CISA (Cross-Input Signature Aggregation) ExplainedCISA (Cross-Input Signature Aggregation) Explained

CISA is a way to combine multiple signature from a transaction into one

This is made possible thanks to the linearity property of Schnorr signatures, which enables aggregation of multiple signatures into a single one.

Originally, CISA was considered for inclusion in Taproot, but the idea was abandoned to keep Taproot simple and manageable.

⚠️ Don’t confuse CISA with protocols like MuSig or FROST
Signature aggregation ≠ Key aggregation

CISA vs Key AggregationCISA vs Key Aggregation

Difference #1:Difference #1:

Difference #2:Difference #2:

• Key Aggregation: The verifier only needs the aggregated public key and a single message.
• CISA: The verifier needs all the individual public keys and their corresponding messages.

Difference #3:Difference #3:

• CISA is used during transaction signing
• MuSig is used during address creation

There are two types of CISA:

• Half-Agg
• Full-Agg

🧵 We’ll explain them in upcoming posts.

More ResourcesMore Resources

• CISA Research
• HRF CISA Research Paper
• Blockstream CISA GitHub