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Network Security Architecture

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Title: Network Security Architecture Author: David Nicol Last modified by: David Nicol Created Date: 4/8/2010 3:35:50 PM Document presentation format – PowerPoint PPT presentation

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Title: Network Security Architecture


1
Network Security Architecture
2
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/war
    p/public/759/ipj_2-2/ipj_2-2_fis1.html

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

4
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

5
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 (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

v
6
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

7
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
  • WEP, WPA, WPA2

8
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
9
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
10
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
11
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 servers certificate
  • Server nonce

11
12
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
    servers 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
13
SSL certificates

13
14
SSL history
  • SSLv2 1994
  • SSLv3 1996
  • Fixed security problems
  • TLS v1.0 1999
  • TLS v1.1 2006

14
15
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
16
SSL sequence
  • Negotiate parameters
  • Key exchange
  • Authentication
  • Session

16
17
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
18
SSL key exchange
  • Diffie-Hellman key exchange
  • RSA-based key exchange
  • Encrypt secret s with public key of server

18
19
SSL session
  • Use ChangeCipherSpec message to start encrypting
    data
  • Encryption RC4, also DES, 3DES, AES, ...
  • Authentication HMAC, using MD5 or SHA1

19
20
SSL sessionpushing 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
21
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
22
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
23
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 dont support IPsec (more
    on why later)
  • Tunnel mode use IPsec between two gateways to
    relay IP packets through untrusted cloud

23
24
Tunnel Mode
H1
H2
24
25
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
26
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

27
AH diagram
HMAC applied only to fields in yellow
27
28
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

29
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

30
AH in Tunnel Mode
  • How to detect
  • tunnel mode

Original IP header
30
31
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
32
ESP diagram
SPI describes encryption
Protocol using TCP is Completely hidden
Padding and pad len support block encryption
32
33
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
34
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
35
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

36
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

37
Multiple VPN Technologies
  • IPSec
  • Confidentiality? Yes
  • Data Integrity? Yes
  • User Authentication? Yes
  • Network access control? Yes
  • Client configuration required.
  • VLAN Layer 2 tunnelling technology
  • Confidentiality? No
  • Data Integrity? No
  • User authentication? Yes
  • Network access control? Yes
  • Not viable over non-VLAN internetworks
  • SSL
  • Confidentiality? Yes
  • Data integrity? Yes
  • User authentication? Yes
  • Network access control? No
  • In addition, limited traffic

38
Security Domains with VPNs
39
Typical corporate network
Firewall
Demilitarized Zone (DMZ)
Intranet
Mail forwarding
DNS (DMZ)
Web Server
File Server
Web Server
Firewall
Mail server
DNS (internal)
User machines
User machines
User machines
Internet
40
VPN using IPSec
  • ESP does the encryption
  • Difficulty with NAT means ESPAuth in tunnel mode
  • Requires VPN gateway---view is a tunnel between
    two trusted networks

40
41
VPN using IPSec
42
Firewall Goal
  • Insert after the fact security by wrapping or
    interposing a filter on network traffic

43
Application Proxy Firewall
  • Firewall software runs in application space on
    the firewall
  • The traffic source must be aware of the proxy and
    add an additional header
  • Leverage basic network stack functionality to
    sanitize application level traffic
  • Block java or active X
  • Filter out bad URLs
  • Ensure well formed protocols or block suspect
    aspects of protocol

44
Packet Filter Firewall
  • Operates at Layer 3 in router or HW firewall
  • Has access to the Layer 3 header and Layer 4
    header
  • Can block traffic based on source and destination
    address, ports, and protocol
  • Does not reconstruct Layer 4 payload, so cannot
    do reliable analysis of layer 4 or higher content

45
Stateful Packet Filters
  • Evolved as packet filters aimed for proxy
    functionality
  • In addition to Layer 3 reassembly, it can
    reconstruct layer 4 traffic
  • Some application layer analysis exists, e.g., for
    HTTP, FTP, H.323
  • Called context-based access control (CBAC) on IOS
  • Configured by fixup command on PIX
  • Some of this analysis is necessary to enable
    address translation and dynamic access for
    negotiated data channels
  • Reconstruction and analysis can be expensive.
  • Must be configured on specified traffic streams
  • At a minimum the user must tell the Firewall what
    kind of traffic to expect on a port
  • Degree of reconstruction varies per platform,
    e.g. IOS does not do IP reassembly

46
Traffic reconstruction
47
Access Control Lists (ACLs)
  • Used to define traffic streams
  • Bind ACLs to interface and action
  • Access Control Entry (ACE) contains
  • Source address
  • Destination Address
  • Protocol, e.g., IP, TCP, UDP, ICMP, GRE
  • Source Port
  • Destination Port
  • ACL runtime lookup
  • Linear
  • N-dimensional tree lookup (PIX Turbo ACL)
  • Object Groups
  • HW classification assists

