• 1. No Pairing
  • No authentication (Identity)
  • No Pairing
  • Open connection - anyone can listen
• 2. Pairing "Just Works" (used when device lacks I/O)
  • Unauthenticated Pairing
  • Encryption
  • Vulnerable to [[04282507300 MITM Man in the Middle Attack]]
  • TK → STK → LTK, but (?) TK = 0
• 3. Authorized Pairing with encryption
  • Uses one of the following methods to confirm identity when pairing…
    • (i) OOB association model
    • (ii) Passkey entry
  • aka LE legacy pairing; TK → STK → LTK
• 4. LE Secure Connections w/ 128-bit ENC key (LESC)
  • Better Cryptography
  • LTK derived directly via ECDH (Elliptic-Curve Diffie-Hellman)

• Passkey Entry (6-digit code) - user types code
• Numeric Key Comparison - user verifies code matches
• OOB / Out of Band method

• TK (Temporary Key)
  • Only used in Pairing Phase
  • Not stored
• STK (Short Term Key)
  • Derived from TK & random values
  • Encrypt connection after Legacy Pairing
  • Not stored, only used for current session
• LTK (Long Term Key)
  • Legacy Pairing: derived from STK
  • Secure Connections: derive directly from ECDH
  • Stored for future connections

'Bonding': Process of storing LTK & other security information for future connections.