Paper 2025/838

KeyJoin: Privacy-Focused CoinJoin Protocol for Bitcoin

Abstract

Bitcoin is based on the Blockchain, an open ledger containing information about each transaction in the Bitcoin network. Blockchain serves many purposes, but it allows anyone to track all transactions and activities of each Bitcoin address. The privacy of the network is being threatened by some organizations that track transactions. Tracking and subsequent filtering of coins lead to the loss of exchangeability of Bitcoin. Despite Bitcoin’s transparency, it is possible to increase user privacy using a variety of existing methods. One of these methods is called CoinJoin, was proposed by Bitcoin developer Greg Maxwell in 2013. This technology involves combining several users transactions to create a single transaction with multiple inputs and outputs, which makes transaction analysis more complicated. This work describes the KeyJoin, a privacy-focused CoinJoin protocol based on the keyed-verification anonymous credentials (KVAC).