Hard Fork Combinator

What Is a Hard Fork Combinator?

A hard fork combinator, originally designed by IOHK, is a tool used to merge protocols specifically on the Cardano blockchain after a hard fork has occurred.

How Does a Hard Fork Occur?

A hard fork typically happens when upgrades are implemented on the blockchain. It requires multi-partner signatures and often modifies certain parameters of the existing protocol.

A hard fork leads to the division of the blockchain into two separate protocols that run parallel to each other, with the new blockchain losing track and history of the previous one.

Usually, hard forks cause downtime on the blockchain, which disrupts transactions and user experience. Another approach is to implement a hard fork on the live blockchain, which may compromise blockchain integrity. For example, the Bitcoin hard fork in 2017 resulted in the splitting of the chain and the creation of Bitcoin Cash (BCH). This had an impact on investor and trader interests.

However, IOHK introduced the concept of a hard fork combinator to effectively address these issues.

What Is a Hard Fork Combinator (HFC)?

A hard fork combinator is primarily used to merge pre and post-upgrade protocols after a hard fork, eliminating the possibility of interruptions or restarts.

During a hard fork, it is practically impossible for all nodes to update to the new parameters and block headers simultaneously without interruptions. Therefore, it becomes necessary to bring the blockchain into downtime, which is disruptive for users.

As a solution to this problem, the IOHK Foundation developed the hard fork combinator (HFC) for the Cardano (ADA) blockchain. This allows multiple protocols to appear as one ledger, eliminating the need for all nodes to update to the new blockchain simultaneously.

In July 2020, Cardano upgraded from Byron (wallet-only protocols) to Shelley (proof-of-stake supported protocols). The hard fork modified the features and overall utility of the blockchain. With over 1 million wallets at that time, a poorly executed hard fork could have spelled disaster for Cardano and its funds.

However, the hard fork combinator was successfully utilized for the first time. On July 29, 2020, at 21:45 UTC, the transition from Byron to Shelley took place seamlessly, without any downtime or errors. Users were informed but not restricted in their usage, and the hard fork occurred in the background, allowing for a gradual transition of nodes over time.

To this day, the Cardano blockchain combines Byron and Shelley blocks. In future upgrades as well, the hard fork combinator will support the transitions.