By EZ in Releases — Jul 10, 2023

Cashu Nutshell v0.12.3: Pay To Pubkey (P2PK)

Cashu is a Chaumian Ecash wallet and mint for Bitcoin Lightning. Cashu Nutshell is the reference implementation in Python.

No Bullshit Bitcoin is funded by our community. Click here to support us.

"This Nutshell release introduces a new token lock type called Pay-to-Pubkey or P2PK."
"This allows you to create ecash tokens that can only be spent by their designated recipient. A token locked with P2PK can be posted online without any third party being able to spend it."

Using P2PK

The receiver generates a public key lock via cashu lock.
The sender locks tokens to this public key via cashu send <amount> --lock <P2PK_lock>.
The receiver then receives the tokens via cashu receive <locked_token>.

Background

"In an upcoming upgrade we will also add DLEQ proofs (PR) which allow anyone to check the validity of the mint's signature on a token without having to contact the mint."
"These two features combined, P2PK and DLEQ proofs, allow for a very interesting use case: publicly verifiable payments to a pubkey in the form of ecash."

"As soon as the ecash is publicly posted, the transaction can be viewed as complete: The token can evidently be spent only by the intended recipient, and the validity of its signature can be verified client-side. In such a case, the recipient of this ecash can remain fully offline but be confident that they received a transaction."

"It gets even ore interesting: This ecash can be attached to anything.... including as a reply to a Nostr note! TBD."
"The P2PK feature also includes a new timelock feature that allows you to release a token from its lock after a certain time has passed. After the timelock is passed, the token can either be spent by everyone."

Note: "This feature is still experimental and some parts are incomplete. Things to add are multisignature spending paths and signature flags that can commit to the outputs of a transaction as well."