48
Ingress and Egress Filtering
  • Ingress filtering
  • Filter out packets from invalid addresses before
    entering your network
  • Egress filtering
  • Filter out packets from invalid addresses before
    leaving your network

49
Denial of Service
  • Example attacks
  • Smurf Attack
  • TCP SYN Attack
  • Teardrop
  • DoS general exploits resource limitations
  • Denial by Consumption
  • Denial by Disruption
  • Denial by Reservation

50
TCP SYN Attack
  • Exploits the three-way handshake

51
TCP SYN Attack Solutions
  • Intermediate Firewall/Router
  • Limit number of half open connections
  • Ingress and egress filtering to reduce spoofed
    addresses
  • Does not help against DDoS bot networks
  • Reactively block attacking addresses
  • Generally expensive to acquire technology to do
    fast enough
  • Fix Protocol - IPv6

52
Teardrop Attack
  • Send series of fragments that don't fit together
  • Poor stack implementations would crash
  • Early windows stacks

Offset 0, len 60
Offset 30, len 90
Offset 41, len 173
53
Address Translation
  • Traditional NAT RFC 3022 Reference RFC
  • Map real address to alias address
  • Real address associated with physical device,
    generally an unroutable address
  • Alias address generally a routeable associated
    with the translation device
  • Originally motivated by limited access to
    publicly routable IP addresses
  • Folks didnt want to pay for addresses and/or
    hassle with getting official addresses

54
Address Translation
  • Later folks said this also added security
  • By hiding structure of internal network
  • Obscuring access to internal machines
  • Adds complexity to firewall technology
  • Must dig around in data stream to rewrite
    references to IP addresses and ports
  • Limits how quickly new protocols can be
    firewalled

55
Address Hiding (NAPT)
  • NAPT Network Address Port Translation
  • Many to few dynamic mapping
  • Packets from a large pool of private addresses
    are mapped to a small pool of public addresses at
    runtime
  • Port remapping makes this sharing more scalable
  • Two real addresses can be rewritten to the same
    alias address
  • Rewrite the source port to differentiate the
    streams
  • Traffic must be initiated from inside, e.g. the
    private address

56
NAT example
57
Static Mapping
  • One-to-one fixed mapping
  • One real address is mapped to one alias address
    at configuration time
  • Traffic can be initiated from either side
  • Used to statically map out small set of servers
    from a network that is otherwise hidden
  • Static port remapping is also available

58
NAT example
192.168.1.5
128.274.15
59
NAT and IPSec AH dont mix
  • Recall the diagram illustrating the fields
    covered by AH
  • AH header created at the sender, src/dest IP
    addresses changed by NAT

60
FW Runtime Characteristics
  • Firewalls track streams of traffic
  • TCP streams are obvious
  • Creates pseudo UDP streams for UCP packets
    between the same addresses and ports that arrive
    near enough to each other
  • Processing first packet in stream is more
    expensive
  • Must evaluate ACLs and calculate address
    translations
  • Subsequent packets get session data from a table

61
Multi-legged Firewalls
  • Historically firewalls have protected inside from
    outside
  • Still true for the most part with personal and
    home firewalls
  • No longer sufficient for larger enterprises
  • PIX security level solution
  • Outbound traffic from low security level
    interface to high security level interface
  • Inbound traffic from high security level
    interface to low security level interface
  • Different requirements for inbound and outbound
    traffic
  • IOS divides interfaces into inside and outside
    groups
  • Address translation can only be defined between
    inside and outside groups
  • Routing conflicts with address translation
  • Address translation specifies both interfaces
  • Must be evaluated before the routing, better be
    consistent

62
Four Legged FW
  • Static translation from DMZ to Customer
  • 10.10.10.10.1 to 128.1.1.1
  • But routing table wants to route 128.1.1.1 from
    DMZ to outside interface
  • Static translation interface selection will win

63
Identity Aware Firewall
  • Use TACACS or Radius to authenticate, authorize,
    account for user with respect to FW
  • For administration of FW
  • For traffic passing through FW
  • PIX cut-through proxy allows authentication on
    one protocol to cover other protocols from same
    source
  • Authorization for executing commands on the
    device
  • Download or enable ACLs
  • XAuth to integrate AAA with VPN authentication
    and other security mechanisms

64
AAA Scenario
65
Is the Firewall Dead?
  • End-to-end security (encryption) renders
    firewalls useless
  • Tunnels hide information that firewalls would
    filter or sanitize
  • With IPSec decrypting and re-encrypting is viable
  • Blurring security domain perimeters
  • Who are you protecting from whom
  • Dynamic entities due to DHCP and laptops
  • More dynamic business arrangements, short term
    partnerships, outsourcing
  • Total Cost of Ownership (TCO) is too high
  • Managing firewalls for a large network is
    expensive
  • Perhaps personal or distributed firewalls are the
    answer?
  • Implementing a Distributed Firewall
    http//www1.cs.columbia.edu/angelos/Papers/df.pdf

