A major issue highlighted on the world wide web today, which is termed extremely important whenever we speak about ‘Bitcoin Forks‘ is the likelihood of ‘Replay Attacks‘. When Bitcoin forked on August 1, 2017 and ‘Bitcoin Cash’ was born, replay protection was a hot topic. When Bitcoin forked to ‘Bitcoin Gold‘ on October 25, the hype around replay protection grew as the core will be released only on November 1. On November 16, when the fork takes place, the community will stand divided, staunchly on the replay protection aspect, as this new forked blockchain core is not expected to have replay protection.
Let’s understand why replay protection is required, and before that, the concept of how two bitcoins come into existence in the first place. This is important to understand before we discuss transaction replay. Whenever Bitcoin forks, the Bitcoin chain upto the predetermined block level is split into two. From the next block onwards, two parallel but entirely different blockchains come alive. The reason we get two bitcoins is because the same address containing the bitcoin from the original chain can now be spent in both the blockchains. For example, let’s say that bitcoin cash was forked after block number 478558; so if 1 bitcoin were held in an address that was part of block number 478558, or any block before that, it can be considered that your bitcoin can be spent twice, once on the original bitcoin blockchain, and then again on bitcoin cash blockchain.