nutshell/docs/specs/00.md

NUT-0 - Notation and Models

Sending user: Alice Receiving user: Carol Mint: Bob

Bob (mint)

• k private key of mint (one for each amount)
• K public key of mint
• Q promise (blinded signature)

Alice (user)

• x random string (secret message), corresponds to point Y on curve
• r private key (blinding factor)
• T blinded message
• Z proof (unblinded signature)

Blind Diffie-Hellmann key exchange (BDHKE)

• Mint Bob publishes K = kG
• Alice picks secret x and computes Y = hash_to_curve(x)
• Alice sends to Bob: T = Y + rG with r being a random nonce
• Bob sends back to Alice blinded key: Q = kT (these two steps are the DH key exchange)
• Alice can calculate the unblinded key as Q - rK = kY + krG - krG = kY = Z
• Alice can take the pair (x, Z) as a token and can send it to Carol.
• Carol can send (x, Z) to Bob who then checks that k*hash_to_curve(x) == Z, and if so treats it as a valid spend of a token, adding x to the list of spent secrets.

0.1 - Models

BlindedMessage

A encrypted ("blinded") secret and an amount sent from Alice to Bob.

{
	"amount": int,
	"B_": str
}

BlindedSignature

A signature on the BlindedMessage sent from Bob to Alice.

{
	"amount": int,
	"C_": str,
	"id": str | None
}

Proof

A Proof is also called a Token and has the following form:

{
	"amount": int, 
	"secret": str,
	"C": str,
	"id": None | str,
	"script": P2SHScript | None,
}

Proofs

A list of Proof's. In general, this will be used for most operations instead of a single Proof. Proofs can be serialized (see Methods/Serialization [TODO: Link Serialization])

0.2 - Methods

Serialization of Proofs

To send and receive Proofs, wallets serialize them in a base64_urlsafe format.

Example:

[
  {
    "id": "DSAl9nvvyfva",
    "amount": 8,
    "secret": "DbRKIya0etdwI5sFAN0AXQ",
    "C": "02df7f2fc29631b71a1db11c163b0b1cb40444aa2b3d253d43b68d77a72ed2d625"
  },
  {
    "id": "DSAl9nvvyfva",
    "amount": 16,
    "secret": "d_PPc5KpuAB2M60WYAW5-Q",
    "C": "0270e0a37f7a0b21eab43af751dd3c03f61f04c626c0448f603f1d1f5ae5a7d7e6"
  }

becomes

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