# What is a hash?

The technology used by VIDT is built around something called a hash. A hash is like a unique digital fingerprint for a file. This fingerprint is calculated using the digital information, the 1s and 0s, that make up a file.

{% hint style="info" %}
When VIDT creates a timestamp, it records the file's hash - its unique fingerprint - and not the file itself.
{% endhint %}

Here's the special thing about a hash: if you have the same file, you will always get the same hash. But, if you change even the smallest thing in the file, you'll get a completely different hash.

## Privacy

Another important thing about a hash is that you can't use it to figure out what the original file was. It's a one-way thing. You can create a hash from a file, but you can't create a file from a hash.

This is why the VIDT timestamp is so valuable. When VIDT creates a timestamp, it records the file's hash - its unique fingerprint - and not the file itself. This hash is proof that the file existed at a specific point in time. This method is both efficient and good for privacy. It gives you a way to prove that a document existed, without having to share the document itself.<br>


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