Network Security Architecture 1 Additional Reading Firewalls and - PowerPoint PPT Presentation

Network Security Architecture 1

Additional Reading  “Firewalls and Internet Security: Repelling the Wily Hacker”, Cheswick, Bellovin, and Rubin. − New second edition  “Firewall and Internet Security, the Second Hundred (Internet) Years” http://www.cisco.com/warp/public/759/ipj_2- 2/ipj_2-2_fis1.html 2

Overview  Network Security Architecture − Wireless − Security Domains − VPN  Firewall Technology − Address Translation − Denial of Service attacks  Intrusion Detection  Both firewalls and IDS are introductions. 3

802.11 or Wi-Fi  IEEE standard for wireless communication − Operates at the physical/data link layer − Operates at the 2.4 or 5 GHz radio bands  Wireless Access Point is the radio base station − The access point acts as a gateway to a wired network e.g., ethernet − Can advertise Service Set Identifier (SSID) or not  Doesn't really matter, watcher will learn active SSIDs  Laptop with wireless card uses 802.11 to communicate with the Access Point 4

WEP  “Wired Equivalency Privacy” -- early technique for encrypting wireless communication  Authenticated devices use a key and initialization vector to seed RC4---a stream cipher v  V (initialization vector) is changed every frame − Dangers of repeated encryption using the same key stream-- XOR of ciphertexts gives XOR of plaintexts  And if some of the plaintext is known, the other is recovered 5

Frame transmission  RC4(v,k) is stream generated by long-lived key k and initialization vector v  v transmitted in the clear  v is only 24 bits long---since k is long-lived (and used by all devices)---you are assured of getting repeated key sequences − And knowing when you have them! Because v is in the clear… 6

Security Mechanisms  MAC restrictions at the access point − “white list” : Protects servers from unexpected clients − Unacceptable in a dynamic environment − No identity integrity. You can reprogram your card to pose as an “accepted” MAC.  IPSec − To access point or some IPSec gateway beyond − Protects clients from wireless sniffers − Used by UIUC wireless networks 802.11i  − Authentication and integrity integral to the 802.11 framework 7 − WEP, WPA, WPA2

Network Security Protocols  SSL/TLS − Secure sockets layer / Transport layer security − Used mainly to secure Web traffic  SSH − Secure Shell − Remote login  IPsec − IP-level security suite 8 8

SSL  Mid ‘90s introduced concerns over credit card transactions over the Internet  SSL designed to respond to thse concerns, develop e-commerce  Initially designed by Netscape, moved to IETF standard later 9 9

SSL model A client and a server  Implements a socket interface  Any socket-based application can be made to run on top of − SSL Protect against:  Eavesdroppers − MITM attacks − Server has X.509 certificate  Client may have a certificate, too − Provides encryption, and authentication of server  10 10

SSL Handshake, (1) Client requests “https” connection with server  Passes information to server in message describing − available protocols Key exchange method (e.g., RSA, Diffie-Hellman, DSA)  Cipher (e.g., Triple DES, AES)  Hash (e.g., HMAC-MD5, HMAC-SHA)  Compression algorithms  Client nonce  Server responds with messages that  Selects (key xchg, cipher, hash, compression) − Provide server’s certificate − Server nonce − 11 11

SSL Handshake, (2) Client verifies server cert  Likely that cert was signed by a CA whose cert is in the − browser already generates pre_master_secret, encrypts using server’s  public key, sends it Client and server separately compute session key and  MAC keys (these from prior random numbers passed) Client sends MAC of all messages it sent to server in  this handshake Server sends MAC of all messages it sent to client in  this exchange 12 12

SSL certificates 13 13

SSL history  SSLv2 1994  SSLv3 1996 − Fixed security problems  TLS v1.0 1999  TLS v1.1 2006 14 14

SSL key lengths  Earlier versions used 40-bit keys for export reasons  Later versions switched to 128-bit keys, with an option to use 40-bit ones with legacy servers/clients  Rollback attack: − MITM 15 15

