Proof of Existence

What is Proof of Existence?

Proof of Existence lets you prove that a specific file (or set of files) existed at a particular point in time. A SHA256 hash of your file is permanently recorded on the Ethereum blockchain. Later, anyone can verify the file by computing its hash and comparing it to the on-chain record.

Step-by-Step Guide

1. 1

   Sign in to your account

   If you don't have an account yet, create one first. No crypto wallet is needed.

2. 2

   Go to Create and choose Credit Card

   Navigate to Create and select the Credit Card option, or go directly to Proof.

3. 3

   Select your file(s)

   Choose a single file, multiple files, or enter a hash manually. Your file is processed locally in your browser — it is never uploaded to our servers.

4. 4

   Review the SHA256 hash

   The computed hash is displayed for your review. For multiple files, a hash list is generated and the final hash is derived from it. You can copy or download the hash list for your records.

5. 5

   Edit the descriptive name (optional)

   A descriptive name defaults to your filename. You can edit it to something more meaningful. This name is stored alongside your proof for easy identification.

6. 6

   Pay with credit card

   Enter your payment details. We accept credit cards, debit cards, Google Pay, and Apple Pay via Stripe. Your hash is recorded on the Ethereum blockchain after payment.

7. 7

   Done — your proof is on the blockchain

   You'll receive a transaction hash and block number as confirmation. Your proof is now permanently recorded and can be viewed on your My NFTs page. From there, you can copy or download your hash. For multi-file submissions, you can also download the full hash list showing each file and its individual SHA256 hash.

How to Verify Later

To verify a file against its blockchain proof, compute the SHA256 hash of the file and compare it to the hash stored on-chain. If the hashes match, the file is identical to what was recorded. Any modification — even a single byte — produces a completely different hash.

For a single-file proof, compute the SHA256 of your file using any tool you trust and compare it to the hash on your My NFTs page.

For a multi-file proof, download the hash list from your My NFTs page. This list contains each filename and its individual SHA256 hash. Recompute the SHA256 of each file with your own tools, then verify each hash matches. The final on-chain hash is the SHA256 of the entire hash list itself, so you can also verify that independently.

Advanced users can also verify a ProofSet from the command line using @alwaysproof/proofset.

Have a Crypto Wallet?

If you have a crypto wallet like MetaMask, you can also record proofs using the NFT Builder. The Builder lets you combine file proofs with messages and other data in a single NFT.