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Security ​

Security Properties ​

There are three security properties that specify what security aims to protect: Confidentiality, Integrity, Availability.

Confidentiality ​

Confidentiality

The property that information is not made available or disclosed to unauthorized individuals, entities, or processes.

Examples: ​

  • Users should not be able to see the balance of other users.
  • Someone who finds a phone should not be able to see the content.

Measures: ​

  • encryption.
  • authentication.
  • access control.

Integrity ​

Integrity

The property that data has not been changed, destroyed, or lost in an unauthorized or accidental manner.

Examples: ​

  • Manipulation of bank records.
  • Manipulation of access logs.
  • Removal of access logs.

Measures: ​

  • Digital signatures.
  • Message Authentication Code.
  • Hash functions.

Availability ​

Availability

Ability to use the required information or resource.

Examples: ​

  • DDoS: Distributed Denial of Service attacks.
  • Badly designed code

Terminology: ​

  • Threat: potential violation of security.
  • Vulnerability: Security relevant software defect that can be exploited to cause an undesired behavior
    • Flaw: defect in design.
    • Bug: defect in implementation.
  • Exploit: method (software) that allows attacker to use a threat to attack.

Threat Modeling ​

approach to identify, quantify and address security risks in an application. Done during the high-level design phase in the waterfall model.

High-level steps for threat modeling:

  1. Understanding the application.
  2. Identifying and categorizing threats.
    • Entry / Exit points
    • Assets
    • Trust levels
  3. Countermeasures and mitigation.

Categorizing Threats ​

  • Spoofing: posing as someone or something else.
  • Tampering: malicious modification of data or code.
  • Repudiation: participating in a transaction and later claiming that it never took place.
  • Information Disclosure: exposure of private information.
  • Denial of Service: render a service unusable.
  • Privilege Escalation: gaining increased capabilities.

Threat / Attack Trees. ​

To understand threats an attack tree can be made.

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An attack tree can be extended with:

  • probabilities.
  • equipment needed.
  • money required.

Mitigation: ​

  • Implementation of security features.
  • Prevention of bugs.
  • Detection, audits.
  • Recovery and response.

Security Design Principles. ​

  • Favor simplicity.
    • Use fail-safe defaults.
    • Do not expect expert users.
  • Trust with reluctance.
    • employ a small trusted computing base.
    • grant the least privilege possible.
      • promote privacy.
      • compartmentalize.
  • Defend in depth.
  • Monitor and trace.

Balancing Security: ​

security must be balanced with:

  • development cost.
  • performance of the application.
  • usability of the application.
  • acceptance by the client/users.

Authentication ​

Authentication is proving that you are you. Authentication can be done with three different factors, or a combination of them. The factors are:

  • Something the user knows:
  • Something the user has
  • Something the user is

Something the user knows: ​

examples of this factor are passwords, pincodes etc. It is very common and easy.

Cons:

  • domino effect when a database is leaked.
  • Passwords are too simple.
  • Managing passwords is hard.
  • Passwords are easily stolen by phishing or sniffing.

Something the user has. ​

Based on having access to a secret. It has variants based on the type of secret.

  • Shared symetric key
  • Private key of a asymetric key pair. and based on additional protection:
  • separate device.
  • tamper proof hardware (token).
  • pin/password protected.

example: RSA securID token

Something the user is: ​

Based on using unique personal attributes for authentication. (biometrics)

example: iris scan, voice, fingerprint, face scan.

Cons:

  • Intrusive
  • Hard to replace
  • false positives/ false negatives.
  • complex and expensive.