COSIC Summer Course 2013
Dr. Ir. Stefaan Seys, KU Leuven, ESAT/COSIC

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Introduction
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Android Security Mechanisms
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… for the End User
… for the Developer
… for the Enterprise
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Looking to the future
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October 2003
August 2005
November 2007
September 2008
October 2009
May 2010
December 2010
February 2011
October 2011
July 2012
October 2012
Android Inc founded by Andy Rubin, Rich Miner,
Nick Sears and Chris White
Google acquires Android Inc
Open Handset Alliance formed, Android unveiled to public
First Android handset:
HTC Dream, Android 1.0
Android 2.0 Eclair
Android 2.2 Froyo
Android 2.3 Gingerbread
Android 3.0 Honeycomb
Android 4.0 Ice Cream Sandwich
Android 4.1 Jelly Bean
Android 4.2 Jelly Bean 4.2
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v2.3 still 25%
[http://www.appbrain.com/stats/top-android-sdk-versions]
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[developer.android.com]
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In the heart of Android lives a Linux kernel
2.6.x until Ice Cream Sandwich, 3.0.x afterwards
Hardware abstraction layer, memory management, network stack,
IPC, file system, etc.
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The kernel runs a set of open source libraries
Graphics, Media, FreeType, WebKit, System C libs, SQLite, etc.
Android runtime : Java core libraries and Dalvik VM
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Android Apps interact with the Application Framework
Activity Mgr, Notification Mgr, Resource Mgr, Package Mgr, Content
Providers, etc.
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[Wikipedia]
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Google has chosen not to use standard Java libraries nor the standard JVM
Instead Google opted for the Dalvik VM
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Reason
Hardware constrains: ARM processor with 128MB RAM and 256MB
Flash
Hardware diversity
Support for Sandboxed application runtimes
Avoid licensing fees to Oracle for J2ME
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Every App runs in its own VM (as apposed to a single VM in J2ME)
New VMs are forked from the Zygote
Dalvik VMs run DEX code
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Complete application packaged in a single .APK file
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Content is signed using the developers private key
It is only used to link apps of the same developer (updates)
Says nothing about the trustworthiness of the app/developer
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Signature only verified at installation
So changes afterwards are not detected
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Every App gets its own unique Linux user id
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Every App gets its own data folder
/data/data/com.example.my_app
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Android 72% market share vs iOS 14%
[Gartner, Q4/2012, 1]
Market share and “openness” makes Android the favored target:
2012 – new threats:
• Android
• iOS
103
1
2012 – new vulnerabilities:
• Android
• iOS
13
387
[Symantec, Q1/2013, 2]
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Attackers are interested in
[F-Secure, Q1/2013, 3]
Making money
Stealing your personal data
 to make money, or
 to set up a targeted attack
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Examples:
Send SMS to premium numbers
Set up calls to premium numbers (while user is sleeping)
Forward all mails, SMS, twitter, etc. to attacker’s server
Send location of user to attacker’s server
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Publish
Malware
Malware with “additional” permissions
Malware that elevates its permissions by exploiting some bug in OS/App (browser)
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Malware kits are also sold....
Currently on high demand: “Perkele”
(Finnish curse; “damn”)
1. Username/password
Internet
2. mTAN
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Cellular
PC Malware
Inject code in web page, ask user to install Perkele on phone
Steal credentials
Perkele
Looks genuine (tailored to bank)
Keeps running in background
Intercepts SMS
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Android installs depend on three parties
Google (developer)
OEM (personalization phase 1)
Carrier (personalization phase 2)
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Short shelf-life of devices (e.g., new Galaxy S every year)
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Meaning short support/no updates by OEM/Carrier
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Resulting in millions of devices with known vulnerabilities
Gingerbread still largest 25% install base
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ARM SoC
Hash(root PK)
INIT
IMAGE
Signature
Cert. chain
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Actual implementation depends on OEM
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“ Unlocking capabilities” also depend on OEM
Samsung ships mostly unlockable
HTC supports official unlocking (voids warranty)
LG ships unlocked, but no default flashing support
Motorola tends to be locked tight (requires exploit)
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SYSTEM
IMAGE
Signature
Cert. chain
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App 1 App 2
Core Libs
Zygote
Separate process
Unique UID
(Core Libs)
Dalvik VM
Separate process
Unique UID
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Every Android App
Runs in its own process
Has its own Dalvik VM instance
Is assigned a unique Linux user ID
Uses Linux file permissions linked to that user ID
(Core Libs)
Dalvik VM
Separate process
Unique UID
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Android does not allow to use “sudo” to gain root privileges
No root shell user over ADB
Apps cannot ask root privileges
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Sandboxing Apps relies on this!
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“ Rooting ” your phone means enabling the use of root privileges
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Access to low-level resources
(network, phone calls, SMS, etc.) is enforced through user and group permissions at kernel level
Higher level permissions restricted by the Android Runtime
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App developers need to specify the required permissions
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Scans apps for “malicious activities” while uploading to
Google Play
Apps are executed on emulator
Easy to detect this….
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Since Jelly Bean 4.2: local version of Bouncer
Will also scan Apps from other stores
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Android Security for the
User

