Welcome to the ATSIAP Year 7-9 Challenge on Cybersecurity (Week 3)


25 July - 2 September 2022, Australia

Vigenère Cipher

In the past two weeks, we have practised with Caesar cipher and random substitution cipher, and we have learned that these two ciphers are vulnerable to letter frequency analysis. This week, we are going to use Vigenère cipher, which scrambles letter frequencies in the ciphertext and renders previous cryptoanalysis useless.

The key in Vigenère cipher is usually a short word. Let us run an example with "YEAR" as the key. Given a message, we will omit the spaces and split the message into texts of the size of the key. In the running example, the key has 4 letters, so we will split the message into pieces of size 4. For instance, if the message is "CYBER SECURITY PROTECTS US", we will split it as below. It may happen that the last piece is not as long as the key, but that's ok.

An example of splitting the message.

Each letter in the key corresponds to a number - the position of the letter in the English alphabet. NOTE that the position starts with 0. That is, A is the 0th letter, B is the 1st letter, C is the 2nd letter, and so on. For example, YEAR corresponds to four numbers: 24, 4, 0, 17. If a letter in the message aligns with Y, then we will shift the letter 24 places to the right in the English alphabet. Note that we are still treating the alphabet as a circular list, so the right of Z is A. Looking at the first piece, "CYBE", we will shift C 24 times to the right, shift Y 4 times to the right, shift B 0 times to the right, and shift E 17 times to the right. Each shift is similar to what we've done in Caesar cipher. The first four letters of the ciphertext are "ACBV". The entire ciphertext of the above message is given below, and the ciphertext is "ACBVPWETSVIKWTRFRICKQYS". We ignore the spaces at the end.

An example of Vigenere cipher.

To decrypt the ciphertext, we need to shift each letter in the ciphertext the corresponding number of times to the left. For example, shifting A 24 times to the left yields C, shifting C 4 times to the left yields Y, shifting B 0 times left yields B, and shifting V 17 times to the left yields E.

Tasks

Now, Jabreen is a part of our, an essential part of our Dreaming, dreamtime story. And it relates to, well, how is the coast formed? The geology of the Gold Coast. In the beginning, the Gold Coast and, for all intents and purposes, the rest of Australia was formless and shapeless; it was just a great big planet. But, for our reasoning, for our story, dreamtime, the Gold Coast was formless and without shape. Into… out of the dreamtime came a giant from the north, Jabreen, you can call him, if you like, J-A-B-R-double E-N, J-A-V-R-double E-N. Take your pick but that’s how it is, the research is. For our convenience we call him Jab-Reen. And he was the giant who came here in the beginning, it was the Dreaming. And the Dreaming was the Gods and that was the beginning of everything. Enter Jabreen, the Dreamtime God, call him the manufacturer if you like. And, so, it was. He came in here and he looked around and for whatever reasons he decided, oh, I’m going to do something about here, about the coast here. He didn’t call it the coast, about the land there. And, so, he got to work. He formed the mountains, borrol, he formed the rivers, ball ballun, and he formed the rivers, well, I just said the rivers because in the rivers he put the fish jalumm, wallul, plenty of fish and other fish. So, that was… the most important thing with us too, we’re environmentalist by nature, taught that way, to respect Mother Earth, all the greenery around us. And, so, he formed… made the trees. Interestingly, too, the trees weren’t just trees without a reason but they were fruit trees. There were vines, fruit vines. Bananas, passionfruit, everything you like to mention. And, so, that was Jabreen. He liked it so much that he shaped it. So, he had that artistic in him, that artistic ability and then he peopled it. He put… the people came in here too, remember? And, so, after he saw it, he loved it. He loved what he saw and he decided, ooh, time for a feed now and a bogey. So, out he went, remember, he’s a giant, high as the storey high-rises down the coast there. So, out he went. How far out did he go? Being a giant, he went out to the horizon. He had a big feed of kabe, K-A-B-E, ‘car-bee,’ some say ‘koo-pay,’ depends who it is telling the story but it all means the same. Native bee honey, essentially. And, so, he washed himself, had a feed, washed himself and he came back and he was satisfied with what he’d seen, made a good job, manufacturer. And, so, he came ashore and then he was going to have a bit of a camp and in doing so he raised his hands… raised his hands up. And, so powerful was he, with his dreamtime creativity, that the ground, molten lava around him, remember it’s all volcanic land around down the coast there, the molten lava came and enshrouded him or wrapped him up. With a result, everything hardened and he went to sleep. Now, if you look carefully as you go down there at Burleigh Heads… Burleigh’s an English name, Jabreen, that’s our name, Jabreen. If you look carefully you’ll see, you walk around the Burleigh mountain, on the north-eastern side there’s a track for visitors and tourists and families, look up. Once you start to sight the Wynnum trees… that’s pandanus, P-A-N-D-A-N-U-S, pandanus trees, look up like that on your left just past the pandanus and you’ll see… guray, they look like fingers and they were. His fingers were poking out or protruding from the volcanic lava where he decided to go to sleep. Even today, thousands of years… timeless, you can’t put a time on this. Thousands and thousands of years later, you look up there, even today, and you’ll see Jabreen’s fingers. The fingers of the giant who made the Gold Coast poking out towards the ocean. That’s the story of Jabreen, The Dreaming God. The key to decrypting the following ciphertext is the name of the Native bee honey.


Dhf wocumyn umdlf aslm poae cyu us dhf roxu xksl mx wimmh zse wjpv uti k cpqzlfb knbpisjw weulyd us lrfeu Vjkonfvo cjtres.

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