Original subtitles

Let's do a quick lap to see how hashing works in the real world.

So as we discussed, one of the biggest applications of hashing is to make sure that the file you have downloaded

has maintained its integrity.

And usually this happens because let's say there's a software, you may have come across it on another

website, not the official website or someone may have shared it with you.

So now you want to check the integrity.

So first of all, we have included a file, letter or text in the resources, you should download it

and then you need to calculate the MD5 hash of the file and note it down.

Next, we are going to modify the file just slightly, will add a single comma, will recalculate the

hash and compare it with the old one to see, you know, whether it changed or not and by how much.

There are a number of websites which allow you to calculate hash without having to download any tools

on your own system.

So one of these is onlinemd5.com

So as you can see, it allows you to calculate MD5, SHA-1 or SHA-256. We will go with MD5.

So you can upload the file and then it's going to calculate the hash.

So let's do that. So here's our file.

I'm just going to paste it here.

So this is the letter and the hash has already been calculated, you can see so this is the MD5

hash of this file, so let's note it down.

So this is the MD5 hash of this file.

Now, let's modify this file by just adding a comma.

Let's save it,

and then repeat the process, so we've just added a comma.

Let's recalculate the hash.

Here we are.

So as you can see, this was the first hash and this is the second hash, we just changed one comma

and you can already see the significant difference between the two hashes.

You may want to experiment with other types of files as well.

For example, you can take an image and maybe change its brightness slightly, but you will see the

same results even if you change one bit in a file.

It is going to significantly change the hash.

That is because the hash goes through a number of series of steps which are dependent on each other.

So if your starting block is different, you're going to end up with a very different hash at the end.

And another point I would like to clarify is that you cannot convert between hashes.

So, for example, if you only have an MD5 hash available of a file, you cannot compare it with

an SHA hash available of that file.

You won't be able to convert between different hash formats.

That concludes our lab.

Thank you.