stream ciphers

Complete

Summary

Stream cipher

  • benefit from one-time pad’s perfect secrecy, without an excessively long key
  • short key will be easier for users to remember

Weakest link

  • the encryption will only be as strong as the short key
  • attacker can just brute-force all the keys, instead of the entire key stream

Reused/predictable IV

  • same idea as resued key in one-time pad
  • leaks information of the plaintext

Concept

Stream cipher

  • deterministic pseudo-random sequence(key stream) generated from the IV
  • use XOR to encrypt the plaintext against the key stream
keystreamMCPRGIVIVplaintext:initializationvector:ciphertext:

CTR mode is a stream cipher

Application

Reused IV(known plaintext attack)