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General Security Concepts

Concepts

Security Basics

📝 Determining and applying the appropriate balance of confidentiality, integrity, and availability (CIA)

Although different, they are not necessarily contradictory - but they all require resources (money) and so the balance should be determined early on in the design process

Confidentiality

  • Prevent disclosure of information to unauthorized parties
  • Numerous methods for keeping data confidential: e.g. access controls, encryption
  • Access Controls: Preferred for data in use and at rest
  • Encryption: Data at rest and in transit

Integrity

  • Protect data from unauthorized alteration
  • e.g. Read-only, Read-and-write, write-only, delete access, etc
  • Integrity contributes to a system's stability and reliability as well as the authenticity of data

Availability

  • Availability needed is determined by criticality of data and purpose in the overall system

Authentication

  • Determining the identity of a user. A user is authenticated before their authorization can be determined.

  • To verify identity, a user can provide:

    • Something you know - e.g. username/password (not very reliable)
    • Something you have - e.g. token
    • Something about you (something you are) e.g. biometrics
      • ❗ Requires extra hardware, lacks specificity

  • New categories

    • what users do (dynamic biometrics such as typing patterns, gait)
    • where a user is (physical location)

  • ATMs use combination of something you know (PIN) and something you have (card) so if the card is lost, someone cannot authenticate as you

Authorization

  • Applies predetermined access levels to the user
  1. Three elements are used
    1. Requestor (subject) - already known due to authentication system
    2. Object
      1. file, program, data, other resource
    3. Type/level of access to be granted
      1. Read, write, create, delete, right to grant access rights to other objects

Accounting (Auditing)

  • Accounting is a means of measuring activity, auditing is the verification of what actual happened and allows management to observe in a nonpartisan manner

  • Accounting can be done in IT systems by logging crucial activity as it occurs

  • Accounting is needed when activity of specific data elements is crucial enough that it may be audited at a later date and time

  • Security level auditing can be performed at several levels:

    • analysis of logging function
    • verification of existence and operation of specific controls
    • etc

  • Auditing takes resources to create, store, and review. Typically defaulted to minimal level so system operator must determine correct level based on system criticality.

  • System criticality is determined by information criticality associated with information manipulated/stored with the system

Non-repudiation

  • Preventing a subject from denying a previous action with an object
  • When authentication, authorization, and auditing are properly configured, non-repudiation is ensured
  • Security requirements must specify the subjects, objects, and events for which non-repudiation is desired

System Tenets

Session Management

  • Design and implementation of controls to ensure that communication channels are secured from unauthorized access and disruption
  • TCP (Transmission Control Protocol)
    • sequential numbering of packets and retransmission for missing packets
    • Prevents unauthorized packets and session hijacking
    • Has overhead
  • UDP (User Datagram Protocol)
    • connection-less/session-less

Exception Management

  • All exceptions must be detected and handled
  • System should not fail in an insecure state
  • Exception should not be leaked

Configuration Management

  • Configuration should be protected from unauthorized changes
  • e.g. separation of duties between production/non-prod personnel

Secure Design Tenets

Good Enough Security

  • Don't spend $10,000 to protect a $20 bill
  • Trade-offs exist between security and other aspects

Least Privilege

  • If a subject may require different levels of security for different tasks, better to switch security levels with specific tasks than run all the time at higher privilege

Separation of Duties

  • No single individual can abuse the system

Defense in Depth

  • i.e. layered security/defense and diversity defense
  • Multiple, overlapping defenses
  • No system is 100% secure - true goal of security is to make cost of compromising greater in time/effort/resources than it is worth
  • Diversity of defense - layers should be dissimilar in nature

Fail-safe

  • When a system experiences a failure, it should fail to a safe state
  • Example: explicit deny
  • CIA need to be appropriately maintained - availability causes the greatest design difficulties

Economy of Mechanism

  • Higher complexity generally results in less security due to lack of understanding and more attack vectors
  • Root cause analysis, especially for potential security issues, is much more difficult in complex systems
  • Rule of thumb: eliminate all nonessential services and protocols

Complete Mediation

  • Authorization is never circumvented, even with repeated access
  • Example: security kernel

Open Design

  • Don't rely on security by obscurity
  • Example: modern cryptography relies on the secrecy of the key, not secrecy of the algorithm

Least Common Mechanism

  • Prevent inadvertent sharing of information by using separate processes when possible

Psychological Acceptability

  • Users will try to get around security if it is seen as an obstacle

Weakest Link

  • Adding to the security of a system is most effective when applied to the weakest link

Leveraging Existing Components

  • Pros: increase efficiency and security
  • Cons: monoculture environment (failures have a larger footprint)

