TSCCall20260428

Hiero Technical Steering Committee Meeting

TL;DR: The committee approved HIP-1427 unanimously and agreed to cancel the following week's call, which falls the morning after HederaCon. Mark Blackman presented HIP-1424 on the block and state Merkle tree hashing scheme for the first time, with its vote deferred to an asynchronous round so it can conclude without depending on attendance.

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Details

Organization: Hiero
Date: April 28, 2026
Time: 10:00 AM ET
Recording: https://zoom.us/rec/share/1-p2_HgcTpYk2jjqwlfKEf1RTChfigWXHCrFn1sL2yJ1tTYbbo2W9mO0zGhwgd8G.76-Au_jkOiApQz_Q

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TSC Attendees

• Alexander Popowycz
• Brandon Davenport
• Hendrik Ebbers
• Milan Wiercx van Rhijn
• Richard Bair
• Stoyan Panayotov

Guests

• Joseph Sinclair
• Mark Blackman
• (Others in the call)

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Agenda

• Short overview of last TSC call
• Any Updates/Events from Communities or members?
  • Hendrik's virtual workshop
  • Heka workshop
• Reminder to attend public community calls + bring more activity into Hiero Discord channels. (Encourage others! 💪)
• HIPs
• Any other business (AOB)

Public Participation

As with every Hiero TSC meeting, this was a public meeting and anyone could attend.
Information about TSC and other Hiero meetings is available on the public calendar.

Code of Conduct

The meeting opened with the usual reminder that discussions are conducted under the Linux Foundation antitrust policy and code of conduct.

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Meeting Summary

• Previous call: Hendrik Ebbers skipped the usual review, not having attended the previous call himself. He said he assumed it had been short, since a number of regular participants had been at another event.
• Community workshops: Hendrik announced two upcoming workshops, both remote, both listed on Meetup and both to be recorded: one in about two weeks on building applications on Hiero, and a second in May on the Heka project and its use for decentralized identity solutions.
• HederaCon: Hendrik noted HederaCon taking place the following week in Miami, with open source discussion on the programme, and said he would be attending in person and would be glad to talk Hiero and open source with anyone there.
• Community announcements: None were raised from the floor when Hendrik opened it up.
• Agenda: With no other items, the call was given over entirely to HIPs.
• HIP-1427: Mark Blackman confirmed that only one of the two HIPs scheduled two weeks earlier had actually been presented, so only HIP-1427 was ready for a vote. Alex Popowycz confirmed he had no outstanding questions, and Hendrik put it to a roll-call vote.
• HIP-1424: Mark Blackman presented it for the first time, Joseph Sinclair deferring the walkthrough to him. Mark described two distinct changes: a hashing prefix that closes a pre-image attack, and a logical block structure built from subtrees.
• HIP-1424, the hashing prefix: Mark explained that a Merkle tree node may have either one or two children, and that without a marker an attacker could construct two children hashing to the same value as one child.
• HIP-1424, why the prefix works: Prefixing each node with its type (00 for a leaf, 01 for an internal node with one child, 02 for a node with two children) makes that substitution change the hash, so the attack fails.
• HIP-1424, block structure: Mark described treating parts of the block as subtrees rolling up to a root, which lets a specific part of the block be verified without hashing the entire block tree and makes it visible which part changed.
• HIP-1424, state proofs: Joseph Sinclair added that including the whole of state and every previous block in the block tree means a block proof verifies both the block contents and the state at the start of that block, which is what enables state proofs, including proofs over older block data.
• HIP-1424, review time: Alex Popowycz said he was still working through the proposal and had no questions yet. Mark said the committee would need a week to read it and that people should know what they are voting on, and Joseph called it mathematically and structurally complex, suggesting two weeks might be warranted.
• HIP-1424, critical path: Alex Popowycz asked to what extent it sits on the critical path for block node deployment. Mark confirmed it is not blocking development at this point, and that a change could still be accommodated if one proved necessary.
• Scheduling: Alex Popowycz raised that HederaCon the following week would affect voting and TSC participation. Hendrik proposed running the HIP-1424 vote asynchronously so it could conclude during the week, and cancelling the following week's call. He asked whether that worked for everyone; Alex agreed and no one objected, so that was the course taken.
• Any other business: None was raised, and the call reached the end of its agenda early.

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Presentations

• HIP-1424: Block and State Merkle Tree Hashing Scheme
  Presented by Mark Blackman, with Joseph Sinclair contributing on state proofs, as two related changes to the block structure: a node-type hashing prefix that closes a pre-image attack in the state Merkle tree, and a subtree-based logical block layout that supports partial verification and state proofs. Introduced for review only, with the vote deferred.

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Key Decisions

• HIP-1427, Historical Record File Wrapping for Block Stream Cutover: Approved unanimously by the TSC members present.
• HIP-1424, Block and State Merkle Tree Hashing Scheme: Introduced for review; no vote was taken during this meeting.
• HIP-1424 vote: To be held asynchronously during the coming week, so it can conclude without depending on attendance.
• Next TSC call: Cancelled, falling the morning after HederaCon.

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Prepared by: Brandon Davenport