How federated Bitcoin sidechains work: pegs, functionaries, and why L-BTC is not base-layer BTC

Bitcoin sidechains are often described as "Bitcoin, but faster." That shorthand hides the real design choice. A federated sidechain moves BTC representation off the base layer into a network whose blocks and peg wallet are run by a known set of operators. Liquid is the production example built on the open-source Elements platform. L-BTC is designed to track BTC 1:1, but it does not inherit Bitcoin's proof-of-work settlement model.

What a federated sidechain is

Liquid is a federated sidechain of Bitcoin. A fixed set of functionaries — currently 15 members, with an 11-of-15 quorum — produces blocks and manages the Bitcoin peg. Functionary operators are well-known Liquid Federation entities such as exchanges and infrastructure providers.

Blocks are produced on a fixed ~1 minute schedule. There is no mining, no difficulty adjustment, and no block reward. The federation signs each block with a threshold signature scheme. Finality on the sidechain therefore comes from federation signatures, not from accumulated work.

The reference node is Elements Core, derived from Bitcoin Core. It adds Confidential Transactions, issued assets, the federated two-way peg, extra opcodes, Simplicity, and federated block signing. Elements can run as a standalone chain or as a pegged sidechain; Liquid is the production Elements-based sidechain.

The Liquid Federation vs functionaries

The Liquid Federation is a broader group of more than 80 Bitcoin-aligned businesses (exchanges, infrastructure firms, asset managers). Only a subset operates functionaries.

Functionaries are specialized servers with tamper-proof HSMs. They have two roles:

• Propose and sign Liquid blocks.
• Manage the two-way peg and secure BTC in the federation multisig wallet on Bitcoin mainchain.

With Dynamic Federations (DynaFed), the design supports adding more functionaries beyond the initial 15. Governance runs through boards (Technology, Membership, Oversight) that federation members elect.

BTC locked for the peg is held in an 11-of-15 multisig. Each of the 15 keys lives on a functionary HSM. Peg-out signing requires that threshold, so the locked BTC remains secure as long as more than two-thirds of functionaries act honestly — the model stated in Liquid documentation and the Liquid whitepaper framing.

The two-way peg, 1:1

Every L-BTC on Liquid is backed by an equivalent amount of BTC held by the Liquid Federation on Bitcoin mainchain. Peg-in sends BTC to the federation and allows claiming L-BTC. Peg-out burns L-BTC and releases BTC. Docs state there is no more L-BTC in circulation than BTC locked by the federation. A Liquid node can be used to check that the issued L-BTC supply matches federation-held BTC.

That 1:1 claim is about backing accounting, not about identical settlement risk. Help Center wording is explicit: L-BTC operates on a different security model from mainchain BTC.

Peg-in: BTC → L-BTC

Anyone with a Liquid node can initiate a peg-in. The documented path:

1. Generate a peg-in address with elements-cli getpeginaddress. This returns a Bitcoin mainchain_address and a claim_script.
2. Send BTC to that federation-controlled mainchain address (a normal Bitcoin transaction).
3. Wait for 102 Bitcoin confirmations (~17 hours). The high confirmation count exists to reduce risk from deep Bitcoin reorganizations that could unwind the deposit and create unbacked L-BTC.
4. Claim L-BTC on Liquid (wallets often automate this). The claim mints an L-BTC UTXO equal to the deposited BTC, minus fees.

Peg-in is the only way new L-BTC is issued. Many users never run a peg-in themselves; exchanges and platforms often hold L-BTC inventory and offer conversion without the full 102-confirmation wait for the end user.

Peg-out: L-BTC → BTC

Peg-out is asymmetric. Blockstream Help Center states that only Liquid Federation members can initiate a peg-out. The member burns L-BTC on the sidechain to release equal BTC from the federation mainchain multisig to a whitelisted member address.

Documented peg-out mechanics:

• Requires two Liquid confirmations before BTC can leave the federation wallet.
• Federation wallet batches peg-outs on a regular basis (Help Center: variable 20–60 minute intervals). Developer docs also describe typical processing on the order of roughly 11–35 minutes per round.
• Whitelisting / Peg-out Authorization Key (PAK) rules bind destinations so that even a compromised functionary set cannot freely redirect BTC to arbitrary attacker addresses; destinations must match authorized entries.

General users convert L-BTC back to BTC indirectly — through a federation member, exchange, or swap — rather than signing a direct federation peg-out.

What you can verify vs what you trust

Verifiable (in principle, with the right tools):

• L-BTC supply vs BTC locked in the federation multisig (1:1 backing claim).
• That Liquid blocks are federation-signed on a ~1 minute schedule, not mined.
• Peg-in confirmation requirements (102 Bitcoin blocks) and the claim path.
• That peg-out destinations are constrained by whitelist / PAK rules.

Trust / operational assumptions:

• That at least the 11-of-15 threshold of functionaries remains honest and online for block production and peg wallet operations.
• That HSMs and geographic distribution of functionaries work as designed.
• That emergency recovery paths (documentation describes a timelocked emergency-key design if the network stops processing for an extended period) are correctly administered.
• That indirect conversion venues (exchanges, swaps) settle as expected when you are not a federation member doing a direct peg-out.

What would weaken the reading: documented change to functionary count or quorum without matching multisig updates; sustained inability of the federation to process peg-outs; or a measured gap between issued L-BTC and locked BTC that node operators cannot reconcile.

Why L-BTC is not base-layer BTC

L-BTC is a sidechain asset whose supply is intended to mirror locked mainchain BTC. It shares Bitcoin's UTXO mental model and an Elements codebase descended from Bitcoin Core. It does not share:

• Proof-of-work block production or Bitcoin's difficulty adjustment.
• Permissionless exit from the peg for every holder (direct peg-out is federation-gated).
• The same failure modes: sidechain liveness and peg release depend on functionary quorum and federation operational processes, not on Bitcoin miners.

In short: L-BTC is a federated claim on BTC held in an 11-of-15 wallet, transferable under Liquid's rules (including confidential amounts by default). Base-layer BTC is settled under Bitcoin consensus. Confusing the ticker with the settlement model is the common error this design invites.

Sources

Liquid developer docs: How Liquid Works; Peg-in and Peg-out. Blockstream Help Center: What is the Liquid Federation?; How does Liquid Bitcoin (LBTC) work?; What is a Liquid peg-in?; What is a Liquid peg-out?. Elements Project overview (elementsproject.org). Figures such as 15 functionaries, 11-of-15 quorum, 102 peg-in confirmations, two Liquid confirmations for peg-out, and 20–60 minute peg-out batching are taken from those documents as of the cited pages.