Proof of Reserves
Proof of Reserves (PoR) is a class of cryptographic and accounting attestations that verify a custodian held specific on-chain assets at a moment in time, typically by publishing a Merkle-tree of customer liabilities alongside an on-chain reserve attestation.
Proof of Reserves emerged from a June 23, 2011 Mt. Gox wallet broadcast, the first widely visible reserve attestation in Bitcoin's history. It was formalized in March 2014 when Kraken implemented the Merkle-tree construction proposed by Greg Maxwell, audited by Stefan Thomas. Adoption remained limited until the November 2022 collapse of FTX, after which Proof of Reserves became the industry-standard response to customer concerns about exchange solvency.
A complete Proof of Reserves program demonstrates two things at the moment of attestation. First, the custodian holds on-chain assets in known wallets, verifiable either by signing messages from those wallets or by moving known amounts through them. Second, customer liabilities, committed via a Merkle-tree that each customer can individually verify against their own balance, sum to a total that does not exceed the on-chain reserves.
Five distinct methodologies now operate under the Proof of Reserves label: wallet-snapshot ("move-coins") PoR, Merkle-tree user-balance attestation, auditor-attested PoR (agreed-upon procedures), zk-SNARK PoR, and real-time/continuous PoR (typically using Chainlink). Each has different properties around privacy, freshness, and auditor involvement.
Proof of Reserves describes the state of reserves at a snapshot in time. It does not establish whether customer assets are segregated, who legally owns them, who controls the keys, what is happening between snapshots, or whether the custodian has counterparty exposure that is not disclosed in the attestation. The practice is necessary but not sufficient as a custody standard. River published an explicit acknowledgment in April 2025: "Proof of Reserves doesn't provide insight into the overall health of the company."
Proof of Reserves is a class of cryptographic and accounting attestations that verify a custodian held specific on-chain assets at a moment in time. Modern PoR typically combines a Merkle-tree of customer liabilities with an on-chain reserve attestation, allowing each customer to verify their individual balance was included in the audited total. Onramp treats Proof of Reserves as necessary but not sufficient, and builds on Multi-Institution Custody for verifiable ownership.
Frequently Asked Questions
What is Proof of Reserves?
Proof of Reserves is a class of cryptographic and accounting attestations that verify a custodian held specific on-chain assets at a moment in time, typically by publishing a Merkle-tree of customer liabilities alongside an on-chain reserve attestation.
When did Proof of Reserves become standard?
Proof of Reserves was formalized in March 2014 when Kraken implemented Greg Maxwell's Merkle-tree construction, but adoption remained limited until the November 2022 collapse of FTX made it the industry-standard response to solvency concerns.
What does Proof of Reserves not prove?
Proof of Reserves describes reserves at a snapshot in time. It does not establish whether customer assets are segregated, who legally owns them, who controls the keys, what happens between snapshots, or whether there is undisclosed counterparty exposure. It is necessary but not sufficient as a custody standard.