0. A Comparison of Android and iOS Security Models
Trevor L. Buttrey
Computer and Information Sciences

1. Computer and Information Sciences
vs.
Computer and Information Sciences

2. Computer and Information Sciences
Reasons for Concern
Smartphones are advancing technologically
Have become popular
People are growing more dependant upon them
Size makes them easy to lose
Security problems are becoming more of an issue as users store more and more personal information on them
Computer and Information Sciences

3. Unsecure Devices Allow
Access to s and social networking accounts
Access to personal messages
Access to phone book
Access to phone accounts
Access to personal and confidential information
Computer and Information Sciences

4. Unsecure Devices Allow
Access to bank accounts
Access to mobile payments
Access to web accounts
Access to passwords
Knowledge of location
Computer and Information Sciences

5. The 5 Security Pillars Traditional Access Controls
Permissions -based Access Control
Encryption
Application Provenance
Isolation
Computer and Information Sciences

6. Traditional Access Controls
Computer and Information Sciences

7. Traditional Access Control
iOS
Password and passcode locking mechanisms
Touch ID
Device self-wipe capabilities
Lockout of internal memory if not unlocked
Memory is soldered to PCB
Computer and Information Sciences

8. Traditional Access Control
Android
Starting with 2.x, password, passcode, and pattern locking mechanism,
4.0 introduced facial recognition
Other locking methods include fingerprint readers and pictures.
Lockout of internal memory if not unlocked
SD card removable
Computer and Information Sciences

9. Computer and Information Sciences
Data Encryption
Computer and Information Sciences

10. Computer and Information Sciences
Data Encryption
iOS (old)
Bi-level encryption
1st Layer encrypts the whole disk
Key is always in memory as background apps need it to run (imperfect)
2nd Layer encrypts , attachments and other data if an app requests to use it (AES-256)
Computer and Information Sciences

11. Computer and Information Sciences
Data Encryption
iOS
Hierarchy of encryption keys:
Passcode Key
Hardware Keys: Unique ID (UID) and device group ID (GID)
AES 256-bit keys
Built Into Hardware and not directly accessible
File System Key
Generated Randomly and stored in Flash Memory
Used to encrypt File Metadata
Per File Key
Encrypted by Class Key for file’s encryption class
Encrypts contents of files on disk
Computer and Information Sciences

12. Computer and Information Sciences
Data Encryption
iOS
Encryption Classes
Complete Protection
Only Decryptable when unlocked, unusable when locked
Protected Unless Open
Uses Asymmetric Elliptic Curves (it’s complicated)
Protected Until First User Authentication
Similar to FDE
No Protection
Only protected by UID
Protected Unless Open:
Makes a PK pair that encrypts the Per File key who is derivable from
PUO private key and file’s ephemeral key
Computer and Information Sciences

13. Computer and Information Sciences
Data Encryption
iOS
Effaceable Storage
Low Level access to storage for secure wiping
Used to erase File System Key
Computer and Information Sciences

14. Computer and Information Sciences
Data Encryption
iOS
Secure enclave
Securely process fingerprints
Is given the key to decrypt the complete protection data class when locked.
Separate and directly inaccessible to OS
Computer and Information Sciences

15. Computer and Information Sciences
Data Encryption
Android
Some data encryption present
Android 3.x “Honeycomb” and above support full filesystem encryption (AES128 CBC & ESSIV:SHA256)
SD card encryption is not supported on any version in AOSP
Device Manufacturers Can implement this themselves
Computer and Information Sciences

16. Computer and Information Sciences
Data Encryption
Android
Samsung Knox:
Brings android closer to iOS
Supports AES-256 encryption of internal storage and SD cards
Computer and Information Sciences

17. Permissions-based Access Control
Computer and Information Sciences

18. Permissions-based Access Control
After an app is installed, it has access to all permitted resources of that device
It can perform any kind of malicious operation using the permissions provided
Computer and Information Sciences

19. Permissions-based Access Control
iOS
Each app is given only certain permissions by iOS
Once installed, user has granted app access to any of the devices resources
Apps can use most resources without additional permission
May access things they don’t need
Does not require permission of the user
Computer and Information Sciences

20. Permissions-based Access Control
Android
Follows Capability-Based Security Model
App must request specific permissions from OS before access
User sees what is being requested and must grant permission before app is installed
Once app is granted permission, it could perform malicious activity using those permissions
Computer and Information Sciences

