Proof of reserves became common after several exchange failures revealed customer assets were missing. The technique demonstrates something real and stops well short of an audit.
What the technique actually proves
An exchange publishes cryptographic evidence that it controls certain blockchain addresses holding assets, alongside a commitment to the total of customer balances it owes.
Customer balances are typically committed using a Merkle tree, a structure where each customer can verify their own balance was included without the exchange revealing anyone else's.
Combining the two gives a claim: assets controlled meet or exceed liabilities to customers at the moment the snapshot was taken.
The liability side is the weak point
Proving control of assets on a public chain is straightforward. Proving that the published liability total includes every customer is not, because liabilities are internal records.
An exchange could omit balances from the tree and appear fully reserved. Individual customers verifying their own inclusion cannot detect an understated total.
This is why attestations by an independent firm are usually paired with the cryptographic proof. The firm's role is to test whether the liability figure is complete.
What a snapshot misses
The proof describes a moment. Assets can be borrowed to satisfy a snapshot and returned afterward, a practice that has been observed in the industry.
Frequent or continuous publication reduces that risk but does not eliminate it. Address control also does not establish that the assets are unencumbered by loans or claims.
A complete picture requires knowing liabilities beyond customer balances, including borrowings, which the technique does not attempt to capture.
How it differs from a financial audit
A financial statement audit examines the whole entity under recognized standards, including internal controls, related party transactions and off-balance-sheet obligations.
Proof of reserves examines one relationship between two figures. Some firms publish agreed-upon procedures reports, which are narrower than an audit and are described as such.
The distinction is easily blurred in marketing. Reading which standard a report was performed under tells you what was actually tested.
Why custody structure matters more
Where customer assets are legally segregated and held by a qualified custodian, the question of whether they exist becomes a matter of custodial records rather than voluntary disclosure.
Regimes that require segregation and independent custody address the underlying problem structurally, whereas proof of reserves addresses it through periodic transparency.
The two approaches answer different questions. One asks whether assets are there today, the other asks whether they can lawfully be used for anything else.