TL;DR: Both platforms run each app in a sandbox with its own identity and private storage, require code signing, gate sensitive resources behind permissions, and offer hardware-backed key storage. Android isolates apps by giving each its own Linux user ID plus SELinux policy, allows installation from sources other than Google Play, and depends on device makers and carriers to ship updates, so the installed base runs many patch levels. iOS confines apps with a kernel-enforced sandbox profile and entitlements, enforces code signing on every executable page, and controls distribution and updates centrally, which shrinks fragmentation but concentrates trust in Apple. Neither platform protects an app from a user who controls their own device, so server-side checks stay authoritative on both.
How to approach it
Lay out the common model (sandbox, signing, permissions, secure storage, platform-mediated communication), then the differences that matter for threat modelling: distribution, update speed, isolation mechanism and how much the device owner can change. End with the assumption both share: the client is not trustworthy for decisions the server should make.
A strong answer
Android
Per-app Linux UID
+ SELinux policy
Sideloading allowed
Play and other stores
Malware distribution outside Play
OEM updates
uneven patch levels
Long tail of unpatched devices
Outcome, safe: Flexible, fragmented
Mainline modules shorten some update paths
iOS
Sandbox profiles
+ entitlements
Code signing every page
App Store review
Unsigned code cannot run
Apple ships updates
fast adoption
Outcome, safe: Uniform, closed
Attacks shift to zero-click chains and social engineering
What both provide.
| Property | Android | iOS |
|---|---|---|
| App isolation | Per-app Linux UID, private data directory, SELinux domains | Sandbox profile per app container, enforced by the kernel's mandatory access control |
| Code identity | APK signing; signature decides updates and signature-level permissions | Code signing by Apple-issued certificates, checked at load and on executable pages |
| Capabilities | Runtime permissions (camera, location, contacts) granted by the user | Entitlements in the signature plus user permission prompts |
| Secure key storage | Android Keystore, hardware-backed in a TEE or StrongBox chip where present | Keychain, with keys optionally in the Secure Enclave |
| Exploit mitigations | ASLR, NX, CFI in system code, hardened allocators | ASLR, NX, code-signing enforcement, pointer authentication on recent devices |
Where they differ, and why it matters.
- Distribution. Android allows sideloading and alternative stores; malware commonly arrives that way, often by persuading users to grant accessibility or overlay permissions. iOS installs come through the App Store by default, with review, although regulation in some regions now allows alternative marketplaces, so "only reviewed apps" is less absolute than it was.
- Updates. Android security fixes depend on the device maker and sometimes the carrier, and devices fall out of support at different times, so a banking app must assume many users run unpatched systems. Google moved many components into modules updated through Play to shorten that gap. iOS updates reach most devices quickly, but older devices still stop receiving them.
- Device owner control. Rooting an Android device (often after unlocking the bootloader) and jailbreaking an iPhone both give the owner control beyond the platform model. Both platforms can report device integrity to a server (Play Integrity, App Attest), which is a signal, not a guarantee.
- Inter-app communication. Android has rich IPC (intents, exported components, content providers) that apps can expose to each other, which is a frequent source of vulnerabilities. iOS offers narrower mechanisms (URL schemes, universal links, app extensions, shared app-group containers).
- Dynamic code. iOS generally forbids apps from generating executable code at runtime (outside the system JIT), which limits some attacks and some instrumentation; Android allows loading code dynamically, which is a supply-chain and review concern.
What neither guarantees. Secrecy of anything shipped in the app (keys, endpoints, logic), integrity of the app on a device the attacker controls, or safety of data an app writes outside protected storage (logs, clipboard, backups, shared folders). The OWASP Mobile Application Security Verification Standard (MASVS) organises these into areas such as storage, cryptography, authentication, network, platform interaction, code quality, resilience and privacy.
The design consequence. Treat the mobile app as a public client running on hostile hardware: keep authoritative decisions, secrets and fraud controls on the server, use platform storage and hardware-backed keys for what must live on the device, and use attestation as a risk input.
What interviewers probe next
- "Is iOS more secure than Android?" For a typical user on a current device, iOS's centralised updates and distribution reduce risk; a current Pixel with timely updates is also strong. For an app's threat model, the right question is what the weakest supported device and OS version can do.
- "What does sideloading change for your app?" Repackaged copies of your app and malware with overlay or accessibility permissions are realistic, so the server must not trust the client and the UI should resist overlays on sensitive screens.
- "Why does Android use Linux user IDs for apps?" It reuses the kernel's existing user isolation: each app's files are owned by its UID and other apps cannot read them without a shared permission mechanism.
What if?
What if · interview follow-ups
Hold your answer as the constraints change
An interviewer asks you to compare what Android and iOS guarantee to a banking app, and what the app must still do itself.
Start here
What do both platforms provide?
What do the two platforms share?
Each app runs in a sandbox with its own identity and private storage, code signing is required, sensitive resources sit behind permissions, and hardware-backed key storage is available.
Carry it forwardSandboxing, signing, permissions and hardware keys.
Weak answerAssuming one platform has no sandbox.
Constraint changes
How does Android isolate apps?
What varies across Android devices?
Each app gets its own Linux user ID plus SELinux policy. Installation from sources other than the store is possible, and device makers ship different versions and patch levels.
Carry it forwardUID isolation plus SELinux; varied fleets.
Weak answerTreating all Android devices as equally patched.
Constraint changes
How does iOS differ?
Can iOS run unsigned code?
It enforces code signing at execution, restricts apps to Apple-signed code from the App Store or managed channels, and controls updates centrally, so fleets are more uniform.
Carry it forwardiOS enforces signing at runtime with uniform updates.
Weak answerAssuming iOS cannot be compromised.
Constraint changes
What do neither guarantee?
What happens on a device the attacker controls?
That the device is not rooted or jailbroken, that the user is not tricked by social engineering, or that the server can trust the client. Malware with accessibility or overlay permissions also works on Android without exploits.
Carry it forwardPlatforms do not make clients trustworthy.
Weak answerRelying on platform security for fraud prevention.
Constraint changes
What must the banking app do itself?
Which controls belong to the bank?
Use hardware-backed keys for tokens, enforce authorisation and limits server-side, use attestation as a risk signal, protect sensitive screens, detect suspicious behaviour and educate users about scams.
Carry it forwardServer-side enforcement plus platform features.
Weak answerOutsourcing security to the OS.
Now defend it
How would you summarise the comparison?
Both sandbox apps, require signing, gate permissions and offer hardware keys; Android varies across devices and allows sideloading, iOS enforces signing at runtime with uniform updates; neither makes the client trustworthy, so the bank must use hardware keys, server-side authorisation and limits, attestation signals and fraud detection.
How it's scored
Weak: "iOS is secure, Android is open." No mechanisms.
Hire: Describes sandboxing, signing, permissions and secure storage on both, and the distribution and update differences.
Strong Hire: Contrasts isolation mechanisms (UID plus SELinux versus sandbox profiles and entitlements), explains why update fragmentation and sideloading change an app's threat model, notes owner control and attestation, and concludes that the server must remain authoritative on both platforms.
Common mistakes
- Treating the platform sandbox as protection against the device's own owner.
- Ignoring old OS versions still in the user base.
- Assuming code shipped in the app can stay secret.
- Forgetting IPC surfaces when comparing the platforms.