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<img src="https://hackmd.io/_uploads/HkEB3VdmT.jpg" width=1024>
<font size="7">FROST CLI #Gordian Meeting
9/6/25</font>

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## <img src="https://i.imgur.com/QyDl5nK.png" width="192" height="192"></br> What is Blockchain Commons?

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* We are a community interested in self-sovereign control of digital assets.
* We bring together stakeholders to collaboratively develop interoperable infrastructure.
* We design decentralized solutions where everyone wins.
* We are a neutral "not-for-profit" that enables people to control their own digital destiny.

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Thank you to our FROST Sponsor!


Become a sponsor!
Mail us at [e-mail]

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## <img src="https://i.imgur.com/QyDl5nK.png" width=50 height="50">Two Great Tools

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* We've been working with two great tools
* ZF FROST
* https://frost.zfnd.org/
* Bitcoin Dev Kit (BDK)
* https://bitcoindevkit.org/

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## 🧩 Our Biggest Puzzle

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* How Do We combine ZF FROST & BDK for PSBT Signing?
* ZF FROST Needed Secp256K1-TR Ciphersuite
* BDK Needed to Apply Signature
- But Also Needed a "Tweak" to Avoid a Taproot Attack
- Transaction hash must be extracted
- Key Material is tweaked
- Signature is reinserted

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## ❄️ ZF FROST

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* We Built on Existing FROST CLI Tools
* https://github.com/ZcashFoundation/frost-tools
* Submitted PR for Secp256K1-TR Ciphersuite
* https://github.com/ZcashFoundation/frost-tools/pull/537
* Also have a branch which does Taproot tweak
* https://github.com/BlockchainCommons/zcash-frost-tools/pull/2
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## 🧰 BDK

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* Extracting hash wasn't available in CLI.
* (Tweaking is an external process.)
* Reinserting signature wasn't available in CLI.
* Had to use libraries & write two tools to extract & reinsert sig
* But:
* It's unclear who should be tweaking.
* There may be privacy concerns for tweaking BIP-32 derivations.
* Tweaking may not be necessary with FROST DKG.
* More on this all after our demo!

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## <img src="https://i.imgur.com/QyDl5nK.png" width=50 height="50">Blockchain Commons Demo

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* Demo:
* Spend Taproot (P2TR) Bitcoin
* On a private regtest network
* Using a 2‑of‑3 FROST signature
* We will:
* Create 3 keyshares with Trusted Dealer
* Create a PSBT
* Run `sighash-helper` to get Taproot key‑path sighash
* Sign with FROST
* Inject signature with `psbt-sig-attach`
* Transmit!
* Over to Wolf!

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## ❄️ ZF FROST DKG Open Questions

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* We were unable to get the ZF Distributed Key Generation (DKG) server to work, it may be a few steps behind the TD (Trusted Dealer) code.
* There doesn't seem to be any standards for the DKG values. I don't believe any of the three DKGs we've tested can be used with a different FROST signing system.
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## ❄️ ZF FROST Open Questions

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**On PRs:**
* What is the status of PRs to ZF FROST?
* Does DKG make that Taproot tweak unnecessary?
* Does it make sense to submit tweak PR?
* Do we need to add optionality to tweak PR?

**On Reviews:**
* Did Schnorr BIP340 get security reviewed?
* Will Zcash be doing more security reviews?

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## 🧰 BDK Open Questions

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* Should BDK expose retrieving hash?
* SHould BDK expose re-inserting signature?
* Who would we talk to to make this happen?
* What if there is no requirement for tweak?
* (e.g., with FROST DKG)

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## 🔮 Other Open Questions

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* Which party is really responsible for applying the Taproot tweak?
* What should be done when it's not required?
* Can we make the tweak more private by doing it at a different place?

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## ❄️ FROST is Coming!

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- We have a variety of resources and results from previous FROST workshops at: https://developer.blockchaincommons.com/frost/
- We will have more focused FROST meetings this fall.
- If you'd like to present, let us know!
- ***Library Implementers:*** Tell us about your tech and roadmap
- ***Developers:*** Tell us about your needs and use cases

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<img src="https://i.imgur.com/QyDl5nK.png" width="128" height="128"></br>

www.BlockchainCommons.com

<img src="https://avatars.githubusercontent.com/ChristopherA?s=195">

Christopher Allen (@ChristopherA)