The Cipher - chapter 2 (short story)

 chapter 1  | chapter 3 | chapter 4

The computer finished booting up. Cassie opened up the browser to get the code into her computer. She checked her emails too, just in case. There was an email with no subject from Phil. Typical.

“Not ASCII, not UTF in any form unless special characters are supposed to mean something, no other common type of encoding I can think of. I’ll check if it’s something super obscure.”

Cassie had been afraid of that. She copied the numbers into a ciphertext to a text file and looked at it.

acbb87bc41b48b4dbc5f9b5716a7199a0959422a802f11b27a98a5d4ff06451afe6d26b68e5d7d2cac34ce32061b744893602e363a31d0a2018dc136ef39515da7826548327b

8fc83ebc51c128282a958aba9c26561a780e7e832a1988d64987d807a489fd2bbd123457e85e2f159685a4be44939c92ee970608b64b347fe17d1c1d3113b37a007edfb51368054c5c3c2da3be8eed0a2cbe

ca5c634da7451865d5a41c08d7968fb67b41652a3a44920f1c7e4f979f1dc23c8e0db94b6e89b00cf8a42d11b514d073e5570e65d240a70c87041f6752ce4e11b6b59f221e55b1a1651d

First things first, she had to find the length of the lines. This was easy enough. She wasn’t going to count it manually – not with this many numbers to count. Instead, she let her word processor do it for her. 140, 164, and 148, counting it line by line. Cassie noticed right away that all these numbers were even. No, not just that. They were divisible by four. That was the largest common factor. This made it very likely that she would have to look at sets of four numbers, which was four hexadecimal digits, or two bytes.

Cassie typed this out in response to Phil and sent it.

The next step, then, was to split the text into groups of four.

acbb 87bc 41b4 8b4d bc5f 9b57 16a7 199a 0959 422a 802f 11b2 7a98 a5d4 ff06 451a fe6d 26b6 8e5d 7d2c ac34 ce32 061b 7448 9360 2e36 3a31 d0a2 018d c136 ef39 515d a782 6548 327b

8fc8 3ebc 51c1 2828 2a95 8aba 9c26 561a 780e 7e83 2a19 88d6 4987 d807 a489 fd2b bd12 3457 e85e 2f15 9685 a4be 4493 9c92 ee97 0608 b64b 347f e17d 1c1d 3113 b37a 007e dfb5 1368 054c 5c3c 2da3 be8e ed0a 2cbe

ca5c 634d a745 1865 d5a4 1c08 d796 8fb6 7b41 652a 3a44 920f 1c7e 4f97 9f1d c23c 8e0d b94b 6e89 b00c f8a4 2d11 b514 d073 e557 0e65 d240 a70c 8704 1f67 52ce 4e11 b6b5 9f22 1e55 b1a1 651d

With that, she had to look for repeats. She couldn’t spot any. This meant she couldn’t attack it with statistical analysis.

What if the order of numbers didn’t matter? If the order mattered, 4 hexadecimal digits would give 43680 possibilities. Very few languages had that many characters. If order didn’t matter, it would be 1820 possible combinations. That was still way too much for most languages. Besides, almost every group of four in this cipher was completely unique. That was way too many combinations for English, at least.

No, this had to be simpler.

She looked at her mails again. There was one from Jake. It was another cipher.

“Dany sent this to my phone just now. She’s enjoying herself thoroughly.”

fe3dab0a1169be5f0a97f14ac7ab3e90756740c5cb1fe9994d9857bdaecba9b6bda371757d8acd544229f359a081

84a9e142604651af01bb551fc2519974be57193caa4812515b25768f86100817cc954a86df5ca01ca4101580d04a896e8863f15a06024d7d0a8383392e7bd83a737f9a8afa07dd8f3c282165745add506e345b52a6222b3e4808c76c4a65f7251b9de9c68483a228a0664712796ac215717a3fbbe29c0998f105044d9f1b

115d417cfa57bebb524d9488e7563bd2dfc9a936d1b1588d7a83d81a48b950215a62c49bd4c0b91a93966c84841dfbc85b04ffcb6497c9be933f9e4252cfbc8ce93ff1abf8c0c62482a641b71e7a6311a3399d2d2e7730ba1dd56439f671c4931d0578a4c35f6b2f0e783db6c8bdb641956f98895f81b9b3432fda9f09a0fe18994b

 

That was a lot of text. Cassie checked the number of characters in each line again. 92, 252, 260. Again, all of them were divisible by four. This had to mean something.

Just then, she got another email from Phil.

“Converting them to denary numbers as is makes no sense, I’m afraid.”

That should have been obvious. The email continued.

“We were taught a little bit about encryption so I’m going to try to apply some of the common encryption algorithms to this problem and see if it makes a difference. Might be limited without a key though, and it's entirely possible it's theoretically impossible to crack in a reasonable time. It’ll take a while, but I’ll automate it.”

