Sidechain

A sidechain is an independent blockchain that connects to a parent blockchain (often called the mainchain or mainnet) through a two-way peg or bridge. This connection lets users move crypto assets from the mainchain onto the sidechain and back again, while the sidechain runs its own rules, validators, and upgrade path.

When assets transfer to a sidechain, they are typically locked on the mainchain and an equivalent representation becomes usable on the sidechain. Later, the sidechain can release proof that the assets should be unlocked back on the mainchain. Depending on the design, this “two-way” movement can be enforced by cryptographic verification, a set of designated validators (a federation), or a bridge mechanism that tracks deposits and withdrawals. Because the sidechain has its own consensus mechanism, it can confirm transactions differently from the parent chain, for example with faster block times or alternative security assumptions.

Sidechains are commonly used to add functionality that is difficult to implement directly on a conservative base layer like Bitcoin, such as richer smart contracts, new transaction types, or more flexible scripting. They can also help with scalability by moving activity off the mainchain while still keeping a pathway back to the primary asset. For instance, a Bitcoin-pegged sidechain can enable BTC to be used in applications that require different features than Bitcoin’s base layer provides, without changing Bitcoin’s core protocol.

Sidechains can improve experimentation and interoperability, but they often introduce additional trust or complexity, especially around the bridge and its security model. If a sidechain or its peg mechanism fails, users may face risks even if the parent chain remains secure.