What is hard fork in the first place? It is when cryptomining and, specifically, client nodes stop agreeing on the protocol rules but keep on sharing the blockchain or permanent transaction ledger made previously one the shared platform. From technical standpoint, a hard fork comes into existence after completion of mining process for the first block of the new chain, although in fact the hard fork chain has to stay alive a lot longer than just one block for everybody else to view it as viable.
A hard fork differs from software fork, where the code is merely utilized for building various products with either little or big changes. Everything in-between Dash and Litcecoin Cash can be considered a software fork of BTC.
The best case of hard fork in the last year’s fork of Bitcoin Cash away from Bitcoin Core. Up to the point when blocks were mined in last year’s August, the BCH blockchain was matching that of Bitcoin, but from that day onwards it transformed into its own entity and step by step gathered its own community, services, and divisions.
What is a replay attack? It is an event where transaction details from on blockchain can be exploited on the other. If it were to take place in BCH when the fork had just occurred, this is how it would have go: a person performs a transaction using one blockchain and then the receiving person utilizes the transaction details to obtain coins on the other blockchain from the sender without his permission to do so.
In the upcoming BCH fork, which is supposed to end up becoming at least two different version of BCH, no native protection from replay attacks will be provided. In all previous hard fork cases, such protection had been provided by at least one of the dev teams.
When the fork takes place, it is advised to refrain from any transactions at all. The customer has to make a decision for themselves as to which iteration of BCH they are intending to utilize the most and keep their digital wallet on that blockchain.
After that, the customer has to install the other version, retrieve their tokens on that blockchain, and sweep all of them to their new address on that blockchain. This way the assets will not be exposed to the risks of replay attacks due to the fact that the tokens are now stored at different addresses between the blockchains. If the customer fails to do so, they are exposing themselves to the risks of replay attacks.