Information Security Notes 2 - Symmetric and Asymmetric Encryption

Symmetric and Asymmetric key

Symmetric

• Share Same Key
• Most classoc crypto are Symmetric
• Encrypts and Decrypts using the same key
• Also called “Secret Key Encryption”

Symmetric Overview

• More secure if the algorithm is opened and publicly review
• Two type of Symmetric
  1. Stream Cipher: the smallest unit to encrypt is one bit
  2. Block Cipher: the smallest unit to encrypt is a block
• Block Ciphers are more secure than most stream ciphers
• Most encryptions scramble the message by substitution and rearrangement for multiple-times
• Security is bounded by the key size.
  • 64bits key => broken with at most 2^64 operations

History - Data Encryption Standard

DES and 3DES should not be adopted today.

• Known more by reading “Meeting in the middle attack”

Asymmetric

• Public Key
• Private Key
• Encrypt with public key; Decrypt with private key
• Also called “Public Key Encryption”
• Everyone can lock but only the one with private key can unlock
• Trapdoor Function: As a function, its function value is very easy to calculate, but the calculation of the inverse solution is very difficult unless some special information is known.

Note that there are many Maths about ECC, AES etc. I will note them if I have time later.