Codebusters

Code Busters was a trial event at the 2016 National Tournament. In this event, up to 3 participants must decode encrypted messages, or they may be required to encode messages with certain advanced ciphers. Competitors are not allowed to bring any resources to this event, but can bring a 4 or 5 function calculator - no scientific or graphing calculators allowed.

Test Description
The test is given in an order of increasing difficulty in an exam booklet, and the supervisor may require answers to be written on index cards instead of the booklet. The very first cryptogram is timed - when solved, a team member should raise their hand/shout "bingo!"/etc to alert the supervisor. Teams will receive bonus points depending on their time, but they may make as many attempts as they want to break the code without any penalties. The first cryptogram may also be used as a tiebreaker. If the first cryptogram is unsolved, teams are automatically put on Tier II. The time bonus for the first code is 1 million divided by the number of seconds taken. Solutions are deemed correct only if the solution is an exact match or differs by only one or two letters.

Because the affine, Hill, and Vigenère ciphers may be hard to decrypt, students may be asked to encrypt with them.

Note: The following cryptogram types are listed in a hierarchy of difficulty.

Mono-alphabetic Substitution
A mono-alphabetic substitution is one where the same plaintext letters are replaced by the same ciphertext letters. Since specific encryption/decryption methods are not mentioned in the rules, a variety of ways will be covered in the following section.

Solving a Caesar Shift cipher
One example of a mono-alphabetic substitution is Caesar shift cipher, where each letter is replaced by one shifted by a certain amount. For example, the following table has each letter shifted three positions to the right.

From this table, it is clear that each shifted letter is the same as the original letter three spaces from it (A becomes D, B becomes E, etc). Thus, a message like "Science Olympiad is cool" would become "Vflhqfh Robpsldg lv frro" using a Caesar shift of 3. The alphabet can be shifted any number of times. This type of cryptogram can be solved through brute force, by taking a section of the message and writing out all 26 possible shifts below it, upon which the message is easily revealed. For example, try to decode "xhntqd". First, write out the ciphertext. Then, write out the possible shifts below it.

After shifting "xhntqd" five times, the plaintext is revealed to be "scioly", and no further shifts need to be tested.

Solving a mono-alphabetic substitution cipher using patterns
This may be the most common way to solve a cipher on a Code Busters test, because the supervisor may not tell you that a Caesar cipher etc. was used to encrypt.


 * 1) Look for words that are only one letter long. These will almost always be A or I, unless the cryptogram is a poem, in which case O may be used.
 * 2) Look for frequency of letters. The 12 most frequent letters in the English alphabet are ETAOIN SHRDLU.
 * 3) Look for contractions. If an apostrophe is seen in the ciphertext, it can be an easy way to start deciphering.

Messages with Spaces and a Hint
These cryptograms are similar to those published in 20th century newspapers.

Messages with Spaces
These cryptograms are similar to NSA and diplomatic messages, and do not have a hint.

Messages with Spaces and Spelling Errors
These cryptograms are similar to FBI and organized crime messages.

Messages without Spaces
These cryptograms are similar to NSA and espionage messages, and have a hint.

Messages without Spaces or Hints
These cryptograms are extremely difficult and may not be tested very frequently.

Messages in Spanish
One cryptogram may be in Spanish as a challenge. At states, there will be exactly one.

Hill Cipher
NOTE: These cryptograms will be matrix based, and only use 2x2 or 3x3 matrices.