Ingredients of Symmetric Encryption:

  • Plain Text : An original / intelligible message or data
  • Cipher text: coded message
  • Enciphering/Encryption: process of converting plain text to cipher text
  • Deciphering/ Decryption: restoring the plain text from the ciphertext
  • Key: the secret material used for performing encryption

Encryption scheme is computationally secure if: 

  • Cost of breaking the cipher exceeds the value of encrypted information 
  • The time required to break the cipher exceeds the useful lifetime of the information

Cryptography: a word with Greek origins, means “secret writing.” However, we use the term to refer to the science and art of transforming messages to make them secure and immune to attacks. 

Cryptanalysis: Techniques for deciphering a message without any knowledge of enciphering details. 

Cryptology: Cryptography + Cryptanalysis

 Steganography: “covered writing,” in contrast with cryptography, which means “secret writing.” Eg: writing with soap in cloth will be visible when we make it wet. 

Types of Operation for Encryption: 

  • Substitution: Replacing one entity with other

  • Transposition: Shuffling the entities

Types of encryption based on number of keys:

  • Symmetric Key Enc: Both sender  Receiver use same single secret key 
  • Asymmetric Key Enc: Both sender  Receiver use different keys (public key & private key) 

Types of Plaintext Processing: 

  • Block Cipher: Processes the input one block element & produce one output block. Eg: shift cipher, rail fence, etc
  • Stream Cipher: Processes the one input element & outputs one element at a time. Eg: DES, AES, etc