Chapter 1




A code is a means of expressing information in a mannerrecognizable only to the sender and intended receiver. To do so, the giveninformation is converted from one form to another using some specific patternor logic. The process of converting the format of the given data into theformat of the code is known as 'encoding' or 'encryption' while the process ofconverting the information from the format of the code to the original formatis known as 'decoding' or 'decryption'. There are infinite numbers of ways inwhich a given piece of information can be coded. Coding can be done usingletter, numbers, symbols or a combination of these.


Letter Coding

In a 'Letter Coding' question, each word of the information iscoded using some property of the letters of the original word. This propertymay be the position of the letter in the English alphabet, the position of aletter in a certain word, vowels and consonants and so on. Once a rule isapplied on any of the properties mentioned above, the code for the originalword is obtained. This code is also occasionally known as a 'cipher'. Questionsin Letter Coding typically provide a word and the encoded version of the word.From these two pieces of information, work out the rule that has been used toencode the word. The question can then either ask for the encoded version of asecond word or the original version of another encoded word. Once the rule isidentified, it applies to all the words that follow the given code.


Letter codes can broadly be grouped into three types:

Rearrangement Ciphers

In a rearrangement cipher, the letters in a word are rearrangedaccording to some definite rule. Fundamentally, this is just a shiftingexercise i.e. the letters in the original word are shifted as per the rule ofthe code. Hence, look at the word and its coded form and see if all the letterspresent in the original word are also present in the coded form. If this is thecase, the code may be a rearrangement code. In a rearrangement cipher, it is agood strategy to number the position of each word as 1, 2, 3 and so on. Forinstance, if the original word is 'VOWEL' and is coded as 'EWLOV', number theletters of the original word as V implies 1, O implies 2, W implies 3 and soon. Hence, VOWEL can be represented as 12345. In the word EWLOV, therepresentation becomes 43521. Thus, the 1st letter becomes the 5th, the3rd becomes the second and so on. Now, if the coded form for a word'DAISY' is required, it becomes 'SIYAD'.