A sidechain is an independent blockchain that runs alongside a parent (main) blockchain, connected through a two-way peg — a mechanism that allows assets to be locked on the main chain and an equivalent amount to be released on the sidechain, and vice versa. The sidechain operates under its own consensus rules, block times, and feature set while maintaining a connection to the security and assets of the main chain.
Sidechains were first formally proposed by Adam Back, Matt Corallo, and others in a 2014 Blockstream whitepaper (“Enabling Blockchain Innovations with Pegged Sidechains”) as a way to extend Bitcoin’s functionality without requiring changes to the Bitcoin protocol itself.
How the Two-Way Peg Works
The core mechanism allowing asset movement between chains:
Moving from Main Chain to Sidechain:
- The BTC is locked (held in a multi-sig or federations wallet)
- After sufficient confirmations, an equivalent amount of “sidechain BTC” (e.g., L-BTC on Liquid) is minted on the sidechain
- User can transact freely on the sidechain
Moving from Sidechain back to Main Chain:
- After a waiting period (SPV proof or federation approval)
- An equivalent amount of BTC is released back to the user on Bitcoin mainchain
Trust Assumptions
- Federated peg: A group of known entities (a federation) holds the locked mainchain funds in multi-sig. Trust is distributed across federation members. If federation members collude, they can steal. Used by: Liquid Network
- Merged mining / Drivechain: Parent chain miners secure the sidechain; enables more decentralized peg with parent chain consensus. Used by: RSK (Rootstock), Drivechain proposals
- Cryptographic peg: Fully trustless using cryptographic proofs (SPV proofs). Not widely deployed due to complexity; requires validation of sidechain headers on Bitcoin
Major Bitcoin Sidechains
The following sections cover this in detail.
Liquid Network (Blockstream)
- Peg mechanism: 11-of-15 federation (major exchanges and Bitcoin companies)
- Features: Confidential transactions (hidden amounts), fast 2-minute blocks, Issued Assets (custom tokens)
- Users: Primarily exchanges and institutional traders settling BTC between each other
- Native asset: L-BTC (liquid bitcoin, 1:1 BTC peg)
RSK (Rootstock)
- Peg mechanism: Merged mining with Bitcoin (miners produce RSK blocks simultaneously)
- Features: Full EVM compatibility — Solidity/Ethereum contracts run on RSK using BTC as gas
- Use case: Brings DeFi to Bitcoin’s liquidity; Bitcoin holders earn yield through RSK DeFi
Stacks Blockchain
- Not technically a sidechain but functionally adjacent
Ethereum Sidechains
Polygon PoS operates as an Ethereum sidechain (technically a commit chain):
- Polygon validators run separately from Ethereum
- State roots are checkpointed to Ethereum periodically
- Different security model from Ethereum L2 rollups — Polygon PoS security depends on its own 100-validator set, not Ethereum validators
Gnosis Chain (formerly xDai):
- An EVM sidechain to Ethereum
- Uses DAI as its native currency for gas
- Fast finality, low fees; known for real-world use cases
Sidechains vs. L2 Rollups
| Property | Sidechain | L2 Rollup |
|---|---|---|
| Security source | Own validators/federation | Inherited from parent chain |
| Data posted to parent | Only state roots (if at all) | Full transaction data (calldata/blobs) |
| Trust model | Trust in the sidechain’s validators | Trust only required for fraud/validity proof |
| Example | Polygon PoS, Liquid, RSK | Optimism, Arbitrum, zkSync |
Sidechains sacrifice some of the parent chain’s security for performance/flexibility; L2 rollups inherit full parent chain security.
Common Misconceptions
“Polygon is an Ethereum L2”
Polygon PoS is a sidechain (or “commit chain”), not an L2 rollup. It has its own validator set and doesn’t inherit Ethereum’s security for transaction validity. Polygon zkEVM is an actual ZK-rollup L2; Polygon PoS is not.
“Sidechains are less legitimate than L2s”
Sidechains predate L2 rollups conceptually and serve different use cases. Liquid Network is used by major Bitcoin institutions daily. RSK has real deployed DeFi protocols. The trust trade-offs are different, not inherently worse for all use cases.
Social Media Sentiment
Sidechains are a well-understood concept in the crypto developer community but have somewhat lost the narrative to L2 rollups, especially in the Ethereum ecosystem. Bitcoin sidechains (Liquid, RSK) are respected tools but remain niche — the Bitcoin community is generally skeptical of complexity additions. The Drivechain debate is ongoing and contentious in Bitcoin circles. Ethereum sidechains like Polygon PoS are sometimes criticized for misrepresenting themselves as L2s, generating legitimate technical debate about the difference.
Last updated: 2026-04
Related Terms
Sources
- Back, A., Corallo, M., Dashjr, L., Friedenbach, M., Maxwell, G., Miller, A., Poelstra, A., Timón, J., & Wuille, P. (2014). Enabling Blockchain Innovations with Pegged Sidechains. Blockstream.
- Lerner, S. D. (2015). RSK: The Security of Merged Mining and the RSK Sidechain Protocol. Rootstock Technical Blog.
- Zamyatin, A., Harz, D., Lind, J., Panayiotou, P., Gervais, A., & Knottenbelt, W. (2019). XCLAIM: Trustless, Interoperable Cryptocurrency-Backed Assets. IEEE S&P.