The wallet used Minibits only as a Cashu mint, so the node could hold and
swap ecash there but had no addressable name at it. This derives a LUD-16
Lightning address (name@minibits.cash) from the node's own ecash wallet and
surfaces it in the ecash Receive tab above the existing paste-token box.
Identity reuses the NUT-13 ecash phrase, so there is no second secret:
- seedHash = sha256(mnemonic.to_seed("")) — the exact hash the Minibits app
stores, so restoring the same phrase recovers the same address both ways;
- Nostr keys via NIP-06 at m/44'/1237'/0'/0/0 (nostr-sdk Keys::from_mnemonic,
pinned by a unit test against the NIP-06 vector so a bump cannot silently
move the derivation and orphan the profile).
Backend (wallet/minibits.rs) implements the verified live /v3 flow: NIP-42
challenge/verify -> JWT, idempotent /profile registration with collision
retry, and /claim polling that NIP-04-decrypts each token (service pubkey read
from the address's own LUD-16 metadata, constant fallback) and redeems it
through ecash::receive_token. Mainnet-only; state cached 0600 in
wallet/minibits.json.
New RPC: wallet.ecash-lnaddress (register-or-read, idempotent) and
wallet.ecash-lnaddress-claim (sweep Lightning payments into ecash). The modal
fetches the address on tab open, renders QR + copy, and sweeps claims while
open; a registration failure is non-fatal so paste-token still works.
Verified end-to-end against production: registered a disposable
@minibits.cash address, confirmed it resolves via /.well-known/lnurlp, and the
claim poll returns cleanly.
Until now every Cashu proof this node held was backed by a secret drawn
from OsRng and written to exactly one file. Losing wallet/ecash.json
lost the coins outright — no phrase to write down, and nothing the mint
could do about it. Ecash is a bearer instrument, so "one file, no
backup" was the sharpest edge in the wallet.
NUT-13 derives each proof's secret and blinding factor from (seed,
keyset id, counter) instead. The wallet becomes a phrase, and the coins
can be re-derived and re-claimed — here or in any other NUT-13 wallet.
The phrase is its own 24 words, derived from the node master seed over a
fixed HKDF path. Both halves matter: it is still covered by the node's
recovery phrase, so there is nothing extra to write down; but it is
portable, so restoring ecash into Minibits or cdk-cli does not mean
handing over the key to the entire node.
It sits on disk unencrypted, deliberately. The master seed needs the
operator's password to open, which no background mint or swap can ask
for; and this file lives beside wallet/ecash.json, which already holds
spendable bearer secrets in plaintext. It regenerates exactly those
secrets, so it is the same sensitivity class as the file next to it.
0600, like identity/nostr_secret, which is derived and persisted the
same way.
Counters are reserved *before* the mint call and never rolled back. A
gap costs a restore scan a few extra probes; a reused counter costs a
coin, because two proofs with the same secret can only be spent once.
Restore is the half that cannot be done offline: a re-derived secret is
not money until the mint's signature over it exists. /v1/restore returns
those signatures; unblinding reconstitutes the proofs. It is additive
and idempotent — coins already held are skipped by secret, spent ones
are counted but not added — so it is safe to press on a working wallet,
which is when someone is most likely to reach for it.
Existing nodes activate on the first visit to Settings → Ecash backup
phrase: that password prompt is the only moment the master seed can
legitimately be opened. New nodes get it at onboarding. Until then the
behaviour is exactly as before — valid proofs, no backup — and the card
says so rather than implying a backup already exists.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
ssmithxandarchipelago