Practice

Junior Example Problem 1: Folding Cipher

What are Folding Cipher?

• A cipher uses the following process to encrypt a message:
  1. Write out the message all in upper case.
  2. Determine the position in the alphabet of the first letter of the message (E = 5, M = 13 and so on). Find the remainder when that number is divided by 3 and add 3 to the remainder (ie 'E' yields 5, 'M' yields 4 and so on).
  3. Rewrite the message in a table using the number calculated in step 2 as the width of the table, working across each row in turn.
  4. Prepare the ciphered message by copying down the columns in turn.

Example

• As an example, take the message 'I WILL ARRIVE MONDAY'. 'I' is character 9 of the alphabet. Dividing 9 by 3 yields a remainder of 0, adding 3 to the remainder yields 3, so we write the message across 3 columns:

  I W
  ILL
   AR
  RIV
  E M
  OND
  AY
  						

• Reading down the columns we obtain as the ciphered message:

  II REOA LAI NYWLRVMD
  						

Instructions

• Write a program which will correctly DECIPHER a message prepared using this cipher and use it to decrypt the message below.
• For clarity, spaces have been replaced by "*".
• No other output should be produced by your program other than the decoded message on one line.

Check Your Solution

Step 1.

Attach your source code. DO NOT ATTACH EXECUTABLES

Step 2.

Enter your solution's output in the text area below.

Step 3.

Click below to test your solution

Example Solution

• Problem solution in C++