ICPSS Lecture Notes - Lesson 3 - Background

Networking

• Computer network connects two or more computing devices of the same or differing types

Types of networks

• Types of networks are categorized by the geographic area they cover
• BAN - body area network – local to a human body
• LAN - local area network – about building sized
• MAN - metropolitan area network – about city-sized, often falls between LAN and WAN and not a common term
• WAN - wide area network - global or regional, such as the internet

Network Topology

• The way in which devices are connected to a network
• Layout and paths
• Common topologies include:
  • Bus topology
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  • Ring topology
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  • Star topology
    • 
  • Extended star topology
    • 
    • central nodes are backbone switches, directing traffic where it is needed
  • Mesh topology
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    • used primarily for redundancy and fault tolerance
    • also often used for wireless networks due to the nature of wireless as a medium

OSI Model

• Open Systems Interconnection

• Multiple protocols at each layer
• Owned by ISO (International Standards Organization)
• Each Layer serves a separate role

• Within a computer each layer uses the services of the layer below it
• Across computers, each layer communicates with the equivalent layer on the other machine
  • It does this by traversing down the layer stack, and back up in the other machine
  • 
  • Differentiates between end-to-tend layer and hop-by-hop layers, indicated in this diagram
• As information traverses down the stack, a header is added by each layer, and is stripped as it traverses back up.
  • 

TCP/IP Protocol Suite

• developed before the OSI model, is similar but doesn’t quite line up
• Is generally more appropriate/accurate to actual protocol usage
• 
• 

Addressing at each layer

Protocols at each layer

• Goes into TCP vs UDP in detail, discusses strengths and tradeoffs
• Addresses the Syn/SynAck/Ack three-way handshake
  • Also mentions the Fin Active close equivalent
• Discusses some control flow stuff in TCP

Security

• CPS security goals are the same as traditional IT security, just harder to accomplish and higher stakes
• The security of a system/application/protocol is relative to:
  • a set of desired properties
  • an adversary with specific capabilities
• Goals are:
  • Confidentiality
  • Integrity
  • Availability

Confidentiality

Tools for Confidentiality

• Encryption – transform information using a secret
• Access control – use rules and policies to limit access to information
  • Authentication – determine identity of a role for someone requesting access
    • Use something someone knows, has, or is
  • Authorization – the determination if a person or system is allowed to access a resource, using a policy
  • Physical security – the establishment of physical barriers to limit access to protected computational resources

Integrity

• The property that information has not been altered in an unauthorized way

Availability

• The propety that information is accessible and modifiable in a timely fashion by those authorized to do so

Other Security Concepts

Assurance

• Refers to how trust is provided and managed in computer systems
• Policies specify behavioral expetations that people or systems have for themselves or others
• Permissions describe the behaviors that are allowed by the agents that interact with a person or system
• Protections describe mechanisms put in place to enforce permissions and policies

Authenticity

• The ability to determine that statements, policies, and permissions issued by persons or systems are genuine
• Digital signatures use cryptographic computations that allow a person or system to commit to the authenticity of their documents in a unique way that achieves nonrepudiation

Anonymity

• The property that certain records or transactions cannot be attributed to any individual
• Aggregation iss the combining of data from many individuals so that disclosed sums or averages cannot be tied to any individual
• Mixing is the intertwining of transactions, information, or communmications in a way that cannot be traced to any individual
• Proxies are trusted agents that are willing to engage in actions for an individual in a way that cannot be traced back to that person
• Psuedonyms are fictional identities that can fill in for real identities in communications and transactions, but are otherwise known only to a trusted entity

Threats and Attacks

Eavesdropping

• The interception of information inteded for someone else during its transmission over a communication channel
• Attack on confidentiality

Alteration

• The unauthorized modification of information
• Attack on integrity

Denial of Service

• The interruption or degradation of a data service or information access
• Attack on availability

