schmidty

bitcoin

Last week many Bitcoin Core developers met up in Frankfurt, Germany as part of their regular twice-yearly in person meetings.

Attendees volunteered to take notes on the unconference-style sessions and I have a pull request to add the notes to the BTC transcripts website:

- ASMap
- Batch Validation
- Secp256k1 and quantum
- CISA
- Cluster mempool
- CMake
- CoreCheck
- Debugging
- Fuzzamoto
- Libsha
- Multiprocess and Mining Interface
- Fingerprinting
- Net / net_processing split
- Package relay
- Private broadcast
- Security audit
- Subject matter experts and working groups
- Sockets abstraction

Additional informal discussions, code reviews, working groups, or other sessions occurred on:

- BIP 3
- Wallet priorities
- Compact Block prefills
- Silent Payments
- btck
- CI
- SwiftSync
- Benchmarking and IBD
- When do Bitcoin Core users upgrade?
- MuSig2
- Kernel
- Working in-person
- Complications with fuzz testing
- BlockTemplateManager
- QML GUI
- Shared Templates BIP
- Headers-first sync
- Batch Validation
- FIBRE
- Consensus Cleanup
- Silent payments libsecp256k1 light client
- Better communicating with the broad community
- Discussion on block 920138 and Bitcoin Core #33687
- Mempool and relay policy
- CI with CTest and CDash

This meeting was sponsored by BTrust who provided the funding for the venue, food, supplies, etc to facilitate the meeting (thank you!).

JD (from localhost research), Emily (from Brink) and myself organized.

A list of previous meetings is here: https://coredev.tech

The PR to the http://btctranscripts.com website is open here, pending approval:
https://github.com/bitcointranscripts/bitcointranscripts/pull/593

Bitcoin Core Developer Event - Frankfurt, Germany

Bitcoin Optech newsletter #378 is here:

- announces four vulnerabilities affecting older versions of the Bitcoin Core full node
- summarizes popular Q&A from Stack Exchange
- Optech Newsletter #378 Podcast
https://bitcoinops.org/en/newsletters/2025/10/31/

Antoine Poinsot recently posted to the Bitcoin-Dev mailing list four Bitcoin Core security advisories for low-severity vulnerabilities that were fixed in Bitcoin Core 30.0...
https://bitcoinops.org/en/newsletters/2025/10/31/#disclosure-of-four-low-severity-vulnerabilities-in-bitcoin-core

Selected Q&A from Bitcoin Stack Exchange:
- Why was -datacarriersize redefined in 2022, and why was the 2023 proposal to expand it not merged?
- What is the smallest valid transaction that can be included in a block?
- Why does Bitcoin Core continue to give witness data a discount even when it is used for inscriptions?
- The ever-growing Bitcoin blockchain size?
- I read that OP_TEMPLATEHASH is a variant of OP_CTV. How do they differ?
https://bitcoinops.org/en/newsletters/2025/10/31/#selected-qa-from-bitcoin-stack-exchange

Bitcoin Optech will host an audio recap discussion of this newsletter on Riverside.fm Tuesday at 16:30 UTC. Join us to discuss or ask questions!
https://riverside.fm/studio/bitcoin-optech

Bitcoin Optech Newsletter #378

Abubakar Sadiq Ismail and Carla Kirk-Cohen joined Optech to discuss Newsletter #377:

- Detecting block template feerate increases using cluster mempool
- Channel jamming mitigation simulation results and updates
- BULL wallet launches, Sparrow 2.3.0 released
- And more

You can listen on our website:
https://bitcoinops.org/en/podcast/2025/10/28/

Fountain:
https://fountain.fm/episode/8ax8Sb0R5uFGbVnvja6L 

Spotify:
https://open.spotify.com/episode/0tCMF2SY7a0RIBj0OPaoqM

Apple Podcasts:
https://podcasts.apple.com/us/podcast/bitcoin-optech-newsletter-377-recap/id1674626983?i=1000734046586 

Bitcoin Optech Newsletter #377 Recap Podcast

Francesco Madonna and supertestnet joined Optech to discuss Newsletter #376:

- Continued discussion of block template sharing
- B-SSL a Secure Bitcoin Signing Layer
- Bitcoin Core 30.0
- And more

You can listen on our website:
https://bitcoinops.org/en/podcast/2025/10/21/

Spotify:
https://open.spotify.com/episode/2aZv1l0GhSlUSoerkK0rgs

Apple Podcasts:
https://podcasts.apple.com/us/podcast/bitcoin-optech-newsletter-376-recap/id1674626983?i=1000733913844


