Auth

Zhaoyu Luo bio photo By Zhaoyu Luo

What “secure” means?

  • Confidentiality
  • Authentication
  • Integrity. Intruder can change message
  • Accountability. No party can deny sending message
  • Availability (DoS)

Crypto introduction

  • Symmetric-Key crypto: algorithm is open and public
  • Asymmetric-Key crypto: public and private key
  • Hash (MD5, SHA1): msg -> digest

Attack Model

  • Intrude between parties
    • replay msg
      • give a nonce (randomly generated for once use) change everytime, e.g., ID, so it would not be done again
    • copy msg
    • alter msg
    • send false msg

Symmetric-Key Auth

  • A and B are who they claim to be
  • Confidentiality

Digital Signatures

  • use same hash function to generate message digest
    • CS = Hash(msg) encrypted by Private_keyA before sending
    • CSC = Hash(msg) encrypted by Shared_keyCK in sending

Reference