SECURITY LECTURE By PRAVIN SHETTY Reduce the baud

SECURITY LECTURE By PRAVIN SHETTY

Reduce the baud rate!! 2

In the last lecture r r r 3 Taxonomy of security attacks Aims or services of security A Model of internetwork security

Security in Computing

In Today’s lecture r r r 5 Computer Security - what we mean? Security goals and vulnerabilities Methods of defence Plan of attack Carrying to (inter)network security.

Computer Security r 6 Computer security deals with the prevention and detection of unauthorised actions by users of a computer system.

The security dilemma r r security deals with the ready availability of valuable assets by authorised agents, and the denial of that access to all others. Security-unaware users have specific security requirements but (usually) no security expertise. But 7

The security dilemma r r r 8 The costs of additional resources to implement security mechanisms can be quantified. Security mechanisms interfere with users, and can lead to loss of productivity. Managing security also costs.

Principles of Security r Principle of easiest penetration í an intruder will use any means of penetration r Principles of timeliness í items only need to be protected until they lose their value r Principles of effectiveness í controls must work, and they should be efficient, easy to use, and appropriate. 9

Risk Analysis r 10 Risk analysis evaluates the cost of implementing security measures as opposed to losing the data and information.

Vulnerabilities r The three broad computing system resources are í hardware b interruption (denial of service), interception (theft) í software b interruption (deletion), interception, modification í data b interruption (loss), interception, modification and fabrication 11

Method of defence r By controls í What should be the focus of the controls? b For example: should protection mechanisms focus on data or operations on that data or on the users who use the data? í Since there are layers of technology, where controls should apply? b Applications, services, operating systems, kernel, hardware. 12

Controls r r 13 Can be applied at hardware, software, physical or polices. Simple mechanisms or lots of features? Should defining and enforcing security mechanism be a centralised function? How to prevent access to the layer below the security mechanism?

Effectiveness of Conrols r Merely having controls does no good unless they are used properly. The factors that affect the effectiveness are í Awareness of protection í Likelihood of users í Overlapping controls í Periodic review 14

Different forms of control r r 15 Authentication Access control

Authentication r Means establishing proof (assurance) of identify. í Proving that the object or the subject is what it claims to be: (is the user the person they say they are? ; is this message actually what was sent by the originator? ) r Usually involves one or a combination of something you are, something you know, and something you have. í (user name, password, possibly some hardware authentication device you can have). 16

Access Control r r r 17 Relates to who (or what) may have access to some object. The object might be tangible, like a tape drive or it can be abstract like a directory in a file system, or a network service on a remote system (like print or mail server). Concern with respect to security is how the object can be accessed; can be used locally or remotely; can it read, written or executed? If so by whom or what, and in what circumstances?

Access Control r r 18 Access control problem is essentially one of authorization, rights, and privileges. There is some standard way to access computing resources (like username and password) while there is NO standard access control scheme for the internet (internetwork).

Security services r r r 19 Authentication Access control Integrity Confidentiality Nonrepudiation Availability

Integrity r r 20 refers to the current condition of some data as compared to their pure and original state. An example in internetworking: a message or file that traverses the network at risk of having data added, removed, or modified along the way.

Integirty r Consider the following message: From: root@temple. csse. monsah. edu. au To: root@beast. csse. monash. edu. au, root@pluto. csse. monash. edu. au Subject: hackers temple. csse has been hacked by intruders. I am working to resolve this problem. Please check your systems for possible intrusion. As a by-product of this email message, the attacker of temple. csse has also compromised an email server at this site (How? ). 21

Integrity r r 22 By monitoring the outbound mail queue, the attacker intercepts this message and rather than deleting it, he takes the following three tacks. Consider the ramifications of these messages that actually received by the root user of the remote sites:

Tack -1 r From: root@temple. csse. monsah. edu. au To: root@beast. csse. monash. edu. au, Subject: hackers temple. csse has been hacked by intruders. I am working to resolve this problem. Please check your systems for possible intrusion. P. S. One of my co-worker will call you very soon to discuss the details with you, and to offer assistance. r r 23 The attacker can gain the access to the root (privileged) account of beast. csse. In addition temple. csse detects and closes the former point of access, the attacker can erase all his/her old footprints!!

Tack-2 r From: root@temple. csse. monsah. edu. au To: root@pluto. csse. monash. edu. au Subject: hackers temple. csse has been hacked by intruders. r 24 Here the intruder has left the notice of temple. csse’s intrusion intact, but removed the advice to check the other systems – to give time to cover the tracks as well another venue to intrude!!

Tack -3 r From: root@beast. csse. monsah. edu. au To: root@pluto. csse. monash. edu. au, Subject: hackers beast. csse has been hacked by intruders. I am working to resolve this problem. Please check your systems for possible intrusion. r 25 The implication of this action is …

Confidentiality r r 26 You might not really care if a few postal employees read a postcard or two, but would you care if every piece of mail you received were paraded in plain view past each person that lives between post office and your home? On internetworking, email, data transfer via FTP and www requests may be handled by intervening networks and devices and anyone with access to them, authorized or not, can read the data/messages.

