Cryptography

Key Type

• Symmetric
• same key to encrypt/decrypt
• fast
• Algorithms:
• DES
• 3DES
• Blowfish
• RC4, RC5, RC6
• AES
• Asymmetric
• slow
• public key
• to encrypt
• share to others/world
• private key
• to decrypt
• keep by owner
• Algorithms:
• RSA
• ECC
• Diffie-Hellman
• El Gamal
• DSA

Methods Of Encryption

• Block Cipher
• use symmetric encryption
• fix-length
• pad added to short blocks
• 
  
• Stream Cipher
• use symmetric encryption
• 1 bit/byte at a time
• should use different IV
• Attributes
• Confusion
• cant determine the key based on ciphertext(encrypted data)
• Diffusion
• 1 change in plain text would output result at least 50% diff

Block Mode 

• Mode is needed when data is larger than block size
• Modes
• ECB - Electronic Code Block
• Weak
• same chipher text for same block
• refer https://www.youtube.com/watch?v=uPiqyQOMH1E , at 1:05
• https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#/media/File:ECB_encryption.svg
• CBC - Cipher Block Chaining
• has additional parameter
• use IV for first block
• use ciphertext for the next block
• usually just XOR the block with the extra param before encrypt using the key
• ref: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#/media/File:CBC_decryption.svg
• CFB - Cipher Feedback
• OFB - Output Feedback
• CTR - Counter

Types of Symmetric

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