Bitcoin Optech Newsletter #376 Recap Podcast

Bitcoin Optech newsletter #377 is here:

- summarizes an idea to use cluster mempool to detect block template feerate increases
- shares an update on channel jamming mitigation simulation results
- summarizes changes to services/client software
- Optech Newsletter #377 Podcast
https://bitcoinops.org/en/newsletters/2025/10/24/

Abubakar Sadiq Ismail recently posted to Delving Bitcoin about the possibility of tracking the potential fee increase from each mempool update to provide a new block template to miners only when the fee rate improvement justifies it...
https://bitcoinops.org/en/newsletters/2025/10/24/#detecting-block-template-feerate-increases-using-cluster-mempool

Carla Kirk-Cohen, in collaboration with Clara Shikhelman and elnosh, posted to Delving Bitcoin about their simulation results and updates with the reputation algorithm for their channel jamming mitigation proposal...
https://bitcoinops.org/en/newsletters/2025/10/24/#channel-jamming-mitigation-simulation-results-and-updates

Changes to services and client software:
- BULL wallet launches
- Sparrow 2.3.0 released
https://bitcoinops.org/en/newsletters/2025/10/24/#changes-to-services-and-client-software

Bitcoin Optech will host an audio recap discussion of this newsletter on Riverside.fm Tuesday at 16:30 UTC. Join us to discuss or ask questions!
https://riverside.fm/studio/bitcoin-optech


Bitcoin Optech Newsletter #377

Bitcoin Core v30: a deeper look

Testing the software to ensure no bugs, etc.

Well that image export of it didnt work, sorry about that.

What is in Bitcoin Core v30? 

This is a link to my twitter thread on the topic.
https://x.com/bitschmidty/status/1976692672023667057

![](https://m.stacker.news/111648)

Bitcoin Optech newsletter #375 is here:

- describes research into tradeoffs between usability and security in threshold signatures
- summarizes an approach to convert nested threshold signatures into a single-layer signing group
- examines the extent to which data could be embedded in the UTXO set under a restrictive set of rules
- recaps the "Compact block harness" PR Review Meeting
- Optech Newsletter #375 Podcast
https://bitcoinops.org/en/newsletters/2025/10/10/

Sindura Saraswathi posted research, co-authored by her and Korok Ray, to Delving Bitcoin about determining the optimal threshold for a multisignature scheme...
https://bitcoinops.org/en/newsletters/2025/10/10/#optimal-threshold-signatures

ZmnSCPxj posted to Delving Bitcoin to describe how to avoid using nested schnorr signatures in some cases that have not been proven safe...
https://bitcoinops.org/en/newsletters/2025/10/10/#flattening-certain-nested-threshold-signatures

Adam “Waxwing” Gibson started a discussion on the mailing list about the extent to which data could be embedded in the UTXO set under a restrictive set of rules for Bitcoin transactions...
https://bitcoinops.org/en/newsletters/2025/10/10/#theoretical-limitations-on-embedding-data-in-the-utxo-set

'Compact block harness' is a PR by Crypt-iQ that increases the fuzz test coverage by adding a test harness for the compact block relay logic...
https://bitcoinops.org/en/newsletters/2025/10/10/#bitcoin-core-pr-review-club

Bitcoin Optech will host an audio recap discussion of this newsletter on Riverside.fm Tuesday at 16:30 UTC. Join us to discuss or ask questions!
https://riverside.fm/studio/bitcoin-optech 

Bitcoin Optech Newsletter #375

Mark “Murch” Erhardt and Mike Schmidt are joined by Gustavo Flores Echaiz to discuss Newsletter #374:

- The script restoration BIPs
- A BDK Wallet release and release candidates from Bitcoin Core and LND
- Our weekly notable code segment

You can listen on our website:
https://bitcoinops.org/en/podcast/2025/10/07/ 

Fountain:
https://fountain.fm/episode/bN5DD679k2z2NLqaNvHQ 

Spotify:
https://open.spotify.com/episode/2Fpd2NSKSAFydTy02y9cUv

Apple Podcasts:
https://podcasts.apple.com/us/podcast/bitcoin-optech-newsletter-374-recap/id1674626983?i=1000730656614

Bitcoin Optech Newsletter #374 Recap Podcast

Some thoughts on Bitcoin Core developer funding

That this was a public venue I thought good to highlight that independence for onlookers as well.