Single Point of Failure

No one single piece should be able to cause the whole system to fail

Security Models

  • Three key elements: people, processes, and technology
  • Controls using 2-3 elements are more effective

Access Control Models

ACL - access control list

MAC - mandatory access control

  • rarely used
  • originated in military
  • restrict based on information sensitivity and clearance to access that information
  • system designers have to determine object/subject relationships before they can be used

DAC - discretionary access control

  • most common
  • originated in military
  • restrict based on identity of subjects/groups they belong to
  • If a subject has permission, it is capable of passing that permission onto any other subject
  • ACLs are the most common mechanism used to implement this control
  • Strength: simplicity
  • Weakness: security is optional, owner has to define access for potentially a plethora of objects

RBAC - role-based access control

pretty common for active directory

RBAC - rule-based access control

  • much less common than role-based
  • Use ACLs that have rules baked in such as only allow access during a certain time-of-day

Access control matrix model

  • strength: simplicity
  • weakness: difficult to implement due to no constraints, doesn't scale well

ABAC - attribute-based access control

  • Example: doctor getting one set of access for a specific patient vs a different patient
  • Represented via eXtensible Access Control Markup Language (XACML)
    • also works for policy-based access control

Bell-LaPadula Confidentiality Model

  1. Two principles
    1. Simple Security Rule - in order to see something, you have to be authorized
      1. Used to preserve confidentiality - e.g. subject with medium clearance can't ready information with high sensitivity, only medium sensitivity
      2. No-read-up
    2. * property (star property)
      1. No-write-down
      2. Subjects can only write to an object if the object has equal or higher classification - e.g. medium clearance can only write to medium sensitivity and above

Take-Grant Model

  • Uses graph theory based on mathematical representation of controls
  • Can be used to definitively determine rights
  • Not typically used to implement access control but rather to analyze implementations

Multilevel Security Model

  • Separate groups have labels, groups act as containers, can be hierarchical

Integrity Models

  • Depending on type of information, can be just as important or more important than confidentiality. e.g. stock prices (public but integrity is crucial)

Biba Integrity Model

  • Preserves information integrity
  • Integrity levels separate permissions
  • Low water mark policy, i.e. no-write-up rule
    • lower integrity subjects can't write up to higher integrity subjects
  • Integrity level of a subject is lowered if it acts on a subject with lower integrity

Clark-Wilson security model

  • Uses transactions
  • Two levels:
    • Constrained data items (CDI)
      • Subject to integrity controls
  • Unconstrained data items (UDI)
  • Two types of processes:
    • Integrity verification processes (IVPs)
      • Ensure CDI data meets constraints
    • Transformation processes (TPs)
      • Change state of data from one to another
      • Data can only be changed by trusted TPs, not users

Example:

  • A bank account balance is a CDI since integrity is important
  • TP is the only way changes can be made
  • IVP ensures balance is correct

Information Flow Models

Brewer-Nash Model (Chinese Wall)

  • Technology employed to prevent access
  • People trained not to compromise information
  • Policies/processes put in place to ensure technology/people are properly used

Data Flow Diagrams (DFDs)

  • Main security issue is protecting information when stored, in transit, and being processed
  • Multiple levels - Level 0 (high level), level 1, level 2 (lowest level)

Use Case Model

  • Functional perspective - how the system uses data

  • Use cases for normal and abnormal use

    • Very important to security to understand use cases and misuse cases

Assurance Models

  • Software assurance - level of confidence that software is free from intentional and accidental vulnerabilities, software functions as intended

Operational model of security

Three methods of managing security:

  1. prevention - access control, firewall, encryption
  2. detection - audit logs, intrusion detection, honeypots
  3. response - backups, incident response teams, forensics

NIST CSF

Standards, guidelines, best practices

5 main categories:

  1. Identify
  2. Protect
  3. Detect
  4. Respond
  5. Recover

Adversaries

Includes mother nature :)

Adversary Type

  • Based on skill level
  1. Script Kiddie - 80-85% of adversaries
  2. Hacker - explorer - 15-20% key adversary due to skill/motivation
    1. Cracker - hacker with malicious intent
  3. Elite - 1-3%
    1. completely underground

Adversary Groups

Skill and capability

  1. Unstructured threat - little or no resources, no specific motivation, typically only an annoyance
  2. Structured threat - specific mission, time and resources
  3. Highly structured threat - organized crime, crimeware
  4. Nation-state threat
    1. Advanced persistent threat (APT) - multiple methods to penetrate and then live undetected
  5. Insider vs outsider

Threat Landscape Shift

  • Around 2005 - criminalization of cyberspace allowing monetization
  • Market for exploits