Contain Yourself: Building Mobile Secure Containers - PowerPoint Presentation

Slide1

Contain Yourself:Building Mobile Secure Containers

Ron GutierrezGotham Digital Science (GDS)Slide2

Outline

2Slide3

Outline

3Slide4

Bring Your Own Device (BYOD)Enterprises are embracing “Bring Your Own Device” (BYOD)

Employees use personal devices to access company resourcesUnlike managed devices, device policies cannot be enforced

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Why BYOD?5Slide6

What are Secure Containers?Data storage protection performed at the application level

Does not rely on OS security features being activatedAllows security policies to be enforced at the application level

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Commercial Solutions7

and many more……Slide8

Why Secure Containers?Orgs want employees to have convenient access to sensitive resources (

email, documents, apps with sensitive data, etc)Allows them to have control of their data on unmanaged devices

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Why Secure Containers?Unmanaged Devices

Organizations cannot enforceDevice is passcode protected (Data Protection)

Device Passcode Policies

Remote Wipes

Device is not Jailbroken

Data Protection (DP)

Developers can opt-in to use DP APIs

Must crack device passcode to access data

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Outline

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How Are Secure Containers Made?Application Wrapping

Functionality injected into existing applicationsEnforces security at the application levelData encryption

a

t

r

est

Authentication

Policy enforcement

No code changes required by developerSlide12

Application Wrapping

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iOS App Wrapping AnalysisCitrix Cloud Gateway MDX Application Wrapping AnalysisTool accepts IPA files

Application is re-signed using Distribution CertificateOutputs a new wrapped IPA file

Let’s analyze the outputSlide14

iOS App Wrapping AnalysisDiffing a pre-wrapped and post-wrapped iOS binary with HexFiend

14

View address offset

with

MachOView

tool to see what was changed

A LC_LOAD_DYLIB is added to the App’s Mach-O Load CommandsSlide15

iOS App Wrapping AnalysisDiffing a pre-wrapped and post-wrapped iOS binary with HexFiend

15

View address offset

with

MachOView

tool to see what was changed

A LC_LOAD_DYLIB is added to the App’s Mach-O Load CommandsSlide16

iOS App Wrapping AnalysisDiffing a pre-wrapped and post-wrapped iOS binary with HexFiend

16

View address offset

with

MachOView

tool to see what was changed

A LC_LOAD_DYLIB is added to the App’s Mach-O Load CommandsSlide17

iOS App Wrapping Analysis

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Updates to the Code Signature of the BinarySlide18

iOS Method Swizzling

Can modify implementations of iOS Objective-C methods

http://cocoadev.com/wiki/MethodSwizzling

Seen in

Cydia

applications

MobileSubstrate

Tweaks

Cycript

18

foh

swizzle?Slide19

iOS App Life Cycle 10119Slide20

iOS App Life Cycle 10120

Let’s swizzle hereSlide21

Swizzle EarlyStatic/Dynamic libraries can overwrite implementations upon startupImplement swizzling within

load method on Obj-C objects

+(void) load

Invoked whenever a class or category is added to the Objective-C runtime; implement this method to perform class-specific behavior upon loading.

The load message is sent to classes and categories that are both dynamically loaded and statically linked, but only if the newly loaded class or category implements a method that can respond.

https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/nsobject_Class/Reference/Reference.html#//apple_ref/occ/clm/NSObject/loadSlide22

Objective-C Swizzling 10122

Method original, swizzled;

original =

class_getInstanceMethod

(class, @selector(

application:didFinishLaunchingWithOptions

:));

swizzled

=

class_getInstanceMethod

(self, @selector(

swizzled_application:didFinishLaunchingWithOptions

:));

method_exchangeImplementations

(original,

swizzled

);Slide23

Objective-C Swizzling 10123

Method original, swizzled;

original =

class_getInstanceMethod

(

class

, @selector(

application:didFinishLaunchingWithOptions

:

));

swizzled

=

class_getInstanceMethod

(self, @selector(

swizzled_application:didFinishLaunchingWithOptions

:));

method_exchangeImplementations

(original,

swizzled

);

Specify class and method to be replacedSlide24

Objective-C Swizzling 10124

Method original, swizzled;

original =

class_getInstanceMethod

(class, @selector(

application:didFinishLaunchingWithOptions

:));

swizzled

=

class_getInstanceMethod

(

self

, @selector(

swizzled_application:didFinishLaunchingWithOptions

:

