3.2 KiB
NUT-6: Split tokens
The split operation is the most important component of the Cashu system. The wallet Alice can use it to redeem tokens (i.e. receive new ones in return) that she received from Carol, or she can split her own tokens to a target amount she needs to send to Carol, if she does not have the necessary amounts to compose the target amount in her wallet already.
The basic idea is that Alice sends Bob a set of Proof's and a set of BlindedMessage's with an equal amount. Additionally, she specifies the amount at which she would like to have the split.
6.1 - Split to send
To make this more clear, we make an example of a typical case of sending tokens from Alice to Carol:
Alice has 64 satoshis in her wallet, composed of two tokens, one worth 32 sats and another two worth 16 sats. She wants to send Carol 40 sats but does not have the necessary tokens to combine them to reach the exact target amount of 40 sats. Alice requests a split from the mint. For that, she sends the mint Bob her tokens (Proofs) worth [32, 16, 16] and asks for a split at amount 40. The mint will then return her new tokens with the amounts [32, 8, 16, 8]. Notice that the first two tokens can now be combined to 40 sats. The original tokens that Alice sent to Bob are now invalidated.
6.2 - Split to receive
Another case of how split can be useful becomes apparent if we follow up the example above where Alice split her tokens ready to be sent to Carol. Carol can receive these tokens, which means to invalidate the tokens she receives and redeem them for new ones, using the same mechanism. Only if Carol redeems them for new tokens that only she can spend, Alice can't double-spend them anymore and this simple transaction can be considered settled. Carol requests a split of the tokens (Proofs) worth [32, 8] at the amount 40 (the total amount) to receive back new tokens with the same total amount.
Example
Request of Alice:
POST https://mint.host:3338/split
With the data being of the form SplitRequest:
{
"proofs": Proofs,
"outputs": BlindedMessages,
"amount": int
}
BlindedMessages is a list (array) of BlindedMessages (see NUT-0).
With curl:
curl -X POST https://mint.host:3338/split -d \
{
"proofs":
[
{
"id": "DSAl9nvvyfva",
"amount": 2,
"secret": "S+tDfc1Lfsrb06zaRdVTed6Izg",
"C": "0242b0fb43804d8ba9a64ceef249ad7a60f42c15fe6d4907238b05e857527832a3"
},
{
...
}
],
"outputs":
[
{
"amount": 2,
"B_": "02634a2c2b34bec9e8a4aba4361f6bf202d7fa2365379b0840afe249a7a9d71239"
},
{
...
}
],
"amount": 40
}
If successful, Bob will respond with a PostSplitResponse
class PostSplitResponse(BaseModel):
fst: BlindedSignatures
snd: BlindedSignatures
BlindedSignatures is a list (array) of BlindedSignatures (see NUT-0).