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

CN8814: Network Security 1

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

10.1.1.1/10.2.1.1

10.1.1.1/10.2.1.1GRE20.1.1.1/30.1.1.1

tunnel

Delivery header

10.1.1.1 10.2.1.1

10.1.0.0/16 10.2.0.0/16

20.1.1.1 30.1.1.1

Public Network

Private network site

Private network site




Structure of a GRE encapsulated packet


IP access of the tunnel through the tunnel interface



serial 0/0

tunnel 0

serial 0/0

tunnel 0

20.1.1.1 30.1.1.1Internet

10.1.0.0/16 10.2.0.0/16

Gateway Gateway

Customer Sites

10.1.1.1/10.2.1.1

10.1.1.1/10.2.1.1

10.1.1.1/10.2.1.1

20.1.1.1/30.1.1.1 GRE 10.1.1.1/10.2.1.1

e0 e0




Tunneling mechanism at IP Outbound traffic

IP

…s0 e0 Tunnel0

Routing table of R1

10.1.0.0/16 e020.1.1.1/30 s010.2.0.0/16 tunnel00.0.0.0/0 s0

10.1.1.1/10.2.1.1

(1)

(2)

(3)

(4)

GRE

(5)

(6)

20.1.1.1/30.1.1.1

(7)

(8)

20.1.1.1/30.1.1.1 [10.1.1.1/10.2.1.1]

(9)




Inbound traffic

IP

…s0 e0 Tunnel0

Routing table of R2

10.2.0.0/16 e030.1.1.1/30 s010.2.0.0/16 tunnel00.0.0.0/0 s0

GRE

20.1.1.1/30.1.1.1 [10.1.1.1/10.2.1.1]

(1)

(2)

(3)

10.1.1.1/10.2.1.1(4)(5)

(6)

(7)

10.1.1.1/10.2.1.1

(8)




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 e020.1.1.1/30 s010.2.0.0/16 tunnel00.0.0.0/0 s0

GRE tunneling with routing




Routing updates(subnets of 10.0.0.0/8)

3. IP Security (IPsec)

IPsec and Dynamic Routing IPsec-protected traffic must be pre-defined

IPsec only supports static routing



10.1.0.0/16 10.2.0.0/16

The IPsec tunnel is setup for the traffic between 10.1.0.0/16 and

10.2.0.0/16

10.3.0.0/16The tunnel will not support the traffic to

the new siteNew site

IPsec tunnel


IPsec/GRE GRE defines a tunnel interface IPsec transport mode provides the security



IP

insideoutside Tunnel0

Routing table10.1.0.0/16 inside30.0.0.0/8 outside10.2.0.0/16 tunnel0

GRE

10.1.1.1/10.2.1.1

(4)

(5)

(6)

IPsec(transport)

Ipsec_protected20.1.1.1/30.1.1.1

(1)(2)

(3)

10.3.0.0./16 tunnel0

10.1.1.1/10.3.1.1


Virtual Tunnel Interface Provide secure tunnel by associating the virtual

interface with IPsec



IP

inside outside Tunnel0

Routing table10.1.0.0/16 inside30.0.0.0/8 outside10.2.0.0/16 tunnel0

IPsec

10.1.1.1/10.2.1.1

(4)

(5)

(6)

Protected packet20.1.1.1/30.1.1.1

(2) (3)10.3.0.0./16 tunnel0

10.1.1.1/10.3.1.1



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



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



CN 8816: Network Security 14

Messages are processed using the current read or write states

Fragment

Type Version Length

ICV

Padding (for CBC block cipher)Pad length

Write/readMAC secret

Write/readKey

(Compressed)


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)




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)



Master secret (48 bytes) Truncated(16 bytes)

MAC clientWrite (Kmc)

MAC serverWrite (Kms)

Client Write Key (Kwc)

Server Write Key (Kws) IVs (options) …


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


Client reponse and change-cipher specification phase



Client Server

Client Certificate

Key exchange

Certificate verify: signature

Change cipher specification

Finished: session authentication

Change cipher specification

O-

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




Client Server

Client Hello: session ID, Nc

Server Hello: Ns

Change cipher spec

Finished

Change cipher spec

Finished

Data

Generate keys

Generate keys




Change Cipher Spec Protocol invoke the transition from the pending states to current

states

Client Server

Currentstates

Currentstates

Pendingstates

Pendingstates

ChangeCipherSpecs Protocol

Kmc, Kwc Kmc, Kwc

Kms, Kws Kms, Kws

(1)(1) ChangeCipherSpecs

(2)

Handshake(3) (3) finished

Handshake(3)

ChangeCipherSpecs Protocol

(4)(4) ChangeCipherSpecs

(5)

(6)(6) finished(6)




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




Web browserSSL-VPN web server

TLS

TCP/UDP

TLS

TCP/UDP

IP IP

eth0tun0 InsideOutside tun0

SSL-VPNclientAppl.

(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)

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

Documents

tunnel0 gre

virtual interface

ip security ipsec ipsecgre

00s0 gre

ipsec transport ipsec

secure tunnel

routing table of r2

network security9