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Virtual Private Networks (VPN)

Virtual Private Networks (VPN). Generic Routing Encapsulation (GRE) TLS (SSL-VPN). 1. Generic Routing Encapsulation (GRE). Tunneling Encapsulation with delivery header The addresses in the delivery header are the addresses of the head-end and the tail-end of the tunnel. Delivery header.

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Virtual Private Networks (VPN)

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  1. Virtual Private Networks (VPN) Generic Routing Encapsulation (GRE) TLS (SSL-VPN) CN8814: Network Security

  2. 1. Generic Routing Encapsulation (GRE) • Tunneling • Encapsulation with delivery header • The addresses in the delivery header are the addresses of the head-end and the tail-end of the tunnel Delivery header 20.1.1.1/30.1.1.1 GRE 10.1.1.1/10.2.1.1 20.1.1.1 30.1.1.1 10.1.1.1/10.2.1.1 tunnel Private network site Private network site 10.1.0.0/16 10.2.0.0/16 Public Network 10.1.1.1 10.2.1.1 CN8816: Network Security

  3. 1. Generic Routing Encapsulation (GRE) • Structure of a GRE encapsulated packet CN8816: Network Security

  4. 1. Generic Routing Encapsulation (GRE) • IP access of the tunnel through the tunnel interface 20.1.1.1/30.1.1.1 GRE 10.1.1.1/10.2.1.1 Gateway Gateway Internet serial 0/0 serial 0/0 20.1.1.1 30.1.1.1 tunnel 0 tunnel 0 10.1.1.1/10.2.1.1 e0 e0 10.1.1.1/10.2.1.1 10.1.1.1/10.2.1.1 10.2.0.0/16 10.1.0.0/16 Customer Sites CN8816: Network Security

  5. 1. Generic Routing Encapsulation (GRE) • Tunneling mechanism at IP • Outbound traffic Routing table of R1 20.1.1.1/30.1.1.1 10.1.0.0/16 e0 20.1.1.1/30 s0 10.2.0.0/16 tunnel0 0.0.0.0/0 s0 (6) (3) GRE IP (7) (4) (5) (2) (8) … s0 e0 Tunnel0 (9) (1) 20.1.1.1/30.1.1.1 [10.1.1.1/10.2.1.1] 10.1.1.1/10.2.1.1 CN8816: Network Security

  6. 1. Generic Routing Encapsulation (GRE) • Inbound traffic Routing table of R2 10.2.0.0/16 e0 30.1.1.1/30 s0 10.2.0.0/16 tunnel0 0.0.0.0/0 s0 (6) (3) GRE IP (5) (4) (2) (7) 10.1.1.1/10.2.1.1 … s0 e0 Tunnel 0 (8) (1) 20.1.1.1/30.1.1.1 [10.1.1.1/10.2.1.1] 10.1.1.1/10.2.1.1 CN8816: Network Security

  7. 1. Generic Routing Encapsulation (GRE) • Example interface tunnel0 ip unnumbered s0 tunnel source s0 tunnel destination 30.1.1.1 ! ip route 10.2.0.0 255.255.0.0 tunnel0 interface tunnel0 ip unnumbered s0 tunnel source s0 tunnel destination 20.1.1.1 ! ip route 10.1.0.0 255.255.0.0 tunnel0 Routing table of R1 10.1.0.0/16 e0 20.1.1.1/30 s0 10.2.0.0/16 tunnel0 0.0.0.0/0 s0 CN8816: Network Security

  8. 1. Generic Routing Encapsulation (GRE) • GRE tunneling with routing Routing updates (subnets of 10.0.0.0/8) CN8816: Network Security

  9. 3. IP Security (IPsec) • IPsec and Dynamic Routing • IPsec-protected traffic must be pre-defined • IPsec only supports static routing The IPsec tunnel is setup for the traffic between 10.1.0.0/16 and 10.2.0.0/16 IPsec tunnel 10.1.0.0/16 10.2.0.0/16 10.3.0.0/16 The tunnel will not support the traffic to the new site New site CN8816: Network Security

  10. 3. IP Security (IPsec) • IPsec/GRE • GRE defines a tunnel interface • IPsec transport mode provides the security Routing table 10.1.0.0/16 inside 30.0.0.0/8 outside 10.2.0.0/16 tunnel0 (4) IP GRE (5) 10.3.0.0./16 tunnel0 IPsec (transport) (2) (1) (3) (6) outside inside Tunnel0 10.1.1.1/10.2.1.1 20.1.1.1/30.1.1.1 Ipsec_protected 10.1.1.1/10.3.1.1 CN8816: Network Security

