Amad KhadimZubair Farooq

Subject :

Encryption Topic :

Presented by :

Network Security

ROAD MAP

ENCRYPTIONBasic Terminology

Why Do We Use Encryption ?

Real Life ExamplesCryptography

Types

Symmetric Asymmetric

Caesar Mono alphabetic One-time pad

Hill Cipher Play Fair Vigenere Cipher

Techniques of Cryptography

Plaintext: The original message

Ciphertext: The coded message

Cipher:Algorithm for transforming plaintext to ciphertext.

Key:Info used in cipher known only to sender/receiver.

BASIC CONCEPTSEncipher (encrypt):

Converting plaintext to ciphertext.

Decipher (decrypt): Recovering ciphertext from plaintext.

Cryptography :Study of encryption principles/methods.

Cryptanalysis (code breaking):The study of principles/ methods of deciphering ciphertext without

knowing key.

Cryptology:The field of both cryptography and cryptanalysis

WHY DO WE USE ENCRYPTION?

To secure important information e.g.

Files on computers Data being passed through the Internet ATM machines E-Commerce

Credit card information

Etc.

Prevents information from getting stolen or read Without encryption, there is no reliable security

REAL LIFE EXAMPLES

Used in the military and the government Now used in everyday life:

Online banking

E-commerce

Student records, health records, tax records etc.

ATM machines

Social networking (emails, texts, instant messengers)

Businesses

SYMMETRIC CRYPTOGRAPHYA cryptography system in which both parties have the same encryption key, as in secret key cryptography. 

ASYMMETRIC CRYPTOGRAPHY

Cryptography in which the key used in decryption is different from that used for encryption

To pass an encrypted message from one person to another, it is first

necessary that both parties have the 'key' for the cipher

Encryption Method: C = P + K Key = 3 Decryption Method: P = C - K Key = 3

CAESAR CIPHER

Caesar Cipher is One of the simplest examples of a substitution cipher, which have been used by Julius Caesar to communicate with his army.

Example: Plain Text: BACHELOR

Key = 3Cipher Text: EDFKHORU

Monoalphabetic Ciphers

The substitution is fixed for each letter of the alphabet.

Thus, if "a" is encrypted to "R", then every time we see the letter "a" in the plaintext,

we replace it with the letter "R" in the ciphertext.

A simple example is where each letter is encrypted as the next letter in the alphabet:

"a simple message“.Plain Text:” a simple message “Cipher Text: B TJNQMF NFTTBHF

A monoalphabetic cipher, also known as a simple substitution cipher, relies on a fixed replacement structure.

One-time Pad Ciphers

The one-time pad is a long sequence of random letters.

These letters are combined with the plaintext message to produce the cipher

text.

To decipher the message, a person must have a copy of the one-time pad to

reverse the process.

A one-time pad should be used only once (hence the name) and then

destroyed.

To encipher a message, you take the first letter in the plaintext message and add

it to the first random letter from the one-time pad.

Suppose you are enciphering the letter S (the 19th letter of the alphabet) and

the one-time pad gives you C (3rd letter of the alphabet).

You add the two letters and subtract 1.

When you add S and C and subtract 1, you get 21 which is U.

Each letter is enciphered in this method.

One-time Pad Example

Plaintext : SECRETMESSAGE

One-time pad: CIJTHUUHMLFRU

Ciphertext : UMLKLNGLEDFXY

Hill Ciphers The Hill Cipher was invented by Lester S. Hill in 1929.

It can work on digraphs (2X2), trigraphs (3X3) or theoretically

any sized blocks.

The Hill Cipher uses an area of mathematics called Linear

Algebra.

It also makes use of Modulo Arithmetic.

The cipher has a significantly more mathematical nature than

some of the others ciphers.

Hill Cipher Example

The key for a hill cipher is a matrix e.g.

In the above case, we have taken the size to be 3×3 Assume we want to encipher the message ATTACK AT DAWN.

We now take the first 3 characters from our plaintext, ATT and create a vector that corresponds to the letters to get: [0 19 19] 

Hill Ciphers example

Playfair Ciphers

Invented by Charles Wheatstone in 1854, but named after his friend

Baron Playfair.

In order to encrypt using the Playfair Cipher, we must first draw up

a Polybius Square.

Its providing a stronger cipher than a Monoalphabetic Cipher.

Playfair Cipher is the best known such cipher.

Playfair Key Matrix

Use a 5 x 5 matrix.

Fill in letters of the key (combine "I" and "J"

in the square).

Fill the rest of matrix with other letters.

E.g. key = PLAYFIRE.

Playfair Rules

Plaintext is encrypted two letters at a time. If a pair is a repeated letter, insert filler like 'X’.

If both letters fall in the same row, replace each with the letter to

its right (circularly).

If both letters fall in the same column, replace each with the

letter below it (circularly).

Otherwise, each letter is replaced by the letter in the same row

but in the column of the other letter of the pair.

“hide the gold in the tree stump”Plain Text :

Rule 1, and split up any double letter digraphs by inserting an "x"

between them.

The first image below shows the initial digraph split of the plaintext, and

the second image displays how we split up the "ee" into "ex" and "es".

The digraph split once we apply Rule 1, and remove any digraphs made from two of the same letter.

Playfair Example

The Vigenere cipher, was invented by a Frenchman, Blaise de

Vigenere in the 16th century.

The Vigenere cipher uses a 26×26 table with A to Z as the row

heading and column heading.

This table is usually referred to as the Vigenere Tableau, Vigenere

Table or Vigenere Square.

Vigenere Ciphers

Vigenere Cipher Table

Vigenere Ciphers

To encrypt a message using the Vigenere

Cipher you first need to choose a keyword

(or keyphrase).

Then repeat this keyword over and over

until it is the same length as the plaintext.

This is called the keystream.

The keystream using the keyword battista