66
Intrusion Detection
  • Holy Grail Detect and correct bad system
    behavior
  • Detection can be viewed in two parts
  • Anomaly detection Use statistical techniques to
    determine unusual behavior
  • Mis-use detection Use signatures to determine
    occurrence of known attacks
  • Detection can be performed on host data (HIDS),
    network data (NIDS), or a hybrid of both

67
Intrusion Handling
  • Preparation for attack
  • Identification of the attack
  • Containment of the attack
  • Gather information about the attacker
  • Honeypots
  • Eradication
  • Broadly quarantine the system so it can do no
    more harm
  • BGP blackholing
  • Tighten firewalls
  • Cleanse the corrupted system
  • Followup phase
  • Gather evidence and take action against the
    attacker

68
Honey Pots
  • Reconnaissance for the good guys
  • Deploy a fake system
  • Observe it being attacked
  • Resource management
  • Cannot be completely passive
  • Must provide enough information to keep attacker
    interested
  • Must ensure that bait does not run away
  • Scale
  • Host, network, dark address space

69
IDS Architecture
  • Agents run at the lowest level gathering data.
    Perform some basic processing.
  • Agents send data to a Director that performs more
    significant processing of the data. Potentially
    there is a hierarchy of agents and directors
  • Director has information from multiple sources
    and can perform a time-based correlation to
    derive more significant actions
  • Directors invoke Notifiers to perform some action
    in response to a detected attack
  • Popup a window on a screen
  • Send an email or a page
  • Send a new syslog message elsewhere.
  • Adjust a firewall or some other policy to block
    future action from the attacker

70
Data Sources
  • Direct data
  • Network packets
  • System calls
  • Indirect data
  • Syslog data, Windows event logs
  • Events from other intrusion detection systems
  • Netflow information generated by routers about
    network traffic

71
Mis-use/Signature Detection
  • Fixed signatures are used in most deployed IDS
    products
  • E.g., Cisco, ISS, Snort
  • Like virus scanners, part of the value of the
    product is the team of people producing new
    signatures for newly observed malevolent behavior
  • The static signature mechanism has obvious
    problems in that a dedicated attacker can adjust
    his behaviour to avoid matching the signature.
  • The volume of signatures can result in many false
    positives
  • Must tune the IDS to match the characteristics of
    your network
  • E.g., what might be unusual in a network of Unix
    systems might be normal in a network of Windows
    Systems (or visa versa)
  • Can result in IDS tuned too low to miss real
    events
  • Can hide real attacks in the mass of false
    positives

72
Example Signature
  • Signature for port sweep
  • A set of TCP packets attempting to connect to a
    sequence of ports on the same device in a fixed
    amount of time
  • In some environments, the admin might run nmap
    periodically to get an inventory of what is on
    the network
  • You would not want to activate this signature in
    that case

73
Anomaly/statistical detection
  • Seems like using statistics will result in a more
    adaptable and self-tuning system
  • Statistics, neural networks, data mining, etc.
  • How do you characterize normal?
  • Create training data from observing good runs
  • E.g., Forrests program system call analysis
  • Use visualization to rely on your eyes
  • How do you adjust to real changes in behaviour?
  • Gradual changes can be easily addressed.
    Gradually adjust expected changes over time
  • Rapid changes can occur. E.g., different
    behaviour after work hours or changing to a work
    on the next project

74
Host Based IDS
  • Tripwire Very basic detection of changes to
    installed binaries
  • More recent HIDS. Look at patterns of actions of
    system calls, file activity, etc. to permit,
    deny, or query operations
  • Cisco Security Agent
  • Symantec
  • McAfee Entercept

75
Classical NIDS deployment
76
NIDS Remediation Options
  • Log the event
  • Drop the connection
  • Reset the connection
  • Change the configuration of a nearby router or
    firewall to block future connections

77
Intrusion Protection Systems (IPS)
  • Another name for inline NIDS
  • Latest buzz among the current NIDS vendors
  • Requires very fast signature handling
  • Slow signature handling will not only miss
    attacks but it will also cause the delay of valid
    traffic
  • Specialized hardware required for high volume
    gateways
  • When IDS is inline, the intrusion detector can
    take direct steps to remediate.
  • If you move IDS into the network processing path,
    how is this different from really clever
    firewalling?

78
Summary
  • Identification of security domains basis of
    perimeter security control
  • Firewall is the main enforcer
  • Intrusion detection introduces deeper analysis
    and potential for more dynamic enforcement
  • Intermediate enforcement can handle some Denial
    of Service attacks
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