Network Security

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Network Security
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Todays Universities CampusPerimeter Security
Anti-virus system
Firewalls
100
Anti-virus system
Remote access VPN, using IPSEC
Access control
96.2
Firewalls
Content filtering
Remote access VPN, using IPSEC
Intrusion Detection System
78.8
Remote access VPN using SSL
Other
78.8
Access control
55.8
Content filtering
57.7
Intrusion Detection System
Remote access VPN using SSL
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11.5
Other
Other includes packet shapers, proxy servers
and smart-card authentication.
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Security challenges for remote offices
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Agenda

• NAT the most common and quite effective
  zero-mainetnance firewall
• PacketFilters and RealFirewalls
• SSL/TLS transport layer security
• Easy to use
• CA infrastructure
• SSH
• IPSec network layer security (VPN)
• Difficult to deploy
• Transport or Tunnel mode

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Use of Private Addresses

• Routers in the public Internet will not route
  packets whose destination are private addresses
• 10.0.0.0/8,
• 172.16.0.0/12,
• 192.168.0.0/16
• However, it is possible for routers in a private
  network to route packets with private addresses
• The same private addresses can be reused in
  different private networks

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Network Address Port Translation (NAPT or
Masquerading)
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Network Address Translation

• NAT is a major problem for media communications!
• NAT

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Types of NAT

1. Full Cone
2. Restricted Cone
3. Port Restricted Cone
4. Symmetric

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Full Cone

• Any computer can send back data to an open port.

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Restricted Cone

• Any computer can send back data to an open port
  AFTER we send data to their IP.

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Port Restricted Cone

• Same as restricted cone but we need to first send
  data to their IP AND the port that will be
  allowed to send back.

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Symmetric
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Typical Call Setup
The Location Service is being queries to check
that the destination IP address represents a
valid registered device, and for its IP Address
DNS Server
DNS Query for the IP Address of the SIP Proxy of
the Destination Domain
Location Service
The INVITE is forwarded
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A request is sent (SIP INVITE) to ESTABLISH a
session
SIP Proxy
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The request is forwarded to the End-Device
SIP Proxy
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SIP IP Phone
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Media Transport
SIP IP Phone
Destination device returns its IP Address to the
originating device and a media connection is
opened
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SIP Signaling and NAT

• SIP itself is usually not the problem.
• The UAC/proxy/etc just send back SIP packets
  based on the rport tag (the received data)
• SIP signaling intervals need to be shorter than
  NAT timeout time.

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Simple NAT Scenario(Bob sending data)
Private address space
Public Internet
Bob
NSIS NAT
Alice
Application-level signaling
NSIS signaling (Reserve Mode)
Data
NSIS signaling (Create Mode)
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STUN Tests

• 4 tests needed.

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RTP-gateway
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NAT Limitations

• Applications with IP-address content
• Need AGL (Application Level Gateway)
• Applications with inter-dependent control and and
  data sessions
• Translation of fragmented FTP control packets
• NAT device can be a target for attacks

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Packet Filtering

• Packet filtering
• Access Control Lists
• source/destination IP address
• source/destination TCP/UDP port
• protocol (TCP, UDP, ICMP, GRE,...)
• IP/TCP header bits (fragmentation, QoS,
  Established)
• Session filtering
• Dynamic Packet Filtering
• Stateful Inspection
• Smart packet filtering
• Context Based Access Control

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SSL/TLS and IPSec
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IPSec

• Security at the network layer
• Can hide data and destination ports
• Dont have to rewrite applications
• Using security gateways in tunnel mode, can be
  done without reconfiguring hosts.

