Name of section dedicated for explaining subjects that are not 100% related to main subject of thesis I am not sure this is the place to ask this question.

I am writing my master thesis and I have sections in preliminaries that don't have anything to do with the main topic of thesis but they further explain things mentioned in preliminaries. My advisor is saying that I should delete those sections but I am thinking maybe there is a better approach.

So, my thesis subject is comparing two cryptography protocols and in preliminaries I explained tools that enables us to understand how powerful these tools are (i.e. if this tool breaks this protocol then this protocol is bad!). But I also added some extra information like this tool also breaks this old protocol so it is a powerful tool.

The extra part that my advisor wants to remove is about 5 pages which includes algorithm as well. I am wondering is there a way to explain thing that are not directly related to main subject of thesis but knowing them would be great. Like a specific section in the end of thesis dedicated for this random stuff. Like an appendix or something. But I believe appendix are for long tables or large figures. I am not sure.

The reason I am asking is that maybe deleting a 5 pages single spaced is not a wise approach knowing that I have spent time writing them and learning them was good too. 

Any help would be appreciated.
If it helps the reader understand your process or your findings then the material should remain. That being said, an extra five pages of material not clearly related to your central concept may be distracting. Placing this material in its own appendix section sounds like a great idea though you do risk having the reader not realize it exists. So, for the sake of overall clarity, introduce the additional material briefly in your introduction or background sections - perhaps for a paragraph at most - then refer to the appendix section for the remaining details.