Layered Protocol Models Sender Identify Recipient Identity Message Data 27 Message Length

A layered protocol stack Layer N-1 Layer 2 Layer 1 28

Protocol enveloping r r 29 Each layer in a protocol stack uses a unique and well-defined message format for communicating with its peer layers on other systems. As message gets passed down from one layer to the next, it is enveloped inside of another message. A new envelop is added at each step. After transmission across the network, the protocol layers on the receiving system strip off their respective envelopes (among other tasks). The original message is passed to the highest layer.

Protocol enveloping 30

Layered Architecture for Networks r r 31 OSI Reference Model Internet’s TCP/IP Model

OSI Reference Model r r OSI reference model is an abstract model, one that defines services and protocols that deliver the services. It does not specify the following: í programming language bindings í operating system bindings í Application interface issues í user interface issues 32

OSI Reference Model Application related services Application Presentation Session Transport Network Data Link Physical 33 Network related services

Internet TCP/IP Model Application Transport (TCP, UDP) Network (IP) Data Link Physical 34

Network Layer - IP r The primary protocol in use at the network layer is the internet protocol (IP) 4 -bit 8 bit Version header length type of service 16 bit 3 bit Identification flags 8 -bit time to live protocol 16 -bit Total Length 13 –bit fragment offset 16 -bit header checksum 32 -bit Source address 32 -bit Destination address Options(if any) and padding Data (variable length) 35

Aside - IP r r r 36 Internet Control Message Protocol (ICMP) influences and somewhat controls the behavior of the IP layer, while actually using IP services to perform its tasks. ICMP monitors and communicates network control information between network participants. The IP layer also is impacted by special routing protocols like Routing Information Protocol (RIP), Internet Group Management Protocol (IGMP), Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP).

Transport layer – TCP & UDP r r 37 Transmission control protocol – connection oriented, full-duplex service User datagram protocol – lightweight connectionless service.

TCP segment 16 -bit Source port number 16 -bit Destination port number 32 -bit Sequence number 32 bit acknowledgement number 4 -bit Header len 6 -bit Reserved Flags 16 -bit TCP Checksum 16 -bit Window Size 16 -bit Urgent pointer Options(if any) and padding Data (variable length) 38

UDP datagram 16 - bit Source Port Number 16 -bit Length 16 -bit Destination Port Number 16 -bit Checksum Date (variable length, if any) 39

Application Layer r r 40 This layer’s protocol is defined by the application. An application engages network services from the TCP or UDO transport layers through one of several APIs, such as Berkeley Sockets on BSD and Transport Layer Interface (TLI) on System V.

Protocol enveloping in the TCP/IP 41

TCP/IP protocol suite Application FTP, SMTP, HTTP, etc TCP UDP ICMP IP Data Link Ethernet, Token Ring, FDDI, etc Physical 42

Security in layered IP r r Security at the IP layer is related to the layer’s function of end-to-end datagram delivery. The security weakness are: í Network snooping í Message replay í Message alteration í Message delay and denial í Authentication issues í Routing attacks 43

Network Snooping r r 44 Attacker observes network traffic without disturbing the transmission (passive) – commonly known as snooping or sniffing. Commonly snooped are user passwords. Sniffing software works by placing a system’s network interface into promiscuous mode. Systems like Unix require superuser or system-level privileges to access the network promiscuously.

Message Relay r Relaying the message to another host and it accepts as if it is trusted. í Example: transfer of password files in a networked unix systems. 45

Message alteration r r 46 Message means the payload of the IP datagram, the router performs routine modifications to the IP datagram header, and sometimes fragments a datagram into several smaller ones (when the length exceeds a limit allowed by the underlying data link layer). No need to suspect message alteration, but techniques such as check sum are not sufficient.

Message Delay and Denial r By gaining authorised control of a router or routing host, then modifying executable code or routing and screening rules used by the code. í need to apply proper authentication and access mechanisms to the routing systems. r By overwhelming a routing device, or one of the communication end systems, with an inordinate amount of network traffic. í easy to detect but difficult to prevent! 47

Authentication issues r r r Authentication at the IP layer is concerned with the identify of computer systems. IP address are software configurable and the mere possession (or fraudulent use) of one enables communication with other systems. Two such techniques to do this are í address masquerading í address spoofing 48

Address Masquerading 49

Address Spoofing r r Also known as TCP sequence number attack. First need to understand how the threeway TCP handshake protocol works. í hanshake means- an assertion that indicates one party’s readiness to send or receive data. When two systems share a hardware connection, two-way handshake is enough. í Since TCP rides on IP – an unreliable, connectionless protocol – a three-way handshake is required. 50

Handshake in TCP SYN+ISN A SYN+ISN B+ ACK(ISNA) Machine A Machine B ACK(ISNB) Application 51 SYN – synchronize request ISN - Initial sequence number ACK – acknowledgement for the ISN Data