryptographically sound proofs of non-primality for large Proth numbers.
    This work gives a surprising application of VDFs in the area of computational
    number theory.\r\n\r\nTogether, our contributions advance both the theoretical
    foundations and the real-world usability of VDFs in general and in particular
    of PoEs, making them more adaptable and secure for current and emerging cryptographic
    applications.@eng"
  bibo_authorlist:
  - foaf_Person:
      foaf_givenName: Charlotte
      foaf_name: Hoffmann, Charlotte
      foaf_surname: Hoffmann
      foaf_workInfoHomepage: http://www.librecat.org/personId=0f78d746-dc7d-11ea-9b2f-83f92091afe7
    orcid: 0000-0003-2027-5549
  bibo_doi: 10.15479/AT-ISTA-20556
  dct_date: 2025^xs_gYear
  dct_isPartOf:
  - http://id.crossref.org/issn/2663-337X
  dct_language: eng
  dct_publisher: Institute of Science and Technology Austria@
  dct_title: Theory and applications of verifiable delay functions@
...