Fault Tolerance & Cybersecurity

🛡️ Fault Tolerance & Security

Part 1 of 7 — Redundancy, Encryption, and Network Security

Fault Tolerance

Fault tolerance is the ability of a system to continue operating when a component fails.

Redundancy

The primary method for achieving fault tolerance is redundancy — having backup components or paths.

Internet Redundancy

    A ---- B ---- C
    |      |      |
    D ---- E ---- F

If the link between B and C fails, data can route A → B → E → F → C or A → D → E → F → C. Multiple paths ensure no single failure brings down the network.

🔑 The Internet was designed with redundancy so that no single point of failure can take down the entire network. Packets automatically reroute around failed links.

Concept Check 🎯

Cybersecurity Fundamentals

Encryption

Encryption transforms readable data (plaintext) into unreadable data (ciphertext) to protect it from unauthorized access.

How HTTPS Uses Both

1. Browser gets web server public key (asymmetric)
2. Browser encrypts a session key with the public key
3. Server decrypts session key with its private key
4. Both sides use the session key (symmetric) for fast communication

Common Threats

Applied Recall ✍️

1. Having multiple backup paths or components so a system continues working after a failure is called _______.

2. Encryption that uses one shared key for both encryption and decryption is called _______ encryption.

3. An attack that tricks users into revealing passwords through fake emails or websites is called _______.

Security Classification 🔍

AP Exam Strategy: Fault Tolerance & Security

• Redundancy is the #1 fault tolerance mechanism — multiple paths and backups
• Know symmetric (one key, fast) vs asymmetric (two keys, secure key exchange)
• HTTPS uses BOTH: asymmetric for initial handshake, symmetric for ongoing communication
• Know common attacks: phishing, malware, DDoS, man-in-the-middle
• A single point of failure means the system is NOT fault tolerant at that point
• More connections in a network = more redundancy = more fault tolerant

AP-Style Application 🎯

🛡️ Fault Tolerance & Security

Part 2 of 7 — Key Processes

Fault Tolerance: Working Despite Failures

A fault-tolerant system continues operating correctly when a component fails. The key idea: redundancy plus a way to detect and recover from failures.

Concept Check 🎯

Why The Internet Survives Failures

The original Internet design (1960s ARPANET) assumed parts of the network would fail. Packet switching + dynamic routing means traffic can flow around broken links automatically.

Backups Are Different From Replication

If a bug DELETES data and replicates the deletion to all replicas, only a backup saves you.

A Tiny Example: Retries With Backoff

    attempt ← 1     REPEAT WHILE attempt ≤ 5:       result ← TRY_REQUEST()       IF result.success THEN STOP       WAIT(2 ^ attempt seconds) // exponential backoff       attempt ← attempt + 1

Exponential backoff prevents retry storms from overwhelming a recovering service.

Applied Recall ✍️

1. Tolerating component failure typically requires _______ — extra capacity / copies.

2. A system that reduces functionality instead of crashing during partial failure is showing _______ degradation.

3. A disk-failure-resistant arrangement of multiple disks is called _______.

Targeted Practice 🔍

AP Exam Strategy: Fault Tolerance

• Redundancy + failover = canonical fault-tolerance answer.
• Distinguish replication (live) from backups (point-in-time).
• The Internet itself is a giant fault-tolerant system.

AP-Style Application 🎯

🛡️ Fault Tolerance & Security

Part 3 of 7 — Patterns & Examples

Security Has Three Goals: CIA

Different threats target different goals; defenses are different for each.

Concept Check 🎯

Common Threats And Defenses

Symmetric vs. Asymmetric Encryption

Real systems use both: asymmetric to safely exchange a symmetric key, then symmetric for bulk traffic.

Hashing Vs Encryption

A password should be hashed (with salt + slow algorithm), not encrypted.