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IPSec Architecture
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Tunnel and Transport Mode

• Authentication Header (AH)
• Authenticates the sender
• Encapsulating Security Payload (ESP)
• Data encryption
• Can be done in two ways
• Transport mode only the transport layer segment
  is encrypted
• Tunnel mode
• encrypt the entire IP datagram
• put it inside another IP datagram

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Tunnel Mode
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SSL and TLS

• SSL designed by Netscape
• TLS IETF standard
• compromise between SSL and a Microsoft protocol
• SSL and TLS provide applications
• Encryption
• Server authentication
• (Optional) client authentication
• SSL programming libraries are pretty easy to use

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SSL Data Processing
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SSL Record Format
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SSL Handshake

• Pretty complicated
• why HTTPS websites seem sooooooo slow.
• Server (and client) authentication
• Negotiation of
• Encryption algorithm
• MAC algorithm
• Encryption key
• Must be done before any data transmission

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SSL/TLS Overview

• SSL Secure Sockets Layer.
• unreleased v1, flawed but useful v2, good v3.
• TLS Transport Layer Security.
• TLS1.0 SSL3.0 with minor tweaks (see later).
• Defined in RFC 2246.
• Open-source implementation at http//www.openssl.o
  rg/.
• SSL/TLS provides security at TCP layer.
• Uses TCP to provide reliable, end-to-end
  transport.
• Applications need some modification.
• In fact, usually a thin layer between TCP and
  HTTP.

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SSL/TLS Basic Features

• SSL/TLS widely used in Web browsers and servers
  to support secure e-commerce over HTTP.
• Built into Microsoft IE, Netscape, Mozilla,
  Apache, IIS,
• The (in)famous browser lock.
• SSL architecture provides two layers
• SSL Record Protocol
• Provides secure, reliable channel to upper layer.
• Upper layer carrying
• SSL Handshake Protocol, Change Cipher Spec.
  Protocol, Alert Protocol, HTTP, any other
  application protocols.

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SSL Protocol Architecture
SSL Change Cipher Spec Protocol
SSL Handshake Protocol
SSL Alert Protocol
HTTP, other apps
SSL Record Protocol
TCP
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TLS Transport Layer Security

• formerly known as SSL Secure Sockets Layer
• Addresses issues of privacy, integrity and
  authentication
• What is it?
• How does it address the issues?
• How is it used

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What is TLS?

• Protocol layer
• Requires reliable transport layer (e.g. TCP)
• Supports any application protocols

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TLS Privacy

• Encrypt message so it cannot be read
• Use conventional cryptography with shared key
• DES, 3DES
• RC2, RC4
• IDEA

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TLSKey Exchange

• Need secure method to exchange secret key
• Use public key encryption for this
• key pair is used - either one can encrypt and
  then the other can decrypt
• slower than conventional cryptography
• share one key, keep the other private
• Choices are RSA or Diffie-Hellman

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TLS Integrity

• Compute fixed-length Message Authentication Code
  (MAC)
• Includes hash of message
• Includes a shared secret
• Include sequence number
• Transmit MAC with message

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TLS Integrity

• Receiver creates new MAC
• should match transmitted MAC
• TLS allows MD5, SHA-1

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TLS Authentication

• Verify identities of participants
• Client authentication is optional
• Certificate is used to associate identity with
  public key and other attributes

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TLS Overview

• Establish a session
• Agree on algorithms
• Share secrets
• Perform authentication
• Transfer application data
• Ensure privacy and integrity

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TLS Architecture

• TLS defines Record Protocol to transfer
  application and TLS information
• A session is established using a Handshake
  Protocol

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TLS Record Protocol
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TLS Handshake

• Negotiate Cipher-Suite Algorithms
• Symmetric cipher to use
• Key exchange method
• Message digest function
• Establish and share master secret
• Optionally authenticate server and/or client

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Handshake Phases

• Hello messages
• Certificate and Key Exchange messages
• Change CipherSpec and Finished messages

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X.509 Certificate Issues

• Certificate Administration is complex
• Hierarchy of Certification Authorities
• Mechanisms for requesting, issuing, revoking
  certificates
• X.500 names are complicated
• Description formats are cumbersome (ASN.1)

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X.509 Alternative SDSI

• SDSI Simple Distributed Security Infrastructure
  (Rivest, Lampson)
• Merging with IETF SPKI Simple Public-Key
  Infrastructure in SDSI 2.0
• Eliminate X.500 names - use DNS and text
• Everyone is their own CA
• Instead of ASN.1 use S-expressions and simple
  syntax
• Name and Authorization certificates

