Increasing Android app security for free

Roberto Gassirà - Roberto Piccirillo

MILAN 25-26 NOVEMBER 2016

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● Senior Security Analysts for Mobile Security Lab○ Vulnerability Assessment (IT, Mobile Application)○ Android Secure Development

Increasing Android app security for freeWho we are

● Roberto Gassirà@robgas

● Roberto Piccirillo@robpicone

Increasing Android app security for freePotentially Hostile Environment

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Mobile Application can run in a Potentially Hostile Environment

Potentially Hostile EnvironmentIntroduction

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Free Open Wifi ...

Potentially Hostile EnvironmentUnreliable Communication Channels

… Free user data

Threat:Traffic Snooping

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Potentially Hostile EnvironmentUnreliable Communication Channels

Free WPA2 Wifi ...

… Free user data (MITM)

Threat: MITM

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Potentially Hostile EnvironmentUnreliable Communication Channels

Under attack...

Threat: Information Gathering

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Rooting

Potentially Hostile EnvironmentTampered Device

BootLoader Unlock Local/remote Exploit

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Rooting -> Android platform security compromised

Potentially Hostile EnvironmentTampered Device

No more application

sandbox

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Potentially Hostile EnvironmentTampered Device

Hooking/Instrumentation

Threat:Code Hijacking

onCreate()

isDeviceTampered()

...()EXIT

falsetrue

Hooking...

isDeviceTampered()

false

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Mobile Threats for Developers

● Advanced Device Owner○ Remove Bloatware/Customization

Attacker

● Mobile Cybercriminal○ Application analysis

● Potentially Harmful Applications○ Steal info/money

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Mobile Threats for DevelopersMalware Infection

Apps from “Unknown sources”

Apps from “Unknown sites”

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Mobile Threats for DevelopersGoogle Security Services for Android

From Android Security 2015

Year in Review - April 2016

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Mobile Threats for Developers

Tampered Device Detection

Free Weapons for Developers

SafetyNet API

● Allows an app to analyze the device where it is installed

● Check if the device has passed the Compatibility Test Suite (CTS)

Check the integrity of the device

(Rooted?Hooked?Infected?)

● Provided by Google Play Services

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Mobile Threats for Developers

Key Material Protection

Free Weapons for Developers

AndroidKeyStore

● Asymmetric and Symmetric Keys (API 23+) Secure Container with Hardware Backend

Secure CommunicationNetwork Security

Configuration

● Network security settings (certificate pinning, trusted CA, ...) customized with a safe and declarative configuration file

Increasing Android app security for freeDetecting Tampered Device

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Detecting Tampered Device

https://developer.android.com/training/safetynet/index.html

Checking Device Compatibility

Access

Google

API

Send

Compatibility

Check

Request

Validate

Compatibility

Check

Response

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Detecting Tampered Device

https://developers.google.com/android/guides/api-client

Access Google API

SafetyNet service

build.gradle

Create an instance of Google API Client

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Detecting Tampered DeviceSend Compatibility Check Request

Generate a random one time nonce to defeat

replay attacks

Send the request

AttestationResult

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● Formatted in JSON Web Signature format○ RSA256 Signed JSON

Detecting Tampered DeviceAttestation Result

JWS Signature

JWS Payload

JWS Header

Device passed Compatibility Test Suite

Device integrity statustrue: OK

false: TAMPERED

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Detecting Tampered Device

● Google provides Android Device Verification API for validating the response

Validate Compatibility Check Response

POST "https://www.googleapis.com/androidcheck/v1/attestations/verify?key="

{ "signedAttestation": }JWS

Signature

JWS Payload

JWS Header

{ “isValidSignature”: true }

Increasing Android app security for freeEnhancing Network Security

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● MITM attack:○ Is a well-known technique used by an attacker to setup a proxy to intercept traffic

between your application and backend servers

● How○ ARP poisoning○ DNS poisoning○ Rouge proxy○ etc

Enhancing Network SecurityMITM attack

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● HTTP and HTTPS:○ HTTP: all data sent are in clear○ HTTPS: all data sent are ciphered (Digital Certificates and Session Keys)

