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DTSTAMP:20260424T040542Z
UID:1760700600@ist.ac.at
DTSTART:20251017T133000
DTEND:20251017T143000
DESCRIPTION:Speaker: Charlotte Hoffmann\nhosted by Maximilian Jösch\nAbstr
 act: Verifiable Delay Functions (VDFs) introduced by Boneh et al. (CRYPTO'
 18) are functions that require a prescribed number of sequential steps T t
 o 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 thei
 r 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.The
  only practical VDFs known to date are based on repeated squaring in hidde
 n order groups. Consider the function VDF(x\,T)=x^(2^T). The iterated squa
 ring 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 p
 rover can compute a proof of exponentiation (PoE) \\pi. Given \\pi\, the o
 utput of VDF can be verified in time much less than T.We first present new
  constructions of statistically sound proofs of exponentiation\, which are
  an important building block in the construction of SNARKs (Succinct Non-I
 nteractive Argument of Knowledge). Statistical soundness means that the pr
 oofs remain secure against computationally unbounded adversaries\, in part
 icular\, it remains secure even when the group order is known. We thereby 
 address limitations in previous PoE protocols which either required (non-s
 tandard) hardness assumptions or a lot of parallel repetitions. Our constr
 uction significantly reduces the proof size of statistically sound PoEs th
 at allow for a structured exponent\, which leads to better efficiency of S
 NARKs and other applications.Secondly\, we introduce improved batching tec
 hniques for PoEs\, which allow multiple proofs to be aggregated and verifi
 ed with minimal overhead. These protocols optimize communication and compu
 tation complexity in large-scale blockchain environments and enable scalab
 le remote benchmarking of parallel computation resources.We then construct
  VDFs with enhanced properties such as zero-knowledge and watermarkability
 . It was shown by Arun\, Bonneau and Clark (ASIACRYPT'22) that these featu
 res enable new cryptographic primitives called short-lived proofs and sign
 atures. The validity of such proofs and signatures expires after a predefi
 ned amount of time $T$\, i.e.\, they are deniable after time $T$. Our cons
 tructions improve upon the constructions by Arun\, Bonneau and Clark in se
 veral dimensions (faster forging times\, arguably weaker assumptions).Fina
 lly\, we apply PoEs in the realm of primality testing\, providing cryptogr
 aphically sound proofs of non-primality for large Proth numbers. This work
  gives a surprising application of VDFs in the area of computational numbe
 r theory.Together\, our contributions advance both the theoretical foundat
 ions and the real-world usability of VDFs in general and in particular of 
 PoEs\, making them more adaptable and secure for current and emerging cryp
 tographic applications.
LOCATION:Central Bldg / 01 / Mondi 4 (01.01.011) and Zoom\, ISTA
ORGANIZER:
SUMMARY:Charlotte Hoffmann: Thesis Defense: Theory and Applications of Veri
 fiable Delay Functions
URL:https://talks-calendar.ista.ac.at/events/6012
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