What is Encryption?

- The translation of data into a secret code

- To read an encrypted file, you must have access to a secret key or password that enables you to decrypt it

- Unencrypted data is called plain text

- encrypted data is referred to as cipher text

Dear students,My phone no.Is 24750331

Ghdu vwxghqwv,Pb skrqh qr.

Lv 57083664

Dear students,My phone no.Is 24750331

Encrypt

Decrypt

Plain text Cipher text

Plain text

Activity

Fgct encuu yg ctg iqkpi vq vcnm cdqwv fcvc gpetarvkqp

Encrypted text:

Original text:

Common algorithms of Encryption

Symmetric Encryption

Asymmetric Encryption

Symmetric Encryption

A type of encryption where the same key is used to encrypt and decrypt the message

Symmetric Encryption (Example)

Plain text 1 0 1 1 0 1 1 0

Key 1 1 0 1 1 1 1 0XOR

Cipher text 0 1 1 0 1 0 0 1

Key 1 1 0 1 1 1 1 0XOR

Plain text 1 0 1 1 0 1 1 0

Encrypt

Decrypt

SameKey

Asymmetric Encryption

Asymmetric encryption (also called public-key encryption) involves a pair of keys - a public and a private key.

The public key is published in a public directory and the corresponding private key is kept secret.

Asymmetric Encryption

The sender of the data encrypts the data with the public key of the receiver

The data can be decrypted only with the private key of the receiver

Asymmetric Encryption

Plain Text

Plain Text

CipherText

How to use two different keys?One key is the inverse of the other:Public key = 3, Private key = 1/3Plain text = 4

Encryption: cipher text = public key * plain text = 3 * 4 = 12

Decryption: plain text = private key * cipher text = 1/3 * 12 = 4

Discussion

What are the uses of encryption?

Activity

Construct a simple algorithm of encryption.