));

method_exchangeImplementations

(original,

swizzled

);

Specify class and method containing your new implementationSlide25

DEMO: Method SWIZZLINGContain Yourself: Building Mobile Secure Containers

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So I heard we are

gonna

get

swizzled

up in this piece?.. Nah mean?Slide26

I Can Swizzle.. Now What?That was a simple POC on how to implement a secure container solution using a static libraryWhat now?Org-wide static library can solve the various common iOS security issuesApparently there is a market for these things as wellSlide27

Outline

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Principles To Live By

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Broken By DesignStoring crypto key on the deviceCrypto key derivation material stored on deviceData storage not protected by app authentication passcode

Authentication Designs

Might as well start encrypting with

ROT13+1

@

YOLOCrypto

approved algorithm

Essentially Security By ObscuritySlide30

Real World ExampleMint - Financial Management ApplicationSupports passcode protectionPasscode is not used to protect any application dataSusceptible to client-side bypass via Runtime Manipulation

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Let’s bypass itSlide31

Bypassing Mint Pin ScreenDecrypt AppStore Binary using ClutchRun class-dump on the decrypted binaryPrints out class information from Mach-O filesIdentify some methods which might control the lock screen

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“Mach-O Man” Randy SavageSlide32

32@interface GalaAppDelegate

: NSObject <UIApplicationDelegate

,

WebServiceDelegate

,

UIAlertViewDelegate

,

BWQuincyManagerDelegate

>

{

[..snip..]

+ (id)

sharedController

;

[..snip..]

- (void)

logInWithUsername

:(id)arg1 password:(id)arg2;

- (void)

logInUsingStoredMintToken

;

- (void)

popAwayLogin

;

- (void)

popUpFirstRunView

;

- (void)

popUpWelcomeView

;

- (void)

updateStatusString

:(id)arg1;

- (void)

setStatusCode

:(

int

)arg1;

- (void)

popAwayPasscode

;

- (void)

popUpPasscode

;

[..snip..]

Mint.app class-dump results snippetSlide33

33@interface GalaAppDelegate

: NSObject <UIApplicationDelegate

,

WebServiceDelegate

,

UIAlertViewDelegate

,

BWQuincyManagerDelegate

>

{

[..snip..]

+ (id)

sharedController

;

[..snip..]

- (void)

logInWithUsername

:(id)arg1 password:(id)arg2;

- (void)

logInUsingStoredMintToken

;

- (void)

popAwayLogin

;

- (void)

popUpFirstRunView

;

- (void)

popUpWelcomeView

;

- (void)

updateStatusString

:(id)arg1;

- (void)

setStatusCode

:(

int

)arg1;

- (void)

popAwayPasscode

;

- (void)

popUpPasscode

;

[..snip..]

Mint.app class-dump results snippetSlide34

Analyze Function via Mobile SubstrateAllows you to hook Obj-C methods on any appUses similar approach as described earlierRequires

jailbroken deviceI like to use Theos for quick and dirty hooking

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http://iphonedevwiki.net/index.php/Theos

Goal is to identify when passcode related methods are calledSlide35

35%hook GalaAppDelegate

- (void)popAwayLogin {

%log;

%

orig

;

}

- (void)

popAwayPasscode

{

%log;

%

orig

;

}

- (void)

popUpPasscode

{

%log;

%

orig

;

}

%end

%

ctor

{

NSLog

(@"Application is now hooked by RG");

%init;

}

Simple

Theos

Tweak to Identify When Calls Are MadeSlide36

36%hook GalaAppDelegate

- (void)popAwayLogin {

%log;

%

orig

;

}

- (void)

popAwayPasscode

{

%log;

%

orig

;

}

- (void)

popUpPasscode

{

%log;

%

orig

;

}

%end

%

ctor

{

NSLog

(@"Application is now hooked by RG");

%init;

}

Simple

Theos

Tweak to Identify When Calls Are Made

Logs method call to console

Calls original methodSlide37

Demo: Using CyCript TO Bypass PincodeContain Yourself: Building Mobile Secure Containers

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Authentication DesignsThings get trickier due to online and offline accessOnline only apps could store keys server-side

Key returned only after successfully authenticatingMust handle server-side key storage.. this may be a painWhat about offline access?App might need access to data with even with no network accessSlide39

39Authentication Design For Online and Offline SupportSlide40

40Authentication Design For Online and Offline SupportSlide41

41Authentication Design For Online and Offline Support

Used to encrypt container dataSlide42

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Authentication Design For Online and Offline Support

