Understand the SHA-256 hash in simple language: a file's fingerprint, a short example, and the commands to generate a hash on your own computer.
1. What is a hash? A fingerprint for your file
Just as every person has a different fingerprint, every file can have a unique "fingerprint" too. That fingerprint is called a hash. SHA-256 is a popular hash algorithm that turns any file into a 64-character code.
Whether the file is 1 KB or 10 GB, a SHA-256 hash is always 64 characters (256 bits) long. For example, this is the hash of the text abc:
2. 5 key properties of SHA-256
- Same file, same hash. Calculate it today or 5 years from now, the same file gives the same hash.
- Fixed length. Whether the input is small or large, the output is always 64 characters.
- A tiny change makes a big difference. Change one letter, one pixel or one frame and the entire hash becomes different.
- One-way. You cannot rebuild the original file from its hash.
- Practically unique. Finding two different files with the same hash (a collision) is so hard that no collision for SHA-256 has ever been found publicly.
3. Example: change one letter and the whole hash changes
Below are the real SHA-256 hashes of 3 short texts. They differ by just a tiny bit, yet the hashes are completely different:
| Text | SHA-256 hash |
|---|---|
hello | 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824 |
Hello | 185f8db32271fe25f561a6fc938b2e264306ec304eda518007d1764826381969 |
hello! | ce06092fb948d9ffac7d1a376e404b26b7575bcc11ee05a4615fef4fec3a308b |
The same happens with a video or an image. Re-saving, compressing or cropping changes the file's bytes, and the hash no longer matches. That is why a timestamp proof only works on the exact original file.
4. How to get the SHA-256 of a file on your computer
Every operating system has a built-in way. Replace video.mp4 with your own file name or full path:
Windows (Command Prompt)
Windows (PowerShell)
Mac
Linux
Don't want to use the command line? Open Proof of Original in your browser and choose your file. The hash is generated right in your browser, the file is never uploaded, and you can copy the hash with the "Copy SHA-256 Hash" button.
5. Where is a hash useful?
- Checking downloads: Many websites publish a SHA-256 next to their file. After downloading, calculate your own hash. If it matches, the file is exactly right and unchanged.
- Finding duplicate files: The same hash means the same content, even if the file names are different.
- Timestamp proof: If a file's hash is recorded with a date in a trusted system, you can later prove that the file existed by that date.
- Digital signatures and blockchain: Both rely on hashes like SHA-256.
6. A hash is not encryption
This is a common confusion. Encryption hides data and the right key can bring it back. A hash can never bring the data back; it is only a fingerprint.
⚠️ One nuance: Don't share the hash of short or guessable text (like "123456" or a common password). Anyone can hash common guesses and compare. The hash of a large, unique file (a video, a design, a document) reveals nothing about it.
7. The role of the hash in Proof of Original
The Proof of Original tool does 3 things: your browser calculates the SHA-256 of your file, only that 32-byte hash is sent to the timestamp servers, and once it is anchored in the Bitcoin blockchain you receive an .ots proof. The file itself never reaches the server.
How this proof is created and what pending or confirmed means is explained in detail in OpenTimestamps and .ots Files Explained. The complete workflow for creators is here: How to Prove Your YouTube Video Is Original.
Try our free Proof of Original tool — works in your browser, your file is never uploaded.
✦ Create a Free Proof