Bitcoin Optech #235

Bitcoin Optech helps Bitcoin users and businesses integrate scaling technologies.

This week’s newsletter summarizes an analysis comparing proposals for ephemeral anchors to SIGHASH_GROUP and relays a request for researchers to investigate how to create proof that an LN async payment was accepted. Also included are our regular sections with summaries of popular questions and answers on the Bitcoin Stack Exchange and descriptions of notable changes to popular Bitcoin infrastructure software.

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COLDCARD Disaster: Weak Entropy Bug Enables Drain of Funds from Seeds Generated Since 2021

A build error present in COLDCARD firmware for more than five years made seeds generated on affected devices predictable, enabling attackers with no access to the hardware to reconstruct private keys offline and sweep the matching addresses.

03 Aug 2026

7 min read

Ashigaru Whirlpool and Terminal v1.0.0 Released

Ashigaru Whirlpool is a ZeroLink coinjoin implementation designed to sever all deterministic links between inputs and outputs, ensuring enhanced bitcoin transaction privacy.

23 Jun 2025

3 min read