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LibraryInteroperability2018Design paperCorpus record

eltoo: A Simplified Update Mechanism for Lightning

Eltoo. Christian Decker, Rusty Russell and Olaoluwa Osuntokun.

Eltoo replaces penalties with a sequence of state numbers. A later state can spend an earlier one. Nothing is confiscated. The latest number wins if it is published in time.

A reading of the public document. Not a copy of it, and not a claim about a later network that reused the name.

A channel protocol that claims 'no penalty' should say which state number wins, and which opcode the chain actually has.
Evidence
Primary paper
Re-measured
No
Assumptions
3
Records linked
4

Code

Source, repository, and what is actually hosted

  • Blockstream, 2018https://blockstream.com/eltoo.pdf
  • The source URL is not a GitHub repository. No code remote is invented.
  • Full text is not mirrored. Public availability is not a licence to copy the file onto this site.
  • Add to a reading list

01 Claim ledger

What the paper is allowed to say

Each row is a sentence already in the study. The status is the same on every row: a model claim, not a live measurement.

  1. Claim 01 · Paper model

    The defect

    Lightning's original update punishes a stale state by taking the cheater's funds. That binds channels to a penalty key and to watchtowers that must see every old state.

  2. Claim 02 · Paper model

    The rule

    Eltoo replaces penalties with a sequence of state numbers. A later state can spend an earlier one. Nothing is confiscated. The latest number wins if it is published in time.

  3. Claim 03 · Paper model

    How it is put together

    States are ordered by a number, not by a punishment transaction. Any later state can attach to an earlier published state. The chain needs a signature rule that respects that number. BIP 118 was the proposed hook.

  4. Claim 04 · Paper model

    Where the claim stops

    Eltoo was a design, not a mainnet activation.

02 Three cuts

Observation, model, falsifier

A desk does not stop at the summary. Each claim is cut three ways, using only this study's own assumptions and checks. Nothing here is a new figure.

  1. 01 The defect

    Observation

    What the study says

    Lightning's original update punishes a stale state by taking the cheater's funds. That binds channels to a penalty key and to watchtowers that must see every old state.

    Model

    What has to hold

    Eltoo was a design, not a mainnet activation.

    Falsifier

    What would retire it

    Which state number beats which?

  2. 02 The rule

    Observation

    What the study says

    Eltoo replaces penalties with a sequence of state numbers. A later state can spend an earlier one. Nothing is confiscated. The latest number wins if it is published in time.

    Model

    What has to hold

    Eltoo was a design, not a mainnet activation.

    Falsifier

    What would retire it

    Which state number beats which?

  3. 03 How it is put together

    Observation

    What the study says

    States are ordered by a number, not by a punishment transaction. Any later state can attach to an earlier published state. The chain needs a signature rule that respects that number. BIP 118 was the proposed hook.

    Model

    What has to hold

    It changes watchtower design. It does not remove the need to notice a publication.

    Falsifier

    What would retire it

    Which state number beats which?

  4. 04 Where the claim stops

    Observation

    What the study says

    Eltoo was a design, not a mainnet activation.

    Model

    What has to hold

    Eltoo was a design, not a mainnet activation.

    Falsifier

    What would retire it

    What opcode does the design require?

03 Sequence

One action, as an operating tape

  1. 01Parties sign a new state with a higher number.
  2. 02If an old state is published, the other party publishes a higher one.
  3. 03After a timeout, the highest published state settles.
  4. 04Which state number beats which?

04 Load-bearing

The argument, and where a pitch drops it

  1. Why it is still on the desk

    The cut

    A channel protocol that claims 'no penalty' should say which state number wins, and which opcode the chain actually has.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    Without the base-layer opcode, it does not run on Bitcoin.

  2. After the text

    The cut

    LN-Symmetry is the later name for this idea. Activation depends on Bitcoin consensus, which is a separate decision.

    Why it carries weight

    If this cut is skipped, the paper's name is being used without the mechanism that makes the name mean anything.

    Where it is dropped

    Eltoo was a design, not a mainnet activation.

05 Register

What has to be true

  • Model · Not re-measured

    Eltoo was a design, not a mainnet activation.

  • Model · Not re-measured

    Without the base-layer opcode, it does not run on Bitcoin.

  • Model · Not re-measured

    It changes watchtower design. It does not remove the need to notice a publication.

06 Divergence

What happened after the paper

LN-Symmetry is the later name for this idea. Activation depends on Bitcoin consensus, which is a separate decision.

A later client, parameter set, or reward formula is a different object. Cite this paper for the mechanism. Cite a primary release for the network. This desk has not re-run the proof.

07 Pre-mortem

What to check before you use the idea

  4. 0 of 3 marked on this browser. A mark is a reading note, not a pass, a rating, or a recommendation.

08 Anatomy

The paper, in the order a builder needs

The problem it names

Lightning's original update punishes a stale state by taking the cheater's funds. That binds channels to a penalty key and to watchtowers that must see every old state.

What the design proposes

  • States are ordered by a number, not by a punishment transaction.
  • Any later state can attach to an earlier published state.
  • The chain needs a signature rule that respects that number. BIP 118 was the proposed hook.

How the mechanism is specified

  • Parties sign a new state with a higher number.
  • If an old state is published, the other party publishes a higher one.
  • After a timeout, the highest published state settles.

What this page does not treat as proven

  • Eltoo was a design, not a mainnet activation.
  • Without the base-layer opcode, it does not run on Bitcoin.
  • It changes watchtower design. It does not remove the need to notice a publication.

Why the desk still reads it

A channel protocol that claims 'no penalty' should say which state number wins, and which opcode the chain actually has.

09 Lexicon

Terms, opened into the record

State number
A counter that lets a later update replace an earlier one.
Symmetry
Both parties use the same update rule, without a penalty key.

10 Repository

Every linked record on this page

Underlined words open a page that already exists: a concept, a protocol profile, a failure record, or another paper. If a word is not underlined, this desk does not have a record for it.

Concepts

This is Blockchain Lab's reading of a public design paper. It is not the paper, not a copy of it, and not an offer of tokens, equity, custody or a partnership. Later network behaviour can diverge from the text. Nothing here is investment, legal or technical advice.

Research status: Design paper. Last reviewed: 1 October 2026. This is a reading of a public paper, not investment, legal or security advice.