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On Bitcoin as a Public Randomness Source

Bitcoin as a beacon. Joseph Bonneau, Jeremy Clark and Steven Goldfeder.

The paper asks when a proof-of-work block hash is a safe public beacon, and how a miner can bias it by withholding or grinding.

A reading of the public paper. Not a copy, not a benchmark, and not a claim about any later network.

An on-chain lottery that uses the next block hash has to price the miner's option to throw the block away.
Evidence
Primary paper
Re-measured
No
Assumptions
3
Records linked
3

Code

Source, repository, and what is actually hosted

  • ePrint 2015/1015https://eprint.iacr.org/2015/1015
  • 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

    Contracts want a public coin that no one can bias. Bitcoin's block hashes were being used as that coin without a theorem.

  2. Claim 02 · Paper model

    The proposal

    The paper asks when a proof-of-work block hash is a safe public beacon, and how a miner can bias it by withholding or grinding.

  3. Claim 03 · Paper model

    A beacon that a miner can reject by discarding a block is not uniform.

    The cost of bias is the cost of throwing away work.

  4. Claim 04 · Paper model

    The bound

    The paper does not bless a particular gambling contract.

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

    Contracts want a public coin that no one can bias. Bitcoin's block hashes were being used as that coin without a theorem.

    Model

    What has to hold

    The paper does not bless a particular gambling contract.

    Falsifier

    What would retire it

    Who can withhold the block that supplies the randomness?

  2. 02 The proposal

    Observation

    What the study says

    The paper asks when a proof-of-work block hash is a safe public beacon, and how a miner can bias it by withholding or grinding.

    Model

    What has to hold

    The paper does not bless a particular gambling contract.

    Falsifier

    What would retire it

    Who can withhold the block that supplies the randomness?

  3. 03 A beacon that a miner can reject by discarding a block is not uniform.

    Observation

    What the study says

    The cost of bias is the cost of throwing away work.

    Model

    What has to hold

    Header chains that are not proof of work do not inherit the argument.

    Falsifier

    What would retire it

    Who can withhold the block that supplies the randomness?

  4. 04 The bound

    Observation

    What the study says

    The paper does not bless a particular gambling contract.

    Model

    What has to hold

    The paper does not bless a particular gambling contract.

    Falsifier

    What would retire it

    Who can withhold the block that supplies the randomness?

03 Sequence

One action, as an operating tape

  1. 01Take a future block hash as the candidate random value.
  2. 02Ask how many blocks a miner would withhold to move that value.
  3. 03Compare that cost with what the application pays an attacker who succeeds.
  4. 04What is the value at stake relative to the block reward?

04 Load-bearing

The argument, and where a pitch drops it

  1. What the paper is for

    The cut

    An on-chain lottery that uses the next block hash has to price the miner's option to throw the block away.

    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

    A later client, parameter or reward formula is a different object from this paragraph.

  2. What happened after

    The cut

    VDFs and RANDAO-style beacons are later designs aimed at the bias this paper names.

    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

    The paper does not bless a particular gambling contract.

05 Register

What has to be true

  • Model · Not re-measured

    The paper does not bless a particular gambling contract.

  • Network · Not re-measured

    It is not a verifiable delay function. Those are a later answer.

  • Cryptography · Not re-measured

    Header chains that are not proof of work do not inherit the argument.

06 Divergence

What happened after the paper

VDFs and RANDAO-style beacons are later designs aimed at the bias this paper names.

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

Contracts want a public coin that no one can bias. Bitcoin's block hashes were being used as that coin without a theorem.

What the design proposes

  • A beacon that a miner can reject by discarding a block is not uniform.
  • The cost of bias is the cost of throwing away work.
  • Applications that need one bit and applications that need many bits are different.

How the mechanism is specified

  • Take a future block hash as the candidate random value.
  • Ask how many blocks a miner would withhold to move that value.
  • Compare that cost with what the application pays an attacker who succeeds.

What this page does not treat as proven

  • The paper does not bless a particular gambling contract.
  • It is not a verifiable delay function. Those are a later answer.
  • Header chains that are not proof of work do not inherit the argument.

Why the desk still reads it

An on-chain lottery that uses the next block hash has to price the miner's option to throw the block away.

09 Lexicon

Terms, opened into the record

Beacon
A public random value later parties should not be able to bias.
Grinding
Retrying a puzzle or a header until the random value is favourable.

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.

Protocols

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.