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TLS Alternatives

• S-HTTP secure HTTP protocol, shttp//
• IPSec secure IP
• SET Secure Electronic Transaction
• Protocol and infrastructure for bank card
  payments
• SASL Simple Authentication and Security Layer
  (RFC 2222)

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6.2 SSH

• SSH overview
• SSH architecture
• SSH security
• Port forwarding with SSH
• SSH applications

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SSH Overview

• SSH Secure Shell.
• Initially designed to replace insecure rsh,
  telnet utilities.
• Secure remote administration (mostly of Unix
  systems).
• Extended to support secure file transfer and
  e-mail.
• Latterly, provide a general secure channel for
  network applications.
• SSH-1 flawed, SSH-2 better security (and
  different architecture).
• SSH provides security at Application layer.
• Only covers traffic explicitly protected.
• Applications need modification, but
  port-forwarding eases some of this (see later).
• Built on top of TCP, reliable transport layer
  protocol.

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SSH Overview

• SSH Communications Security (SCS).
• www.ssh.com.
• Founded by Tatu Ylonen, writer of SSH-1.
• SSH is a trademark of SCS.
• Open source version from OpenSSH.
• IETF Secure Shell (SECSH) working group.
• Standard for SSH in preparation.
• www.ietf.org/html.charters/secsh-charter.html.
• Long-running confusion and dispute over naming.

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SSH-2 Architecture

• SSH-2 adopts a three layer architecture
• SSH Transport Layer Protocol.
• Initial connection.
• Server authentication (almost always).
• Sets up secure channel between client and server.
• SSH Authentication Protocol
• Client authentication over secure transport layer
  channel.
• SSH Connection Protocol
• Supports multiple connections over a single
  transport layer protocol secure channel.
• Efficiency (session re-use).

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SSH-2 Architecture
Applications
SSH Connection Protocol
SSH Authentication Protocol
SSH Transport Layer Protocol
TCP
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SSH-2 Security Goals

• Server (nearly) always authenticated in transport
  layer protocol.
• Client (nearly) always authenticated in
  authentication protocol.
• By public key (DSS, RSA, SPKI, OpenPGP).
• Or simple password for particular application
  over secure channel.
• Establishment of a fresh, shared secret.
• Shared secret used to derive further keys,
  similar to SSL/IPSec.
• For confidentiality and authentication in SSH
  transport layer protocol.
• Secure ciphersuite negotiation.
• Encryption, MAC, and compression algorithms.
• Server authentication and key exchange methods.

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SSH-2 Algorithms

• Key establishment through Diffie-Hellman key
  exchange.
• Variety of groups supported.
• Server authentication via RSA or DSS signatures
  on nonces (and other fields).
• HMAC-SHA1 or HMAC-MD5 for MAC algorithm.
• 3DES, RC4, or AES finalists (Rijndael/Serpent).
• Pseudo-random function for key derivation.
• Small number of official algorithms with simple
  DNS-based naming of private methods.

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SSH-1 versus SSH-2

• Many vulnerabilities have been found in SSH-1 .
• SSH-1 Insertion attack exploiting weak integrity
  mechanism (CRC-32) and unprotected packet length
  field.
• SSHv1.5 session key retrieval attack
  (theoretical).
• Man-in-the-middle attacks (using e.g. dsniff).
• DoS attacks.
• Overload server with connection requests.
• Buffer overflows.
• But SSH-1 widely deployed.
• And SSH-1 supports
• Wider range of client authentication methods
  (.rhosts and Kerberos).
• Wider range of platforms.