Applied Recall ✍️

1. The "C" in CIA stands for _______.

2. Encryption that uses one shared key is called _______.

3. A one-way function that produces a fixed-size digest is called a _______.

Targeted Practice 🔍

AP Exam Strategy: Security Basics

• CIA: confidentiality / integrity / availability.
• Match defense to threat.
• Hashes ≠ encryption — passwords get hashed.
• Real systems use symmetric + asymmetric together.

AP-Style Application 🎯

🛡️ Fault Tolerance & Security

Part 4 of 7 — Connections & Interactions

Security & Fault Tolerance Connect Across CSP

Concept Check 🎯

Defense In Depth

No single defense is enough. Layer them:

If one layer fails, others still hold.

Threat Modeling

Ask: who would attack this, why, and how? Common categories: nation-states, organized crime, opportunistic attackers, disgruntled insiders, accidental damage.

Security Is A Process, Not A Product

Tools alone don't make a system secure. Patching, monitoring, and incident response matter as much as initial design.

Applied Recall ✍️

1. Layering multiple security defenses is called defense in _______.

2. A formal exercise to ask "who would attack this and how" is called _______ modeling.

3. A system's ability to keep responding during partial failure is _______ tolerance.

Targeted Practice 🔍

AP Exam Strategy: Cross-Topic Security

• Defense in depth — layered defenses.
• Threat modeling identifies WHO and HOW.
• Backups + replication + monitoring + response = comprehensive resilience.

AP-Style Application 🎯

🛡️ Fault Tolerance & Security

Part 5 of 7 — Change Over Time

How Security & Fault Tolerance Have Evolved

Concept Check 🎯

Notable Modern Shifts

"Security Through Obscurity" Doesn't Work

Hiding the algorithm isn't a substitute for sound design. Strong cryptography is public — its security depends on the key, not the secrecy of the method.

Applied Recall ✍️

1. A model that does NOT trust any network and verifies every request is called _______ trust.

2. An attack on a popular library to compromise its many downstream users is a _______-chain attack.

3. Cryptography designed to resist future quantum-computer attacks is called _______-quantum.

Targeted Practice 🔍

AP Exam Strategy: Security Evolution

• Modern attackers exploit supply chain, not always users directly.
• Zero trust is the dominant new architecture.
• AI changes the threat landscape (phishing quality up).

AP-Style Application 🎯

🛡️ Fault Tolerance & Security

Part 6 of 7 — Problem-Solving Workshop

Fault Tolerance & Security Workshop

Concept Check 🎯

Worked: Designing An Outage-Resistant Service

Worked: A Phishing Triage

1. Don't click.
2. Check sender domain (often misspelled).
3. Hover URLs to see the actual destination.
4. Verify out-of-band (call the company at a known number).
5. Report to IT / mark as phishing.

Worked: Choosing Authentication

Applied Recall ✍️

1. A deployment style that gradually rolls out to a small fraction first is called a _______ release.

2. A document teammates follow during an outage is called a _______.

3. After an incident, the team usually runs a _______-mortem to learn from it.

Targeted Practice 🔍

AP Exam Strategy: Workshop

• Plan for failure: redundancy + monitoring + runbooks + drills.
• Layered authentication based on use case.
• Canary releases reduce blast radius of bad changes.

AP-Style Application 🎯

🛡️ Fault Tolerance & Security

Part 7 of 7 — AP Review

AP Exam Recap — Fault Tolerance & Security

Concept Check 🎯

Final Vocab

Common Pitfalls

• Confusing replication and backup.
• Storing passwords in plaintext or reversible encryption.
• Treating security as a one-time install.
• No incident plan / runbooks / drills.
• Trusting the network instead of verifying each request.

Applied Recall ✍️

1. The "I" in CIA stands for _______.

2. An attack that overwhelms a service to deny availability is a _______ attack.

3. A second proof of identity beyond the password is the second _______.

Targeted Practice 🔍

Final Exam Tips

• CIA framing for security questions.
• Replication ≠ backup.
• Defense in depth, MFA, TLS, hashed passwords.
• Process matters: patches, monitoring, drills, post-mortems.

AP-Style Application 🎯