Code busters

Plain Text

A Message before it is encrypted.

Xenocrypt

A Spanish cryptogram. Used as a challenging question. 27 letter alphabet, includes ñ. The most common words are DE, LA, QUE, EL, EN. It is helpful to have a partner who knows at least some Spanish.

Cipher Text

A message that has been encrypted. Usually a scramble of letters.

Vigenère Cipher

A method of encrypting text by applying a series of alphabetical shifts (Caesar shifts) based on the letters of a keyword. To encrypt a message and key is given. Then take the 2 letters that go together and find where they intersect on the table. To decrypt take the letter from the key and find where the cipher text letter is in the column. If a table isn't given add the 2 numbers together (A=0 - Z=25). Then use mod 26 to find the number of the cipher text. Do opposite to decrypt.

Mono-alphabetic substitution

A substitution cipher that only incorporates a single alphabet in the encryption process. Can include hints, spaces, and spelling errors. Look for singular letters, contractions, double letters, common words (the, and), and common letters (E).

Caesar Cipher

A substitution cipher that shifts characters a certain number of positions in the alphabet. Best to use brute force an try all combinations.

Running Key Cipher

A variation of the Vigenère Cipher. Uses a line or paragraph rather than a repeated word as the key.

Hill Cipher

Are matrix based, only use 2x2 and 3x3 matrices (4 or 3 letter words). Use the 0-25 alphabet. Break the plain text message down into groups of 2. Add a z if the last letter is alone. Take the key word and set it up (in parenthesis) so the first 2 letters are on top of the next 2. The multiple it by the first group of plain text. Then swap it in for their numeric values. Multiple A & E and B & F then add their products together. Keep them stacked like when it started. Apply mod 26. The number you are left with is the numeric value for your first cipher text letter. Repeat with the rest of the groups. (A B) x (E) (C D) x (F)

Affine Cipher and Modular Arithmetic

Each letter in the alphabet is given a number 0-25. The encryption is E(x)=(ax+b) mod 26. a & b are integers that are plugged into the formula. a and b are given to encrypt. Plug the number value of the plain text in x and the add mod 26 to get the number of the cipher text. To decrypt use D(x)=a−1(x−b) mod 26. To find a use brute force table. ta mod 26 =1, (t = 1-26). Sometimes a hint you just plug them into the equation and solve it like system of equations (Algebra Class).

Sir Arthur Conan Doyle's Cipher

Has appeared in test before but it's not common. Could be a bonus question. It is a substitution cipher where each letter is a picture of a stick figure dancing. A figure holding a flag always indicates that it is the end of a sentence. O & A, R & I, and T & E are flipped. N & S have the same legs and right arm.

Baconian Cipher

Replaces each plain text letter with a 5 letter combination of a & b. Like binary where a = 0 and b = 1. It can be a 24 as well as a 26 letter alphabet. I & J , U & V have the same combo.

Mod 26

To do mod 26 you can just take the large number you are left with and keep subtracting 26 until you get a number 0-25. You can also take the large number and divide it by 26, then subtract the number to the left of the decimal so it leave you with a number less than 1. Finally multiply it by 26 and the number your left with is your answer.

Atbash Cipher

Reverses the alphabet ( A becomes Z, B becomes Y ... ) - Mono-Alphabet Substitution Cipher. Uses the formula E(x)=D(x)=25−x