 Everybody Mr. Gibson here next lesson in cryptography today. We're going to be talking about the vision air cipher Which is another poly? Alphabetic cipher and we'll see a little bit about it and how to use it So the visioner cipher is a way of generating that running key that we've seen already with the tabular rectum It's actually vented by someone named Giovanna Batista Balazzo in 1553 And it was known for a very long time as the sheaf into sheaf rubble Pardon my French, but that that is French for the unbreakable cipher and It was so popular Over the years and it was very unbreakable for so long you can see it vented in 1553. It wasn't broken until 1863 by Friedrich Kassiski They've been partially broken before that by Charles Babbage Maybe only about 15 years earlier than that But it wasn't until Friedrich Kassiski Kassiski came around that it was completely broken And we'll actually look at the worker Friedrich Kassiski in a future unit To figure out how we can we can crack the vision air cipher So you'll notice we keep calling it a vision air cipher even though it was invented by somebody else This is Blaise division air. He actually did not create the vision air cipher, but it had been misattributed to him Quite some time ago and took on his name despite him not coming up with it He created the auto key cipher, which is a different polyathletic cipher. That's very similar to the vision air cipher We'll see how that plays into this in a future lesson So let's look at the cipher We're gonna need a keyword and a plain text The keyword is a single word Written over and over and over again So we can see here that our keyword would be the word unicorn And then we just write that over and over and over to generate the running key So in our particular case, here's our keyword unicorn and then there's the corresponding running key and Like with the other tabular recta base cipher is what we do with that running key Is we write it on top of our plain text lining up one letter at a time And then we go over to the tabular recta And we can encypher it using the exact same strategy that we've seen in previous lessons And we can see we get a nice looking cipher text That's pretty much it for the how the vision air cipher works Deciphering the exact same way you write the running key over your over your cipher text Use a tabular recta to get back to the plain text. We won't show that here We've seen it in the last couple lessons But one thing we might want to talk about is why would we want to use the vision air cipher over any of the other Polyalphabetic ciphers that will have been talking about Well one the keyword is kind of nice the keyword gives you a lot of different key options Unlike the try themia cipher where you had an algorithm. We saw we kind of capped out at around 650 possible keys With the vision air the keyword is as big or as short as you want it and the longer and longer the The keyword is the less possible repetitions that we're going to see in our cipher text So let's take a look at the security of the vision air cipher And watch this play out here So let's say we have our running key of just uni. So we're going to shorten it down to three letters And we're going to take the opening line from pride and prejudice as our plain text What we'll see is that Every letter in the plain text is going to get matched back up to a letter in the running key But because our running key repeats There's going to be about in this case a third of our characters are paired back with the key letter of you So when we create those cipher texts Those groups of cipher text letters that correspond back to the letter you and the running key for to look at just those They follow a Caesar distribution and that shouldn't be surprising Because that group of characters was essentially created using a Caesar cipher every plain text letter Had the value that corresponds to you 20 Added to it to get to the cipher text letter. So if you look at just those letters, it should look like a Caesar distribution And as you move down the line and we look at the letters that were encrypted using the running key value of n those characters follow a Caesar distribution and The same for letter I But when we look at all of these together We can see that the distribution does not look like Caesar We don't have anything really above 8% And we don't have any character with a value of close to 0% the closest in this examples are D and L But it kind of overall has the effect of flattening out our Distribution which makes it a lot harder to identify the key or even the cipher that was used to create it We can see this again if we Lengthen out our running key. So it's the word you knees with an S at the end repeated over and over and over We can see that we have a corresponding Bar chart for each grouping of letters all of which follow the Caesar cipher pattern in the distribution But taken all at once Those patterns disappear we get lumped together and this is flattened out even more now we have no single character with a frequency over 6% and Most characters have a frequency above 2% So all of those predictable variations that we see as a result of the Caesar cipher Disappear when we use the vision air cipher and in fact the longer the keyword is that we use to generate the running key The flatter and flatter our distribution and the cipher text will become So that's the vision air cipher in a future unit. We're going to learn how we can actually still crack this Uh, this cipher open as we mentioned will look at the work of kisiski who first realized that There's a there's a nice way to identify that a particular Cipher text was in ciphered using a poly alphabetic cipher But then also went on further to tell you how long that keyword is that was used to generate the cipher text That's it for today. Thanks for watching. We'll catch you on the next one