21. Permissions-based Access Control
Android vs. iOS
Android allows more access to the system than iOS does
Android only gives explicit permissions to apps while apps installed on iOS can perform any operation as defined by the OS
Computer and Information Sciences

22. Default App Permissions: Android vs. iOS
Internet
Phone Number
YouTube History
Read SD Card
Address Book
Music/Video Files
WiFi Connection Logs
List of Installed Apps
Calendar
Safari Search History
Mic and Video Camera
Launch An Installed App
Device UID
Auto-Complete
Computer and Information Sciences

23. Requestable App Permissions: Android vs. iOS
Location (GPS)
Prevent Phone From Sleeping
Fine Location (GPS)
Coarse Location (Network)
Internet
Push Notifications
Record Audio
SMS/MMS Send/Receive
Calendar
Address Book
Make Phone Call
Manage Accounts
Music/Video/Picture
SD Read/Write
Make and Terminate Calls
Send SMS/MMS
Control NFC
Access Device Logs
Obtain Task List
Make Bluetooth Connections
Computer and Information Sciences

24. Computer and Information Sciences
Which is Legitimate?
AndroidOS.FakePlayer
Legit Video Player
Computer and Information Sciences

25. Application Provenance
Computer and Information Sciences

26. Application Provenance
iOS
Robust signing system
Apple provides digital certificate only to those who register
$100 per year
Thorough analysis of apps, takes weeks
Computer and Information Sciences

27. Application Provenance
Android
Not a robust signing system
Anonymous signing certificates can be made without oversight from Google
Allows legitimate applications to be repackaged after adding malware
Although not signed with the same signature, they will be signed, and can be distributed on the web.
Computer and Information Sciences

28. Computer and Information Sciences
Isolation
Computer and Information Sciences

29. Computer and Information Sciences
Programming
iOS:
All apps are Objective-C or Swift
Android:
Apps run in Dalvik JVM
Android does not use that as main form of isolation as not all code run in the VM
Most web browsers use significant amounts of native code
Computer and Information Sciences

30. Computer and Information Sciences
Isolation
iOS
Sandboxed
Own home directory
Must use APIs to access or modify system settings
Cannot communicate with other apps directly
Nothing runs as root except kernel
Computer and Information Sciences

31. Computer and Information Sciences
Isolation
iOS
Declared Entitlements
Digitally signed
Allow extra permissions
Alternative to running as root
Computer and Information Sciences

32. Computer and Information Sciences
Isolation
Android
Sandboxing
Uses native Linux user-based permissions model
Each app is it’s own user
Secured by the Linux kernel itself
Computer and Information Sciences

33. Computer and Information Sciences
Isolation
Android
Samsung Knox:
Further separates applications
Prevents access to Android APIs
Reduces API set allows data in, but not out
Computer and Information Sciences

34. Jailbreaking, Rooting, and Exploits
Computer and Information Sciences

35. Jailbreaking, Rooting, and Exploits
iOS
Jailbreaking: Uses exploits (buffer overflows among other things) to allow unsigned code to run
Android
Rooting: Uses exploits (usually buffer overflows) to load a su binary (usually harder than it sounds) to allow apps to run with elevated privileges
Computer and Information Sciences

36. Jailbreaking, Rooting, and Exploits
The Point:
Although the uses for the exploits are usually beneficial for the user, their existence represents flaws in OS’s that can be leveraged by malicious apps.
Computer and Information Sciences

37. Jailbreaking and Rooting
Advantages:
The (hacking) community can push out patches for other exploits faster than the manufactures (iOS PDF)
Finer control over the system
Computer and Information Sciences

38. Jailbreaking and Rooting
Disadvantages:
May cause security vulnerabilities
May “brick” the device
May void the warranty
Computer and Information Sciences

39. Computer and Information Sciences
After running the exploits, the device may become vulnerable in other ways (iPhone.Ikee)
Computer and Information Sciences

40. Computer and Information Sciences
Summary
Both have Strong Isolation
iOS’s Permission system is static, but due to vetting process harder for apps to abuse them.
Android’s Permission system is flexible, but requires user vigilance.
Both have Strong Traditional access controls
Both have encryption on recent versions, however android 2.x versions don’t have any and 3.x+ encryption pales compared to iOS
Apple has a stronger vetting process, but also takes longer for app updates
Android has weaker vetting process, but updates get pushed out almost immediately
Computer and Information Sciences

41. Computer and Information Sciences
xkcd,com
Computer and Information Sciences