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From a 2011 study
[McAfee, Ponemom Inst., 4]
140,000 out of 3.3M (4.1%) of smart phones were lost or stolen in 1 year
10,000 were recovered
47% lost at home or hotel room, 29% while in transit
Smartphone Honey Stick Project
[Symantec, 2012, 5]
50 `prepped’ smartphone intentionally ‘lost’ in various cities in
US
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96% were accessed by the finders, about 85% checked data on phone
43% opened the ‘online banking’ app
53% opened the ‘salaries’ file
60% checked personal mail
72% opened photos
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Your data is only protected against trivial methods when
1.
2.
3.
screen lock is enabled (properly), and
ADB debugging is disabled, and the bootloader is locked
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Unfortunately
Some phones come with an unlocked bootloader (e.g., Sprint Galaxy S4)
Screen lock used < 50% [4]
Screen lock has its limits
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Some Apps need bypass screen lock, bugs…
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Phone App
Viber
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Skype
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“Smudge attack”
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Some of sensor can be used as a “side channel” to capture PINs
The accelerometer
The front-facing camera
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“Given physical access, your data is only as secure as your attacker is lazy or ignorant ”
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“Not motivated”:
You are lucky, your data is safe.
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“Motivated but not very skilled”:
RIFF Box and others (pre-programmed JTAG debuggers)
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“Motivated and skilled”:
Nothing to prevent data theft…
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> Android 4.0 (end 2011) supports disk encryption
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Based on dm-crypt
Only /data partition (not full disk) aes-cbc-essiv:sha256 with 128-bit keys
Salt and E(DEK) stored on disk
Password or PIN
Salt
PBKDF2
AES
KEK
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Weaknesses
Brute force short PINs
[6]
“Frost” tool
[7]
AES
DEK
/data
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Can only be used with an unlocked bootloader!
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No trivial attack vector
No
No
Screenlock?
No
Yes
Unlocked bootloader?
ADB enabled
Yes
Use tool like odin3 to unlock the bootloader
Yes
“Root” the phone and dump flash using ADB or
Install recovery image to dump flash
Use JTAG or other means to dump flash
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No
File system encryption?
Yes
Brute force password
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ADB white list
Upon installation, your Android SDK will generate a random
RSA key
Can be circumvented when using an unlocked bootloader!
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Premium SMS confirmation
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Android Security for the
Developer

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App’s files are private by default
Onwed by their own UID
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Unless developer choses otherwise
MODE_WORLD_WRITEABLE or MODE_WORLD_READABLE
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Apps signed with same key can run with same UID and access each other’s files
/mnt/sdcard is world readable/writeable
Meaning your pictures...
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Sandbox
Weak App
ACCESS_FINE_LOCATION
Inter Process Call that does not require any permissions, e.g.,
ContentProvider
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Android uses custom version of Bouncy Castle
Prevents inclusion of official release in apps
Use Spongy Castle as work around
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Android includes openssl libs
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Android ICS 4.0 adds VPN API
Adds Key Chain API
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Android build system includes support for ProGuard removes unused code renaming classes, fields, and methods
Makes reverse engineering more difficult
Smaller .apk files package a; public class a
{ static String a = "Hello"; static String b = "Wwlhkd16uqE3UT941ut57Xw8OP4" static void a() {
System.out.println(a);
} public static void main(String[] args) { a();
}
}
Why use it? Because .apk -> source is trivial....
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Tool chain to obtain code from any app in Android
Get apk from phone (“root”) apk dex jar source unzip
Extract dex from apk package dex2jar
Translate dex to jar
JD-GUI
Decompile bytecode to source
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Android platform provides an extensible DRM framework
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Actual DRM mechanisms provided by third parties
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Hides details of DRM to app developers
[Android documentation]
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Android Security for the
Enterprise

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> Android 2.2 Froyo: Android Device Admin API
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“Administrators” capabilities:
(Remotely) wipe the data
Request to change or set password
(disable pattern lock)
Set password rules and expiration
Set max failed login attempts
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Lock or erase the device
Lock the screen
Enable storage encryption
Disable the camera
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Pre Android ICS 4.0
L2TP, L2TP/IPSec PSK,
L2TP RSA and PPTP
Not useful for majority of enterprise VPNs
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ICS 4.0 adds support for pure IPSec VPNs for better compatibility
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New VPN API that allows SSL VPN clients to be deployed as Apps
E.g., Cisco Anyconnect requires a “rooted” device prior to
ICS4.0
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TEE (Trusted Execution Environment)
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Hardware enforced isolation from OS
Runs on the main device chipset
Has privileged access to device resources
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(Mostly) implemented using ARM Trustzone
Example: Samsung KNOX
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[GlobalPlatform]
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[GlobalPlatform]
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TEE has direct access to screen without OS involvement
Allows secure entry and verification of PINs, passwords, etc.
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Allow secure storage of cryptographic keys and their use in an isolated environment
Prevents exploits (remote or local) from stealing these keys
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Allows secure storage of server certificates
Prevents Man-in-the-Middle attacks
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Further TEE standardisation
Who can install
Trusted Applications (TA)?
Downloadable TA’s?
TA certification?
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Users do not understand
“security indicators”
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[Trusted Foundations]
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[1] http://www.gartner.com/it/page.jsp?id=2237315
[2] Symantec Internet Security Threat Report 2013
[3] F-Secure Mobile Threat Report January-March 2013
[4] McAfee and the Ponemom Institute, The Lost Smartphone
Problem: Benchmark study of U.S. organizations, Oct. 2011
[5] The Symantec Smartphone Honey Stick Project, Mar. 2012
[6] Cannon, T., and Bradford, S. Into the Droid: Gaining Access to Android User Data. In DefCon '12 (July 2012), VIA Forensics
[7] Tilo M•uller, Michael Spreitzenbarth, and Felix C. Freiling,
Frost: Forensic Recovery of Scrambled Telephones
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