MWixnet

This is an implementation of @tromp's CoinSwap Proposal with some slight modifications.

A set of n CoinSwap servers (node_i with i=1...n) are agreed upon in advance. They each have a known public key.

SWAP API

The first CoinSwap server (n₁) provides the swap API, publicly available for use by GRIN wallets.

jsonrpc: 2.0 method: swap params:

[{
    "comsig": "0835f4b8b9cd286c9e35475f575c3e4ae71ceb4ff36598504662627afd628a17d6ba7dedb1aa4c47f0fabad026b76fc86d06f3bef8d0621b8ac4601d4b1b98401586ca3374a401508f32049212478ae91cfa474dfaa5ef2c3dd559d5a292e02334",
    "onion": {
        "commit": "099a8922343f242dd3da29935ba5bbc7e38bf68eccfb8c96aec87aec0535199139",
        "data":[
            "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"
        ],
        "pubkey": "033946e6a495e7278027b38be3d500cfc23d3e0836f1b7e24513841437f316ccb0"
    }
}]

Data Provisioning

Inputs

C_in: UTXO commitment to swap
x_in: Blinding factor of C_in
K_1...n: The public keys of all n servers

Procedure

Choose random x_i for each node n_i and create a Payload (P_i) for each containing x_i
Build a rangeproof for C_n=C_in+(Σx_1...n)*G and include it in payload P_n
Choose random initial ephemeral keypair (r₁, R₁)
Derive remaining ephemeral keypairs such that r_i+1=r_i*Sha256(R_i||s_i) where s_i=ECDH(R_i, K_i)
For each node n_i, use ChaCha20 stream cipher with key=HmacSha256("MWIXNET"||s_i) and nonce "NONCE1234567" to encrypt payloads P_i...n

Input Validation

Node n₁ verifies that C_in is in the current UTXO set
Node n₁ verifies the commitment signature is valid for C_in, proving ownership of the input

Output derivation, Output validation, Kernel derivation, and Aggregation steps remain unchanged from the original design

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