CISA (English)
08 Apr 2025
What is CISA?
- “Cross-input signature aggregation”
What is that?
- Combining together signatures on different inputs
- Not the same thing as key aggregation
- Can be either of:
- Half Aggregation (s values combined)
- Full Aggregation (r and s values combined)
- Hybrid?
- Can be either of:
- Transaction-wide Aggregation
- Block-wide Aggregation
What are the benefits of this?
- Space and fee savings
- Privacy
- common-input ownership heuristic
- anonymity set
- collaborative transactions become the default
- reduced stigma to coinjoins
- Computational efficiency (full-agg only)
- Bandwidth
- Lightning gossip (no soft fork required)
- Incentivizes reducing utxoset
Drawbacks
- Needs a soft fork
- Full-agg
- needs an interactive coordination protocol before it makes sense to recommend a soft fork
- as it would make the common-input ownership heuristic even worse (obvious that full-agg inputs belong to the same user)
- Block-agg
- Groot conflicts
Use cases
- Coinjoins and other interactive protocols
- Consolidation (dust would be easier to rescue)
- New business models for collaborative txs
Status
- Half-agg BIP
- Need BIPs for:
Questions
- What are the relative benefits of half vs full aggregation?
- What are the relative benefits of transaction-wide vs block-wide aggregation?