Secure Design Questions
Part of the Cybersecurity Roadmap
In short
"Design a secure login system" checks whether you think about threats before code. Walk through the flow, name the risks at each step and the control that answers each one.
'How would you design a secure login system?' — testing Phase 10's threat modeling and secure design thinking applied to a concrete scenario.
Think of it like this
Designing a bank branch
An architect planning a bank puts the vault at the back, a guard at the door, cameras everywhere and a two key rule for the vault. Each choice answers a specific risk. Secure design interviews want that same reasoning: risk, then control.
Watch it happen
A secure login, step by step
POST /login (HTTPS)
1/6Credentials travel only over TLS, so nobody on the network can read them.
The big ideas
What you need to know
Threat model first
Ask what you protect, from whom and how. STRIDE is a handy checklist: spoofing, tampering, repudiation, info disclosure, denial of service, privilege escalation.
Defence in depth
Layer controls so one failure is not fatal: TLS, rate limits, hashing, MFA, monitoring.
Least privilege
Services and users get only the access they need. The login service should not be able to drop tables.
Generic error messages
Say "invalid email or password", not which part was wrong, to avoid leaking which accounts exist.
Save yourself the pain
Common mistakes
Oops
Jumping straight to a tech stack without naming threats.
Do this instead
Start with assets and threats, then justify each control by the risk it reduces.
Oops
Forgetting the recovery flow, like password reset.
Do this instead
Reset and account recovery are common weak spots. Secure them with expiring single use tokens.
Your mission
Threat model a login page
Quick check
Why should a login error say "invalid email or password" instead of "email not found"?
Go deeper
- 1Practice a repeatable structure: identify assets, threats, and controls for a given design.
- 2Prepare 1-2 fully worked-through examples (e.g. secure authentication flow).
- 3Practice justifying trade-offs (usability vs security) explicitly as part of your answer.
More applied & scenario at this stop
Vulnerability Prioritization Scenarios
Compliance & Risk Questions
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