Hashing is a cryptographic function that takes a fingerprint from a specific set 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 unmodified 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 is easy to go from a data set to a checksum, but it is almost impossible to go from a checksum back to the original data. Entering a given set of data into the SHA-256 hashing algorithm will always produce the same checksum. But if the data changes even slightly, the checksum will be different.

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Some examples:

 

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

 

69d201d23281f3f6ade4443933a760d34d817dbc8e97d7d04e418be2839bbbaf

 

Now let's slightly modify the sentence and add an exclamation mark. The sentence will then become ‘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 about the data, the result is a totally 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.