Segwit2x is so much in the news but all the articles get so much technical that people get completely lost. So i am going to try and explain it in simple terms in the below article.
Basic
Bitcoin is a cryptocurrency which uses the Blockchain technology. Blockchain is merely a chain of Block where the new transactions form a new block and gets attached to the previous block forming the Chain of Block.
Blocks & Limits
Blocks gets discovered roughly every 10 minutes ( Not the case with other cryptocurrences ).
When Satoshi created these things, he kept 1 MB as a limit for each block. This was during the birth of bitcoin when the block were almost empty.
Rise of Transaction fee
Bitcoin became very popular. So the number of transactions increased. 1 MB block size was not enough to hold the transactions happening in the 10 minute time frame. This caused the delay in the creation of next block. Because of this delay the senders of the transactions were pressured to increase the transaction fees. Sooner the block filled up more the transaction fee increased. Hence bitcoin trasactions became very expensive.
Solution
Eventually the Bitcoin developers had to come up with a solution and it was SegWit (SEGgregated WITness). By introducing this Segwit in their software they were able to seperate the transaction data from the signature data. So they were able to store 4 times more transactions as earlier. All weren't happy with this since they prefered to increase the block size. Increasing the block size is dangerous since it involves a hard fork. Hard Fork happens when Comuputers running new versions of software are no longer compatible with computers that run the old version. On May 23, 2017, an agreement was signed by major bitcoin comapanies and miners representing higher haspower that they will activate Segwit and agreed to double the block size around Nov 16, 2017. Hence the name Segwit2x.
Replay attack during Hard Fork
So what is a replay attack. Let's say Trump has 10 Bitcoin prior to the fork. So once the fork arrives he will have 10 Bitcoin Legacy and 10 Bitcoin New. Now let's say that Trump is sending 10 Bitcoin Legacy to Hilary. Now as this transaction becomes public, an attacker can replay the same transaction in the new chain. This is possible since the during the fork, the transactions will be valid for both Legacy and New chain. But the attacker is not going get anything in his wallet but Trump is going to loose both Bitcoin Legacy and Bitcoin New.
But do remember that possibilities are always end less
Source:
https://cointelegraph.com/news/bitcoins-upcoming-segwit2x-hard-fork-put-in-laymans-terms
https://themerkle.com/what-is-a-bitcoin-replay-attack/
https://cointelegraph.com/storage/uploads/view/ 172a2b71edf41a04092dceaf1f999977.png
