Trust and Threats

• security eventually fails – assumption on trust of another
• threat is just a potential failure scenario
• security comes with a cost (usually)
• research into a trusted computing base
• original internet did not consider threats from within the network

Example Security Systems

• varied layers of security implementation depending on applications
  • Application to IP
  • PGP, SSH, TLS/SSL, IPSec, 802.11i

PGP

• provides authentication, confidentiality, data integrity
• relies on a “web of trust”
• sender/receive with public/private key
  • sign message with private key
  • encrypt message with newly generated one-time session key
  • encrypt session key with bob’s public key, and append that to the message
  • base64 encode the ascii-compatible representation
• PGP doesn’t defend against lost mail, but alice can at least be guaranteed only bob can read the message

SSH

• 3 protocols
  • SSH-TRANS
    • establish secure communication channel - similar to TLS?
    • make assumption typically when connecting that the server you connect to is “legit”
    • server always starts connection with its public key
  • SSH-AUTH
    • user authenticates with password/cert
  • SSH-CONN

TLS

• SSL originally developed by netscape
• negotiate cryptography algorithms at runtime
  • data integrity hash
  • secret-key cipher for confidentiality
  • session key establishment
  • (optional) compression
• session-based handshake to obtain “master secret”
  • client-server: list of algo combinations
  • server-client: chosen algo combinations
  • server-client: server authentication msgs
  • client-server: client authentication messages
  • client-server: HMAC of master secret and previous messages as seen by client
  • server-client: HMAC of master secret and previous messages as seen by server
• record protocol
  • within a session, TLS adds confidentiality to underlying transport. data sent through tls is:
    • fragmented/coalesced
    • optionally compressed
    • integrity protected with hmac
    • encrypted with secret-key cipher
    • passed to transport layer for transmission
  • TLS can resume a session (optimize away handshake)
    • originally due to bad original http implementation
• TLS1.3 improves resumption to send a secure ticket instead of unsecured session ID

IPSec

• security implemented at lowest layer
• required in ipv6
• IPSec provides
  • Authentication Header (AH)
  • Encapsulating Security Payload (ESP)
  • Internet Security Association and Key Management Protocol (ISAKMP)
• Security association (SA) is a one-way connection with security properties
• ipsec uses an SPI (ID number on IP packet)
  • SA established/negiotated, modified, deleted with ISAKMP
• transport mode and tunnel mode
  • transport mode acts like normal TCP/UDP
  • tunnel mode encapsulates data as an IP packet
• ESP has header an trailer on data in tunnel mode

802.11i

• standard for encrypting wireless traffic
• WEP broken early
• WPA3 replacement
• WPA result is a pairwise master key
• personal mode uses weaker security (PSK)
• EAP (extensible authentication protocol) used between AP and Authentication server to check if device can connect to network
• need to have mutual authentication between AP and AS
• after obtaining pairwise master key, AP and device execute session establishment protocol with a 4-way handshake
  • result is Pairwise transient key (set of keys), session key, temporal key

Firewalls

• blocks network traffic on particular network ports
• assumes internal computer is trusted zone
• NAT+firewall occasionally found in same device