CODING AND DECODING

PRESENTED BY:Ronika

SnigdhaSudikshaTavishi

CODE

A code is a rule for converting a piece of information (for example, a letter, word, phrase, or gesture) into another form or representation (one sign into another sign), not necessarily of the same type.

Encoding is the process by which information from a source is converted into symbols to be communicated. Decoding is the reverse process, converting these code symbols back into information understandable by a receiver.

One reason for coding is to enable communication in places where ordinary spoken or written language is difficult or impossible.

The simplest form of a code is the "jargon code", in which a particular arbitrary phrase is used as code.Jargon codes have been used for a long time, most significantly in World War II,

when they were used to send commands over broadcast radio to resistance fighters

“The nightingale sings at dawn” -- corresponds to a

particular predefined message and the actual

meaning of this might be: “The supply drop will take place at 1hrs tomorrow”.

“BOXER SEVEN SEEK TIGER5 AT RED CORAL” This uses "code words" to report that a friendly

military force code named BOXER SEVEN is now hunting an enemy force code named TIGER5 at a

location codenamed RED CORAL. This particular code is weak in that the "SEEK" and "AT" words provide

information to a code breaker on the structure of the message. In

practice, military codes are often defined as "code numbers" rather

than code words, using a codebook that provides a dictionary of code

numbers and their equivalent words.

CEASER CIPHERS Caesar cipher used by Julius Caesar to communicate

with his army. Caesar is considered to be one of the first persons to have ever employed encryption for the sake of securing messages. Caesar decided that shifting each letter in the message would be his standard algorithm, and so he informed all of his generals of his decision, and was then able to send them secured messages. Using the Caesar Shift (3 to the right), the message,

"RETURN TO ROME" would be encrypted as, "UHWXUA WR URPH’’

Thus, the Caesar cipher is a shift cipher since the ciphertext alphabet is derived from the plaintext alphabet by shifting each letter a certain number of spaces.

THE FAULT, DEAR BRUTUS, LIES NOT IN OUR STARS BUT IN OURSELVES.

would be enciphered as MAX YTNEM, WXTK UKNMNL, EBXL GHM BG HNK

LMTKL UNM BG HNKLXEOXL.

A B C D E F G H I J

D E F G H I J K L M

K L M N O P Q R S T

N O P Q R S T U V W

DIFFERENCE BETWEEN CODES AND CIPHERS

CODES•A code is a system of signals that is used to represent letters or numbers in transmitting a message. In other words, a code deals with phrases and sentences or whole words. For example, this symbol means:  = "Send help at once.

CIPHERS

•A cipher deals with letters. It is a message written in letters in a predetermined code. This means that a cipher is a system of communication that uses letters instead of phrases and such.

TREASON•After getting a hang of code- breaking by shifting the letters forward and backwards, it is realized that there are 25 possible way of deciphering a message. Further, in an attempt to secure messages, symbols were used, vis a vis, A as =, B as * etc.

•So, what about coding messages another way?

For a long time, people thought this type of code would be really hard to crack. It would take the enemy far too long to figure out what letter of the alphabet each symbol stood for just by trying all the possible combinations of letters and symbols. There are 400 million billion billion possible combinations!!!!

Letter sent by Mary Queen of Scots to her co-conspirator Anthony Babington. Every symbol stands for a letter of the alphabet.

A special type of code was used by Mary Queen of Scots when she was plotting against Elizabeth the First. Mary wanted to kill Elizabeth so that she herself could become Queen of England and was sending coded messages of this sort to her co-conspirator Anthony Babington. Unfortunately for Mary, there is a very simple way of cracking this code that doesn't involve trial and error, but which does involve, surprise, surprise, maths.

Way of solving the message: Letters in a language are pretty unusual because some

get used more often than other letters. In most of dictionary words and names have the letter ‘’e’’, which most frequently occurs, then ‘t’, then ‘a’, as shown below:

All Elizabeth the First's Spy-Master had to do to crack Mary's code, was to look through the coded message and count the number of times each symbol came up. The symbol that came up the most would probably stand for the letter 'E'.

When you crack codes like this, by looking for the most common letter, it's called 'frequency analysis', and it was this clever method of cracking codes that resulted in Mary having her head cut off.

CHOP!!!

Modern cryptography involves disciplines of computer, mathematics and engineering.

Various coding/decoding methods are extensively used in communication and computer technology , for storage and transmission purpose.

MODERN CRYPTOGRAPHY

SEMAPHORE Semaphore, is a method of coding , where the

configuration of flags held by a signaller or the arms of a semaphore tower, encodes parts of the message, typically individual letters and numbers. Another person standing a great distance away can interpret the flags and reproduce the words sent.

Chappe telegraph, or Napoleonic semaphore is a system of conveying information by means of visual signals, using towers with pivoting shutters, also known as blades or paddles. Information is encoded by the position of the mechanical elements; it is read when the shutter is in a fixed position.

Semaphore are virtually used to transmit information over long distances. Some semaphore used which are used in navigation ships for maritime security through visual signals or hand- held flags are:

SEMAPHORE SIGNAL

ENIGMA

Enigma machines were used by German

military for encryption and decryption of the

secret messages during the world war II.

Although the machine was initially invented for

commercial purposes in Bank , however it was found to be useful and

extensively used during war period.

The Enigma machine is a combination of

mechanical and electrical subsystems , consisting of key boards, a set of rotors

and electrical circuits.

When a key is pressed, the circuit gets completed with

current flowing through various components and ultimately lighting the

display lamp indicating the output letter.

The Polish & British mathematicians made great effort to understand this machine and developed decryption methods.

The machine was based on mathematical models of encryption .

SET OF ENIGMA ROTORS

ENIGMA MACHINES

Morse code is a method for transmitting

information, using standardized

sequences of short and long marks or pulses - commonly known as "dots" and "dashes" -

for the letters, numerals, punctuation and special characters

of a message.

it was also extensively used for early radio

communication beginning in the 1890s.

However, with the development of more

advanced communications technologies, the widespread use of Morse code is now

largely obsolete.

When using morse code, a dash is equal to

three dots. A space between parts of the

same letter is equal to one dot. A space

between two letters is equal to three dots and

a space between two words is equal to five

dots.

MORSE CODE

CONVETING MORSE CODE INTO ENGLISH

Leonardo Da Vinci, Mona Lisa

INTO MORSE CODE ... .. -. -.-. --- -- .--. .-.. . -

. -... ..- - .--. .-.. . .- ... . --. .. ...- . -- . .- .. -. -- .- - .... ...

Telegraph-Morse Code

Machine

THANKYOUHAPPY

CODING