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DTSTART:20260329T030000
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DTSTAMP:20260416T053239Z
UID:1773738000@ist.ac.at
DTSTART:20260317T100000
DTEND:20260317T110000
DESCRIPTION:Speaker: Mirza Baig\nhosted by Julia Reisenbauer\nAbstract: Blo
 ckchains enable distributed consensus in permissionless settings\, where p
 articipants are unknown\, dynamically changing\, and do not trust each oth
 er. While Bitcoin\, based on Proof-of-Work (PoW)\, was the first protocol 
 in this model\, significant research has focused on permissionless protoco
 ls using alternative physical resources\, specifically Proof-of-Space (PoS
 pace) and Verifiable Delay Functions (VDFs). This thesis investigates the 
 theoretical limits and design space of longest-chain protocols in the full
 y permissionless and dynamically available settings using these three reso
 urces. First\, we address the feasibility of blockchains relying solely on
  storage as a resource. We prove a fundamental impossibility result: there
  exists no secure longest-chain protocol based exclusively on Proof-of-Spa
 ce in the fully permissionless or dynamically available settings. Further\
 , we quantify the adversarial capabilities required to execute a double-sp
 end attack. Our result formally justifies the necessity of coupling PoSpac
 e with time-dependent primitives (such as VDFs) or to move to less permiss
 ive settings (quasi-permissionless or permissioned) to ensure security.Sec
 ond\, we generalize Nakamoto-like heaviest chain consensus to protocols ut
 ilizing combinations of multiple physical resources. We analyze chain sele
 ction rules governed by a weight function Γ(S\, V\,W)\, which assigns wei
 ght to blocks based on recorded Space (S)\, VDF speed (V )\, and Work (W).
  We provide a complete classification of secure weight functions\, proving
  that a weight function is secure against private double-spend attacks if 
 and only if it is homogeneous in the timed resources (V\,W) and sub-homoge
 neous in S. This framework unifies existing protocols like Bitcoin and Chi
 a under a single theoretical model and provides a powerful tool for design
 ing new longest-chain blockchains from a mix of physical resources.
LOCATION:Moonstone Bldg / Ground floor / Seminar Room C (I24.EG.030c) and Z
 oom\, ISTA
ORGANIZER:
SUMMARY:Mirza Baig: Thesis Defense: On Secure Chain Selection Rules from Ph
 ysical Resources in a Permissionless Setting
URL:https://talks-calendar.ista.ac.at/events/6331
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