Bird of Prey 2: non-malleable Schnorr + PQ signatures

The empirical analysis of ML-DSA-87 on a live SHA-256 Proof of Work (PoW) chain provides detailed insights into the data sizing requirements per transaction input. The breakdown shows that each input consists of approximately 4,627 bytes for the signature, 2,592 bytes for the public key, and an additional 41 bytes overhead, culminating in a total of around 7,260 bytes per input. This size is notably larger — about 68 times — than a typical Pay to Witness Public Key Hash (P2WPKH) input.

In a practical application scenario, a transaction with 715,001 outputs was analyzed, which resulted in a total data size of approximately 29MB for the Fan Out sweep. The construction and signing phase of this transaction took roughly 1.15 hours using high-performance hardware, specifically an AMD EPYC-class processor. Additionally, the process of fee rebumping and full resigning required about 10 minutes extra. These findings align with observations made by developer sipa, highlighting that the post-quantum (PQ) blob significantly impacts the data footprint, dominating the block space used in such transactions. In contrast, the Schnorr R component, at only 32 bytes, is negligible at this scale.

The extensive data and methodology used in this analysis are crucial for understanding and discussing block space budgeting in the context of enhanced cryptographic measures like the PQ signatures. These details are essential for stakeholders considering hybridization depending on their specific threat models. For further reading and in-depth understanding, the complete dataset and methodology can be accessed via the published study on Empirical ML-DSA-87 data from a live SHA-256 PoW chain. This resource is particularly relevant to discussions about BIP 360 witness version 3 sizing.