Class 12

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Class 12CSCI 6433Dave Roberts

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Agenda• FTP• TELNET• SSH• Programming for the Internet• Internet Security• Summary

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FTP

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File Transfer Protocol FTPFTP provides the ability to transfer files between computers.

FTP uses two TCP connections between client and server:• control connection is maintained throughout the

session, used only for passing control information• data connection is established each time data is

sent from server to client or client to server

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An FTP Session

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TELNET

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TELNET• Telnet provides a bidirectional, interactive text-

oriented facility using a virtual terminal connection.• User data is sent in-band with Telnet control

information• Telnet provides a command-line interface (usually,

to an operating system) on a remote host

Question: what transport protocol does Telnet use?

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TELNET and Security• Original TELNET implementation had no security• Dialogues can be intercepted, including passwords• New protocol, SSH, provides features of TELNET

along with encryption of communications and authentication

• Most TELNET installations are now being updated to new security features; SSH is used instead

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Secure Shell SSH• Cryptographic network protocol for secure data

communication, remote command-line login between two networked computers.

• Connects using a secure channel over an insecure network

• Server and client run SSH server and SSH client• Designed as replacement for TELNET

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Programmed File Transfer

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Program Use of TCP• Sockets available for programming are:

Datagram sockets using UPD Stream sockets using TCP Raw sockets that use IP

• Most applications use datagram or stream sockets• A socket is identified by:• Local socket address (IP address and port number)• For TCP only: Remote socket address (IP address and port number)• Socket pairs:• Socket pair is a 4-tuple of local and remote IP addresses, port

numbers TCP: each socket pair has a socket number UDP: each socket pair has a socket number

• How to implement API is left to each operating system

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Windows Socket API (Winsock)• Provides access to network services in Windows

environment• Uses TCP/IP• Based on Berkeley sockets API• API guarantees that conforming application will

work with a conforming protocol implementation from any vendor

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Winsock OperationClient

• Initialize Winsock.• Create a socket.• Connect to the server.• Send and receive data.• Disconnect.

Server

• Initialize Winsock.• Create a socket.• Bind the socket.• Listen on the socket for a

client.• Accept a connection from a

client.• Receive and send data.• Disconnect.

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Some Winsock Commands• Accept—permits an incoming connection attempt on a

socket• Bind—associates a local address with a socket• Listen—places a socket in a state of listening for an

incoming connection• Connect—establishes a connection to a specified socket• Send—send data on a connected socket• Recv—receive data from a connected socket• Transmitfile—transmits file data over a connected

socket• Closesocket—close an existing socket

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Internet Security

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First…• A general comment about security.• The greatest security weakness is…• People!• Often, technical weaknesses are exploited by

obtaining help from people.

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Information Policy• Information policy is essential for security

Who is allowed to access what information Rules associated with dissemination Rules for acting on violations

• People are always the weak links in security Policy weaknesses cause mistakes Policy weaknesses can be exploited

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• Tonight we talk about Internet security, so we’ll omit people from the discussion. But understand that people are the weakest link, and that security policy is required in order for technical protections to work.

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Agenda• The Problem• Attacks• Security measures

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Early vs. later designLater designs tend to have protection features• DNS• SMTP• HTTP

The “guts” don’t have good security• IP• Network Layer

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Early IPv6• The first spec for IPv6 incorporated mandatory

encryption for all communications• Later, encryption was made optional• In IPv6, encryption is part of IP itself, can span

packets• Great improvement over IPv4, where IPSec is above

IP, so IP header is not protected

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Attacks• Malware• Denial-of-service attack• Social engineering• Eavesdropping • Password guessing• War dialing—software and modem calls desktop computers, looks

for paths into corporate networks• Denial of service attacks—overwhelms capacity of a computer so

that it can’t process legitimate work• Protocol-based attacks—exploiting weaknesses in protocols• Source Quench• ARP Spoofing• Host attacks—exploiting weaknesses in hosts

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Malware• Viruses—program that can replicate itself and

spread to other computers• Trojan horse—program that appears to be

harmless but hides malicious functions• Spyware—program that collects information with

the user’s knowledge• Worm—standalone malware that replicates itself

in order to spread to other computers• Bot—program that runs an automated task over

the Internet

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Internet Protocol security• Network layer security

IPsec Protocol TLS (formerly known as SSL)

• Email security

• Background

• Pretty Good Privacy (PGP)

• Multipurpose Internet Mail Extensions (MIME)

• Message Authentication Code

• Firewalls

• Role of firewalls in Internet security and web security

• Types of firewalls• Packet filters• Circuit-level gateways• Application-level gateways

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Ipsec core protocols

IPsec Authentication Header

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IPsec Encapsulating Security Payload

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IPSec Implementation• Two methods:1. Router implementation: implement for pairs of

routers that route datagrams outside the organization (“bump in the wire”)

2. End Host Implementation: enables end-to-end security between any two devices on the network (“bump in the stack”)

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IPSec “bump in the wire”

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IPSec “bump in the stack”

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IpSec Modes1. Transport Mode: protocol protects the message

passed from the transport layer2. Tunnel Mode: protocol protects a complete

encapsulated IP diagram after the IP header has been applied

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Transport mode

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Tunnel mode

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TLS (formerly SSL)• SSL was originally developed by Netscape through

Version 3.0• Now called Transport Layer Security (TLS)• Encryption takes place at the application layer• Uses asymmetric cryptography for key exchange,

symmetric cryptography for information protection, message authentication codes for message integrity

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Uses of SSL• Variations of TLS are now in use in• HTTP• SMTP• Internet faxing• VOIP

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Connecting• Some protocols use a different port number (i.e.,

port 443 for HTTPS)• Others use regular port number, have the client

request switching the connection to TLS (i.e., STARTTLS command for SMTP)

