NUT-XX: Get quotes by pubkeys by callebtc · Pull Request #341 · cashubtc/nuts

callebtc · 2026-02-16T12:38:36Z

supersedes #329
Get NUT-20 quotes by pubkeys. Requires signatures to prove possession of the corresponding private keys.

robwoodgate

The signature scheme is a bit worrying, but otherwise just some nit/questions for clarity.

robwoodgate · 2026-02-16T13:33:38Z

+- `pubkeys` is an array of hex-encoded compressed secp256k1 NUT-20 public keys (33 bytes each)
+- `pubkey_signatures` is an array of hex-encoded Schnorr signatures on `pubkeys` in the same order (64 bytes each)
+
+The wallet **MUST** provide a valid signature in `pubkey_signatures` for each public key in `pubkeys` with the corresponding private key in the same order as the `pubkeys` array. The message to sign is the byte representation of the public key.


I think signature on the plain public key is pretty risky, as it allows signature replay in any "proof of key ownership" context, or even for future uses on other endpoints and other mints.

It would be better defined as a signature on a domain separated message like we do in P2BK / keyset v2

eg: SHA-256( b"Cashu_NUTXX_QUOTE_v1" || MINT_URL || method || pubkey )

or

eg: SHA-256( b"Cashu_NUTXX_QUOTE_v1" || NONCE || pubkey ) where NONCE is a random shared nonce, supplied in a nonce param: { "pubkeys": <Array[str]>, "pubkey_signatures": <Array[str]>, "nonce": str }

)

good point!

robwoodgate · 2026-02-16T13:37:30Z

+  "quotes": <Array[MintQuoteResponse]>
+}
+```
+


We should probably specify what happens if any signature is invalid. Does entire op fail, or does mint return only the valid ones? What happens if more/fewer sigs are provided than pubkeys?

I think we should match the plan for batched minting where if any are invalid the whole op fails.

Agree. It lowers the abuse surface too, because a mint can reject at first invalid signature (or on mismatch key/sig count), rather than continue processing.

I added a suggestion to the request section above, but it could be moved to response section if preferred.

robwoodgate · 2026-02-17T15:28:41Z

+- `pubkeys` is an array of hex-encoded compressed secp256k1 NUT-20 public keys (33 bytes each)
+- `pubkey_signatures` is an array of hex-encoded Schnorr signatures on `pubkeys` in the same order (64 bytes each)
+
+The wallet **MUST** provide a valid signature in `pubkey_signatures` for each public key in `pubkeys` with the corresponding private key in the same order as the `pubkeys` array. The message to sign is the byte representation of the public key.


Suggested change

The wallet **MUST** provide a valid signature in `pubkey_signatures` for each public key in `pubkeys` with the corresponding private key in the same order as the `pubkeys` array. The message to sign is the byte representation of the public key.

The wallet **MUST** provide a valid signature in `pubkey_signatures` for each public key in `pubkeys` with the corresponding private key in the same order as the `pubkeys` array. The message to sign is the byte representation of the public key.

### Signature Validation Failure

If there is a mismatch between signature and pubkey counts, or **any signature is invalid**, the mint MUST reject the request and return an error.

Co-authored-by: Rob Woodgate <robwoodgate@users.noreply.github.com>

TheMhv · 2026-03-31T13:25:08Z

@@ -0,0 +1,60 @@
+# NUT-29: Mint Quote Lookup by Public Key


This needs a new NUT number, NUT-29 is already defined in NUT-29: Batched Minting

Generally we us XX and just define before merge

TheMhv · 2026-03-31T13:27:49Z

+
+```json
+{
+  "29": {


This needs a new NUT number, NUT-29 is already defined in NUT-29: Batched Minting

Same thing here

a1denvalu3 · 2026-04-10T17:16:59Z

+- `pubkeys` is an array of hex-encoded compressed secp256k1 NUT-20 public keys (33 bytes each)
+- `pubkey_signatures` is an array of hex-encoded Schnorr signatures on `pubkeys` in the same order (64 bytes each)
+
+The wallet **MUST** provide a valid signature in `pubkey_signatures` for each public key in `pubkeys` with the corresponding private key in the same order as the `pubkeys` array. The message to sign is the byte representation of the public key.


