Ouroboros Peras

Implementation Progress Update and Discussion

April 27, 2026

Agenda

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1. Generic voting committees + Peras instance
2. ObjectDiffusion reintroduction + PerasCertDB rework
3. Peras Testnet
4. Consensus ↔ Ledger
5. Discussion

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Disclaimer

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• Ouroboros Peras is a protocol that enables significantly faster settlement times under optimistic conditions

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• At a fixed schedule, all pools vote for a recent block
• If sufficiently many pools vote for the same block, this block receives a boost, making it unlikely to be rolled back
• Otherwise, the system enters a cooldown period, during which no voting takes place

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• More resources: https://github.com/tweag/cardano-peras#resources-on-peras�
• In these slides, “Peras” refers to the pre-alpha and caught-up version of the protocol.

See here for more information:

https://github.com/tweag/cardano-peras/blob/main/docs/pre-alpha.md

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• Past demos (recordings, slides, etc.): https://tweag.github.io/cardano-website/

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Generic voting committees +

Peras instance

Goals

• Select a subset of voters from the SPOs
• Allow Peras and Leios to reuse as much code as possible
• Easily compare across different committee selection schemes

What we have so far

• Generic voting committee API 🚀
• wFA^LS and EveryoneVotes implementations ✅🔎
• Initial BLS crypto backend for voting committees ✅
• Concrete Peras instance ✅
• BLS crypto
• Concrete votes and certificates with serialization
• Supports both wFA^LS and EveryoneVotes
• Comprehensive test suite for all the components ✅

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ObjectDiffusion reintroduction +

PerasCertDB rework

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• ObjectDiffusion is the common protocol used to diffuse certs and votes across the network�(based on a modified version of TxSubmission).�It spans both ouroboros-network and ouroboros-consensus codebases�
• Initially merged in December 2025, but reverted because of a yet-unmerged dependency on ouroboros-network
• The needed PR has been merged recently in ouroboros-network, so we were able to resume the efforts to update, review and merge the ObjectDiffusion code in ouroboros-consensus�
• This update effort also included a reworked PerasCertDB interface with a clearer STM vs IO interface (easier to understand which operation has in-memory effects VS on-disk effects)
• The newly merged version in ouroboros-consensus instantiates ObjectDiffusion for both Cert Diffusion (plugged on PerasCertDB) and Vote Diffusion (plugged on PerasVoteDB)

(the december version only included a Cert diffusion instance)

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We should be able to deploy ObjectDiffusion on the testnet very soon!

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Peras Testnet

Goals

• Environment to simulate real-world network
• Generic enough tooling to be used across developing other cardano projects
• Developer friendly - Low cognitive overhead for building and running

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Testing Workflow

• Spin up multiple nodes locally
• Simulate controlled partition or latency in the network
• Verify the results

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Peras Testnet

What we have so far

• Simulation of a network with induced latency
• A clean UI to visualise and verify

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Next steps: Visualising Peras

• We want to partition the network to allow nodes to vote for different blocks.
• We want to verify that all participants still follow the correct chain that is boosted.
• The nodes may sometimes roll back to a shorter chain that is boosted

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Peras Testnet

Try it out:

nix run github:tweag/cardano-peras#testnet

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Consensus ↔ Ledger

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• We had a joint Consensus↔Ledger (and Leios!) meeting to understand where certain parts of the Peras implementation should live in (i.e. cardano-base, cardano-ledger, or ouroboros-consensus).

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• Our take: it’s much faster to develop as much as possible within Consensus and move things later (when preparing Peras for mainnet)

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• Consensus* is that this is OK for pre-alpha Peras, but for mainnet:
• Expensive computations happening at epoch boundaries need to be done incrementally (Ledger has support for this)
• Block body serialization/validation should ideally be handled by Ledger

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[*] pun intended

Consensus ↔ Ledger

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Peras certificates in blocks 🚧

• We have extended Dijkstra block bodies with a placeholder for Peras certificates
• We are extending these placeholders with opaque (bytestring) blobs (thanks Aleks!)
• Ledger can fully encode/decode them, leaving (semantic) validation to Consensus

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Stateful voting committee handles 🚧

• Keep track of multiple voting committee compositions (last two epochs)
• Dispatch operations to the correct one (depending on the election ID of the resource)
• Recompute the current stake distribution “summary” at the beginning of each epoch
• Provide a “realized” API for forging/verifying votes and certificates
• No need to handle private keys manually when forging votes (similar to BlockForging)
• No manual error handling (most errors should trigger disconnection or crashing)

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Updated

roadmap

(link)

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THANK YOU!