# Prosatt and hashing

When you enter into a contract with us, our general terms and conditions normally apply. We publish these general terms and conditions on our website. We want to ensure you that our general terms and conditions that are online today are identical to the general terms and conditions that are online tomorrow. You can check this yourself, via hashing. On this page, we explain how this works.

##### 1. What is hashing?

Hashing is a cryptographic function that fingerprints a specific collection of data, such as a text fragment or a PDF file. It then calculates the "hash" or "checksum" of the data, which can be used to verify that you are using an unaltered copy of that data. The checksum takes the form of a series of numbers and letters of a fixed length, also called a string.

There are many different hashing algorithms. At Prosatt we use SHA-256, a secure and well-known method.

Hashing is a one-way process. It's easy to go from a data set to a checksum, but it's almost impossible to go from a checksum back to the original data. If you enter a certain set of data into the SHA-256 hashing algorithm, it will always return the same checksum. But if the data changes even slightly, the checksum will be different.

Some examples:

Let's look at a simple text fragment, such as the sentence "Prosatt, your partner for growth", and calculate the SHA-256 checksum. If we do that, we get the following checksum:

*69d201d23281f3f6ade4443933a760d34d817dbc8e97d7d04e418be2839bbbaf*

Now let's edit the sentence slightly and add an exclamation mark. The sentence then becomes "Prosatt, your partner for growth!". If we calculate the SHA-256 checksum of this sentence, we get the following checksum:

*8a2c3c7d4ad2c41bf13e7e77048ba9e3c4bee58dbfe173ddab66acd39d36997a*

As you can see, if anything changes in the data, the result is a completely different checksum.

The same applies when we calculate the checksum of a PDF file. If we start from the same PDF file, the SHA-256 checksum is always the same. But as soon as we change anything in the PDF, the checksum will be completely different. Therefore, the checksum can be used to confirm the version of the PDF file.

##### 2. How does this work for Prosatt's general conditions?

We publish our general terms and conditions on our website as a PDF file. For example, if you click on the URL https://www.prosatt.be/document/share/6/a7b6be2c-351a-42c1-b1db-501441f24091, you will be able to download a PDF file containing the Dutch version 1.0 of our general terms and conditions. This PDF has the file name Prosatt Algemene Voorwaarden_Versie 1.0_20231001.

If you only know the URL where you can find these terms and conditions, you will not know whether the PDF file you can download today is the same as the PDF file you could download yesterday. But if you know the URL and the checksum of the PDF file, you can check at any time whether the PDF file is still the same.

The SHA-256 hash (or checksum) of these Dutch general terms and conditions is the following:

*8dfdf86ee723e6df33487dbd6201036b92b164b774bac61d866f50b375282623*

For convenience, we usually only list the first eight characters, i.e. *8dfdf86e*. This is sufficient in practice, because any change to the PDF file will cause the entire checksum to be completely different, including the first eight characters.

You can re-download the file at any time and check whether the checksum is still the same. Below we explain how to do this.

##### 3. How do you find the checksum of a PDF file?

Perhaps you are working on a PC with the 7-zip program installed. In that case, you can easily find the checksum by performing the following steps:

· Download the file into your documents folder;

· Right click;

· Go to “CRC SHA” and then click “SHA-256”.

Your PC will then automatically display the checksum of the file.

If you don't have a PC with 7-zip, the easiest way to check the hash of a file is to upload it to a website that can calculate a hash. For example, you can use the following website:

https://emn178.github.io/online-tools/sha256_checksum.html

You can select the file for which you want to calculate the checksum and drag it to the "Drop File Here" box. You can also click on the words "Drop File Here" to browse for a file on your system. After you do this, the website will provide the SHA-256 hash in the field called “output”.

We hope that after this explanation, you can get started with Prosatt's general conditions without any problems!