CISA in 60 Seconds: Fabian Jahr on BIP 459

One question, one minute. 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. This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit insider.btcpp.dev/subscribe