Bitcoin Optech newsletter #374 is here:

- links to the draft BIPs for Script Restoration
- Bitcoin Core 30.0rc2
- Optech Newsletter #374 Podcast
https://bitcoinops.org/en/newsletters/2025/10/03/

Rusty Russell posted to the Bitcoin-Dev mailing list a summary and four BIPs in various stages of draft relating to a proposal to restore Script’s capabilities in a new tapscript version...
https://bitcoinops.org/en/newsletters/2025/10/03/#draft-bips-for-script-restoration

Bitcoin Optech will host an audio recap discussion of this newsletter on Riverside.fm Tuesday at 16:30 UTC. Join us to discuss or ask questions!
https://riverside.fm/studio/bitcoin-optech

Bitcoin Optech Newsletter #374

Matt Morehouse, Daniela Brozzoni, and Gustavo Flores Echaiz joined Optech to discuss Newsletter #373:

- Eclair vulnerability
- Research into feerate settings
- 12 Bitcoin Stack Exchange questions with an OP_RETURN focus
- Bitcoin Core 30.1 release candidate and testing guide
- And more

You can listen on our website: https://bitcoinops.org/en/podcast/2025/09/30/

Fountain: https://fountain.fm/episode/HUKeJE4y8iPGSD9WL4VS

Spotify: https://open.spotify.com/episode/55tV1tepMDPFtcONy8kHQI

Apple Podcasts: https://podcasts.apple.com/us/podcast/bitcoin-optech-newsletter-373-recap/id1674626983?i=1000729551630

Bitcoin Optech Newsletter #373 Recap Podcast

I posted this on X/Twitter the other day and perhaps folks here would be interested in the perspective. The posts tags many individuals and organizations (so much so that Twitter made me split it into 2 tweets) so its harder to reproduce here. 

https://x.com/bitschmidty/status/1971612924180369799
https://x.com/bitschmidty/status/1971612926462329199

Dont believe the catastrophizing - a perspective on Bitcoin development

Hey @theariard Im not sure what you mean. This was just me being overly-communicative on the independence of the engineers we sponsor at Brink.

Fuzz testing and Bitcoin Core...

We received a pretty overwhelming response to our recent job post for a Bitcoin Core Fuzzing Internship at Brink.

Brink received over 70 applications for the role with many qualified candidates.

After the results of a coding challenge, we decided to actually move forward with two engineers for the 3 month role.

Dongjia Zhang is a Ph.D. fuzzing researcher and maintainer of the LibAFL fuzzing library used to fuzz test Bitcoin Core.

Stratos has a background in vulnerability research and will join Dongjia in working with Niklas in the coming months to enhance the fuzz testing capabilities in Bitcoin Core.

Fuzz testing is the idea of throwing a bunch of quasi-random inputs at various functions of a codebase and seeing if anything abnormal happens. Think of it like mining for bugs.

There is work in both the Bitcoin Core codebase as well as fuzz tooling (like fuzzamoto) in order to test more and more of Bitcoin Core in this way.

Here is a bit more about fuzz testing in Bitcoin Core: https://brink.dev/blog/2023/07/14/fuzzing/

Here is a conversation we had with Matt Morehouse on fuzz testing the Lightning Network:
https://brink.dev/blog/2024/06/25/eng-call-fuzz-testing-lightning/

Marco recently completed his year long onsite fuzzing fellowship at Brink and provided some thoughts as well: https://brink.dev/blog/2025/07/31/marco-fuzzing-fellowship/

Brink is proud to support the build out of further fuzzing capabilities in the Bitcoin Core codebase as well as other ecosystem softwares. We have not had intern roles before either and are excited to see how it works out.

Welcome Dongjia and Stratos!
https://brink.dev/programs#brink_interns 

Brink announces funding for two fuzz testing interns for Bitcoin Core

Bitcoin Optech Newsletter #373 is here:

- summarizes a vulnerability affecting old versions of Eclair
- summarizes research into full node feerate settings
- summarizes popular Q&A from Stack Exchange
- Optech Newsletter #373 Podcast
https://bitcoinops.org/en/newsletters/2025/09/26/

Matt Morehouse posted to Delving Bitcoin to announce the responsible disclosure of a vulnerability affecting older versions of Eclair...
https://bitcoinops.org/en/newsletters/2025/09/26/#eclair-vulnerability

Daniela Brozzoni posted to Delving Bitcoin the results of a scan of almost 30,000 full nodes that were accepting incoming connections...
https://bitcoinops.org/en/newsletters/2025/09/26/#research-into-feerate-settings

