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# System prepended metadata

title: Exploring Impossibility in Dynamically Available Protocols

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# Exploring Impossibility in Dynamically Available Protocols

Dynamically Available protocols are used as fork choice rules to get the tip of the chain until is finalised by a BFT based gadget like Casper. But until finalisation, the chain can reorg. 

LMD-GHOST is suseptible to reorg attacks like ex-ante where an honest proposers block might not be included in the canonical chain. To prevent this, protocols like GoldFish and RLMD GHOST were developed but they sacrifice on asynchrony resiliance or sub committess. 

In this blog I want to think about establishing an impossibility between these properties. 

### Setup

Lets have a network which is reorg resilliant and works under asynchrony. Now I let's try to understand the metric of number of nodes it can support. 

Currently ethereum has around 1 million total validators but in a slot only 30,000 vote. So having no sub committees mean a million signatures need to propagated and aggregated in a single slot which will greatly increase the time. 

### Split View 

To reduce the slot size, we must use a subset of these operators. Now in an asynchornous network, if we don't receive votes from some validators, then we do not know if its because of network delay or if the validator is witholding votes to execute an ex-ante attack. 

So to ensure there is no reorg attack, we cannot take a subset of validator set because controlling 51% of the entire validator set is considered practically impossible. 

From the other view, if you want sub committes then you must decide that after some bound if votes are not recieved then the validator is malicious and its vote is discarded. But having a set time bound means this mechanism would not work in asynchorny. 

Hence there exists an impossibilty that a reorg resilliant dynamically available protocol cannot have both sub sampling and asynchrony resillience. 