Never persist keysSlide43

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Authentication Design For Online and Offline Support

Never persist keys

Crypto is hard.. bewareSlide44

Offline AuthenticationCommon Issues

Stored data not encrypted using passphrase derived keyCauses offline authentication to be susceptible to bypassWeak Key Derivation Function Used

PBKDF2 (minimum 4096 iterations) recommended

Insufficient passphrase complexity enforcement

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Weak Real World ExamplePassword & Data VaultPassword vault authentication uses

bcrypt Bcrypt is fairly resistant to offline brute force attacks

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But…

how is the symmetric key generated? Slide46

Weak Real World Examplespublic Encryption(String paramString

){ byte

[]

arrayOfByte

= new byte[16];

arrayOfByte

[0

] = 0;

[..

snip..]

arrayOfByte

[15

] = 0;

[..snip..]

try {

this.key

= new

SecretKeySpec

(this.sha1HashBytes, "AES");

this.ips

= new

IvParameterSpec

(

arrayOfByte

);

[..snip..]

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Decompiled Android Code From Application

Single iteration

SHA256 hash of passphraseSlide47

Brute Force Time Comparisons47

Algorithm Time (s)

PBKDF2 (4096

iters

)

317.647

SHA256

0.001

SHA256 + AES Decrypt

0.080

Merkle-Damgard

hash functions and AES are fast

Susceptible to offline brute forcingSlide48

Outline

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Completeness of ImplementationThe solution must not only consider the obvious APIsHow about the subtle OS “features” that cache data?

NSHTTPCookieStorage on Persistent CookiesNSURLRequest Caches

Document Interactions API

iOS Snapshots

Keyboard Caching

How about Keychain Data?

Are filenames also encrypted?

You Complete MeSlide50

Good For Enterprise (GFE)iOS Document Interaction API used for handling documentsSave document into the GFE Container

Email document through corporate email within GFEAllows GFE to be used to open specific file types in iOS

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Good For Enterprise (GFE)Open-in must bypass iOS SandboxiOS System writes the file to GFE App Container

Documents/Inbox folderFile is not protected by the GFE data encryptionFile persists unencrypted for an extended period

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Client’s Custom Secure ContainerMissed wrapping calls to NSHTTPCookieStorage

Apps store persistent cookies in plaintextLibrary/Cookies/Cookies.binarycookies

The cookie store also not removed on data wipes

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Outline

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Remote WipesThe traditional iOS MDM remote wipes cannot be usedRemote wipes must be triggered at app level

iOS limitations allow apps to only enforce wipe while active54

Isn’t iOS 7 Supposed To Have Some

New Background Features? Slide55

Remote Wipes in iOS 7iOS 7 added Background Modes CapabilityBackground fetch to poll for remote resets periodicallyRequires wrapping to modify Info.plist file

Sounds promising, more research neededRemote NotificationsNot practical for application wrapping solutionsRequires:

APNS Service Setup

Application specific APNS certificates

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Client-side Policy EnforcementAll client-side restrictions can be bypassed

Pick your poisonIntercept & modify policies as they are sent to the deviceModify policies while cached on the device

Runtime hooking of policy handling methods

Performed checks server-side where possible

Move critical pieces of code to low level code

Obj

-C is easy to reverse.. make it harder for the bad guys

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Jailbreak DetectionMost of the exploits pointed out require a JailbreakPreventing secure containers from running on Jailbroken device goes a long wayIf you can’t bypass Xcon

Cydia app, epic failDetection should be low-level and difficult to reversehttp://appminder.nesolabs.de/

Jailbreak Detection Generator in ASM +

AntiDebugging

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Thanks For Coming!Come visit the GDS & Send Safely Booth!Check out the GDS Blog for updates on this topic Slides and Code will be posted to GDS Github page

https://github.com/GDSSecurity58

Contact Info:

email:

rgutierrez@gdssecurity.com

twitter: @rgutie01

github

: https://github.com/rongutierrezSlide59

Imageshttp://business.bt.com/it-support-and-security/bring-your-own-device/http://media.desura.com/cache/images/members/1/404/403836/thumb_940x3000/370353317d04acc2b8df61a95d9b78f3.jpghttp://cache.boston.com/bonzai-fba/Globe_Photo/2012/05/21/mbta__1337592242_8154.JPG

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