Peg-Guard

A peg-guard is a security mechanism in a sidechain peg system designed to prevent fraudulent withdrawals - especially the catastrophic failure mode where a bug or attack lets someone "print" pegged BTC out of thin air, creating sidechain tokens that aren't backed by actual mainnet BTC reserves.

What a peg-guard needs to protect against:

• Sidechain consensus bugs. A bug that lets invalid blocks pass could create sidechain tokens that shouldn't exist. If those tokens then get peg-out approval, real BTC drains from the locked reserve.
• Inflation in sidechain code. Software bugs that issue more sidechain tokens than were locked via peg-ins.
• Collusion among peg operators. Federation members signing peg-outs not backed by valid peg-ins.

Common peg-guard implementations:

• Multi-signature thresholds on peg-out. Requiring 11 of 15 functionary signatures means a single rogue operator can't drain funds. Used by Liquid.
• Independent validation. Each signer checks the sidechain state and the peg-out request before signing. This catches a bad peg-out only if the checking software itself is sound. If every signer runs the same flawed code, they can all accept the bad coins.
• Audit reserves. Some sidechains publish proof-of-reserves regularly so users can verify the peg backing matches the issued tokens. Liquid's peg wallet is public, and mempool's Liquid explorer shows its BTC next to the L-BTC in circulation.
• Slow withdrawal windows (drivechain style). Long delays before peg-outs finalize give time to detect anomalies.

In Liquid specifically, the "peg-guard" framing isn't formally branded, but several layers do the job. Each functionary's hardware module signs a peg-out only if the coins go back to the federation or to an address registered under a member's peg-out authorization key (PAK), and changes to the PAK list take three days. The federation's charter tells members to keep the wallet that receives their peg-out BTC offline, so a payout against bad coins can still be caught before it moves on. There is no separate check that the reserve still matches the L-BTC in circulation; the functionaries rely on the sidechain's own validation. In September 2026 that validation failed: a bug let an attacker create about 4,000 unbacked L-BTC, the functionaries signed a peg-out of about 3,996 BTC, and the member whose service processed it had kept its peg-out key online and forwarded the BTC automatically. The attacker later returned 3,400 BTC (see Liquid Network).

For users, the peg-guard isn't directly visible but is part of what makes a sidechain peg trustworthy enough to use at scale. A sidechain with a strong peg-guard is one where consensus bugs don't immediately drain the BTC reserve.