What a query cannot tell you

Graduate · enrolled learners

This lesson opens with Proof of reserves after FTX, late 2022.

What happened

After FTX collapsed, exchanges rushed to publish proof of reserves: lists of wallets and signatures showing they controlled on-chain assets at customer scale. It was meant to reassure, and read carelessly it did. But analysts and cryptographers, including Ethereum's Vitalik Buterin, set out the missing half: a proof of solvency needs a proof of assets and a proof of liabilities, the total of customer deposits, which the chain does not hold and which has to come from the exchange's own records, for example as a Merkle tree of customer balances. Wallets alone show assets and say nothing about liabilities, so an exchange can prove it holds a billion dollars while owing customers two billion, and the on-chain query cannot see the difference. Worse, a reserve snapshot can be dressed: Kraken's own disclosure says a proof of reserves cannot prove funds were not borrowed to pass the review, and Buterin warned that exchanges could shuttle the same collateral between each other, so that the wallet looks full at the instant measured. Every reserve number was a true on-chain fact and none of them, alone, proved solvency, because solvency is assets minus liabilities and the chain shows only the first term.

The decision point

Proof of reserves is the clean statement of this course's boundary. The query was honest: those wallets really held those assets at that block. The conclusion people drew, therefore the exchange is solvent, did not follow, because the thing that decides solvency, what the exchange owes, lives off-chain and no query can retrieve it. This is the fourth and final skill of learning to query: knowing exactly what the answer does and does not cover. The chain shows what an entity holds and what has moved; it does not show what it owes, why it acted, or what it agreed off-chain, and a snapshot can be arranged for the moment it is taken. An analyst who stops at the on-chain half and reports solvency has overstated the evidence. The discipline is to state the query's answer precisely and name the off-chain information still required before any conclusion rests on it.

Orientation and Year One are open: anyone can read them without an account. From Year Two onward the lessons are for enrolled learners, because progress through the later years only means anything if it is tracked against a record.

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