UTXO probing attack using payjoin

In the discussion regarding the nuances of Bitcoin transactions, particularly focusing on privacy and user autonomy, several key points were made about the methods available to users for managing their transactions. Coin control and labeling are highlighted as effective strategies for enhancing privacy by allowing users to select specific coins for transactions manually. This approach is contrasted with the consolidation of inputs, which could potentially compromise privacy by making techniques like silent payments and coinjoin less effective.

The conversation also touches upon payjoin, a method that requires users to share Unspent Transaction Outputs (UTXOs) and a receiving address in response to the original Partially Signed Bitcoin Transaction (PSBT). While this can be seen as a limitation, it's suggested that using swapped coins might offer a workaround. In this context, octojoin is introduced as a superior solution that does not necessitate any input from the recipient, thus maintaining the recipient's ignorance about the sender's intentions prior to a payjoin transaction.

Furthermore, the discussion acknowledges the potential vulnerabilities associated with payjoin transactions, especially in the face of adversaries with sufficient motivation and resources to monitor wallet activities. The ease with which an attacker could exploit payjoin transactions, particularly through automated systems like BTCPay Server, is underscored as a significant concern.

Lastly, the text mentions a demonstration where the cost implications of these transactions were considered negligible, which suggests a potential area for future adjustments by platforms such as bullbitcoin. This aspect of the conversation implies an ongoing evolution in the understanding and implementation of privacy-focused transaction methods within the Bitcoin ecosystem.