Announcing DahLIAS! ? The first crypto protocol for full cross-input signature aggregation that allows reusing Bitcoin's curve secp256k1.

On April 17th, 2025, researcher Ncklr announced the launch of DahLIAS ("Discrete Logarithm-Based Interactive Aggregate Signatures"), a new cryptographic protocol designed to enable full cross-input signature aggregation while remaining compatible with Bitcoin's existing secp256k1 elliptic curve.

Researchers have developed a new cryptographic protocol called Discrete Logarithm-Based Interactive Aggregate Signatures (DahLIAS), which aims to enable full cross-input signature aggregation while remaining compatible with Bitcoin's secp256k1 elliptic curve.

Announcing DahLIAS! ?

The first crypto protocol for full cross-input signature aggregation that allows reusing Bitcoin's curve secp256k1.

64B sigs

~2x faster verification than half-agg'd Schnorr sigs

2-round signing

Kudos to the team: @real_or_random @yannickseurin! ? pic.twitter.com/rOic8Gt0AT— Ncklr (@ncklr) April 17, 2025

DahLIAS introduces a 64-byte aggregate signature structure, achieving roughly double the verification speed compared to half-aggregated Schnorr signatures. Notably, DahLIAS requires only a two-round signing process among participants. This design offers potential improvements in both transaction efficiency and scalability for Bitcoin and related protocols.

The full academic paper detailing DahLIAS is available on the International Association for Cryptologic Research (IACR) ePrint archive, providing an in-depth explanation of the scheme's technical underpinnings and security assumptions.

DahLIAS builds on broader research efforts into Cross-Input Signature Aggregation (CISA) for Bitcoin, an area of active development aimed at reducing transaction sizes, lowering fees, and improving privacy. A 2024 research paper sponsored by the Human Rights Foundation (HRF) outlined the significance of CISA for Bitcoin's future.

"Aggregating multiple signatures across transaction inputs could lower transaction costs, encourage privacy-enhancing tools like CoinJoin, and reduce network congestion, ultimately paving the way for a more efficient and scalable Bitcoin network," the HRF paper stated.

Bitcoin's Taproot upgrade in 2021 introduced Schnorr signatures, enabling limited forms of aggregation within single multi-signature transactions. However, cross-input aggregation—combining signatures across multiple inputs with different ownership—remained a complex challenge due to technical risks such as rogue key attacks and interactivity requirements.

DahLIAS addresses some of these challenges by leveraging interactive aggregation while maintaining compatibility with Bitcoin's established cryptographic standards. Although its adoption would require further development and potentially consensus changes, DahLIAS represents a notable advancement in ongoing efforts to make Bitcoin transactions more efficient and private.

The DahLIAS project was developed by a team including cryptographers Yannick Seurin and Tim Ruffing, with contributions from Ncklr, highlighting the collaboration between academic research and Bitcoin development communities.

Further research and real-world testing will determine whether DahLIAS or similar protocols will be proposed for integration into Bitcoin's protocol roadmap.