Replay Protection
A mechanism that prevents a transaction valid on one chain from also being validly replayed on a related chain after a fork.
Replay protection is a mechanism that prevents a transaction signed and broadcast on one chain from also being validly "replayed" — rebroadcast and accepted — on a related chain, most commonly the two resulting chains after a contentious hard fork (see Kaavon's "Hard Fork" glossary definition) where both chains initially share identical transaction history and rules.
Without replay protection, a user intending to transact on only one of the two post-fork chains could unintentionally have that same transaction also executed on the other chain, since both chains would initially consider it valid — a real, documented risk during several historical contentious hard forks.
Examples
- Without replay protection, a transaction intended for only one post-fork chain could unintentionally also execute on the other chain, since both initially share the same rules.
- Replay protection has been a real, documented concern during several historical contentious hard forks, specifically to prevent this unintended cross-chain execution.