Message Integrity.md

• Ensures that attackers cannot modify messages without being detected
• Message Verifier:
  • Random Function
    • Giant lookup table, provably secure but impractical
  • Pseudorandom Function
    • Functions all known to Mallory, choose n-bit index key known only to recv, sender
  • Cryptographic Hashes
    • Fixed function, no key
    • Properties:
      • Preimage resistance:Given output h, hard to find input m s.t. h = H(m)
      • Second-preimage resistance:Given input m1 , hard to different m 2 s.t. H(m1 ) = H(m2 )
      • Collision resistance:Hard to find any pair of inputs m1 ,m 2 s.t. H(m1 )=H(m2 )
    • Examples:
      • Insecure: #MD5 #SHA-1
      • Secure: [[SHA-256]], SHA-512, SHA-3
• Psudorandom Generator #PRG