Hello, and welcome to this lesson on what is a hash? We mentioned hashing algorithms before and they are a fundamental part of blockchain and cryptography in general. But why is the hash a hash is essentially a one way function where its aim is to take some data as input. So imagine this is data. And what it does is it I put something totally different that does not resemble its original form. And it is not reversible.

It is not reversible. So, if you have this output, you can't just get that and reverse reverse it into its original form, or digital content, web That is sort of image, or a video file, or even a text document is literally just ones and zeros and a hash function. A hash function, there are plenty of them out there, we'll cover some of them in a moment. A hash function takes any digital content, literally anything on your computer, any file anything, is a piece of digital content and produces a unique or I shouldn't exactly say unique, it's unique enough and I again, I explain what that means in a moment as well. hash value that can be used to determine almost at the validity of that file on the original source. And it's always going to be the same for that particular file.

A very, very common format for hashes is hex decimal, it could be something else, it doesn't have to be EXA decimal, but that is a very, very common format. any modifications done to that file, so imagine if we have a bunch of strings. Right, so more. So we have this text file that has these numbers in there essentially strings. If this produces one result, if we were to go and change just one of these values, so let's just change this to a free the output will now be totally different. It will be totally different.

So any small or large modification will result in a hash value that is absolutely different and that's one of the core parts of hashing algorithms, most of the time the output is significantly smaller than the input file. And the algorithm is designed to ensure the input data cannot be retrieved or calculated like I said, from the output data, hence the term one way function and to wrap up hashing algorithms have free main requirements. And the free requirements are it needs to be reasonably fast to generate the hash rate morphing in reasonably fast wouldn't Faster, the better be great. And no, because if it's too quick, it's concerned for security reason, because when people and computers are trying to hack information that have been hashed using one way system, one of the things they will do is actually use the original hashing algorithm and just put a whole bunch of information and just random text random files through the algorithm.

And if it's too fast, they will easily be able to get to what that original hash is, and there'll be a compare and say, Okay, this was the fall so nice to be reasonably fast, but not too fast. And another main thing, if you change one bit, the entire hash must change. So even one bit change should result and an entire lead different different hash value. And finally, it must be unique enough to prevent hash collision so must be unique enough to prevent hash collisions Because ultimately, if you have let's say a hashing algorithm which has a length of 128 bits, there are only so many different unique values that this hashing algorithm can pump out. And with the tremendous amount of other documents alone that are out there, there's bound to be some hash collisions. But as long as the hash collisions can be prevented from actually occurring with, let's say, people and individuals that are most likely to have data that are common, and they're going to be sort of compared with each other, it's okay.

So the last thing I'm going to cover is the hashing algorithms that are out there. Some of them there's one called MD five. This is no longer used for a long time. This was used for passwords. This is so easy to crack now. If you were to get a MD five value printer Google and just do a search, Google will most likely to give you the result.

There's just so many websites out there that have a catalogue of most of the results of envy five is this terrible after that Sha one was developed that was very secure. That's it looking like it's probably cracked. Now, there's a number one called Sha two. And a new standard has been designed for often you get the name Shaw free. And that was just published in 2015. And what you're seeing a lot of time is hashing algorithm like Sha 256 show 128.

And this is essentially the number of bits that the actual algorithm pumps out. So the higher the number of bits, the more uniqueness that it can take. But on the flip side, the more complexity in terms of the pros. Simple computers are getting faster so we can handle more complex hashing algorithms. So that's it for hashing algorithms. If you have any questions, feel free to ask them to me, and I look forward to seeing you in the next video.