That would be possible, yes, and Phil would do the job better than anyone. He would likely to find the answer too – Dany was a computer science student like him, so she likely had the same sort of knowledge base to start with. After all, that was how she broke Lex’s puzzle a week ago – Cassie was already familiar with the things he used as keys in that puzzle. In this case, well, Phil had that advantage.

Staring at it wasn’t giving Cassie any ideas. She watched something instead. Actually, she did that for a couple of hours, went out to buy something for dinner, returned to her room, and watched something again for another hour while having dinner. Then she opened the computer again. There was an email from Phil.

“Put everything together, program is running. So far, I’m not seeing any results. Will nap while it runs. Ciao.”

Typical Phil. He had the ability to nap anywhere at any time, and as usual, he put it to full use.

Cassie stared at the numbers again. There was no flash of inspiration at once. Then it struck. Would it be just modulus 26 like with all regular ciphers? That was entirely possible. Also, everything being divisible by 4 could be a huge coincidence.

Or maybe it was padded out that way on purpose.

Cassie tried the numbers pair by pair.

The first pair, ac would translate to 172 in denary numbers. The remainder when divided by 26 was 16. Q was the 17^th letter in the alphabet, or number 16 when starting from zero. This would still make sense.

The next, BB, gave the answer 5. That was a problem – 5 corresponded to F. There were no words that started with QF as far as Cassie knew. She decided to try another pair for good luck. The next pair, 87, gave 5 again. QFF? The next pair gave G. QFFG. This was not good, unless it was a double layered cipher of some sort.

Anyway, she could try to translate this my hand, or she could use Phil to do the translation for her. This was precisely the kind of thing he was good at. She dropped him an email and tried to find something to watch. She found nothing. She checked her emails just in case, and Phil’s answer was there.

QFFGNYJZGRZJWLZYJLOQYVRWSWJEVGRAUFMAMPVSQAYYGBMURSUCGXAGBLLCFFDPLAXUYTNSKGDLOOQTIEAMIAQOWBQZGGVFIHIHTRHSAJYQVVUDIIQRAQEVGIAXAXRVCDXTXSAWPZTAFYOITHIMDKSIUOVZLRYXFICIHUNATNXQGQQPCWBVDDMIMNDXGHUMOITRZUALVJOXCMLMFEFZEYARAZDIEHVFXD

That made absolutely no sense, but it was sufficient for a frequency analysis at the very least.

The distribution did not look too bad, but it didn’t look too hopeful either.

There was another email from Phil. “Cassie, this doesn’t look like a simple substitution cipher, the distribution of letters is all wrong. My program is still running and it hasn’t caught anything yet either.”

He probably reached that conclusion by some form of statistical analysis. He knew what he was doing, but Cassie wasn’t quite ready to give up yet.

Then, Jake sent yet another cipher.

226e8d44288c80bc87352674536e677c59a56f9efd9a37866534acaab75f467bbb0144bd9e9c16a6f237606a8560a914

83a3dac99938cec60412262f73ac8b6cfe2a102e45a0a0014306ad4d48af2828491af74ddb094363a667308fc008e6941e605a90dcd3b9aeb77fad963b0e4eac3eb951bcd574d823458946895e3cdb9e1836b908bb536a644f37de971921b915c037b9987e6d1b5044401ec8ad75

bb6e55c6b05b8683a533f72f7590ae7a2c7e635938373509eaaee0c2cdc00daf2f59f4ca053fa705eca8729eef1fb876d939

42c3e9a44988d839bd9fe777559e4e4a4f0631a7024e953e997dd90a1f226521cfae237200357d9100cf1373f34ebc452a716755707a45ae726e5619

 

The lengths of the lines in this were again 96, 220, 100, 120. Again, all of these were divisible by four. This could not be a coincidence. This had to mean something.

Could it be a four-digit number in hexadecimal? No way. That was way too much information for a letter of English. As far as Cassie knew, Dany spoke neither Chinese nor Japanese, or any other language that would need so many characters. Okay, it was possible is was an abugida, either a South Asian or South East Asian language, counting letters and vowel marker combinations as letters, but that surely wouldn’t take more than three hexadecimal digits.

In short, Cassie was completely stumped.

Then Cassie received another email. She checked it.

“Dany suspects I’ve already given the cipher to all of you. She’s in an extremely good mood for some reason. It’s great, but it’s also a little weird because I can’t make head or tail of the situation. You will have to crack it. My reputation depends on it. I’ll bring snacks and give you moral support.”

Typical Jake. But right now, she could do with snacks and moral support.

END OF CHAPTER TWO

Read previous chapters: chapter 1

Next chapter: chapter 3 | chapter 4

Thank you for reading! Do let me know if you manage to crack the cipher (hint: It doesn't require a key). The next chapter will be uploaded next Monday, 4th April.

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Until next time!