Crypto Exchange HLD: The Double-Entry Ledger That Never Loses a Coin

A crypto exchange matches buy and sell orders — but the order book is the easy half, and we already built that in the Zerodha matching-engine write-up. The genuinely scary half is the money. When billions of dollars move between accounts every day, a single arithmetic slip that creates or destroys value is catastrophic and, on a blockchain, often irreversible. So the heart of an exchange isn't the matcher — it's the double-entry ledger that makes losing a coin mathematically impossible, plus the hot/cold wallet custody that keeps the actual coins safe. This article is the accounting-and-custod…