Christian Lewe, a researcher at Alpen Labs, explains the one-time signature schemes used in BitVM bridges: Lamport, Winternitz, and adaptor signatures. He describes how anti-chain Winternitz counters the malleability of ordinary hash chains, why these signatures support off-chain proof and fraud-proof workflows, and why BitVM currently needs them under Bitcoin Script’s opcode limitations.

The conversation then turns to the potential of `OP_CHECKSIGFROMSTACK` and Schnorr signatures, which could make the bridge construction more efficient if activated. Christian also discusses witness encryption, PIPEs v2, the difficulty of cryptographic research, and Alpen Labs’ work toward simpler, more secure bridges.

At his first Bitcoin conference, Julian is enjoying the chance to meet people he previously knew only through Twitter.

00:40 — What Is Script Restoration?

Script Restoration is a broad effort to make Bitcoin Script more expressive. The goal is to give developers a stronger foundation for building new protocols on Bitcoin.

01:48 — Why Drop “Great” from the Name?

The proposal is now called simply “Script Restoration.” It restores historical functionality while extending Script with newer capabilities.

02:51 — Continuing Rusty Russell’s Work

Rusty Russell’s research and writing helped shape the proposal. Julian continued developing those ideas after seeing that few others were actively working on them.

05:06 — Is Script Restoration a Single BIP?

Rather than one large proposal, Script Restoration comprises multiple BIPs addressing computational budgeting, restored functionality, introspection, and related extensions.

06:52 — Covenant and Introspection Opcodes

The conversation covers OP_TX, PREVOUTs, and selector-based transaction introspection, comparing this general approach with OP_TXHASH, TEMPLATEHASH, and CTV.

09:12 — Script Restoration and Simplicity

Extending the existing scripting language is compared with replacing it more comprehensively. Script Restoration represents a smaller departure from Bitcoin’s current design than Simplicity.

11:13 — What Makes Script Restoration Exciting?

Research around verifiable computation could bring new capabilities to Bitcoin. Greater expressivity may improve scalability, privacy, and the user experience.

13:08 — Benefits for Bitcoin Users

Script Restoration is a low-level change intended primarily for developers and researchers. Users would experience its benefits indirectly through better wallets, protocols, and second layers.

15:23 — What Is ShieldedCSV?

ShieldedCSV is presented as a client-side validation design offering privacy and scalability. The blockchain would prevent double-spending without publicly validating every transaction.

16:44 — Making Permissionless Bridging Feasible

Script Restoration could provide the primitives needed for permissionless bridging. That could make designs such as ShieldedCSV more practical without relying on one-way bridges.

19:28 — Taproot, Ark, and Unknown Possibilities

Taproot and Ark illustrate how a protocol upgrade’s best applications may emerge later. Script Restoration could similarly unlock ideas that researchers have not conceived yet.

19:43 — Following Julian’s Work

Listeners are invited to read and review the published BIPs or contact Julian on X. The next steps include testing the implementation on the Bitcoin Inquisition signet and gathering more feedback.

Fabian Jahr explains **CISA** — Cross-Input Signature Aggregation — compressing every signature in a Bitcoin transaction into one.

The more inputs a transaction has, the more it saves. So the biggest winners are the transactions that need the most inputs: **CoinJoin and PayJoin**, expensive today precisely because each participant brings their own signature. CISA drops that penalty, making collaborative transactions cheaper without giving up their privacy. And it isn’t only a cypherpunk concern — anyone batching payments, exchanges most of all, pays the same per-signature cost.

CISA is an umbrella rather than a single proposal. Two BIPs, both authored by Fabian, are the building blocks: **BIP 458** (half-aggregation — non-interactive, roughly halves signature size) and **BIP 459** (full-aggregation — interactive, DahLIAS, one 64-byte signature for the whole transaction).

**Guest:** Fabian Jahr, Bitcoin Core contributor, author of BIP 458 and BIP 459 and of the Human Rights Foundation’s CISA research paper.

**Links**

- Optech — https://bitcoinops.org/en/topics/cross-input-signature-aggregation/

- HRF research paper — https://hrf.org/latest/cisa-research-paper/

- cisaresearch.org — https://cisaresearch.org/

*Recorded live at bitcoin++ Toronto 2026.*