Codebusters B/C

[RasmitDevkota]

Where can I find an as-easy-as-possible explanation of how to decrypt an Affine cipher with key? I am pretty confused with the math.

to decrypt affine cipher, you need 3 values. a, b, and t. the decryption formula is t(x-b) mod26.
the easiest way to look at it is to see t as a^-1, where at mod26 has to equal 1.
to find the value of t, just use a.
for example, let's say a = 7 and b = 39.
to find 7t mod26 = 1, you just have to try every value. in this case, t = 15.
therefore, your decryption formula in this case would be 15(x-39) mod26.
hope that helps.

One tiny but significant thing to mention - you don't have to try every value, the inverses mod 26 of all the numbers that can be your value appear in the reference sheet, it's the two-row table on the first page, where each column is a pair of inverses.

Also, as a general recommendation - the Scioly.org Wiki page for Codebusters has great explanations of most ciphers, both decoding and encoding (where applicable). It's not perfect or comprehensive but it's the best first place to check!

[pumptato-cat]

How do you guys solve Morbit/Pollux/Baconian on Scilympiad? I'm copying the problem down on paper and it takes way too long.

[chioneg]

Does anyone know whether the Morse Code portion is using International Morse Code or American Morse Code?
Thanks in advance!

[pumptato-cat]

Morse Code ciphers use the International Morse Code alphabet.

[Sorrow2]

Does anyone know how to do pollux, fractionated morse code cipher and morbit?

[Sorrow2]

Does anyone know how to do pollux, fractionated morse code cipher and morbit?

also baconian i think those are on my state tournament.

[PBJSandwich]

Hello friends, first post here. I am wondering whether Codebusters will be returning for 2024 and 2025. The event has repeated for 5 times in a row which is quite an amount for a repeating event. Will next year mark its death?

https://scioly.org/wiki/index.php/Past_Event_Rotations

[bangtanarmy7]

Does anyone know how to do pollux, fractionated morse code cipher and morbit?

so for most of the ciphers, I use this https://www.youtube.com/@nancywang5952/featured channel, and this girl explains the basics really well, as well as shortcuts for some of the ciphers.

[randomdogonapc]

Haven’t posted on this particular forum yet, but just wanted to ask about some people’s strategies. It seems impossible to do the harder ciphers consistently(patristocrats, Cryptarithms, etc.). Pollux ciphers and Morbit ciphers are some of the easier and reliable ciphers, while aristocrats are not very consistent but still the most common cipher. The low point ciphers(Caesar and Atbash) are usually easy and our team has gone for them on every invitational. What ciphers are you guys prioritizing and which are you guys skipping?

Also, does anybody know how to use the alphabet square provided on tests? They have half of the alphabet instead of the full one used on regular alphabet squares used for vigenere/Porta cipher.

[Mythic]

If we get less than 2 mistakes on a Special Bonus Question or the Timed Question are we supposed to get the Bonus Points?