VPN? VPN VPN Tunneling L2F PPTP L2tp IPSEC IKE -2 -

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1 VPN ( )

2 VPN? VPN VPN Tunneling L2F PPTP L2tp IPSEC IKE -2 -

3 VPN Virtual Private Network : Extranet Intranet -3 -

4 -4 -

5 , network network network network, -5 -

6 Network interactive (, ) contents hosting, -6 -

7 , (,, ) (resource) QoS (best-effort), QoS,, (Leased Line), VPN +, -7 -

8 WAN network Leased Line, FrameRelay intranet -8 -

9 (VPN) ISP ISP ISP POP network, QoS pop : points of presence ISP -9 -

10 VPN, mobile user, telecommuter, extranet

11 VPN ( )

12 intranet VPN : LAN. Extranet VPN : Intranet VPN Remote Access VPN. Remote Access VPN : ISP

13 - 13 -

14 DATA Key management LAN to LAN Dial-up to LAN VPN IPSec(IP Security) Tunnel Endpoints Transit Internetwork Header Payload Transit Internetwork Tunnel Payload Tunneled Payload

15 VPN server Router firewall VPN client, - checkpoint, radguard, vpnet, shiva router access server VPN router VPN point-to-point tunneling - router cisco, shiva, intel,... firewall VPN bottleneck checkpoint,,

16 VPN Remote Access VPN PSTN, ISDN, DSL, Cable Modem... LAN to LAN VPN(Site-to-site VPN) LAN to LAN VPN LAN to Client VPN ISP VPN

17 Mobile Worker, Telecommuter, Client Initiated VPN PC QoS NAS( Network Access Server) Initiated VPN ISP

18 Client Initiated VPN PC VPN S/W server(gateway) tunnel public IP public IP : internet private IP : network : VPN S/W, upgrade Tunneling IPSec PPTP, L2TP

19 Client Initiated VPN

20 NAS Initiated VPN ISP NAS(Network Access Server) server(gateway) tunnel NAS VPN private IP internet, network client VPN s/w Tunneling L2TP, L2F cisco, Lucent, 3Com

21 NAS Initiated VPN

22 network network IP VPN CPE based VPN site VPN Core based VPN ISP VPN MPLS * CPE : Customer Promise Equipment

23 CPE based VPN VPN Microsoft, Novell, Checkpoint, VPNet, Lucent, Cisco, 3Com, CPE VPN ISP VPN management network manage Firewall manage VPN manage Tunneling IPSec

24 CPE based VPN

25 Core based VPN ISP (Router..) VPN VPN Core network QoS Service Management Tunneling IPSec MPLS

26 Core based VPN MPLS (Multi-Protocol Label Switching) Cisco Tag switching ATM, FrameRelay Label packet forwarding load Traffic Engineering QoS service

27 Core based VPN

28 LAN to LAN VPN VLL(Virtual Leased Line) Remote Authentication Dial-in User Service (RADIUS)

29 LAN to Client VPN PC VPN RAS

30 ISP VPN ISP VPN

31 - 31 -

32 Tunneling point-to-point tunnel Security Quality of Services Leased Line, FR Bandwidth

33 Tunneling Layer2 L2F(layer 2 Forwarding) PPTP(Point-to-Point Tunneling Protocol) L2TP(Layer 2 Tunneling Protocol) Layer 3 IPSEC(Internet Protocol Security) ATMP(Ascend Tunnel Management Protocol) VTP(Virtual Tunneling Protocol)

34 Tunneling

35 Security authentication( ) Integrity( ) encryption( ) DES (Data Encryption Standard) : CPU intensive 3DES RC5 MPPE

36 Quality of Service(QoS) Bandwidth RSVP : cisco CR-LDP : nortel diffserv (Differentiated Service) RFC 2474 RFC

37 L2F(Layer 2 Forwarding) Cisco, Nortel, Shiva ISP server tunnel server L2F tunnel direct-dial PPP/RAS home site home site gateway server domain ID FrameRelay ATM (tunneling IP ) PPP(point-to-point) : TACACSA+, RADIUS

38 - 38 -

39 L2F(Layer 2 Forwarding)

40 L2F Flow (PPP authentication)

41 L2F Tunnel Authentication

42 Frame

43 PPTP ( Point-to-Point Tunneling Protocol) 3COM, Microsoft, Ascend, US Robotics first popular tunneling standard, PPP Client/Server Windows 95 Windows NT 4.0 Mobile user home site Allows you to tunnel or encapsulate IPX and NetBEUI packets in a standard TCP/IP dial-up connection or a dedicated Internet connection PPTP uses the security policy you already have set up on the network Over 90 million PCs are PPTP-enabled--unlike other protocols

44 Bi-directional Tunnel Two mode client enabled ISP enabled Non IP protocol : IPX, Appletalk PAP, CHAP, MS-CHAP RC4(40bits/128bits) Microsoft dependent (Windows NT ) RAS vendor

