BIP-301
Blind Merged Mining

What is BIP-301?

BIP-301, also known as "Blind Merged Mining" (BMM), is the companion proposal to BIP-300. While BIP-300 defines how sidechains are created and how deposits/withdrawals work, BIP-301 defines how sidechain blocks are produced and secured using Bitcoin's proof-of-work — without requiring Bitcoin miners to run sidechain nodes.

The key insight: Bitcoin miners don't need to understand or validate sidechain transactions. They just need to commit to sidechain block hashes in their Bitcoin blocks. The sidechain's own nodes handle validation.

The Problem BMM Solves

Traditional merged mining (as used by Namecoin) requires miners to run both the parent chain and the child chain software. This creates significant friction:

• Miners must install, configure, and maintain additional software for each merge-mined chain.
• If there are 10 sidechains, miners need 10 additional node setups.
• Most miners won't bother, leading to low merge-mining participation and weaker security.

BMM eliminates this entirely. Bitcoin miners are blind to the sidechain — they don't run it, don't validate it, and don't even know what's in the sidechain blocks they commit to.

How Blind Merged Mining Works

The BMM Request

Here's the flow:

1. Sidechain node operators build blocks

   A sidechain miner (who runs both a Bitcoin node and a sidechain node) assembles a candidate sidechain block and computes its hash.

2. They create a BMM Request on L1

   The sidechain miner creates a small Bitcoin transaction that says: "I'll pay X satoshis to whichever Bitcoin miner includes my sidechain block hash in their next block." This is the BMM bid.

3. Bitcoin miners include the highest BMM bid

   Bitcoin miners see these BMM requests as ordinary transactions with fees. They include the highest-paying one — collecting the fee without needing to know anything about the sidechain.

4. The sidechain block is confirmed

   Once the Bitcoin block is mined, the sidechain block hash is permanently committed to Bitcoin's blockchain. The sidechain network accepts this block as valid because it's backed by Bitcoin's proof-of-work.

The Key Insight: Market-Based Security

BMM creates a market for sidechain block production. Sidechain miners compete by bidding for the right to produce the next sidechain block. The revenue from sidechain transaction fees funds these bids. Bitcoin miners simply collect the highest bid as profit.

Sidechain Transaction Fees
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        v
Sidechain Miner collects fees, builds block
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        v
BMM Bid (pays Bitcoin miner to commit block hash)
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        v
Bitcoin Miner includes bid in L1 block (earns extra revenue)
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        v
Sidechain block is confirmed by Bitcoin's PoW

Security Properties

What Bitcoin Miners Guarantee

• Ordering: Only one sidechain block per Bitcoin block per sidechain slot. No forks.
• Immutability: Once committed, the sidechain block hash can't be changed without reorganizing Bitcoin itself.
• Availability: As long as at least one sidechain miner is willing to bid, blocks keep being produced.

What Bitcoin Miners Don't Guarantee

• Validity: Miners don't check if sidechain transactions are valid. That's the sidechain network's job.
• Liveness: If no one bids for sidechain blocks, the sidechain stalls (but funds remain safe via BIP-300).

BMM vs Traditional Merged Mining

BIP-301 and Coinshift

Coinshift runs on a BIP-300 sidechain whose blocks are produced via BIP-301 Blind Merged Mining. This means:

• Coinshift's sidechain blocks are as immutable as Bitcoin blocks — they're committed to Bitcoin's blockchain via BMM.
• Swap output locks are enforced by Bitcoin's proof-of-work — no one can reverse a committed sidechain block without 51%-attacking Bitcoin.
• The sidechain can run its own custom consensus rules (swap state machine, output locking, expiration) while inheriting Bitcoin-grade security for block ordering.

Together, BIP-300 + BIP-301 provide the foundation that makes Coinshift's trustless swaps possible: a sidechain that is secured by Bitcoin miners, governed by hashrate escrow, and capable of running application-specific logic like the swap protocol.