feat: nut19 signature on mint request

19.md

@@ -0,0 +1,154 @@
+# NUT-19: Signature on Mint Quote
+
+`optional`
+
+This NUT defines a protocol extension that enables signature-based authentication for mint quote redemption. When requesting a mint quote, clients can provide a public key. The mint will then require a valid signature from the corresponding secret key before processing the mint.
+Caution: If the mint does not support this NUT, anyone with the mint quote id will be able to mint even without providing a signature.
+
+# Mint quote
+
+To request a mint quote, the wallet of `Alice` makes a `POST /v1/mint/quote/{method}` request where `method` is the payment method requested (here `bolt11`).
+
+```http
+POST https://mint.host:3338/v1/mint/quote/bolt11
+```
+
+The wallet of `Alice` includes the following `PostMintQuoteBolt11Request` data in its request:
+
+```json
+{
+  "amount": <int>,
+  "unit": <str_enum["sat"]>,
+  "description": <str|null>,
+  "pubkey": <str|null> <-- New
+}
+```
+
+with the requested `amount` and the `unit`. An optional `description` can be passed if the mint signals support for it in `MintMethodSetting`. `pubkey` is the public key that will be required for signature verification during the minting process. The mint will only mint ecash after receiving a valid signature from the corresponding private key in the `PostMintRequest`.
+The mint `Bob` then responds with a `PostMintQuoteBolt11Response`:
+
+```json
+{
+  "quote": <str>,
+  "request": <str>,
+  "state": <str_enum[STATE]>,
+  "expiry": <int>
+}
+```
+
+Where `quote` is the quote ID and `request` is the payment request to fulfill. `expiry` is the Unix timestamp until which the mint quote is valid.
+`state` is an enum string field with possible values `"UNPAID"`, `"PAID"`, `"ISSUED"`:
+
+- `"UNPAID"` means that the quote's request has not been paid yet.
+- `"PAID"` means that the request has been paid.
+- `"ISSUED"` means that the quote has already been issued.
+
+## Example
+
+Request of `Alice` with curl:
+
+```bash
+curl -X POST http://localhost:3338/v1/mint/quote/bolt11 -d '{"amount": 10, "unit": "sat", "pubkey": "03d56ce4e446a85bbdaa547b4ec2b073d40ff802831352b8272b7dd7a4de5a7cac"}' -H "Content-Type: application/json"
+```
+
+Response of `Bob`:
+
+```json
+{
+  "quote": "9d745270-1405-46de-b5c5-e2762b4f5e00",
+  "request": "lnbc100n1pj4apw9...",
+  "state": "UNPAID",
+  "expiry": 1701704757
+}
+```
+
+#### Signature scheme
+
+To mint a quote where a public key was provided, the minter needs to include signatures in the `PostMintBolt11Request`. We use `libsecp256k1`'s serialized 64-byte Schnorr signatures on the SHA256 hash of the message to sign. The message to sign is the field `PostMintQuoteBolt11Response.quote`.
+
+# Minting tokens
+
+After requesting a mint quote and paying the request, the wallet proceeds with minting new tokens by calling the `POST /v1/mint/{method}` endpoint where `method` is the payment method requested (here `bolt11`).
+
+```http
+POST https://mint.host:3338/v1/mint/bolt11
+```
+
+The wallet `Alice` includes the following `PostMintBolt11Request` data in its request
+
+```json
+{
+  "quote": <str>,
+  "outputs": <Array[BlindedMessage]>,
+  "witness": <str|null> <-- New
+}
+```
+
+with the `quote` being the quote ID from the previous step and `outputs` being `BlindedMessages` (see [NUT-00][00]) that the wallet requests signatures on whose sum is `amount` as requested in the quote. `witness` is the signature on the mint quote id as defined above.
+The mint `Bob` then responds with a `PostMintBolt11Response`:
+
+```json
+{
+  "signatures": <Array[BlindSignature]>
+}
+```
+
+where `signatures` is an array of blind signatures on the outputs.
+
+## Example
+
+Request of `Alice` with curl:
+
+```bash
+curl -X POST https://mint.host:3338/v1/mint/bolt11 -H "Content-Type: application/json" -d \
+'{
+  "quote": "9d745270-1405-46de-b5c5-e2762b4f5e00",
+  "outputs": [
+    {
+      "amount": 8,
+      "id": "009a1f293253e41e",
+      "B_": "035015e6d7ade60ba8426cefaf1832bbd27257636e44a76b922d78e79b47cb689d"
+    },
+    {
+      "amount": 2,
+      "id": "009a1f293253e41e",
+      "B_": "0288d7649652d0a83fc9c966c969fb217f15904431e61a44b14999fabc1b5d9ac6"
+    }
+  ],
+  "witness": "d9be080b33179387e504bb6991ea41ae0dd715e28b01ce9f63d57198a095bccc776874914288e6989e97ac9d255ac667c205fa8d90a211184b417b4ffdd24092"
+
+}'
+```
+
+Response of `Bob`:
+
+```json
+{
+  "signatures": [
+    {
+      "id": "009a1f293253e41e",
+      "amount": 2,
+      "C_": "0224f1c4c564230ad3d96c5033efdc425582397a5a7691d600202732edc6d4b1ec"
+    },
+    {
+      "id": "009a1f293253e41e",
+      "amount": 8,
+      "C_": "0277d1de806ed177007e5b94a8139343b6382e472c752a74e99949d511f7194f6c"
+    }
+  ]
+}
+```
+
+If the invoice was not paid yet, `Bob` responds with an error. In that case, `Alice` **CAN** repeat the same request until the Lightning invoice is settled, as in NUT04. If `Alice` does not include a witness on the `PostMintBolt11Request` but did include a `pubkey` in the `PostMintBolt11QuoteRequest` the `Bob` **MUST** respond with an error, `Alice` **CAN** repeat the request with a witness in order to mint the ecash.
+
+## Settings
+
+The settings for this NUT indicate the support for requiring a signature before minting. They are part of the info response of the mint ([NUT-06][06]) which in this case reads
+
+```json
+{
+  "19": {
+    "supported": <bool>
+  }
+}
+```