● Implement MITM attack on HTTP (easier)

● Implement MITM attack on HTTPS (harder)○ Not impossible

Enhancing Network SecurityMITM with HTTP or HTTPS

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Enhancing Network SecurityHow SSL works

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Digital certificateNetwork Security Configuration

● Most important:○ Common name

○ Issuer name

○ Not Valid Before

○ Not Valid After

○ Public Key

○ Signature

Remember “Public Key Info” section

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● Use HTTPS is not enough to mitigate some risks due to MITM Attacks○ But in almost all cases should be mandatory use it

● To be more secure it’s important:○ Check the common name of server digital certificate○ Verify the issuer of server digital certificate○ Trust the issuer of server digital certificate

● In the last years is usual:○ Check the server public key (Pinning certificate or sometime called SSL Pinning)○ More code to implement this technique

Enhancing Network SecurityHTTPS key security points

Android Nougat offers new features to perform easily checks to make HTTPS more secure

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● Uses declarative configuration file to:○ Enforce HTTPS for specified domain used into your application○ Use certificate pinning ○ Trust only specific Certification Authority or use specific Self-signed certificate○ Debug secure connections without modify code

● What you need:

Enhancing Network SecurityNetwork Security Configuration

AndroidManifest.xml

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Enhancing Network SecurityConfiguration file format

Contains all Network Configuration

Default configuration for all connections

Configurations for one or more domains

Configurations valid only for debug purpose

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● Get error when try to connect using HTTP

Enhancing Network SecurityEnforce HTTPS

Enforce HTTPS

HTTP Connection

Error:“Cleartext HTTP traffic to

android-developers.blogspot.it not permitted”

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● Use yours CA to verify yours certificate

Enhancing Network SecurityDigital Certificate with custom CA

Enforce HTTPS for the domaincodemotion.milan.2016

Use cacert certificate to verify server certificate

● If cacert is not used the app get an error

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● Force your application to use a specific public key● In previous Android version you had to write boring code to implement

certificate pinning● Now you need calculate the sha256 of Public Key Info of X509 digital

certificate

Enhancing Network SecurityCertificate pinning

sha256 base64

PinDigest

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● If server public key is different the application get an error

Enhancing Network SecurityCertificate pinning

● Add PinDigest with Expiration date

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● In our analysis is horrible to find out the all SSL checks are off to overcame problem into development environment

● Now it is possible to add debug configuration without modify any line of code

● When you build in “release-mode” debug configuration is not considered

Enhancing Network SecuritySafe debug

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● You could define a base configuration for all connections

● You could insert more PinDigest

● You could define which CA store will be used to verify certificates:○ User○ System

● You could use self signed-certificate

Enhancing Network SecurityOther options

Increasing Android app security for freeKey Management Evolution

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Key Management Evolution

● Android KeyStore Provider introduced with API level 18○ Based on Android Keystore System to store cryptographic keys

● Until API level 22 only asymmetric keys○ For info: https://speakerdeck.com/mseclab/android-key-management

● With API level 23+ also symmetric Keys

AndroidKeyStore Provider

Asymmetric

Asymmetric + Symmetric

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Key Management EvolutionGenerating Symmetric Key

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Key Management EvolutionFingerprint Authentication

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Key Management EvolutionAndroidKeyStore Security Features

● Preventing extraction of the key material from application process

● Preventing extraction of the key material from Android device

● Key material never enters the application process:○ App cryptographic operations are performed by system process ○

● Key materials may be bound to the secure hardware:○ Trust Execution Environment (TEE)○ Secure Element

● More and more processors are equipped with TEE:○ Snapdragon 808 (Nexus 5x), Snapdragon 810 (Nexus 6P), Snapdragon 820 (Galaxy S7)

etc

Increasing Android app security for freeThe Bill

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The Bill

● Detecting Tampered Device: Free

● Enhancing Network Security: Free

● Key Management Evolution: Free

Total = Free :)

How much costs

Web: www.mseclab.com www.consulkthink.itMail: research@mseclab.comTelefono:+39-06-4549 2416Fax:+39-06-4549 2454

Grazie per l’attenzione