  11. 3. IP Security (IPsec) • Virtual Tunnel Interface • Provide secure tunnel by associating the virtual interface with IPsec 20.1.1.1/30.1.1.1 Protected packet Routing table 10.1.0.0/16 inside 30.0.0.0/8 outside 10.2.0.0/16 tunnel0 (5) IP IPsec 10.3.0.0./16 tunnel0 (3) (2) (6) (4) inside outside Tunnel0 10.1.1.1/10.2.1.1 10.1.1.1/10.3.1.1 CN8816: Network Security

  12. 2. Transport-Layer Security (TLS) • TLS architecture • Provide security connection between two application entities Error and alert reporting -Authentication -Cipher suit negotiation -Keys generation Encryption, MIC & Compression CN8816: Network Security

  13. 2. Transport-Layer Security • TLS Record protocol • Four connection states: current read and write states, and the pending read and write states • Security parameters: • Connection end (client/server) • Bulk encryption algorithm: type, key_size, … • MAC algorithm: hash_size • Compression algorithm • Master Secret • Client random, Nc • Server random, Ns • Keys • Client_MAC_Write, Server_MAC_Write, Client_Write_Key, Server_Write_Key, IVs CN8816: Network Security

  14. 2. Transport-Layer Security • Messages are processed using the current read or write states Type Version Length Write/read MAC secret Fragment (Compressed) Write/read Key ICV Padding (for CBC block cipher) Pad length CN 8816: Network Security

  15. 2. Transport-Layer Security • Key Generation • Master_secret = PRF(gxy mod N, “master secret”, Nc+Ns) • x and y are the DE parameters • Nc and Ns are the nonces generated by the client and the server, respectively • Master_secret is always 48 bytes • PRF(secret, label, seed) = P_hash(secret, label+seed) • P_hash(secret, seed) = HMAC(secret, A(1)+seed) + HMAC(secret, A(2)+seed) + … + HMAC(secret, A(n)+seed) • A(0) = seed A(i) = HMAC(secret, A(i-1) CN 8816: Network Security

  16. 2. Transport-Layer Security • By default, the hash used in HMAC is SHA-256 • Need two HMAC iterations to generate the Master secret • Key generation • Key_block = PRF(Master_secret, “key expansion”, Ns+Nc) Truncated (16 bytes) Master secret (48 bytes) MAC client Write (Kmc) MAC server Write (Kms) Client Write Key (Kwc) Server Write Key (Kws) IVs (options) … CN 8816: Network Security

  17. 2. Transport-Layer Security • Handshake protocol • Client hello and server response phase Client Server Client Hello: session ID, Nc, cipher suit list, compression alg. list Server Hello: Ns, cipher suit, compression alg. Server Certificate O+ Key Exchange: Signature O+ Certificate request O- Server Hello Done O+ => Often; O- => Less often CN 8816: Network Security

  18. 2. Transport-Layer Security • Client reponse and change-cipher specification phase Client Server Client Certificate O- Key exchange Certificate verify: signature O- Change cipher specification Finished: session authentication Change cipher specification Finished: session authentication Application Data CN 8816: Network Security

  19. 2. Transport-Layer Security • The handshake protocol allows quick setup of new TLS connection using the old session master secret • The master secret is allowed to be kept for 24 hours Client Server Client Hello: session ID, Nc Generate keys Server Hello: Ns Generate keys Change cipher spec Finished Change cipher spec Finished Data CN 8816: Network Security

  20. 2. Transport-Layer Security • Change Cipher Spec Protocol • invoke the transition from the pending states to current states Client Server Pending states Kmc, Kwc Kmc, Kwc Pending states Kms, Kws Kms, Kws (1) ChangeCipherSpecs (4) ChangeCipher Specs Protocol (1) ChangeCipher Specs Protocol (5) (2) (4) ChangeCipherSpecs (3) (3) finished (3) Handshake Handshake (6) (6) finished (6) Current states Current states CN8816: Network Security

  21. 2. Transport-Layer Security • Alert Protocol • Alert messages convey the severity of the message and a description of the alert • Alert levels: warning or fatal • Alert messages with a level of fatal result in the immediate termination of the connection • Alert types: • Close notification • Error alerts CN8816: Network Security

  22. 2. Transport-Layer Security • SSL (TLS) VPN • Tunnel interface is used to support secure tunnel connection SSL-VPN client SSL-VPN web server • Upload of SSL-VPN client Appl. Web browser (1) (9) (3) (17) (2) TLS handshake protocol (5) TLS TLS (18) (10) (16) TCP/UDP TCP/UDP (15) (6) (11) (8) IP IP (19) (7) (12) (14) (20) (13)TLS protected datagram tun0 eth0 Outside Inside tun0 CN8816: Network Security

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