5. Java
• Developed by Sun Microsystems in the early 1990s
• Platform Independent – write once run anywhere!
• Compiled to byte code that runs on a Virtual Machine
• “Java is Secure”
6. Java 2 Security Model
• Language Security Features
• Platform Security
• Crypto APIs
• Authentication & Access Control APIs
• Secure Communication APIs
• Key Management APIs
7. JDK 1.0 Sandbox Model
• Very restricted model
• Local code is trusted
• Remote code is not trusted
8. JDK 1.1 Security Model
• Signed applet model
• Trusted code has privileges
• Untrusted code runs in sandbox
9. Java 2 Sandbox Model
• Fine grained access control
• Configurable Security Policy
• No built-in concept of trusted
local code
10. Security Policy File Example
// If the code is signed by ”Pragati", grant it read/write access to all files in /tmp/pragati
grant signedBy ”Pragati" {
permission java.io.FilePermission "/tmp/pragati/*", "read,write";
};
// If the code is signed by ”John", grant it read/write access to all files in /tmp/john
grant signedBy ”John" {
permission java.io.FilePermission "/tmp/john/*", "read,write”;
};
// Grant everyone the following permission:
grant {
permission java.io.FilePermission "/tmp/pragati/*", "read";
};
11. Protection Domains
Domain name “Pragati”
Pragati’s certificate
Read/write access to /temp/pragati/*
Domain name “John”
John’s certificate
Read/write access to /temp/john/*
Read access to /temp/pragati/*
…………..
Protection Domain = Code Source + Permission
12. Protection Domains
A domain conceptually encloses a set of classes whose instances
are granted the same set of permissions.
13. Java 2 Platform Security Model
Operating System
Remote Class Files Local Class FilesSigned Class Files
Bytecode Verifier
Class LoaderCore API Class Files
Core Java API
Security Package
Key Database
Security Manager
Access Controller
14. Java Language Security
• Programs cannot access arbitrary memory locations
• Variables cannot be used before initialization
• Access methods are strictly adhered to
• Entities declared final must not be changed
• Objects cannot be arbitrarily cast into other objects
• Array bounds must be checked on all array accesses
16. Bytecode Verifier
Mini theorem prover
Enforces language rules
Delayed bytecode verification
Runtime binding
Operating System
Remote Class Files Local Class FilesSigned Class Files
Bytecode Verifier
Class LoaderCore API Class Files
Core Java API
Security Package
Key Database
Security Manager
Access Controller
17. Class Loader
Loads classes in namespace
Set permission for each class it loads
Link type checks for type safety
Operating System
Remote Class Files Local Class FilesSigned Class Files
Bytecode Verifier
Class LoaderCore API Class Files
Core Java API
Security Package
Key Database
Security Manager
Access Controller
18. Java APIs and Security Package
Classes in java.security package
Classes in security extensions
Basis for application signing
Operating System
Remote Class Files Local Class FilesSigned Class Files
Bytecode Verifier
Class LoaderCore API Class Files
Core Java API
Security Package
Key Database
Security Manager
Access Controller
19. Security Manager & Access Controller
Security manager exists for historical reasons
Access control to system resources
Policy enforcement
Operating System
Remote Class Files Local Class FilesSigned Class Files
Bytecode Verifier
Class LoaderCore API Class Files
Core Java API
Security Package
Key Database
Security Manager
Access Controller
Security manager exists for historical reasons
Access control to system resources
Policy enforcement
Default only for applets
20. Key Database
Create / verify digital signatures
Operating System
Remote Class Files Local Class FilesSigned Class Files
Bytecode Verifier
Class LoaderCore API Class Files
Core Java API
Security Package
Key Database
Security Manager
Access Controller
22. Java 2 Security Model
• All code runs in a sandbox
• All classes are loaded with full bytecode verification
• All classes are loaded with Java language features
• Signed classes verify the integrity and origination of Java
classes
• Security policy provides fine-grained access
• Crypto APIs
30. Middleware
• Libraries for code execution
• Libraries for services
• Take care of device specific issues
• Compiled to machine language
• Native and Java code
31. Java Virtual Machine?
• There is no JVM in Android platform
• No byte code is executed
• JAR file will not run on Android platform
33. Dalvik Virtual Machine
• Dalvik does not align to Java SE or Java ME
• Library built on a subset of the Apache Harmony Java
• Highly optimized VM to support multiple VM instances
• Register based architecture
• Shared constant pool
• Executes Dalvik executables (.dex)
36. Dalvik Virtual Machine
• No security manager
• Permissions are enforced in OS and not in VM
• As of Android 2.2 Dalvik has a JIT compiler
• Dalvik Bytecode verification mainly for optimization
• GC for each VM instance
37. Android Application Structure
• Application is made of components
• Activity: Define screens
• Service: Background processing
• Broadcast Receiver: Mailbox for messages from other
applications
• Content Provider: Relational database for sharing information
38. Android Application Structure
• Applications communicate through Intents
• Secure RPC using Binder
• AndroidManifest.xml defines policy for application
39. Permission Protection Levels
• Normal
android.permission.VIBRATE
com.android.alarm.permission.SET_ALARM
• Dangerous
android.permission.SEND_SMS
android.permission.CALL_PHONE
• Signature
android.permission.FORCE_STOP_PACKAGES
android.permission.INJECT_EVENTS
• SignatureOrSystem
android.permission.ACCESS_USB
android.permission.SET_TIME
All components are secured by permissions
Developers can define their own permissions as well
40. Application Layer Security
• Permissions restrict component interaction
• Permission labels defined in AndroidManifest.xml
• Applications are self-signed; no CA required
• Signatures define persistence and authorship
41. Android Security Model
• Linux process sandbox
• Permission based component interaction
• Dalvik is not a security boundary
• All applications need to be signed
• Signature define persistence and authorship
• Install time security decisions
• Crypto APIs
permission: type, name, and action of permissionCode source: location and signer of codeProtection domain: permission + codePolicy file: defines protection domainKeystore: verifies identity
Total system RAM is 64 MB; available after low level startup: 40MB and after high level services have started: 20 MB and large system libs 10 MB
"java.version" property returns "java.class.version" invariably returns 50"user.home" and "user.name" properties do not existHighly optimized VM to support multiple VM instances with own address space and separate memoryRelies on Linux kernel for underlying functionality such as threading and low-level memory managementLibrary built on a subset of the Apache Harmony JavaMemory is clean (mmap() and unwritten)) or dirty (malloc)Shared memory: used by many processesPrivate memory used by one process
ExamplesDex structures are using valid indices and offsets and code can’t misbehaveOptimaization: byte swapping (not needed on ARM)m static linking, pruning empty methodsRelies on Linux kernel for underlying functionality Garbage Collector is independent for each process but respect sharingBytecode verifierOptimization“Exact” GCIntra-application SecurityAnalysis & Debugging