Chapter 3:Cryptography (16M) Visit for more Learning Resources

CRYPTOGRAPHY Cryptography is the science and art of transforming messages to make them secure and immune to attack.

Cryptography It is an art of writing in secret message. It is important when communicating over untrusted medium. It protects data from alteration Three schems of cruptography are: Secret key cryptography Public key cryptography Hash Functions

Cryptanalysis The process of trying to break cipher text message to obtain the original message itself is known as cryptanalysis.

Cryptology It is combination of cryptography and cryptanalysis.

Encryption and Decryption The process of encoding plain text into cipher text message is known as Encryption.

Decryption: The reverse process of transforming cipher text message back to plain text message is called decryption.

Encryption and Decryption process In the communication, the computer at sender‘s end usually transforms a plain text into cipher text by performing encryption by applying encryption algorithm. The encrypted cipher text is then sent to the receiver over the network. The receiver‘s computer then takes the encrypted message and then perform the reverse of encryption i.e. decryption by applying decryption algorithm.

Encryption and Decryption process

SUBSTITUTION CIPHERS A substitution technique is one in which the letters/number/symbols of plain text are replaced by other letters/numbers/symbols.

Substitution cipher techniques Caesar's Cipher Mono-Alphabetic Cipher A Homophonic Substitution Cipher A Polygram Substitution Cipher A Polyalphabetic Substitution Cipher e.g.Vigenere Cipher One time Pad(Vernam Cipher)

TRANSPOSITION CIPHER In the transposition technique the positions of letters/numbers/symbols in plain text is changed with one another. 1 2 3 4 5 6 M E T A F R P Y 4 2 1 6 3 5 T E M F A P R Y

Transposition cipher techniques Rail Fence Cipher Coulmnar Transposition Simple Coulmnar Transposition Double Coulmnar Transposition For more detail contact us