CN8814: Network Security1 Virtual Private Networks (VPN) Generic Routing Encapsulation (GRE) TLS (SSL-VPN)

Virtual Private Networks (VPN) CN8816: Network Security2 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 / GRE / tunnel Delivery header / / Public Network Private network site Private network site

Virtual Private Networks (VPN) CN8816: Network Security3 1. Generic Routing Encapsulation (GRE) Structure of a GRE encapsulated packet

1. Generic Routing Encapsulation (GRE) IP access of the tunnel through the tunnel interface Virtual Private Networks (VPN) CN8816: Network Security4 serial 0/0 tunnel 0 serial 0/0 tunnel Internet / /16 Gateway Customer Sites / / GRE / e0

Virtual Private Networks (VPN) CN8816: Network Security5 1. Generic Routing Encapsulation (GRE) Tunneling mechanism at IP Outbound traffic IP … s0e0Tunnel0 Routing table of R /16e /30s /16tunnel /0s / (1) (2) (3) (4) GRE (5) (6) / (7) (8) / [ / ] (9)

Virtual Private Networks (VPN) CN8816: Network Security6 1. Generic Routing Encapsulation (GRE) Inbound traffic IP … s0e0Tunnel 0 Routing table of R /16e /30s /16tunnel /0s0 GRE / [ / ] (1) (2) (3) / (4) (5) (6) (7) / (8)

Virtual Private Networks (VPN) CN8816: Network Security7 1. Generic Routing Encapsulation (GRE) Example interface tunnel0 ip unnumbered s0 tunnel source s0 tunnel destination ! ip route tunnel0 interface tunnel0 ip unnumbered s0 tunnel source s0 tunnel destination ! ip route tunnel0 Routing table of R /16e /30s /16tunnel /0s0

GRE tunneling with routing Virtual Private Networks (VPN) CN8816: Network Security8 1. Generic Routing Encapsulation (GRE) Routing updates (subnets of /8)

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

3. IP Security (IPsec) IPsec/GRE GRE defines a tunnel interface IPsec transport mode provides the security Virtual Private Networks (VPN) CN8816: Network Security10 IP insideoutside Tunnel0 Routing table /16 inside /8 outside /16 tunnel0 GRE / (4) (5) (6) IPsec (transport) Ipsec_protected / (1) (2) (3) /16 tunnel /

3. IP Security (IPsec) Virtual Tunnel Interface Provide secure tunnel by associating the virtual interface with IPsec Virtual Private Networks (VPN) CN8816: Network Security11 IP insideoutside Tunnel0 Routing table /16 inside /8 outside /16 tunnel0 IPsec / (4) (5) (6) Protected packet / (2) (3) /16 tunnel /

Virtual Private Networks (VPN) CN8816: Network Security12 2. Transport-Layer Security (TLS) TLS architecture Provide security connection between two application entities -Authentication -Cipher suit negotiation -Keys generation Encryption, MIC & Compression Error and alert reporting

Virtual Private Networks (VPN) CN8816: Network Security13 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

2. Transport-Layer Security Virtual Private Networks (VPN) CN 8816: Network Security14 Messages are processed using the current read or write states Fragment TypeVersionLength ICV Padding (for CBC block cipher) Pad length Write/read MAC secret Write/read Key (Compressed)

2. Transport-Layer Security Key Generation Master_secret = PRF(g xy 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) Virtual Private Networks (VPN) CN 8816: Network Security15

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) Virtual Private Networks (VPN) CN 8816: Network Security16 Master secret (48 bytes) Truncated (16 bytes) MAC client Write (Kmc) MAC server Write (Kms) Client Write Key (Kwc) Server Write Key (Kws) IVs (options)…

2. Transport-Layer Security Handshake protocol Client hello and server response phase Virtual Private Networks (VPN) CN 8816: Network Security17 ClientServer 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

2. Transport-Layer Security Client reponse and change-cipher specification phase Virtual Private Networks (VPN) CN 8816: Network Security18 ClientServer Client Certificate Key exchange Certificate verify: signature Change cipher specification Finished: session authentication Change cipher specification O- Finished: session authentication Application Data

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 Virtual Private Networks (VPN) CN 8816: Network Security19 2. Transport-Layer Security Client Server Client Hello: session ID, Nc Server Hello: Ns Change cipher spec Finished Change cipher spec Finished Data Generate keys

Virtual Private Networks (VPN) CN8816: Network Security20 2. Transport-Layer Security Change Cipher Spec Protocol invoke the transition from the pending states to current states ClientServer Current states Current states Pending states Pending states ChangeCipher Specs Protocol K mc, K wc K ms, K ws (1) (1) ChangeCipherSpecs (2) Handshake (3) (3) finished Handshake (3) ChangeCipher Specs Protocol (4) (4) ChangeCipherSpecs (5) (6)(6) finished (6)

Virtual Private Networks (VPN) CN8816: Network Security21 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

SSL (TLS) VPN Tunnel interface is used to support secure tunnel connection Virtual Private Networks (VPN) CN8816: Network Security22 2. Transport-Layer Security Web browser SSL-VPN web server TLS TCP/UDP TLS TCP/UDP IP eth0tun0InsideOutsidetun0 SSL-VPN client Appl. (1) (2) TLS handshake protocol (3) (4)Upload of SSL- VPN client (5) (6) (7) (8) (9) (10) (11) (12) (13)TLS protected datagram (14) (15) (16) (17) (18) (19) (20)