Sourced from latest @tuma's Last week in bitcoin (Oct 27 - Nov 2) fromm the Bitcoin++ insider https://insider.btcpp.dev/p/last-week-in-bitcoin-oct-27-nov-2
During the monthly call, on Thursday 30th, Cashu developers presented a new specification that lays the foundation for creating offline unilateral Spilman channels1. This NUT allows a sender to send a huge number of high-frequency payments while preparing just a few proofs, reducing bandwidth usage and strain on the mint.
To establish a channel, Alice takes Carol’s public key and outputs and, with a mint supporting NUT-112, creates a set of 2-of-2 multisig proofs of various amounts, where both Alice and Carol’s signatures are needed to redeem.
Once the channel has been established, Carol can verify the signature from Alice without the need to involve the mint. Carol can unilaterally exit at any time, by sending the latest signature to the mint. Alice must wait for Carol to sign a release transaction for the remaining funds. However, even in case of non-cooperation, a locktime allows Alice to be refunded after a certain amount of time has passed.
Footnotes
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Spillman payment channels are unidirectional (there is a payer and a payee, and it is not possible to transfer money back in the reverse direction). Spillman payment channels expire after a specific time, and the receiver needs to close the channel before the expiration. https://en.bitcoin.it/wiki/Payment_channels#Spillman-style_payment_channels ↩
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This NUT describes Pay-to-Public-Key (P2PK) which is one kind of spending condition based on NUT-10's well-known Secret. Using P2PK, we can lock ecash tokens to a receiver's ECC public key and require a Schnorr signature with the corresponding private key to unlock the ecash. The spending condition is enforced by the mint. https://github.com/cashubtc/nuts/blob/main/11.md ↩