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Ouroboros Praos: An Adaptively-Secure, Semi-synchronous Proof-of-Stake Protocol

Ouroboros Praos. Bernardo David, Peter Gaži, Aggelos Kiayias and Alexander Russell.

Praos hides who the slot leader is until they speak, and it tolerates a semi-synchronous delay, so an adaptive adversary cannot target the leader in advance.

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

If a proof-of-stake chain publishes the next leader before the slot, it has given up the property this paper added.
Evidence
Primary paper
Re-measured
No
Assumptions
3
Records linked
3

Code

Source, repository, and what is actually hosted

  • ePrint 2017/573https://eprint.iacr.org/2017/573
  • 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

    The first Ouroboros proof assumed a synchronous network and a stake distribution the adversary could not react to inside an epoch.

  2. Claim 02 · Paper model

    The rule

    Praos hides who the slot leader is until they speak, and it tolerates a semi-synchronous delay, so an adaptive adversary cannot target the leader in advance.

  3. Claim 03 · Paper model

    How it is put together

    Leaders are elected by a verifiable random function on the stake snapshot. The VRF output is private until the block is published. Empty slots are normal. The chain grows when someone speaks.

  4. Claim 04 · Paper model

    Where the claim stops

    Praos is not the Cardano network's parameter page.

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

    The first Ouroboros proof assumed a synchronous network and a stake distribution the adversary could not react to inside an epoch.

    Model

    What has to hold

    Praos is not the Cardano network's parameter page.

    Falsifier

    What would retire it

    What delay does semi-synchronous mean in this deployment?

  2. 02 The rule

    Observation

    What the study says

    Praos hides who the slot leader is until they speak, and it tolerates a semi-synchronous delay, so an adaptive adversary cannot target the leader in advance.

    Model

    What has to hold

    Adaptive security here is about rushing the leader, not about smart-contract bugs.

    Falsifier

    What would retire it

    Is the slot leader hidden until the block?

  3. 03 How it is put together

    Observation

    What the study says

    Leaders are elected by a verifiable random function on the stake snapshot. The VRF output is private until the block is published. Empty slots are normal. The chain grows when someone speaks.

    Model

    What has to hold

    Adaptive security here is about rushing the leader, not about smart-contract bugs.

    Falsifier

    What would retire it

    Is the slot leader hidden until the block?

  4. 04 Where the claim stops

    Observation

    What the study says

    Praos is not the Cardano network's parameter page.

    Model

    What has to hold

    Praos is not the Cardano network's parameter page.

    Falsifier

    What would retire it

    Is the slot leader hidden until the block?

03 Sequence

One action, as an operating tape

  1. 01A party checks locally whether their key won the slot.
  2. 02They extend the chain the fork-choice rule prefers.
  3. 03Other parties verify the VRF and the stake that was allowed to win.
  4. 04Is the slot leader hidden until the block?

04 Load-bearing

The argument, and where a pitch drops it

  1. Why it is still on the desk

    The cut

    If a proof-of-stake chain publishes the next leader before the slot, it has given up the property this paper added.

    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

    Adaptive security here is about rushing the leader, not about smart-contract bugs.

  2. After the text

    The cut

    Cardano's later protocol lineage cites Praos. Delegation, rewards and governance are separate documents.

    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

    Praos is not the Cardano network's parameter page.

05 Register

What has to be true

  • Network · Not re-measured

    Praos is not the Cardano network's parameter page.

  • Model · Not re-measured

    It does not set a yield.

  • Model · Not re-measured

    Adaptive security here is about rushing the leader, not about smart-contract bugs.

06 Divergence

What happened after the paper

Cardano's later protocol lineage cites Praos. Delegation, rewards and governance are separate documents.

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

The first Ouroboros proof assumed a synchronous network and a stake distribution the adversary could not react to inside an epoch.

What the design proposes

  • Leaders are elected by a verifiable random function on the stake snapshot.
  • The VRF output is private until the block is published.
  • Empty slots are normal. The chain grows when someone speaks.

How the mechanism is specified

  • A party checks locally whether their key won the slot.
  • They extend the chain the fork-choice rule prefers.
  • Other parties verify the VRF and the stake that was allowed to win.

What this page does not treat as proven

  • Praos is not the Cardano network's parameter page.
  • It does not set a yield.
  • Adaptive security here is about rushing the leader, not about smart-contract bugs.

Why the desk still reads it

If a proof-of-stake chain publishes the next leader before the slot, it has given up the property this paper added.

09 Lexicon

Terms, opened into the record

VRF
A function only the key holder can evaluate, and anyone can check.
Adaptive adversary
One that can corrupt a party after seeing who must speak.

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.