error_codes.md

@@ -16,6 +16,7 @@
 | 20005 | Quote is pending                                | [NUT-04][04], [NUT-05][05]               |
 | 20006 | Invoice already paid                            | [NUT-05][05]                             |
 | 20007 | Quote is expired                                | [NUT-04][04], [NUT-05][05]               |
+| 20008 | Witness not provided for mint quote             | [NUT-19][19]                             |
 
 [00]: 00.md
 [01]: 01.md
@@ -30,3 +31,4 @@
 [10]: 10.md
 [11]: 11.md
 [12]: 12.md
+[19]: 19.md

tests/19-tests.md

@@ -0,0 +1,21 @@
+# NUT-19 Test Vectors
+
+The following is a `PostMintBolt11Request` with a valid signature. Where the `pubkey` in the `PostMintQuoteBolt11Request` is `03d56ce4e446a85bbdaa547b4ec2b073d40ff802831352b8272b7dd7a4de5a7cac`.
+
+```json
+{
+  "quote": "9d745270-1405-46de-b5c5-e2762b4f5e00",
+  "outputs": [],
+  "witness": "d9be080b33179387e504bb6991ea41ae0dd715e28b01ce9f63d57198a095bccc776874914288e6989e97ac9d255ac667c205fa8d90a211184b417b4ffdd24092"
+}
+```
+
+The following is a `PostMintBolt11Request` with an invalid signature. Where the `pubkey` in the `PostMintQuoteBolt11Request` is `03d56ce4e446a85bbdaa547b4ec2b073d40ff802831352b8272b7dd7a4de5a7cac`.
+
+```json
+{
+  "quote": "9d745270-1405-46de-b5c5-e2762b4f5e00",
+  "outputs": [],
+  "witness": "cb2b8e7ea69362dfe2a07093f2bbc319226db33db2ef686c940b5ec976bcbfc78df0cd35b3e998adf437b09ee2c950bd66dfe9eb64abd706e43ebc7c669c36c3"
+}
+```