ENCRYPTION

Intercepting data

Data that is transmitted over a network can be intercepted

• Any intercepted data can be read and understood unless measures are taken to prevent it from being interpreted
• These measures are known as encryption

Asymmetric encryption uses one key.

Encryption

The encoding of data so that it can no longer easily be understood 

• A simple shift cipher might encode ‘Box345’ as follows: 

“Box345” 🡪     🡪 “Dqz567”

            Encryption algorithm

If you are using a normal message in an encrypted message, the normal message is known as plain text. The encrypted message process is known as cipher text. 

• Plaintext: the original message to be encrypted
• Ciphertext: the encrypted message
• Encryption: the process of converting plaintext into ciphertext
• Key: a sequence of numbers used to encrypt or decrypt, often data using a mathematical formula
• Encryption algorithm: the formula for encrypting the plaintext

Symmetric Encryption

Symmetric encryption uses one key which is known as a public key. This is the same key that you use to encrypt the message and decrypt the message. 

• The public key (Symmetric encryption)
  • A single key is used to encrypt and decrypt a message and must be given to the recipient of your message to decrypt the data

• The private key (Asymmetric encryption)
  • Two keys are used – one to encrypt and the other to decrypt data
  • This is more secure as it means that you never have to send or reveal your decryption key

Asymmetric Encryption

Asymmetric encryption uses two separate, but related keys known as public and private keys

Both keys are made together- public and private keys are made together and are a pair.

The public key is used to encrypt the file and is given to everyone/ made available to others 

The private key is used to decrypt the file and only you are allowed to access the file to decrypt it. 

Caesar shift cipher

The earliest known substitution cipher was invented by Julius Caesar 

• Each letter is replaced by the letter n positions further on in the alphabet
• n is the key and is used to encrypt and decrypt the message
• This is an example of symmetric encryption

Ciphertext to plaintext: it’s moving right to left using the shift key 

Plaintext to ciphertext: it moves from left to right using the shift key 

The objective of cryptanalysis is to decode the ciphertext – typically by finding out the secret key.