CIA Triad and Contextual Security Controls
Identify the property a scenario needs before proposing a control. Explain how a measure reduces a specific failure and what useful work or responsibility remains.
Before you start
- Distinguish an authorised reader, an authorised change and required usable service.
- Explain a control’s mechanism and the trust assumptions supporting it.
Watch, pause, try
Video by Professor Messer. Use the general Professor Messer explanation for the three security goals. Apply the written Pearson lesson and NIST definitions to the actual asset and failure. Qualify simplified hash/signature examples: a hash sent beside alterable data is not authenticated evidence by itself, and a complete signature scheme is not a universal instruction to encrypt with a private key.
Viewing focus: Distinguish confidentiality, integrity and availability
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: A laboratory record keeps the number 18 but an unauthorised action changes its unit; another incident deletes the only usable copy. Explain the affected CIA goals and why a single incident need not fit exactly one category. Suggest controls tied to the actual failure paths.
Show answer and reasoning
Changing the unit improperly changes the information’s meaning, affecting integrity even though the number remains 18. Deletion can affect integrity and availability when authorised users lose required information. Restrict change/delete permissions, protect relevant audit evidence and provide a recovery design with retained versions and tested access. Explain each mechanism and remaining failure dependencies rather than merely list three security words.
After watching 2: A sender sends data and an unkeyed hash through a channel where an adversary can replace both. A recipient recomputes the hash and announces that a match proves trusted origin. Evaluate that conclusion and distinguish a successful multi-factor login from permission to edit every record.
Show answer and reasoning
An adversary can alter the data and replace its unkeyed hash, so matching them does not establish trusted origin under that threat. Use an appropriate authenticated reference, MAC or verified signature scheme with sound key/trust handling. Multi-factor authentication supports an identity claim; authorisation still determines which records and operations that identity may access. Neither check alone supplies every confidentiality, integrity and availability requirement.
What you'll be able to do
- Distinguish confidentiality, integrity and availability
- Match controls to concrete information-system failures
- Evaluate trade-offs without claiming one control solves everything
Name the property and affected information
Confidentiality means preventing unauthorised disclosure: who may read the information? Integrity concerns protection against improper alteration or destruction and the trustworthiness of the information’s state. Availability concerns authorised users receiving usable service/data when required. One incident can affect several properties, so justify the dominant link rather than treating the categories as exclusive boxes.
For a laboratory record system, publicly exposing private results is a confidentiality failure. Silently changing a reading or its unit is an integrity failure. A service outage that prevents staff retrieving required records is an availability failure. The context determines impact: a copy available only in an unreadable format may not meet the user’s required service.
Connect mechanisms to the threat
Access control restricts permitted actions, while authentication helps establish the identity to which those permissions apply. Encryption can protect confidentiality across a defined boundary; suitable cryptographic authentication can help detect unauthorised message changes. Input validation addresses allowed values but does not by itself prove a sender is authorised. Audit records can support investigation if their protection and review are adequate.
Backups, replication, redundancy, capacity planning and recovery procedures can support availability or restoration, depending on the failure. Copies that share one failed power supply or synchronise every deletion do not address every outage or loss. Explain the relevant independence, recovery time and retained version requirements. A list of security terms without the failure mechanism is a weak evaluation.
Evaluate the whole control and its costs
A strongly encrypted archive may protect confidentiality, but losing every legitimate decryption key can make it unavailable. A fail-open service policy may preserve access during a dependency failure while exposing information that should have remained restricted. These are design trade-offs to analyse against requirements, not excuses to ignore either property.
A sound answer identifies the asset, threat/failure, weakness, consequence and control, then explains residual limitations. A firewall can reduce specified unwanted traffic but cannot guarantee application correctness or safe insider actions. A checksum can reveal some corruption without authenticating an active sender. Combine proportionate controls and define who maintains them rather than claiming that one purchase or one algorithm creates complete security.
| Scenario failure | Property affected | Example response to justify |
|---|---|---|
| Private record read by an unauthorised account | Confidentiality | Appropriate access control and protected channels/storage |
| Reading or unit altered improperly | Integrity | Authorisation, validated changes and suitable protected evidence |
| Required system unreachable | Availability | Appropriate redundancy, recovery and capacity |
| Encryption key lost | Availability of protected information | Controlled recoverability consistent with access requirements |
Work through the problem
Attempt the task before opening its worked response. Record each change of state, explain the rule used, and check the result against the original requirements. Code examples labelled Python 3 use that language’s conventions; pseudocode states its own assumptions.
Example 1A stored reading is changed from 8 to 80 by an unauthorised action. Identify the principal property and a linked control.
Example 2Every record is encrypted correctly, but the only key is lost. Which requirement can fail?
Common mistakes to avoid
Key takeaways
- CIA names requirements for information and service.
- Match controls to specific failure mechanisms.
- Evaluate combined responsibilities, costs and residual limits.
Explore further
- Pearson YCP01 official specification (opens in a new tab)
Check the International A-level requirements and relevant numbered points; this course remains in progress.
- Pearson International Computer Science subject guide (opens in a new tab)
Official introduction to the four examined units and their theory/practical purposes.
- Topic reading and reference (opens in a new tab)
Use the relevant board requirement or primary technical reference alongside the written examples.
- The CIA Triad - CompTIA Security+ SY0-701 - 1.2 — Professor Messer (opens in a new tab)
Original publisher or creator source for the embedded explanation; apply the stated viewing scope.
- NIST confidentiality terminology (opens in a new tab)
Read the definitions in their cited source context and apply them to the affected information.
- NIST availability terminology (opens in a new tab)
Relate timely authorised access to usable service and the actual recovery requirement.
Return to this tomorrow
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
- Authentication and authorisation are identical:
- A control evaluation should include:
Test yourself
Answer a few questions, then review anything you missed.
Keep practising
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.