In 2024, the Human Rights Foundation (HRF) launched a research fellowship to explore the implications of Cross-Input Signature Aggregation (CISA), a proposed Bitcoin upgrade that would significantly lower the cost of private transactions. Currently, privacy-protecting Bitcoin transactions incur additional fees, limiting the number of users willing or able to use these methods. Moreover, these extra fees can create a vulnerability for individuals operating in authoritarian regimes, who may question why users choose privacy-enhancing measures.

The CISA fellowship was awarded to open-source developer Fabian Jahr, who spent six months researching CISA’s potential impact. We’re excited to share his findings in this 38-page report. Jahr does masterful work revisiting Bitcoin’s history of upgrades and why CISA may be the next logical step after SegWit and Taproot.