Selected Q&A from Bitcoin Stack Exchange:
- Implications of OP_RETURN changes in upcoming Bitcoin Core version 30.0?
- If OP_RETURN relay limits are ineffective, why remove the safeguard instead of keeping it as a default discouragement?
- What are the worst-case stress scenarios from uncapped OP_RETURNs in Bitcoin Core v30?
- If OP_RETURN needed more room, why was the 80-byte cap removed instead of being raised to 160?
- If arbitrary data is inevitable, does removing OP_RETURN limits shift demand toward more harmful storage methods (like UTXO-inflating addresses)?
- If OP_RETURN uncapping doesn’t increase the UTXO set, how does it still contribute to blockchain bloat and centralization pressure?
- How does uncapping OP_RETURN impact long-term fee-market quality and security budget?
- Assurance blockchain will not suffer from illegal content with 100KB OP_RETURN?
- What analysis shows OP_RETURN uncapping won’t harm block propagation or orphan risk? 
- Where does Bitcoin Core keep the XOR obfuscation keys for both block data files and level DB indexes?
- How robust is 1p1c transaction relay in bitcoin core 28.0?
- How can I allow getblocktemplate to include sub 1 sat/vbyte transactions?
https://bitcoinops.org/en/newsletters/2025/09/26/#selected-qa-from-bitcoin-stack-exchange

Bitcoin Optech will host an audio recap discussion of this newsletter on Riverside.fm Tuesday at 16:30 UTC. Join us to discuss or ask questions!
https://riverside.fm/studio/bitcoin-optech

Bitcoin Optech Newsletter #373

Jan B has put together a guide for testing the updates in the forthcoming Bitcoin Core v30.0 release.

Testing a few components in your setup and providing feedback is valuable!



Bitcoin Core 30.0 Release Candidate Testing Guide

The topic of non-developer contributions to Bitcoin and Bitcoin Core came up in a thread the other day. So I wanted to elevate this list, in case people are interested.

Ways to contribute other than code:

**Education / Outreach**
Optech
Conferences
Saving Satoshi
Fundraising
Bitdevs

**User feedback**
Reproducing issues
Priorities?

**Security**
Dependency auditing
CVE disclosure
Mailing list
Pen testing

**Dev Tooling**
CI
Signet
Fuzzing
Drahtbot
Corecheck,dev
Bitcoin dev wiki

**Mentoring**
Developer hubs
Review clubs

**Release Process**
Testing guide
Building binaries
Signing binaries
translations
Packaging for distro

**Monitoring**
b10c stuff etc

**Standardization**
BIPs
Bolts etc

**Events**
Coredev
Online communication channels
Mailing list
Delving
IRC
Twitter / etc
Stack exchange
http://bitcoincore.org
Backups of stuff

**Dev Infrastructure**
Fuzzing
Devops stuff
Dns seeds

**User feedback**
Outward
Talk to miners? Exchanges? Surveys

**Research**
BRW

Janitor work
Reproducing

**Other items listed:**
Coredev
conference
BIPs (review, reading)
Stack exchange
CI
Fuzzer machines
Devops
Monitoring
http://bitcoincore.org maintaining/hosting
Signet / inquisition
Utilities for interacting with Bitcoin (Core)
Educational stuff like saving satoshi
Delving
Mailing list
Backup of delving/mailing list/github comments
IRC and logs
Drahtbot / meetingbot
Bitcoinacks (?)
Fundraising
Developer hubs
Review clubs
Technical talks / podcasts / outreach
Bitdevs
Deterministic builds (running)
Dns seed
Dependency auditing/pruning
Architecture CI doesn’t account for
Reproducing issues
Moderation of github
Research Week
Twitter threads
Translations
Security
Security mailing list
CVE management / disclosure etc
Pen testing
http://Corecheck.dev
Core dev wiki
Bitcoin wiki
Summaries of communal knowledge
Optech
Release packaging for distros
Janitoring old issues/PRs
BOSS program
Summer of Bitcoin

Original:
https://btctranscripts.com/bitcoin-core-dev-tech/2025-02/non-development-contributions

How to contribute to Bitcoin or Bitcoin Core other than code

ZmnSCPxj and Constantine Doumanidis joined Optech to discuss Newsletter #372:

- LSP-funded redundant overpayments
- Partitioning and eclipse attacks using BGP interception 
- Changes to services and client software
- Bitcoin Core 30.0rc1 
- And more

You can listen on our website: https://bitcoinops.org/en/podcast/2025/09/23/

Fountain: https://fountain.fm/episode/roAtQyqbkVOkZxNBz4z0

Spotify: https://open.spotify.com/episode/6lQx7XYXHK6o4u6iEjt1x6

Apple Podcasts: https://podcasts.apple.com/us/podcast/bitcoin-optech-newsletter-372-recap/id1674626983?i=1000728103838