SSL sequence  Negotiate parameters  Key exchange  Authentication  Session 16 16

SSL negotiation  Choice of cipher suites, key exchange algorithms, protocol versions  E.g. : choice of 40- or 128-bit keys for export reasons  Rollback attack: MITM chooses least secure parameters 17 17

SSL key exchange  Diffie-Hellman key exchange  RSA-based key exchange − Encrypt secret s with public key of server 18 18

SSL session  Use ChangeCipherSpec message to start encrypting data  Encryption: RC4, also DES, 3DES, AES, ...  Authentication: HMAC, using MD5 or SHA1 19 19

SSL session…pushing the bits Blocks, sized up to 18K Algorithm agreed-up on in handshake MAC added for authentication Algorithm, key, agreed-up on in handshake Passed on to TCP 20 20

SSL pitfalls  Hard to set up − Expensive certificates − Resource-intensive Insufficient verification  Do people notice the lock icon? − Do people check the URL? − Improper use  21 21

IPsec Designed as part of IPv6 suite  One of the key features v6 was supposed to bring − Backported to IPv4  Two options: AH (authentication) and ESP  (encapsulated security) Two modes: transport and tunnel  Readable resource  http://www.unixwiz.net/techtips/iguide-ipsec.html 22 22

Transport vs. Tunnel Mode Grand vision: eventually, all IP packets will be  encrypted and authenticated Transport mode: add headers to IP to do so  May include encryption, authentication, or both Reality: Most computers don’t support IPsec (more on  why later) Tunnel mode: use IPsec between two gateways to  relay IP packets through “untrusted cloud” 23 23

Tunnel Mode P P P P P P H1 H2 24 24

AH - Authentication Simple design: add header with authentication data  Security parameters − Authentication data : just an HMAC with − shared key to compute Integrity Check Value (ICV) Different of the HMAC architecture picture 25 25

AH Header  Next hdr is protocol type of the following header  AH Length gives size of AH header  SPI -- sort of a switch code indicating which set of security parameters apply  Sequence number --- basically a nonce to prevent replay attacks  HMAC field 26

AH diagram HMAC applied only to fields in yellow 27 27

Piggybacking AH on IPv4  The structure allows IPSec logic to − peel off the AH header, do verification and/or decoding, − Modify “length” and “next protocol” fields to be that of an AH-free IP packet − Push the packet up the stack with higher levels none the wiser that IPSec was present 28

Tunneling in IPSec  Change the source and destination addresses to be the tunnel endpoints  IPSec tunnel endpoints strip off AH header, to authentication and endcoding  Original IP packet is part of the payload, just released into the local network 29

AH in Tunnel Mode How to detect tunnel mode Original IP header 30 30

ESP - Encapsulated Security Payload  Encapsulate data − Encapsulate datagram rather than add a header − Encrypt & authenticate Authentication header based only on encapsulation--- not Iaddresses---hold that thought--- 31 31

ESP diagram SPI describes encryption Protocol using TCP is Completely hidden Padding and pad len support block encryption 32 32

Key management ESP and AH use session keys  Sessions are called Security Associations  Indexed by protocol, IP address, SPI − ISAKMP: Internet Security Association Key  Management Protocol Authenticates parties − Establishes session keys − Authentication  Big global PKI (DNSSEC??) − Manual configuration − 33 33

IPsec redux Deployment of IPsec limited  Some reasons  Global PKI infrastructure hard to set up − Fixes a “solved” problem − SSL & SSH work well  IPsec success: VPNs  Use tunnel mode of IPsec − 34 34

Perimeter Defense  Is it adequate? − Locating and securing all perimeter points is quite difficult  Less effective for large border − Inspecting/ensuring that remote connections are adequately protected is difficult − Insiders attack is often the most damaging 35

Virtual Private Networks  A private network that is configured within a public network  A VPN “appears” to be dedicated network to customer  The customer is actually “sharing” trunks and other physical infrastructure with other customers  Security? − Depends on implementing protocol 36