Many, including Satoshi, believed cryptocurrencies provided privacy for payments. In reality, cryptocurrency is Twitter for your bank account. Worse, the current set of decoy transaction–based approaches commonly believed to provide privacy—including coinjoin and cryptonote/Monero—provide fundamentally flawed privacy protections. Where did we go wrong? This talk covers how to critically evaluate the privacy provided by any proposed protocol for payment privacy. Through a series of thought experi…