Theory: The CIA Triad
Every security decision in this course is judged against three goals: Confidentiality, Integrity and Availability, together called the CIA Triad. When something goes wrong, the first analytical step is always to ask which leg(s) of the triad were violated. This is the single most-tested skill from Week 1.
| Leg | Plain-language question |
|---|
| Confidentiality | Is it still secret? |
| Integrity | Is it correct? |
| Availability | Can authorized users access it? |
Confidentiality
Confidentiality means ensuring information is accessible only to those authorized to see it, that is, preventing unauthorized disclosure.
- Example: a hospital restricts patient records so only treating staff can view them, using access controls and encryption for data at rest and in transit.
- When it fails: an employee’s laptop with unencrypted customer data is stolen; thousands of records are exposed and the organization faces legal liability.
The key verb is see / disclose / expose. Nothing has to be changed or deleted for confidentiality to be lost.
Integrity
Integrity means ensuring information is accurate, complete, and unaltered except by authorized action.
- Example: a bank uses checksums and audit logs so any unauthorized change to an account balance is detected immediately and can be traced.
- When it fails: an attacker modifies a wire-transfer amount in transit, silently redirecting funds; the change goes unnoticed until reconciliation.
The key verb is change / alter / falsify. Integrity covers both malicious changes and accidental corruption, and it includes being able to detect that a change happened.
Availability
Availability means ensuring information and systems are accessible to authorized users when needed.
- Example: an e-commerce site uses load balancing and redundant servers so it stays online during traffic spikes or hardware failure.
- When it fails: a ransomware attack encrypts a hospital’s systems, taking patient records offline for days and disrupting care.
The key verb is reach / use / access in time. Data that is perfectly secret and perfectly correct is still useless if nobody can get to it when it matters.
Common mistake: calling ransomware a confidentiality breach by default. Encrypting files so the owner cannot use them is primarily an availability attack. It becomes a confidentiality breach too only if the attacker also copies/leaks the data (modern “double extortion” ransomware often does both).
Identifying the Violated Leg(s)
A reliable method for any scenario:
- Was information seen by someone who shouldn’t see it? → Confidentiality.
- Was information changed, falsified, or corrupted (or can we no longer trust it)? → Integrity.
- Were authorized users unable to access information or a service when needed? → Availability.
An incident can violate more than one leg. Answer each question separately rather than looking for the single “best” one, unless the question asks which is affected most.
Diagram loads as you scroll.
Common Threats to Each Leg
The lecture groups typical threats by the leg they most directly attack:
| Confidentiality | Integrity | Availability |
|---|
| Phishing (stealing credentials/data) | Man-in-the-Middle (altering data in transit) | Ransomware (locking data) |
| Data breach | Malware (corrupting or changing data) | DDoS (overwhelming a service) |
| Spyware | Social engineering (tricking someone into making an unauthorized change) | Account takeover (locking the real user out) |
Real attacks rarely stay in one column. A phishing email may steal a password (C), which is then used to change records (I) or lock the owner out (A). Use the table as a starting point, then analyze what actually happened in the scenario.
The Triad in Tension
Strengthening one goal often costs another. Good security management means choosing the right balance for the organization.
| More… | …can cost |
|---|
| Confidentiality (stricter access controls) | Slows legitimate users, hurting Availability |
| Integrity (extra verification steps, approvals, checksums) | Adds friction and cost, competing with Availability |
| Availability (simplifying access for uptime) | Can weaken Confidentiality and Integrity controls |
Discussion: The Locked-Down Records
A hospital locks down patient records so tightly that doctors cannot access them during an emergency. Which leg failed?
Availability. The records stayed confidential and correct, but authorized users (the doctors) could not reach them when needed. Over-protecting one leg caused another to fail, and here the failure could cost a life. This is why hospitals use “break-glass” emergency access: a doctor can override restrictions in an emergency, and the override is logged and reviewed afterwards.
How Strict Should Security Be?
Beyond the CIA trade-offs, security competes with three practical demands:
- Functionality: the system must still work normally after security is installed.