• Once connection is made, then asymmetric cryptography is used to negotiate the session and authenticate

• Then symmetric cryptography is used to protect the data transfer

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SMTP Security• SMTP-AUTH extension (RFC 2554) defines

authentication methods for SMTP• SMTP-AUTH provides a method to specify a security

mechanism, authenticate the exchange and negotiate a security profile

• Felt to be too complex for widespread adoption• Anti-Spam Research Group of the ITEF is working on

flexible, lightweight, scalable methods for source authentication

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Security Techniques• Perimeter security—provide some kind of network

boundary and divide service and network availability between “inside” and “outside”, determining the services and networks available to outsiders, extent to which outsiders can use resources

• Encryption—used to hide data, used for many aspects of security

• Authentication and authorization—reliably identify authorized users and allow access

• Intrusion detection—detecting actions that attempt to compromise confidentiality, integrity or availability of a resource

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Internet Security• Security is difficult because datagram contents cannot be trusted• Datagrams pass through uncontrolled

intermediaries, can be changed• Authentication based on source addresses

can’t be trusted• Strong authentication based on encryption is

more trustworthy• Encryption protects information in transit from change or access

• A trusted key authority is needed if encryption is to offer more than protection of information while in transit.

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Intrusion detection• Detecting all possible intrusion attempts is not

computable; too many computations, always one more method

• Typically heuristics, clustering algorithms, statistics are used as the basis for techniques

• Network IDS (NIDS) examines traffic at all layers, analyzes for suspicious activity

• WLAN IDS also looks for attempts to connect to rogue devices

• Host-based IDS (HIDS) analyze traffic and system-specific settings. Installed, configured on each machine.

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IDS Types• Signature-based—relies on known traffic patterns,

looks for anomalous patterns. Can be fooled by attack that is a small change from normal traffic. Usually very effective.

• Anomaly-based—detects any traffic that is incorrect or otherwise not normal.

• Stateful protocol inspection—like anomaly-based detection, but can examine traffic at network, transport layer and vendor-specific traffic at the application layer

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SMTP Security• Easy to spoof an email address• Many security changes to SMTP have been

resisted; some popular features:• Checking IP address of a device attempting connection

against a “white list”• Limiting commands such as EXPN to prevent

unauthorized users from determining the e-mail addresses of users on mailing lists.

• Checking validity of envelope information before accepting a message for delivery.

• Limiting the size of e-mail messages that may be sent or the number that may be sent in a given period of time.

• Logging all access to the server to keep records of server use and check for abuse.

• Encryption can be used along with MIME encoding

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Firewalls• Housing—separates garage from house or one

apartment from another• Automobiles—separates engine from passenger

compartment• Firewalls are intended to keep a fire localized until

residents can escape and help can arrive

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Firewalls• Often must protect a network from unwanted communication• Internet firewall is the common mechanism for internet access control• Firewall placed at the connection to external networks, partitions into two regions, inside and outside• Firewalls must be placed at all Internet connections, forming a security perimeter• A firewall is a router with filtering capabilities

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Firewall Properties1. Single point connection between 2 or more

networks where all traffic must pass2. Traffic can be controlled through the device3. All traffic is logged

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Firewall Implementation• Routers usually have a function called packet filter

—will block datagrams by source, by application, etc.

• This is most often stateless filtering• Often, packet filter is a board in the router• No TCP/IP standard for packet filters, left up to

vendors

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Types of Packet Filters1. Static—filter rules must be changed manually2. Dynamic—outside process changes the rules

dynamically 3. Stateful inspection—dynamic, but including

detailed inspection of data contained in the IP packet

Dynamic and stateful firewalls keep a dynamic state table to make changes to the filtering rules based on events

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Packet Filtering Example

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Stateful Firewalls• Allows clients inside firewall to use services outside the firewall by keeping track of the state of network connections• Watches outgoing connections, passes only packets that follow known connection patterns• Techniques:• Soft state—timer removes inactive state

information after a timeout• Connection monitoring—firewall watches

packets, removes information when flow terminates

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Application Firewalls• Firewall function at the application level• Provides multiple application proxies• Understand the operation of an application• Check messages and ensure that they follow the

pattern of the application• Bad messages are not passed on• Proxies can sometimes be tricked; important to

install new software releases promptly

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Proxy Access• Generally it’s impossible to make all computers in an organization secure• So one is made secure with application gateways, placed between firewalls• This bastion host serves as a proxy for computers inside the network to access the Internet• Firewalls are configured to pass only traffic to or from the bastion host• Bastion host can inspect contents of traffic going through it, or it can just pass the traffic

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One-router DMZ

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One-router DMZ

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Firewall effect

From this level of

risk

To this

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Summary• Internet must connect organizations with limited mutual trust

• IPsec protects at the IP layer, allows authentication or encryption of data, tunneling to protect packet content

• TLS is used for protection at the transport layer, added to applications

• IDSes watch for behavior that indicates inappropriate activity

• Firewalls are used at Internet connections

• DMZs can provide considerable isolation

• Note that all of these have been added on to the Internet, rather than designed in at the outset

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What we’ve talked about

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Protocol Dependencies• We can now look at a complete picture of Internet

protocols and how they depend on each other.

• The chart illuminates some basic choices of Internet protocol architecture

• Does today’s technology still require the difference between UDP and TCP?

• Could ECC be used and a single protocol used to replace both UDP and TCP?

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Protocol Dependencies

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IP as Universal Connector

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Summary• Rich functionality of TCP/IP comes from

services provided by applications

• Client on one machine can communicate with a server on a different type of machine

• Intermediate machines do not have to forward whole messages

• There are complex interdependencies among the protocols

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