45 L2TP : Layer2 Tunneling Protocol remote LAC(L2TP Access Server) Home gateway LNS(L2TP Network Server) remote access cost overhead flexibility scalability client initiated VPN

46 Hybrid of L2F and PPTP Emerging standard for VPN tunneling Multiple protocol : IP, IPX, AppleTalk non-ip network LAN-to-LAN VPN WAN : X.25, ATM, Frame Relay, SONET network traffic flow control : server congestion handling ( netw ork access system home gateway ) LAC (L2TP Access Concentrator) ISP NAS LNS (L2TP Network Server) edge (router, firewall)

47 L2TP Tunnel Structure

48 L2TP Incomming Call Flow emote user ISP PPP. SP Network LAC POP PPP Link nd User LNS LCP Negotiation LAC CHAP PAP End User Authentication ser name, Domain name User VPDN client User VPDN Client Client Access. VPDN client user name End Point mapping The LNS ) unnel End Point LAC LNS Session Tunnel. unnel L2TP Session End User. AC LCP CAHP/PAP Authentication LNS

49 2 Message Type ( ) - Control message : Establish, Maintenance, Clearing. L2TP Control Channel - Data message : Encapsulation PPP. Packet Loss Retransmit. 0 L2TP 32 T L X X S X O P X X X X Ver Tunnel ID Ns (opt) Offset size(opt) Length(opt) Session ID Nr (opt) Offset size(opt)

50 - - T bit: Message. 0 Data message 1 Control message -L bit : 1 Length. Control message 1. - X bit : - S bit : 1 Ns Nr. Control message 1. - O bit : 1 Offset. Control message 0. - P bit : 1 Data message Local queuing. Data message. Control message 0 - Ver : 2 L2TP 1 L2F - Length : Message - Tunnel ID : Control Connection ID - Session ID : Session ID - Ns : Data Control Message Sequence Number Nr: Control message Sequence Number Offset : Payload T L X X S X O P X X X X Ver Tunnel ID Ns (opt) Offset size(opt) L2TP Length(opt) Session ID Nr (opt) Offset size(opt)

51 L2F/L2TP opertation

52 PPTP L2TP Media IP GRE PPP PPP Payload draft-ietf-pppext-pptp-07.txt Media IP L2TP L2TP Payload draft-ietf-pppext-l2tp-12.txt

53 IETF IPSec working Group VPN tunneling layer 3 IPv6 Non-IPSec protocol Authentication Header(AH) protocol : Packet Payload Encrypt. Encapsulating Security Payload(ESP) protocol : Fully Encrypt Overload Encryption Algorithms DES(Data Encryt Standards), 3DES, RC5 Authentication Algorithms MD(Message Digest )5->128bit, SHA(Secure Hash Algorithm)1->160 bit IKE

54 (Authentication Header) ESP(Encapsulation Security Payload) IP (Security Association)

55 Enables transmission of sensitive information over unprotected networks such as the Internet IPSec (Confidentiality): packets encrypted before transmission (Integrity): authenticates packets at the destination peer to ensure that data has not been tampered during transmission (Authentication): peers authenticate source of all IPSEC protected packets (Anti-replay): prevents capture and replay of packets

56 . IPSec. IPSec RFC RFC 1825 : Security Architecture for the Internet Protocol RFC 1826 : IP Authentication Header RFC 1827 : IP Encapsulating Security Payload (ESP) RFC 1828 : IP Authentication Using Keyed MD5 (Message Digest) RFC 1829 : The ESP DES-CBC Transform RFC 2085 : HMAC-MD5 IP Authentication with Replay Prevention RFC 2104 : HMAC: Keyed-Hashing for Message Authentication

57 AH - Authentication Header IP datagram authentication, integrity data integrity, data origin authentication, optional Anti-replay protection : RFC 2402 inserted after the IP header and before any upper layer headers (integrity) MD5,SHA-1 message checksum IP (secret shared key) Replay AH header sequence number

58 IP Payload IP IP AH Payload AH IP IP AH Payload Next Payload (16 bits) Security Parameter Index (SPI) (32 bits) Sequence Number (32 bits) Authentication Data ( ) 32 bits

59 IP Payload IP IP IP Payload IP IP AH IP Payload AH IP

60 ESP - Encapsulating Security Payload Payload Encrypt -> AH Overhead IP datagram confidentiality, integrity data confidentiality optional data integrity, peer authentication, anti-replay protection : RFC 2406 Inserted after the IP header and before any upper layer headers DES(Data Eecrytion Standard, 53bit)/3DES IP packet : Replay sequence number

61 IP ESP Payload ESP tail ESP Auth Authentication Encryption Security Parameter Index Sequence Number Payload Data ( ) Padding (0~255 bytes) Pad Next Authentication Data ( ) 32 bits