- Ease of use: users should be able to use the system easily.
- Cost: building security must not cost more than it is worth.
Picture a triangle with Security, Functionality and Ease of use at its corners. Moving toward one corner moves away from the others: a system with ten-factor login is very secure but hard to use; a system with no login is easy but insecure. Cost constrains how far you can move at all. The manager’s job is to find the point that fits the organization’s needs and risk appetite, not to maximize security at any price.
When an exam scenario describes users bypassing a control (sharing passwords, propping doors open, emailing files to personal accounts), the root cause is often a control that went too far toward security at the expense of ease of use. A strong answer names the trade-off.
Worked Examples
Exercise 1
For each incident, state which CIA leg(s) were violated:
(a) A DDoS attack makes a university website unreachable for six hours.
(b) A student changes their own grade in the registration database.
(c) A celebrity’s medical file is viewed by a curious hospital clerk who is not involved in their care.
(d) A power failure corrupts half of the records in an inventory database, and no backup exists.
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Solution
Apply the three questions (seen? changed? blocked?) to each.
- (a) Nothing was seen or changed; users simply could not reach the site → Availability.
- (b) Data was changed without authorization → Integrity.
- (c) Data was seen by someone not authorized to see it, even though they are an employee → Confidentiality.
- (d) Records are corrupted (no longer accurate) → Integrity; and the lost records cannot be used by anyone → Availability.
(a) A; (b) I; (c) C; (d) I and A.
Exercise 2
Ransomware encrypts a hospital’s servers. The attackers also upload a copy of 50,000 patient records to their own server and threaten to publish them. Which legs are violated? Which is the most urgent for patient care?
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Solution
- Encryption prevents staff from opening records → Availability.
- Patient records were copied to an attacker’s server → Confidentiality.
- Integrity is not clearly violated: the data was encrypted (made unusable), not falsified. However, until restored records are verified, staff should treat integrity as uncertain.
For patient care, losing access to records, medication histories and allergies directly endangers treatment right now, so Availability is the most urgent. Confidentiality causes serious legal and reputational harm but less immediate clinical danger.
Violated: Availability and Confidentiality; most urgent for care: Availability.
Exercise 3
A company requires managers to approve every change to customer bank details, and each approval takes two days. Customers complain they cannot update their details in time to receive refunds. Identify which CIA goal the control strengthens, which it weakens, and suggest a more balanced approach.
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Solution
- Strengthened: approval of every change protects bank details from unauthorized modification → Integrity.
- Weakened: customers cannot get the update done when they need it → Availability (and ease of use).
- Balance: keep verification but make it faster, for example, require the customer to confirm the change through a second channel (one-time code to their registered phone) instead of a two-day manual approval, and reserve manual review for high-risk cases (very large refunds, recently changed contact details).
The control strengthens Integrity at the cost of Availability; a risk-based, faster verification step restores the balance.
Exercise 4
A government agency decides to remove passwords from its internal document system “so staff never get locked out.” Using the security–functionality–ease-of-use triangle, evaluate this decision.
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Solution
- The decision moves the system strongly toward ease of use (and availability): no forgotten-password lockouts.
- It moves far away from security: anyone who reaches the network, including visitors on the network or malware on any PC, can read and change documents. Both confidentiality and integrity are now unprotected.
- The lockout problem had cheaper, balanced fixes: self-service password reset, single sign-on, or a help-desk unlock process.
The decision is poorly balanced: it solves an ease-of-use problem by giving up confidentiality and integrity almost completely, when cheaper middle-ground options exist.
Exercise 5
An attacker on the same café Wi-Fi as a user intercepts the user’s connection to an online shop and changes the delivery address in the order before it reaches the shop. Name the threat and the CIA leg it primarily attacks.
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Solution
- The attacker sits between the user and the shop and modifies data in transit: this is a Man-in-the-Middle (MitM) attack.
- The order data was altered without authorization, and the shop cannot tell; the information is no longer accurate.
(The attacker also saw the order, which touches confidentiality, but the harm described is the change.)
Threat: Man-in-the-Middle; primarily attacks Integrity.