nutshell/docs/specs/04.md

NUT-4: Mint tokens

After requesting a mint (see #3 [TODO: Link]) and paying the invoice that was returned by the mint, a wallet proceeds with requesting tokens from the mint in return for paying the invoice.

For that, a wallet sends a POST /mint&payment_hash=<hash> request with a JSON body to the mint. The body MUST include BlindedMessages that are worth a maximum of <amount_sat> [TODO: Refer to BlindedMessages]. If successful (i.e. the invoice has been previously paid and the BlindedMessages are valid), the mint responds with Promises [TODO: Link Promises].

Example

Request of Alice:

POST https://mint.host:3338/mint&payment_hash=67d1d9ea6ada225c115418671b64a

With the json payload data being of the form PostMintRequest:

{
  "outputs": `BlindedMessages`
}

BlindedMessages is a list (array) of BlindedMessages (see NUT-0).

With curl:

curl -X POST https://mint.host:3338/mint&payment_hash=67d1d9ea6ada225c115418671b64a -d \
{
  "outputs": 
  [
    {
    "amount": 2, 
    "B_": "02634a2c2b34bec9e8a4aba4361f6bf202d7fa2365379b0840afe249a7a9d71239"
    },
    {
    "amount": 8, 
    "B_": "03b54ab451b15005f2c64d38fc512fca695914c8fd5094ee044e5724ad41fda247"
    }
  ]
}

Response of Bob:

If the invoice was successfully paid, Bob responds with a PostMintResponse which is a list of BlindedSignature's (see NUT-0).

{
"promises":
  [
    {
    "id": "DSAl9nvvyfva",
    "amount": 2,
    "C_": "03e61daa438fc7bcc53f6920ec6c8c357c24094fb04c1fc60e2606df4910b21ffb"
    },
    {
    "id": "DSAl9nvvyfva",
    "amount": 8,
    "C_": "03fd4ce5a16b65576145949e6f99f445f8249fee17c606b688b504a849cdc452de"
    },
  ]
}

If the invoice was not paid yet, Bob responds with an error. In that case, Alice CAN repeat the same response until the Lightning invoice is settled.

Unblinding signatures

Upon receiving the PostMintResponse with the list of BlindedSignature's from the mint Bob, a wallet Alice MUST then unblind the BlindedSignature's from Bob (see BDHKE NUT-0) to generate a list of Proof's. A Proof is effectively an ecash Token and can later be used to redeem the token. The wallet MUST store the Proof in its database.

A list multiple Proof's is called Proofs and has the form:

{
"proofs" : 
  [
    {
    "id": "DSAl9nvvyfva",
    "amount": 2,
    "secret": "S+tDfc1Lfsrb06zaRdVTed6Izg",
    "C": "0242b0fb43804d8ba9a64ceef249ad7a60f42c15fe6d4907238b05e857527832a3"
    },
    {
    ...
    }
  ]
}