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SSH Port Forwarding
Without SSH or port forwarding.
LS Loginserver
UM Usersmachine
MI Mail inserver
Src UM Dest LS Port 23
MO Mail outserver
Src UM Dest MI Port 113
Src UM Dest MO Port 25
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SSH Port Forwarding

• Recall TCP port number identifies application.
• SSH on local machine
• Intercepts traffic bound for server.
• Translates standard TCP port numbers.
• E.g. port 113 ? port 5113.
• Sends packets to SSH-enabled server through SSH
  secure channel.
• SSH-enabled server
• Receives traffic.
• Re-translates port numbers.
• E.g. port 5113 ? port 113.
• Forwards traffic to appropriate server using
  internal network.

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SSH Port Forwarding
With SSH and port forwarding.
MI Mail inserver
LS SSH-enabled loginserver
UM Usersmachine
MO Mail outserver
Src UM Dest LS Port 23
Src UM Dest MO Port 25Src UM Dest LS
Port 5025Src LS Dest MO Port 25
Src UM Dest MI Port 113Src UM Dest LS
Port 5113Src LS Dest MI Port 113
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SSH Applications

• Anonymous ftp for software updates, patches...
• No client authentication needed, but clients want
  to be sure of origin and integrity of software.
• Secure ftp.
• E.g.upload of webpages to webserver using sftp.
• Server now needs to authenticate clients.
• Username and password may be sufficient,
  transmitted over secure SSH transport layer
  protocol.
• Secure remote administration.
• SysAdmin (client) sets up terminal on remote
  machine.
• SysAdmin password protected by SSH transport
  layer protocol.
• SysAdmin commands protected by SSH connection
  protocol.
• Guerilla Virtual Private Network.
• E.g. use SSH port forwarding to secure e-mail
  communications.

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6.3 Comparing IPSec, SSL/TLS, SSH

• All three have initial (authenticated) key
  establishment then key derivation.
• IKE in IPSec
• Handshake Protocol in SSL/TLS (can be
  unauthenticated!)
• Authentication Protocol in SSH
• All protect ciphersuite negotiation.
• All three use keys established to build a secure
  channel.

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Comparing IPSec, SSL/TLS, SSH

• Operate at different network layers.
• This brings pros and cons for each protocol
  suite.
• Recall Where shall we put security? discussion.
• Naturally support different application types,
  can all be used to build VPNs.
• All practical, but not simple.
• Complexity leads to vulnerabilities.
• Complexity makes configuration and management
  harder.
• Complexity can create computational bottlenecks.
• Complexity necessary to give both flexibility and
  security.

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Comparing IPSec, SSL/TLS, SSH

• Security of all three undermined by
• Implementation weaknesses.
• Weak server platform security.
• Worms, malicious code, rootkits,
• Weak user platform security.
• Keystroke loggers, malware,
• Limited deployment of certificates and
  infrastructure to support them.
• Especially client certificates.
• Lack of user awareness and education.
• Users click-through on certificate warnings.
• Users fail to check URLs.
• Users send sensitive account details to bogus
  websites (phishing) in response to
  official-looking e-mail.

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Secure Protocols Last Words

• A (mis)quote from Eugene Spafford
• Using encryption on the Internet is the
  equivalent of arranging an armored car to deliver
  credit-card information from someone living in a
  cardboard box to someone living on a park bench.

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What is a VPN
Public networks are used to move information
between trusted network segments using shared
facilities like frame relay or atm
A VIRTUAL Private Network replaces all of the
above utilizing the public Internet Performance
and availability depend on your ISP and the
Internet
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VPN Implementations
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VPN as your Intranet
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VPN Components
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Technologies
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Application Layer SSL
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Tunnel vs Transport

• Transport
• Implemented by the end point systems
• Real address to real address
• Cannot go through other networks
• Tunnel
• Encapsulation of the original IP packet in
  another packet
• Can go through other networks
• End systems need not support this
• Often PC to a box on the inside

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PPTP Free from Microsoft
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PPTP Security
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Outgoing PPTP Client Through NAT
web server
Internet
a
10.0.0.2
NAT
b
204.x.1.10
10.0.0.1
10.0.0.3
c
10.0.0.4
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VPN Comparisons
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So why have a private network QOS not fully
cooked

• Very dependent on your ISP
• Real hard to do across ISPs
• So no guarantee of performance