Secure Systems Design Principles
Secure Systems Design Principles: What to Do and What to Avoid
A secure system is not born out of chance. It is shaped by deliberate choices, guided by principles that keep it resilient in the face of accidents, attacks, and failures. THis Choices are better made during the planning and design phases not at the tail-end. Security and reliability are not âadd-onsâ layered after a system is built; they are the stone and mortar from which the walls are raised.
Think of it like a castle: its strength lies not in a single tall tower, but in foundations set deep, walls reinforced, gates controlled, and watchtowers layered with overlapping fields of view. The brilliance of the design is not in its decoration, but in its enduring ability to withstand both siege and time.
In the same way, secure systems are crafted through discipline, not luck. They must anticipate failure, resist intrusion, and remain usable to the people they serve.
Below, weâll explore the core principles of secure system design, and the bad security practices to avoid.
1. Least Privilege: No One Gets the Master Key
Every process, user, or service should have only the access it truly needs. Nothing more.
- A cloud storage bucket should not default to public.
- A mobile app requesting GPS does not also need your contact list.
This principle, articulated by Saltzer & Schroeder (1975), remains timeless. Breaches from S3 leaks to misconfigured Firebase apps show what happens when too many keys are cut.
2. Defense in Depth: Layered Protection
A single lock or firewall is brittle. Systems need multiple, independent safeguards, so that if one fails, others hold.
- In APIs: authentication plus input validation plus throttling.
- In cloud: IAM roles plus network segmentation plus monitoring.
Adkins et al. (Building Secure and Reliable Systems, 2020) stress that resilience depends on âoverlapping protections that degrade gracefully.â
3. Fail Secure, Fail Loud: A Safe Collapse
Every system eventually encounters failure. The goal is not to prevent all failures -impossible- but to ensure they fail in ways that are safe and visible.
- A payment request should be denied rather than misprocessed.
- An API under attack should throttle and log, not silently corrupt data.
Silent failure is dangerous. Better to reject securely and visibly than to allow compromise unnoticed.
4. Separation of Duties: No Single Point of Betrayal
Fraud and insider abuse thrive where one person has unchecked control. Systems must divide power.
- No developer deploys code directly to production.
- No financial transaction above a threshold executes without dual approval.
This principle is architectural, not bureaucratic. Security depends on distributing trust.
5. Psychological Acceptability: Security Without Madness
A secure system must also be usable. If controls feel hostile, users will bypass them.
- Password rules that demand hieroglyphs produce sticky notes under keyboards.
- MFA flows that feel like punishment invite shadow IT.
If security feels impossible, it will be ignored. Usability is a security requirement, not a convenience.
6. Economy of Mechanism - Keep it Simple Small(KISS): Simplicity as Strength
Complexity is the Enemy of Security. Each new feature, exception, or hidden dependency is another crack in the foundation.
Ross Anderson (Security Engineering, 2020) reminds us: âComplexity is the enemy of security.â
The Equifax breach (2017) showed how sprawling, poorly understood systems rot faster than they can be patched. The strongest systems are often the simplest.
Bad Security Practices to Avoid
Strong security design is not just about following good principles. Itâs also about refusing shortcuts and illusions that make systems brittle. Here are the most dangerous ones:
1. Complexity for Its Own Sake
Unnecessary layers and convoluted dependencies create blind spots.
- Example: The Equifax breach involved an unpatched Apache Struts component buried in legacy systems no one tracked.
2. Security by Obscurity
Relying on secrecy to hide flaws is wishful thinking.
- Example: Hardcoded âhiddenâ credentials in apps are easily exposed through reverse engineering.
3. Fail Open
Allowing access on error is like leaving the vault open when alarms glitch.
- Example: Token validation services that default to âallowâ when down.
4. Overtrusting Defaults
Factory settings prioritize ease of setup, not security.
- Example: Public-by-default S3 buckets exposing millions of records.
5. Perimeter-Only Security
Assuming attackers canât get inside ignores phishing, stolen credentials, and insiders.
- Example: Targetâs 2013 breach began with compromised third-party vendor access.
6. Ignoring Usability
Controls that frustrate users will be bypassed.
- Example: Overly complex VPNs push employees toward unauthorized apps.
7. Patchwork Security
Tacking on tools without integration gives the illusion of defense.
- Example: Firewalls and IDS without secure coding practices or monitoring.
In Conclusion
Secure system design is not about piling on endless controls. It is about clarity of principle: granting only what is necessary, layering protections, ensuring failures are safe, dividing responsibility, respecting users, and keeping things simple.
Equally, it is about avoiding the traps of obscurity, complexity, defaults, and misplaced trust.
When security is designed well, it does not call attention to itself. It simply works â dependable, resilient, and ready for whatever comes.
References
- Saltzer, J.H., & Schroeder, M.D. (1975). The Protection of Information in Computer Systems. Proceedings of the IEEE.
- Heather Adkins, Betsy Beyer, Paul Blankinship, Ana Oprea, Adam Stubblefield. Building Secure and Reliable Systems. OâReilly Media, 2020.
- Ross Anderson. Security Engineering (3rd ed.). Wiley, 2020.
- Kerckhoffs, A. (1883). La Cryptographie Militaire. Journal des sciences militaires.
- OWASP Foundation. (2023). OWASP Top 10: Security by Design Principles.
- Breach Reports: Equifax (2017), Target (2013), Firebase Misconfigurations (2021).