Masquerading

• The fabrication of information that is purported to be from someone who is not actually the author
• Attack on authenticity

Repudiation

• The denial of a commitment or data receipt
• Attack on authenticity

Correlation and Traceback

• The integration of multiple data sources and information flows to determine the source of a particular data stream or piece of information
• Attacks on anonymity

Ten Security Principles

• Economy of mechanism
  • complexity is the enemy of security. keep it simple
• Fail-safe defaults
  • the default configuration should have a conservative protection scheme
  • e.g. minimal access rights keeps user-level damage low
• Complete mediation
  • every access to a resource must be checked for compliance
  • things like caching permissions are scary
• Open design
  • security should be publicly available for better scrutiny of security
  • only secrets should be secret
• Separation of privilege
  • multiple conditions should be required to get at protected things
• Least privilege
  • what it says on the tin. compromise is kept cheaper if your lost password only gets at your stuff
• Least common mechanism
  • if multiple users share a computer they should have separate accounts
  • avoid sharing stuff wherever possible
• Psychological acceptability
  • if security makes no sense or is hard or jarring, people will avoid using it
• Work factor
  • keep in mind your threat model, scope security measures appropriately to avoid wasting resources you might need elsewhere
• Compromise recording
  • sometimes it is more desirable to record details of an intrustion
  • e.g., affording IP cameras is maybe better than a fleet of guards

Cryptographic concepts

Encryption

• a means to allow two parties, customarily called Alice and Bob, to establish confidential communication over an insecure channel that is subject to eavesdropping

Cryptosystem Characteristics

Can be described by:

• the set of possible plaintexts
• the set of possible ciphertexts
• the set of encryption keys
• the set of decryption keys
• the correspondence between encryption keys and decryption keys
• the encyrption algorithm to use
• the decryption algorithm to use

Symmetric Cryptosystems

• Alice and Bob share a secret key, which is used for both encryption and decryption
• key distribution requires each pari of communicating parties to share a separate secret key
• requires ((n * (n-1) )/ 2) keys

Public-Key Cryptography

• Uses public keys for encryption, private keys for decryption
• Only one key is needed for each recipient, with public and private components, n key pairs
• Can also be used to provide non-repudiation via signatures. Use a private key to sign/encrypt, anyone can then use public key to decrypt for confirmation
  • Can also sign hash instead, slightly more secure

Cryptographic Hash Functions

• A compression function that maps an arbitrary-length file/input to a fixed-length hash/output
• To be considered “cryptographic” a hash function must have the following properties
  • Must be “one-way”, e.g. it is simple to compute the hash given an input, but very difficult to get the input given only the hash
  • Should be collision-resistant, meaning that it should be very difficult to find two inputs that give the same hash output
• Message authentication codes
  • MAC enables data integrity, generated using hash function and a shared secret
  • similar to salting password hashes
  • recomputing hash with secret will show if file has been changed

Control Systems

• Controlling complex systems like the power grid

Introduction

• Understand and control segments of complex environments known as systems
• Room being heated system:
  • Temperature gauge
    • aka sensor
  • Room being heated
    • aka system or process
  • furnace
    • aka actuator
  • thermostat
    • aka controller
• Foundation provided by linear systems theory

Open-Loop Conrol System

• Defined as a system without feedback
  • e.g. a space heater

Closed-Loop Control System

• In contrast, closed-loop system uses a measure to compare actual output with desired output
  • e.g. home HVAC system instead of a space heater
• Many advantages over open-loop control

Multi-Loop Feedback Control System

• Both inner and outer loops have controller and sensor

Multivariable Control System

• As systems become complex, multiple sensors and controllers must all be kept in the loop and their behavior monitored and adjusted
  • e.g. humidity and pressure, in addition to temperature, for an HVAC system

Automation

• The control of an industrial process by automatic rather than manual means
• Necessary for complex systems

Productivity

• Defined here for our purposes as the ratio of physical output to physical input