62 IP Payload IP IP IP Payload IP IP ESP IP Payload ESP tail ESP Auth Encrypted Authenticated

63 Transport Mode IP payload Encrypt original IP header. byte. Public network device Source/Destination. QoS Processing. IP header clear 4 Traffic. AH-transfer mode IP header AH IP payload Authenticated except for mutable fields in IP header ESP-transfer mode IP header ESP header IP payload ESP trailer ESP auth Encrypted Authenticated

64 Tunnel Mode Original IP datagram Encrypt New IP Payload. Router Ipsec proxy Router Hosts Encryption Source Router Encrypt Ipsec Forwarding. Destination Router. End system Ipsec modyfi. Traffic. AH-tunnel mode New IP header AH IP header IP payload Authenticated except for mutable fields in New IP header ESP-tunnel mode New IP header ESP header IP header IP payload ESP trailer ESP auth Encrypted Authenticated

65 Transport Mode Tunnel Mode

66 Transport Mode Tunnel Mode IP Hdr AH TCP Hdr Data Authenticated Outer Original IP Hdr AH Inner IP Hdr TCP Hdr Data Authenticated IP Hdr ESP TCP Hdr Data Authenticated Encrypted Outer Original IP Hdr ESP Inner IP Hdr TCP Hdr Data Authenticated Encrypted IP Hdr AH ESP TCP Hdr Data Authenticated Encrypted

67 ESP : host AH : secure gateway Host A Secure gateway 1 Secure gateway 2 Host B IPSEC Authentication only Encryption and authentication IPSEC Between Host A and Secure gateway 1 IP header ESP header Payload ESP trailer ESP auth etween two ecure gateways New IP header AH IP header ESP header Payload ESP trailer ESP auth etween Host B and ecure gateway 2 IP header ESP header Payload ESP trailer ESP auth AH Added ESP applied packet

68 IPSec IP Certificate Authority Non-IPSec VPN VPN L2F, L2TP, PPTP, SOCKS

69 ( ) VPN LAN-to-LAN VPN Dialup-to-LAN VPN IPv6 Non-IPSec

70 Security association(sa) nego : protocol,, key key SA under IPSEC specifies next things the mode of the authentication algorithm used in AH and the keys to that authentication algorithm the ESP encryption algorithm mode and the keys to that encryption algorithm. the presence and size of(or absence of) any cryptographic synchronization to be used in that encryption algorithm. how you authenticate your communications(using what protocol, what encrypting algorithm, and what key). how you make your communication private(what algorithm, and what key). how often those keys are to be changed. the authentication algorithm mode, and transform for use in ESP plus the keys to be used by that algorithm. the key lifetimes. the lifetime of the SA itself

71 SA VPN SA SPI SA : SPI : SA unique number(32bit), AH /ESP header

72 Internet Key Exchange (IKE) a powerful, flexible negotiation protocol that allows users to agree on authentication methods, encryption methods, the keys to use, how long to use the keys before changing them, and that allows smart, secure key exchange key : Diffie-Helman Strong data encryption requires frequent key change Phase I - IKE peer secure channel Phase II - peer SA negotiation Dynamically exchanges keys for bulk data encryption

73 Internet Key Exchange (IKE)

74 Internet Key Exchange (IKE) Coupled with IPSec s key management systems Employed to exchange information used to generate encryption key Agrees on encryption and data authentication algorithms Each participant has pair of keys; one private and one public. Digital signatures supplied by a Certificate Authority. This is a Top Secret Message for ACME Customers The Customers Data + + The Encryption Operation (e.g. DES) The Key = The Encrypted Data

75 Encrypted communication Transmitted sender Ciphertext plaintext Encryption Decryption receiver plaintext Encryption Key Secret key public key Decryption Key secret key single key, encryption key decryption key symmetric key, N N key public key a pair of keys, public key private key asymmetric key

76 Secret key -> Private Enterprise Network DES(Data Encryption Standard) Triple-DES IDEA, Blowfish, CAST-128 DES block cipher : 64bit plaintext ==> 64bit ciphertext key length = 56 bits 16 permutation( ) of secret key Triple-DES DES 3 key length = 56bit * 3 = 168 bits

77 DES 3-DES DES : brute-force attack, plaintext resource 3-DES : brute-force attack computer system Transmitted sender Ciphertext plaintext Encryption Decryption receiver plaintext Secret Key Secret Key

78 Public key RSA(Rivest-Shamir-Adleman) system 2 key (Public key, Private key) Public key :, Private key : receiver,, Transmitted sender Ciphertext plaintext Encryption Decryption receiver plaintext Receiver s Public Key Receiver s Private Key

79 Public key -> CPU load secret key key digital signature application encryption : sender : receiver public key receiver: receiver private key authentication : sender : sender private key everyone : sender public key

80 PKI :,,, PKI

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