# RFC-8001/MultiPartyTransactions

Maintainer(s): SW van heerden

Copyright 2019 The Tari Development Community

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## Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 (covering RFC2119 and RFC8174) when, and only when, they appear in all capitals, as shown here.

## Disclaimer

The purpose of this document and its content is for information purposes only and may be subject to change or update without notice.

This document may include preliminary concepts that may or may not be in the process of being developed by the Tari community. The release of this document is intended solely for review and discussion by the community regarding the technological merits of the potential system outlined herein.

## Goals

This document describes a few extension to MimbleWimble to allow multi-party UTXOs.

## Description

#### Multi Party UTXO

Normal MimbleWimble does not have the concept of a multisig UTXO. The UTXO is a commitment C(v,r) = r·G + v·H with the value blinded. However, the blinding factor r can be composed of multiple blinding factors where r = r1 + r2 + ... + rn, as Pedersen commitments are linear.

The output commitment can then be constructed as C(v,r) = r1·G + r2·G + ... + rn·G + v·H = (r1 + r2 + ... + rn)·G + v·H. This can be exploited for multiple users where each participant has their own ri and keeps their private blinding factor hidden and only provides their public blinding factor.

The base layer is oblivious as to how the commitment and related signature were constructed. To open such commitments (in order to spend it) only the n-of-n blinding factor r is required, and not the original aggregated signature that was used to sign the transaction. The parties that wants to open the commitment needs to collaborate to produce the n-of-n blinding factor r.