A static schnorr signature allows replay attacks: if I observe a signature i can use it to query the status of a quote again and again.

a1denvalu3 · 2026-04-17T10:12:24Z

I've opened a PR with the updated signature logic and test vectors here: #363

robwoodgate · 2026-04-17T16:22:12Z

I've opened a PR with the updated signature logic and test vectors here: #363

I support @a1denvalu3 's approach in #363 - using a timestamp also allows a mint to prevent reuse of the signature after xx minutes too.

It would be even better with a domain prefix, in case a similar scheme is used later on elsewhere:

SHA-256( b"Cashu_NUTXX_QUOTE_v1" || pubkey || timestamp || mint_pubkey )

But with a timestamp max age specified, the reuse window would be minimal in any case.

c03rad0r · 2026-06-03T16:42:09Z

Thanks for opening this — it's great to see this direction being taken seriously. I'm building an ESP32-based captive portal (TollGate) that provides WiFi access in exchange for ecash payments. My use case: a mining proxy on the ESP32 connects to a hashpool translator via SV1 stratum. The translator mints ehash tokens for the miner's locking pubkey and currently pushes them downstream via a custom mining.token notification.

This NUT ("Get quotes by pubkeys") would let me eliminate the translator middleman — the ESP32 could directly query the mint for quotes attributed to its pubkey, receive tokens without the push notification hack. This is especially important for resource-constrained devices where running a full translator is impractical.

The domain-separated signature scheme in #363 (timestamp + mint pubkey) looks solid. I'm really looking forward to using this functionality — happy to test with my ESP32 implementation once the spec stabilizes.

average-gary and others added 4 commits January 12, 2026 15:51

feat(NUT-28): Add third-party mint quotes specification

c75351c

fix: simplify

a6976af

shorter, and array of pubkeys

23e3731

makes no sense

595957a

github-project-automation Bot added this to nuts Feb 16, 2026

github-project-automation Bot moved this to Backlog in nuts Feb 16, 2026

callebtc mentioned this pull request Feb 16, 2026

NUT-XX: get locked mint quotes by public keys #329

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callebtc added 3 commits February 16, 2026 13:39

remove error codes

2d958c8

readme

07e23e9

add signatures

c729245

callebtc changed the title ~~Get quotes by pubkeys~~ NUT-XX: Get quotes by pubkeys Feb 16, 2026

callebtc added 3 commits February 16, 2026 14:13

rename to xx.md

fe6e2d0

Merge branch 'main' into get-quotes-by-pubkeys

f274e0f

prettier

149eea9

robwoodgate suggested changes Feb 16, 2026

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robwoodgate reviewed Feb 17, 2026

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callebtc and others added 2 commits February 26, 2026 16:22

Update xx.md

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Co-authored-by: Rob Woodgate <robwoodgate@users.noreply.github.com>

Update xx.md

dfbf965

Co-authored-by: Rob Woodgate <robwoodgate@users.noreply.github.com>

a1denvalu3 approved these changes Mar 19, 2026

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d4rp4t mentioned this pull request Mar 19, 2026

feat: mintquote by pubkeys models Kukks/DotNut#34

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d4rp4t approved these changes Mar 19, 2026

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thesimplekid mentioned this pull request Mar 19, 2026

New Nut: Implement get quotes by pubkeys cashubtc/cdk#1746

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thesimplekid mentioned this pull request Mar 29, 2026

Extend NUT-13 to derive NUT-20 quote signing keys from seed #356

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TheMhv reviewed Mar 31, 2026

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TheMhv mentioned this pull request Apr 3, 2026

NUT-XX: Mint Quote Lookup by Public Key cashubtc/cdk#1834

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a1denvalu3 reviewed Apr 10, 2026

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a1denvalu3 mentioned this pull request Apr 17, 2026

Update NUT-29 signature message to include mint pubkey and timestamp #363

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a1denvalu3 commented Apr 17, 2026

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