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BOLT #0: Introduction and Index

Welcome, friend! These Basis of Lightning Technology (BOLT) documents describe a layer-2 protocol for off-chain bitcoin transfer by mutual cooperation, relying on on-chain transactions for enforcement if necessary.

Some requirements are subtle; we have tried to highlight motivations and reasoning behind the results you see here. I'm sure we've fallen short; if you find any part confusing or wrong, please contact us and help us improve.

This is version 0.

  1. BOLT #1: Base Protocol
  2. BOLT #2: Peer Protocol for Channel Management
  3. BOLT #3: Bitcoin Transaction and Script Formats
  4. BOLT #4: Onion Routing Protocol
  5. BOLT #5: Recommendations for On-chain Transaction Handling
  6. BOLT #7: P2P Node and Channel Discovery
  7. BOLT #8: Encrypted and Authenticated Transport
  8. BOLT #9: Assigned Feature Flags
  9. BOLT #10: DNS Bootstrap and Assisted Node Location
  10. BOLT #11: Invoice Protocol for Lightning Payments

Glossary and Terminology Guide

  • Node:

    • A computer or other device connected to the Bitcoin network.

  • Peers:

    • Nodes transacting bitcoins with one another through a channel.

  • MSAT:

    • A millisatoshi, often used as a field name.

  • Funding transaction:

    • An irreversible on-chain transaction that pays to both peers on a channel. It can only be spent by mutual consent.

  • Channel:

    • A fast, off-chain method of mutual exchange between two peers. To transact funds, peers exchange signatures to create an updated commitment transaction.

  • Commitment transaction:

    • A transaction that spends the funding transaction. Each peer holds the other peer's signature for this transaction, so that each always has a commitment transaction that it can spend. After a new commitment transaction is negotiated, the old one is revoked.

  • HTLC: Hashed Time Locked Contract.

    • A conditional payment between two peers: the recipient can spend the payment by presenting its signature and a payment preimage, otherwise the payer can cancel the contract by spending it after a given time. These are implemented as outputs from the commitment transaction.

  • Payment hash:

    • The HTLC contains the payment hash, which is the hash of the payment preimage.

  • Payment preimage:

    • Proof that payment has been received, held by the final recipient, who is the only person who knows this secret. The final recipient releases the preimage in order to release funds. The payment preimage is hashed as the payment hash in the HTLC.

  • Commitment revocation secret key:

    • Every commitment transaction has a unique commitment revocation secret-key value that allows the other peer to spend all outputs immediately: revealing this key is how old commitment transactions are revoked. To support revocation, each output of the commitment transaction refers to the commitment revocation public key.

  • Per-commitment secret:

    • Every commitment transaction derives its keys from a per-commitment secret, which is generated such that the series of per-commitment secrets for all previous commitments can be stored compactly.

  • Mutual close:

    • A cooperative close of a channel, accomplished by broadcasting an unconditional spend of the funding transaction with an output to each peer (unless one output is too small, and thus is not included).

  • Unilateral close:

    • An uncooperative close of a channel, accomplished by broadcasting a commitment transaction. This transaction is larger (i.e. less efficient) than a mutual close transaction, and the peer whose commitment is broadcast cannot access its own outputs for some previously-negotiated duration.

  • Revoked transaction close:

    • An invalid close of a channel, accomplished by broadcasting a revoked commitment transaction. Since the other peer knows the commitment revocation secret key, it can create a penalty transaction.

  • Penalty transaction:

    • A transaction that spends all outputs of a revoked commitment transaction, using the commitment revocation secret key. A peer uses this if the other peer tries to "cheat" by broadcasting a revoked commitment transaction.

  • Commitment number:

    • A 48-bit incrementing counter for each commitment transaction; counters are independent for each peer in the channel and start at 0.

  • It's ok to be odd:

    • A rule applied to some numeric fields that indicates either optional or compulsory support for features. Even numbers indicate that both endpoints MUST support the feature in question, while odd numbers indicate that the feature MAY be disregarded by the other endpoint.

  • chain_hash:

    • Used in several of the BOLT documents to denote the genesis hash of a target blockchain. This allows nodes to create and reference channels on several blockchains. Nodes are to ignore any messages that reference a chain_hash that are unknown to them. Unlike bitcoin-cli, the hash is not reversed but is used directly.

      For the main chain Bitcoin blockchain, the chain_hash value MUST be (encoded in hex): 6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000.

Theme Song

  Why this network could be democratic...
  Numismatic...
  Cryptographic!
  Why it could be released Lightning!
  (Release Lightning!)


  We'll have some timelocked contracts with hashed pubkeys, oh yeah.
  (Keep talking, whoa keep talkin')
  We'll segregate the witness for trustless starts, oh yeah.
  (I'll get the money, I've got to get the money)
  With dynamic onion routes, they'll be shakin' in their boots;
  You know that's just the truth, we'll be scaling through the roof.
  Release Lightning!
  (Go, go, go, go; go, go, go, go, go, go)


  [Chorus:]
  Oh released Lightning, it's better than a debit card..
  (Release Lightning, go release Lightning!)
  With released Lightning, micropayments just ain't hard...
  (Release Lightning, go release Lightning!)
  Then kaboom: we'll hit the moon -- release Lightning!
  (Go, go, go, go; go, go, go, go, go, go)


  We'll have QR codes, and smartphone apps, oh yeah.
  (Ooo ooo ooo ooo ooo ooo ooo)
  P2P messaging, and passive incomes, oh yeah.
  (Ooo ooo ooo ooo ooo ooo ooo)
  Outsourced closure watch, gives me feelings in my crotch.
  You'll know it's not a brag when the repo gets a tag:
  Released Lightning.


  [Chorus]
  [Instrumental, ~1m10s]
  [Chorus]
  (Lightning! Lightning! Lightning! Lightning!
   Lightning! Lightning! Lightning! Lightning!)


  C'mon guys, let's get to work!

-- Anthony Towns [email protected]

Authors

[ FIXME: Insert Author List ]

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.